PISA printing soluble solids using stereolithography

Abstract

Photosensitive printing inks, methods of 3D printing those inks, and 3D-printed structures are provided. The printing inks comprise a polymer scaffold, a phase-separating monomer, a photoinitiator, and preferably a photoabsorber dispersed or dissolved in a solvent system. The polymer scaffold comprises a polymer functionalized with at least two chain transfer or RAFT agents. The polymer scaffold and solvent system are selected so that the polymer scaffold is soluble in that solvent system. Additionally, the phase-separating monomer and solvent system are selected so that the phase- separating monomer is insoluble in the solvent system and so that phase-separating monomer will undergo photoinitiated chain extension to form polymer chains that are soluble in the solvent system. The provided inks can be efficiently printed to form structures that lack (or substantially lack) chemical crosslinks, thus relying on physical crosslinking to maintain shape. The resulting structures have shorter and / or controlled dissolution rates, making them useful for biomedical and other applications.

Description

PISA PRINTING SOLUBLE SOLIDS USING STEREOLITHOGRAPHYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 641,715, filed May 2, 2024, entitled PISA PRINTING SOLUBLE SOLIDS USING STEREOLITHOGRAPHY, the entirety of which is incorporated by reference herein.BACKGROUNDField

[0002] The present disclosure relates to novel photosensitive resins, printing inks, and methods of using the foregoing in 3D printing in biomedical and other applications.Description of Related Art

[0003] The development of vascularized tissue via 3D printing presents substantial challenges, particularly in replicating the detailed vascular networks intrinsic to the human body. A critical requirement for tissue viability is the proximity of cells to a blood supply, ideally within 100 to 200 micrometers, to ensure adequate diffusion of nutrients and oxygen. Thus, engineered tissues necessitate a perfusable vascular network that closely mimics natural tissue capillarity. Traditional bioprinting methods, which are based on a point-by-point extrusion process, are constrained by slow speeds and low spatial resolution, impeding the replication of the fine, functional vasculature structures. Digital Light Processing (DLP) printers print the entire XY plane at once for each layer and current state-of-the-art commercial systems are capable of resolutions between 5 and 20 microns. Despite having both a speed and resolution advantage, the application of DLP printers in tissue engineering and organ-on-a-chip applications has been limited because these systems cannot dissolve in physiological fluids.SUMMARY

[0004] The present disclosure broadly provides a method of forming a structure. The method comprises (i) exposing a first printing ink to light so as to form a first printed layer, (ii) exposing a second printing ink to light so as to form a second printed layer against the first printed layer, and (iii) repeating exposing (ii) one or more times so as to form one or more additional printed layers, wherein (i), (ii), and (iii) result in the formation of said structure. The first printing ink comprises a polymer scaffold, a phase-separating monomer, and a photoinitiator dispersed or dissolved in a solvent system, and the polymer scaffold comprises a polymer having at least two chain transfer agents. The first andsecond printing inks can be chemically the same as, or chemically different from, one another. Additionally, the one or more further printing inks can be chemically the same as one or both of the first and second printing inks, or chemically different from one or both of the first and second printing inks.

[0005] The disclosure is also concerned with three-dimensional structures formed by the above method, as well as methods of using those structures.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure (Fig.) 1 is a schematic drawing of a digital light projection (DLP) stereolithography 3D printer;

[0007] Fig. 2 is a schematic depiction of the physical crosslinking of polymer-induced self- assembly (PISA) resins utilizing difunctional polyethylene glycol macro-CTAs;

[0008] Fig. 3 is a schematic depiction of interparticle bridging (left) and interparticle knots (right) that contribute to physical crosslinking in the disclosed photosensitive compositions;

[0009] Fig. 4 is a photograph of the monofunctional polyethylene glycol macro-CTA PISA studies with DAAm in water (Example 1);

[0010] Fig. 5 is a photograph of a DAAm PISA frog without MBAc crosslinker dissolved in DMF following 3D printing, thus indicating physical crosslinking of the part (Example 1);

[0011] Fig. 6 is a photograph of a DAAm PISA frog with MBAc crosslinker that swelled but didn’t dissolve in DMF following 3D printing, thus indicating a light level of crosslinking of the part (Example 1);

[0012] Fig. 7 is a graph showing GPC traces for the difunctional polyethylene glycol macro-CTA and DAAm PISA polymer polymerized from this difunctional polyethylene glycol macro-CTA (Example 1);

[0013] Fig. 8 provides graphs of the stress vs. strain for DAAm PISA dogbones with 2.5 wt. % MBAc crosslinker (chemically crosslinked, left) and with 0 wt. % MBAc crosslinker (physically crosslinked, right);

[0014] Fig. 9 provides graphs of the stress vs. strain for AA-co-DMAPS PISA dogbones with 2.5 wt. % MBAc crosslinker (chemically crosslinked, left) and with 0 wt. % MBAc crosslinker (physically crosslinked, right) (Example 1);

[0015] Fig. 10 is an image of the CAD files for the 3D scaffolds used for controlled dissolution tests of Example 1 ;

[0016] Fig. 11 is a photograph of 3D structures printed with resins that did and did not contain crosslinker, as described in Example 1 ;

[0017] Fig. 12 provides GPC traces for poly(DMA-co-HEAm) polymers targeting various DPs (Example 2);

[0018] Fig. 13 is a dynamic light scattering (DLS) graph for large functional polymer (LFP) (also referred to as CTA-functionalized scaffold (CFS)) or 10% BTP-grafted poly(DMA-co-HEAm) macro- CTA (Example 2);

[0019] Fig. 14 is a graph of the]H NMR traces for purified ungrafted and grafted DPI 0,000 CTS scaffolds (Example 2);

[0020] Fig. 15 shows the UV-Vis spectra for BTP-grafted and ungrafted CFS scaffolds compared to a solvent-only blank (91% isopropanol) (Example 2);

[0021] Fig. 16 contains photographs of PIS A-printed parts from 10% BTP-grafted DP 10,000 CFS DAAM PISA resin printed at a normal exposure time of 10 s per layer (Example 2);

[0022] Fig. 17 is a photograph of a logo printed at a normal exposure times of 10 s per layer using 10% BTP-grafted DP 500 CFS DAAm PISA resin (Example 2);

[0023] Fig. 18 is a photograph of a 10% BTP-grafted DP 500 CFS DAAm PISA resin printed lattice cube at a normal exposure time of 10 s per layer (Example 2);

[0024] Fig. 19 contains scanning electron microscope (SEM) images of a cured, lyophilized part using 10% grafted CFS PISA resins with a DP 500 targeted DAAm block (Example 2);

[0025] Fig. 20 shows AFM imaging of 10% grafted CFS PISA resins with a DP 500 targeted DAAm (Example 2);

[0026] Fig. 21 shows the results of dissolution studies for CFS DAAm PISA resins at varying combinations of DP and CTA graft density of the CFS (Example 2);

[0027] Fig. 22 shows the results of dissolution studies of 10% DCT-grafted CFS HPMA PISA resins (Example 2);

[0028] Fig. 23 shows the results of dissolution studies of 5% BTP-grafted CFS DAAm PISA resins with free 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (CCC; Example 2);

[0029] Fig. 24 provides graphs of the elastic modulus, strain-to-break, and toughness properties as a function of DP using fixed solids content (25 wt. %) and fixed BTP graft density (10%), as described in Example 2;

[0030] Fig. 25 contains graphs of the elastic modulus, strain-to-break, and toughness properties as a function of increasing BTP graft density at a fixed DP (1,000) and fixed solids content (25 wt %);

[0031] Fig. 26 provides graphs of the elastic modulus, strain-to-break, and toughness properties as function of solids content at a fixed DP 500 and fixed BTP graft density (10%);

[0032] Fig. 27 shows the Beer’s Law standard curve (left) measured in 91% isopropyl alcohol for BTP RAFT agent and the absorbance spectra (right) for DMA RSS polymer made with BTP RSN compared to the absorbance spectra for a blank sample (91% isopropyl alcohol) (Example 3);

[0033] Fig. 28 shows the dissolution rate of PISA-cured resins as a function of increasing mole fraction of BAm relative to AM in the fixed DP 1,000 core-forming block (Example 3);

[0034] Fig. 29 shows the dissolution rate of PISA-cured parts as a function of increasing DP of the core-forming block at a fixed molar composition of 95 mol % AM and 5 mol % BAM (Example 3);

[0035] Fig. 30 is a photograph of DLP-printed microneedles made using PISA-based RSS resins (Example 3);

[0036] Fig. 31 is a photograph of DLP-printed microneedles made using PISA-based RSS resins (Example 3);

[0037] Fig. 32 is a photograph of the microneedles of Figs. 30 (right) and 31 (left) in lx PBS following the dissolution of the platform supporting them (Example 3);

[0038] Fig. 33 provides SEM images of microneedles having horizontal / vertical orientation (Example 3);

[0039] Fig. 34 provides SEM images of microneedles having diagonal orientation (Example 3);

[0040] Fig. 35 shows the AFM characterizations (scale bar: 150 nm) of PISA printing resins, including topography image of cured PISA resin containing 0.1 wt. % LAP photoinitiator (top left), AFM topography image of cured PISA resin containing 0.1 wt. % LAP and a target DP of 500 (top middle), AFM 3D view of cured sample with 0.1 wt. % LAP (top right), and AFM 2D topography images of those same cured samples (bottom) (Example 3);

[0041] Fig. 36 is a graph of the drug release profile of 10C AM from cured crosslinker-containing, PISA-based microneedle resins, released slowly into serum up to 6% over a period of 8 hours (Example 3);

[0042] Fig. 37 is a graph of the drug release profile of MBT from cured crosslinker-containing, PISA-based microneedle resins, where the MBT release increased to greater than 20% over a period of 4 hours into PBS buffer (Example 3);

[0043] Fig. 38 is a graph of the drug release profile of MBT from cured PISA-based microneedle resins absent of MBAc crosslinker (Example 3);

[0044] Fig. 39 shows AM / HEAM dragonflies (DP 250 AM / DP250 HEAM and DMA one-pot method in ethanol);

[0045] Fig. 40 shows DAAM dragonflies (DP 250 DAAM and DMA one-pot method in water);

[0046] Fig. 41 shows IB A dragonflies (DP 150 IB A and DMA one-pot method in an 85 ethanol / 15 water mixture); and

[0047] Fig. 42 provides optical images of 3D printed blood vessels using AM and DAAM based resins.DETAILED DESCRIPTION

[0048] The present disclosure is concerned with methods of 3D printing that can be used to develop vascularized tissue, for drug delivery, and other biomedical applications, and particularly those requiring biodegradable structures. The method broadly involves preparing a polymer scaffold and then exposing that polymer scaffold to electromagnetic radiation (e.g., UV light, visible light) in the presence of phase-separating monomers, a photoinitiator, and preferably a photoabsorber in a solvent(s) in which the scaffold is soluble and the phase-separating monomers are insoluble.POLYMER SCAFFOLD

[0049] The polymer scaffold, or “Macro-CTA,” comprises a polymer that is functionalized with at least two chain transfer agents (CTAs). Suitable polymers are chosen to function as a stabilizing agent in 3D printing ink solvents and should be solvophilic towards those solvents and will be soluble in the solvent used in the 3D printing ink. As used herein, a component is considered soluble in a solvent or a mixture of solvents (e.g., a mixture of a hydrophilic solvent with a less hydrophilic solvent, a mixture of a hydrophilic solvent with a hydrophobic solvent, etc.) if, at a concentration of about 0.1 g / mL, at least about 95% by weight of that component dissolves in that solvent (or solvent mixture) after about 10 minutes of mixing under ambient conditions (i.e., about 20°C to about 25°C). In other embodiments, a component is considered soluble in a solvent (or solvent mixture) if, at a concentration of about 50%, at least about 95% by weight of that component dissolves in that solvent (or solvent mixture) after about 10 minutes of mixing under ambient conditions (i.e., about 20°C to about 25°C).

[0050] The polymer can be a homopolymer or a copolymer. More than one polymer type can also be utilized. Suitable polymers and / or copolymers include those containing reactive groups that can be conjugated to RAFT CTAs including hydroxyl, amine, thiol, and / or epoxide groups. Examples of suitable reactive monomers include glycidyl methacrylate, hydroxyethyl methacrylate, (meth)acrylic acid, acrylic acid, hydroxyethyl acrylamide, and / or hydroxyethyl acrylate. Examples of suitable polymers include one or more of polyethylene glycol, [epoxycyclohexylethyl)methylsiloxane]- dimethyl siloxane copolymer (E-PDMS), biopolymers (e.g., proteins such as gelatin, growth factors, etc. polysaccharides such as alginate, chitosan, etc.), polymeric drugs, or combinations of the foregoing.

[0051] Suitable polymers also include those comprising monomers chosen from one or more of N’N-dimethylacrylamide, N-(2-hydroxyethyl)acrylamide, benzyl methacrylate benzyl acrylate, mono- 2-(methacryloyloxy)ethyl succinate 2-carboxyethyl acrylate 2-carboxyethyl acrylate oligomers, styrene, methyl methacrylate, ethyl acrylate, propyl acrylate, and / or methyl acrylate. In one or more embodiments, comonomers can be included to change the solubility characteristics of the final polymer and / or to change the CTA density along the polymer backbone. Examples of such comonomers include hydrophobic acrylates, acrylamides, methacrylates, and / or hydrophilic monomers such as dimethyl acrylamide, polyethylene glycol methacrylates with various PEG lengths, and / or zwitterionic monomers (e.g., DM APS).

[0052] Suitable CTAs for use in the present methods include typical reversible addition-fragmentation chain-transfer (RAFT) polymerization agents, including macromolecular design by interchange of xanthates (MADIX) agents. In some embodiments, the CTAs are thiocarbonylthio compounds such as dithioesters, dithiocarbamates, tri thiocarbonates, dithiobenzoates, and xanthates. Examples of suitable CTAs include those chosen from one or more of 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid (DCT), 2- butylthiocarbonothioylthio)propanoic acid (BTP), 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4- cyanopentanoic acid (CCC), dibenzyl trithiocarbonate, 3-((((l- carboxyethyl)thio)carbonothioyl)thio)propanoic acid, 2-(((dodecylthio)carbonothioyl)thio)propanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, 4-((((2- carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, cyanomethyl methyl(phenyl)carbamodithioate, 2-cyanobutan-2-yl dodecyl carbonotrithioate, bis(dodecylsulfanyl thiocarbonyl)disulfide, methyl 4-cyano-4-(dodecylthiocarbonothioylthio)pentanoate, 2-cyanobutan-2- yl methyl(piridin-4-yl)carbamodithioate, bis(carboxyethylsulfanyl thiocarbonyl)disulfide, bis(methyl- pyridin-4-yl-amino-thiocarbonyl)disulfide, cyanomethyl (3,5-dimethyl-lH-pyrazole)-carbodithioate, benzyl 3 ,5 -dimethyl- 1 H-pyrazole- 1 -carbodithioate, bis(3 ,5-dimethyl- 1 H-pyrazol- 1 - ylthiocarbonyl)disulfide, 2-cyanobutanyl-2-yl 3, 5-dimethy 1-1 H-pyrazole- 1 -carbodithioate, bis(4- chloro-3,5-dimethyl-lH-pyrazolesulfanylthiocarbonyl)disulfide, 2-cyanobutan-2-yl 4-chloro-3,5- dimethyl- 1 H-pyrazole- 1 -carbodithioate, 2-(buty Ithiocarbonothioy lthio)propanoic acid, 4-cy ano-4- (((dodecylthio)carbonothioyl)thio)pentanoic acid, 2-cyano-5-hydroxypentan-2-yl dodecyl trithiocarbonate, 1 ,4-phenylenebis(methylene) didodecyl dicarbonotrithioate, 4-cyano-4- (phenylcarbonothioylthio)pentanoic acid, 2,2'-[carbonothioylbis(thio)]bis[2-methylpropanoic acid], methyl 3-((l-methoxy-l-oxopropan-2-ylthio)carbonothioylthio)propanoate, benzyl butyl carbonotrithioate, 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, methyl 4-cyano-4-(dodecylthiocarbonothioylthio)pentanoate, or combinations of the foregoing.

[0053] The polymer scaffold can be synthesized by combining the above-described polymer in a reaction solvent with the CTA and a catalyst under conditions to functionalize the polymer with the CTA. To determine the molar concentration of the CTA, UV-Vis spectroscopy at a given mass of polymer can be used. This technique can provide more consistent results than using the molar mass of the polymer determined by GPC because there can be error associated with the GPC measurement. For example, in one technique, a 1 mg / mL solution of the macro-CTA can be made, and the concentration of CTA in that solution can be determined using UV-Vis spectroscopy using an extinction coefficient that is determined by running a standard curve with the starting CTA. After the polymer scaffold is formed, appropriate purification and solvent removal steps can be carried out to isolate the formed polymer scaffold or macro-CTA.

[0054] In embodiments where the polymer still needs to be formed, the one or more type of the above-described monomers can be subjected to RAFT polymerization by adding the monomers to a reaction solvent (preferably water), along with a photoinitiator and preferably a photoabsorber. Polymerization can then be carried out by exposing to light (e.g., at a wavelength of about 100 nm to about 700 nm, about 100 nm to about 400 nm, about 400 nm to about 700 nm) for the appropriate time frame (e.g., about 36 to about 50 hours), followed by any appropriate purification steps to remove unreacted monomer, excess photoinitiator and / or photoabsorber, and / or solvent so as to isolate the polymer. The isolated polymer can then be grafted with the particular CTAs in a reaction solvent in the presence of a catalyst, so as to functionalize the polymer with the CTA. Again, appropriate purification and solvent removal steps can be carried out to isolate the formed polymer scaffold or macro-CTA.

[0055] In a further embodiment, a “one-pot” synthesis method can be employed. This approach relies on the RAFT copolymerization of a monomer (e.g., DMA) with a small fraction of crosslinker (e.g., bisacrylamide) in a monomer: CTA: crosslinker ratio of 100:1 :0.7. Under mild conditions, the reaction can proceed to quantitative conversion within about 18 hours, yielding a concentrated polymer scaffold (macro-CTA) solution that can be used directly without further purification. This protocol produces nano-crosslinked scaffolds that remain soluble, with particle sizes below about 15 nm. Furthermore, to circumvent the need for extensive oxygen removal during the polymerization, a photoinitiated electron transfer (PET) RAFT procedure using green light illumination, Eosin Y, and triethylammonium hydroxide (TEAOH) can be employed. This PET RAFT method similarly reaches full conversion within 24 hours, affording a concentrated polymer scaffold solution suitable for direct application. It will be appreciated that by minimizing the number of synthetic steps and eliminatinglaborious purification procedures, both the thermal and PET RAFT protocols make PISA Printing more approachable and cost-effective for a wide range of research and manufacturing settings.

[0056] Regardless of how the polymer scaffold is formed, the degree of polymerization (DP) is typically about 100 to about 10,000, preferably about 100 to about 8,000, more preferably about 200 to about 5,000, and even more preferably about 200 to about 1,000. As used herein, DP is determined by multiplying the target DP by the conversion ( / ?) of monomer to polymer during the polymerization process. To do this, a Nuclear Magnetic Resonance (’ H NMR) scan can be taken prior to and immediately after polymerization to determine the conversion. This is done by spiking the polymerization solution with an internal standard (N’N-dimethylformamide or DMF) and integrating the area under the vinyl peaks of the monomer (2 / 3 H, 5.5 - 6.5 ppm) with respect to the DMF peak (]H, 8 ppm) and then determining the % reduction in area under the vinyl peaks during the polymerization process. This is known as the conversion, p.

[0057] Additionally, the average level of CTA grafted to the polymer, referred to as “graft density” of the polymer scaffold, is typically about 0.5% to about 15%, preferably about 0.5% to about 10%. Graft density is determined by UV-Vis, as described in Example 1.

[0058] In some embodiments, the average number of CTA groups present per polymer scaffold is at least 2, preferably at least about 20, more preferably about least about 50, even more preferably at least about 70. Additionally or alternatively, the average number of CTA groups present per polymer scaffold is 2 to about 150, preferably about 10 to about 125, more preferably about 25 to about 100, and even more preferably about 50 to about 100. The average number of CTA groups present per polymer scaffold is determined by UV-Vis. A known concentration of macro-CTA is prepared in water at a concentration in terms of g / L, and the absorbance is measured at 325 nm. A standard curve for the individual CTA compound is then constructed by varying the concentration of CTA in samples and measuring each sample’s absorbance value at 325 nm. This standard curve plots concentration (M) versus absorbance (unitless), and an equation for the slope of the generated curve is determined. The absorbance value obtained from the macro-CTA can then by plugged into the standard curve slope equation to determine the CTA concentration in solution in terms of mole / L. The concentration of CTA in solution (mole / L) is then divided by the concentration of macro-CTA in solution (g / L) to gives the number of CTAs (in moles) per g of polymer.PRINTING INKS

[0059] Printing inks for use herein are photosensitive and can be formed by mixing the previously described polymer scaffolds with a phase-separating monomer(s), photoinitiator(s), and preferably aphotoabsorber(s) in a solvent system. The ink can be prepared at the time of use, or it can be prepared in advance and stored in a light-free manner until the time of use.

[0060] The phase-separating monomer should be chosen so that it is soluble in the printing ink solvent system but that, upon photopolymerization, will form polymer chains that are insoluble in the printing ink solvent system. As used herein, a component is considered insoluble in a solvent if, at a concentration greater than 0.1 g / mL, less than about 5% by weight of that component dissolves in that solvent after about 10 minutes of mixing under ambient conditions (i.e., about 20°C to about 25°C).

[0061] Typical such phase-separating monomers include those chosen from one or more of diacetone acrylamide (DAAm), acrylic acid (AA), [2-(methacryloyloxy)ethyl]dimethyl-(3- sulfopropyl)ammonium hydroxide (DMAPS), hydroxypropyl methacrylate (HPMA), acrylamide (AM), 2-hydroxyethyl acrylamide (HEAM), isobornyl acrylate (IBA), methyl methacrylate, butyl acrylate, and / or butyl methacrylate.

[0062] The polymer scaffold and phase-separating monomer(s) can be included at varying quantities, depending on the desired properties in the final printed structure. In some embodiments, this involves a molar ratio of phase-separating monomer to CTA of about 25:1 to about 2,000: 1, preferably about 25: 1 to about 1,000: 1, more preferably about 40: 1 to about 750:1, and even more preferably about 100:1 to about 500:1. This typically results in the polymer scaffold being present in the printing ink at a level of about 10% to about 50% by weight, more preferably about 10% to about 40% by weight, and even more preferably about 10% to about 35% by weight, based on the weight of total solids in the printing ink taken as 100% by weight. The phase-separating monomer is typically present in the printing ink at a level of about 10% to about 50% by weight, more preferably about 10% to about 40% by weight, based on the weight of total solids in the printing ink taken as 100% by weight.

[0063] In some embodiments, weight ratio of phase-separating monomer to polymer scaffold is about 0.5: 1 to about 5: 1. In other embodiments, the weight ratio of phase-separating monomer to polymer scaffold is about 1: 1. In one or more embodiments, the combined weight of the polymer scaffold and the phase- separating monomer is about 20% to about 40% by weight, and preferably about 25% to about 35% by weight, based on the total weight of the printing ink taken as 100% by weight.

[0064] The solvent system can include only one solvent or a mixture of two or more solvents. Suitable solvents include any solvent that does not inhibit free radical polymerizations or destroy the CTA (RAFT) agents or phase-separating monomers can be used. Preferred solvents are generally nonvolatile, and preferably non-corrosive. Additionally, the solvent(s) are selected so that both the polymer scaffold and the phase-separating monomer are soluble therein, but that the polymer formed from the phase-separating monomer is insoluble in that solvent(s). For mixed solvents, this typicallythis involves mixing two miscible or partially miscible solvents with different polarities such that hydrophobic or hydrophilic monomers can be dissolved with scaffolds with different polarities. For example, a polydimethylsiloxane scaffold is highly hydrophobic while acrylic acid is hydrophilic. However, they both dissolve in toluene. Alternatively, a more polar like ethyl acetate could be added to the solvent system to effect dissolution.

[0065] With the foregoing criteria in mind, typical printing ink solvent systems include water, acetic acid, ethanol, or mixtures thereof. In some embodiments, there may polymers and monomers where no suitable co-solvent exists. In those embodiments, mixing two or more solvents could allow both the polymer scaffold and the phase-separating monomers to be soluble. For example, suitable a solvent mixture could include ethanol and / or methanol with water, dioxane and hexane, dioxane toluene, acetic acid and water, acetic acid and ethyl acetate, butyl acetate and isopropanol, etc.

[0066] In one or more embodiments, the solvent system is substantially free of solvents comprising phenol groups. In the same or different embodiments, the solvent system is substantially free of chlorinated solvents (e.g., chloroform). Additionally or alternatively, the solvent system is substantially free of primary and / or secondary amine solvents. As used in this context, “substantially free” means that the solvent system comprises less than about 2%, preferably less than about 1%, and even more preferably about 0% by weight of the particular solvent, wherein the percentages by weight are based on the weight of the solvent system taken as 100% by weight.

[0067] The total solvent system levels in the printing ink will typically be about 55% to about 90% by weight, more preferably about 60% to about 85% by weight, and even more preferably about 60% to about 75% by weight, based on the weight of the printing ink taken as 100% by weight. The total solids level in the printing ink is about 10% to about 50% by weight, preferably about 15% to about 45% by weight, and more preferably about 25% to about 40% by weight, based on the weight of the printing ink taken as 100% by weight.

[0068] Any photoinitiator capable of creating a reactive species upon exposure to light is suitable for use herein. Some examples include one or more chosen from lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP), diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO), benzoyl peroxide, bisacylphosphine oxide, benzophenone, phenanthrenequinone, 1 -phenyl- 1,2 propanodione, or combinations of the foregoing. The photoinitiator is typically present in the printing ink at a level of about 0.1% to about 10% by weight, more preferably about 0.5% to about 5% by weight, and even more preferably about 0.5% to about 3% by weight, based on the weight of total solids in the printing ink taken as 100% by weight.

[0069] Any photoabsorber that absorbs or reduces the energy of light can be used in the printing inks. Examples of such photoabsorbers include one or more chosen from phenol red, tartrazine, OilRed O, methylene blue, coccine, or crystal violet. The photoabsorber is typically present in the printing ink at a level of about 0.5% to about 7% by weight, more preferably about 0.5% to about 5% by weight, and even more preferably about 1% to about 3% by weight, based on the weight of total solids in the printing ink taken as 100% by weight.

[0070] In one or more embodiments, the printing ink is substantially free of crosslinking agents (i.e., agents that cause covalent or chemical crosslinking to take place between polymer chains). That is, in these embodiments, the printing ink comprises less than about 2%, preferably less than about 1 %, and even more preferably about 0% by weight crosslinking agents, wherein the percentages by weight are based on the total solids in the printing ink taken as 100% by weight.

[0071] In alternative embodiments, the printing ink may include a small amount of crosslinking agent to effect light (covalent) crosslinking between polymer chains, particularly in situations where there is a desire to fine tune the dissolution rate of the final structure. Crosslinking agents having two highly reactive double bonds (e.g., acrylate, methacrylate, acrylamide, methacrylamide, maleimide, and / or styrenic groups) will polymerize early in the process, yielding limited morphologies in the phase-separated domain. Thus, an asymmetric crosslinking agent where one of the double bonds is highly reactive like those listed above and one of the double bonds is considerably less reactive towards free radicals is desirable. In this scenario, the highly reactive monomer polymerizes first and is evenly distributed throughout the phase separated domain while the less reactive monomer does not react until later in the polymerization, after the morphologies have formed. In these embodiments, the crosslinking agent is present at levels of about 0.1% to about 4% by weight, preferably about 0.1% to about 3% by weight, and more preferably about 0.5% to about 2.5% by weight, wherein the percentages by weight are based on the total solids in the printing ink taken as 100% by weight.

[0072] In some embodiments, the printing inks can include one or more optional components, in addition to the foregoing. Examples of potential additives include, but are not limited to, crosslinkers, surfactants, wetting agents, dyes, colorants and pigments, drugs, small molecule, peptides, proteins, mRNA, siRNA, DNA, or other nucleic acids or nucleic acid systems, or combinations of the foregoing. These optional components would be selected depending on the desired properties and use of the final composition.

[0073] In one or more embodiments, the printing ink consists essentially of, or even consists of, the polymer scaffold(s), phase-separating monomer(s), photoiniator(s), and photoabsorber(s) dispersed or dissolved in the solvent system.PRINTING METHODS

[0074] The above-described printing inks can be used in any equipment or process that utilizes exposure to light energy to carry out a reaction, but it is particularly well-suited for additive manufacturing or 3D printing by digital light processing (DLP). Suitable DLP equipment for use herein includes any commercially available DLP printers (such as the Anycubic Photon D2 DLP Printer, the Phrozen Sonic Mini 8K DLP Printer), by simply following typical processes for that equipment. Additionally, any 3D printing slicer software that is compatible with the selected DLP printer is suitable for use herein, with one example being the software sold by Chitubox.

[0075] Fig. 1 provides a schematic depiction of the DLP printing process. The platform moves vertically along the Z-axis to create a hardened (or lightly cure in those embodiments where a small amount of crosslinking agent is present) model in a layer-by-layer fashion from a liquid resin (i.e., the above-described printing ink) contained in a tank. The process leverages a light source (UV in this instance, but other sources could be used, including visible light) projected through a lens system that is reflected off a mirror to harden (or lightly cure) specific areas of the resin in the printing ink (i.e., the printing ink changes from flowable to nonflowable in the areas that were exposed to light. Thus, the printing process involves selectively exposing the printing ink to UV light, forming one (printed) layer at a time. Layer thickness can be quite thin, with typical thicknesses being less than about 200 pm, preferably less than about 150 pm, more preferably less than about 100 pm, and even more preferably about 20 pm to about 100 pm. Additionally, because the printing ink is selectively exposed to light, the printed layer will usually comprise a pattern (lines, shapes, etc.), depending on the cross- sectional shape of that particular layer in the final overall printed structure.

[0076] During this exposure, the photoinitiator initiates chain-extending of the phase-separating monomer(s) from the CTA groups on the polymer scaffold. The polymer “arms” or branches formed during this chain extension are insoluble in the printing ink solvent system, thus allowing them to form phase-separated domains. The average degree of polymerization of these arms is typically about 20 to about 5,000, preferably about 50 to about 3,000, more preferably about 75 to about 1,500, and even more preferably about 90 to about 1 ,000.

[0077] In embodiments where the printing ink does not include a crosslinking agent, no covalent or chemical crosslinking takes place between polymer chains during this exposure. Rather, the phaseseparating monomers that are chain-extended from the CTA groups will form phase-separate domains from the polymer of the polymer scaffold. The polymer of the polymer scaffold functions as stabilizing segments. These actions lead to the formation of physical crosslinking or solvophobic segment entanglements caused by interparticle bridging and interparticle knots (schematically depicted in Figs. 2-3).

[0078] In embodiments where no crosslinking agent is included in the printing ink, the printed layers are free of chemical crosslinking between polymer chains and only include physical crosslinking between polymer chains, as described above. That is, the chemical crosslink density is less than about 1 mol / nm3of hardened material, and preferably about 0 mol / nm3of hardened material. In embodiments where a small amount of crosslinking agent is included to adjust the dissolution rate of the final structure, there will be light covalent crosslinking, with the remainder of the crosslinking being physical crosslinking. As used herein, crosslink density can be determined by ASTM-D2765.In one or more embodiments, (1 ) materials are considered uncrosslinked if those materials dissolve by at least about 98% (and preferably about 100%) and can be run on a GPC system, (2) materials are considered lightly crosslinked if they dissolve by at least about 98% (and preferably about 100%) but form nanostructures that cannot be dissolved, and (3) materials are considered crosslinked if they dissolve by about 2% or less (and preferably about 0%), or swell but do not dissolve.

[0079] Typical exposure wavelengths are about 100 nm to about 700 nm, preferably about 100 nm to about 450 nm, more preferably about 350 nm to about 450 nm, and even more preferably about 400 nm to about 405 nm, with the latter being the typical wavelength of a commercial digital light projection (DLP) 3D printer. Typical intensities are about 0.75 to about 2.5 mW / cm2. Typical UV exposure times are less than about 90 seconds / layer, and preferably less than about 60 seconds / layer. In some embodiments, UV exposure time is about 5 to about 90 seconds / layer, preferably about 5 to about 60 seconds / layer, and even more preferably about 5 to about 30 seconds / layer.

[0080] It will be appreciated that the compositions and methods herein can form three-dimensional structures of any shape, size, dimension, etc., desired for the end use, and these structures can be printed much more rapidly than prior art structures. Additionally, high resolutions can be obtained by this method. That is, feature sizes about 50 pm or smaller are achievable. In some embodiments, the resolution is about 1 pm to about 50 pm, preferably about 1 pm to about 40 pm, more preferably about 1 pm to about 30 pm, and even more preferably about 1 pm to about 20 pm.

[0081]

[0082] In the same or different embodiments, the structures formed herein will have an elastic modulus (determined as described in Example 2) of about 50 kPa to about 400 kPa, preferably with greater moduli values overall.

[0083] In the same or different embodiments, the structures formed herein will have a strain-to- break (determined as described in Example 2) of about 200% to about 1,200%. The preference for strain-to-break depends and can vary on the specific application of the part.

[0084] In the same or different embodiments, the structures formed herein will have a toughness (determined as described in Example 2) of about 100 kJ / m3to about 1,300 kJ / m3, preferably with greater overall toughness values.

[0085] In the same or different embodiments, the structures formed herein will have a dissolution rate (determined as described in Example 2) of about 4 mg / min to about 28 mg / min, preferably with higher values for applications such as tissue engineering scaffolds and cell adhesion and preferably lower values for microneedle applications that require faster dissolution rates.

[0086] It will be appreciated that the foregoing properties of this material and method allow for the final structures to be designed for, and used in, a wide variety of end uses, including fugitive scaffolds, dissolvable microneedles, tissue engineering, drug delivery systems (including those requiring sustained drug release), development of vascularized structures, microfluidic devices, and other fields requiring precisely tailored materials.

[0087] In drug delivery systems, polymerizable drugs (e.g., such as a prodrug) can be copolymerized when the polymer scaffold or macro-CTA is formed, so that the formed polymer scaffold is drug-bearing. In other embodiments, the species to be delivered can be physically encapsulated in the formed structure.

[0088] Additional advantages of the various embodiments will be apparent to those skilled in the art upon review of the disclosure herein and the working examples below. It will be appreciated that the various embodiments described herein are not necessarily mutually exclusive unless otherwise indicated herein. For example, a feature described or depicted in one embodiment may also be included in other embodiments but is not necessarily included. Thus, the present disclosure encompasses a variety of combinations and / or integrations of the specific embodiments described herein.

[0089] As used herein, the phrase "and / or," when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing or excluding components A, B, and / or C, the composition can contain or exclude A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0090] The present description also uses numerical ranges to quantify certain parameters relating to various embodiments. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claim limitations that only recite the upper value of the range. For example, a disclosed numerical range of about 10 to about 100 provides literal support for a claim reciting "greater than about 10" (with no upper bounds) and a claim reciting "less than about 100" (with no lower bounds).

[0091] Additionally, “a” is intended to include one and more than one, unless specified otherwise.EXAMPLES

[0092] The following examples set forth methods in accordance with the disclosure. It is to be understood, however, that these examples are provided by way of illustration, and nothing therein should be taken as a limitation upon the overall scope.EXAMPLE 1Printing Diacetone Acrylamide with Difunctional Polyethylene Glycol Macro-CTA1. Materials

[0093] Poly(ethylene glycol) (PEG, MW=10,000 Da), poly(ethylene glycol) mono methyl ether (PEGME, MW=5,000 Da), and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (DM APS, 95%) were obtained from Sigma- Aldrich.

[0094] 2-Butanone (>99%), ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (>95%), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (TPO, >96%), acrylic acid (AA, >99%), and glacial acetic acid (>99.5%) were obtained from TCI America.

[0095] Diacetone acrylamide (DAAm, 99%) and N,N’ -methylenebisacrylamide (MB Ac, 97%) were obtained from Alfa Aesar.

[0096] Lithium bromide (>99%), 4-dimethylaminopyridine (DMAP, >99%), and 3-(3- dimethylaminopropyl)-l-ethyl-carbodiimide hydrochloride (EDC, >99%) were obtained from Chem Impex International.

[0097] Acetone (>99.5%) was obtained from Fisher Scientific.

[0098] 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid (DCT, 97%) was obtained from Boron Molecular.

[0099] Phenol Red (-95%) was obtained from Aldrich Chemical Co.2. Synthesis of Lithium Phenyl-2,4,6-Trimethylbenzoylphosphinate (LAP) Photoinitialor [000100] To a 250-mL beaker containing 100 mL of 2-butanone, ethyl phenyl(2,4,6- trimethylbenzoyl)phosphinate (5.73 g, 18.1 mmoles) and lithium bromide (6.30 g, 72.7 mmoles) were added and stirred into solution. Once dissolved, the mixture was heated in a 60°C water bath for 24 hours. The precipitated product was vacuum-filtered, washed four times with 2-butanone, and vacuumed dry to obtain the pure white solid (3.47 g, -65% yield).3. Synthesis of Difunctional PEG Macro-CTA[000101] To a 300-mL beaker containing dichloromethane (-100 mL), PEG (8.26 g, 0.826 mmoles), DCT (1.00 g, 2.48 mmoles), and DMAP (0.302 g, 2.48 mmoles) were added and magnetically stirred into solution. Once homogenized, EDC (0.475 g, 2.48 mmoles) was slowly fed into the solution, and the mixture was allowed to react overnight. Following reaction, the mixture was dialyzed in SpectraPor Regenerated Cellulose Dialysis tubing (6 - 8 kDa cutoff) against acetone for 3 days to remove any excess DCT. This was followed by dialysis against distilled water to remove residual acetone. The purified solution was frozen and lyophilized to obtain the final product.[000102] The difunctional PEG macro-CTA was characterized via]H Nuclear Magnetic Resonance (NMR, Broker 400MHz) and UV-Vis Spectrometry (Tecan Infinite M Nano+).]H NMR in CDCh was used to identify the appearance of the ester peak (4H, -4.2 ppm) that forms during reaction between PEG and the DCT RAFT agent. Integration of these ester protons with respect to the methylene protons of PEG (-3.8 ppm) indicated the efficiency of the esterification reaction. UV-Vis was used to quantify the CTA density per gram of polymer for the synthesized macro-CTAs (10 mg / mL in solution) utilizing DCT as a standard curve in 70% isopropanol at a wavelength of 325 nm. GPC of samples were measured using DMF + 0.1 wt% LiBr as the mobile phase and PS as the calibration standards.4. Synthesis of Monofunctional PEG Macro-CTA[000103] To a 100-mL beaker containing dichloromethane (-50 mL), PEGME (4.13 g, 0.825 mmoles), DCT (0.500 g, 0.124 mmoles), and DMAP (0.151 g, 0.124 mmoles) were added and magnetically stirred into solution. Once homogenized, EDC (0.237, 0.124 mmoles) was slowly fed into the solution, and the mixture was allowed to react overnight. Following reaction, the mixture was dialyzed in SpectraPor Regenerated Cellulose Dialysis tubing (3.5 kDa cutoff) against acetone for 3 days to remove excess DCT. The solution was then dialyzed against water for two days, frozen and lyophilized.[000104] To verify that physical crosslinking of PISA resins is a result of multi-functional RAFT macro-CTAs, UV curing trials of PISA resins that employed monofunctional RAFT macro-CTAs were studied. CTA density of the macro-CTA was determined via UV-Vis using Beer’s Law standard curve. The DP (degree of polymerization) of the chain-extended solvophobic block (DAAm) was varied (DP 250, 500, 750, 1000). Total solids concentration for the prepared monofunctional resins was fixed at 40 wt. %, and photoinitiator concentration was kept fixed at 0.5 wt. % with respect to solids. DAAm monomer, monofunctional PEG macro-CTA and distilled water were added to a 50-mL tube and vortexed until homogeneous. The LAP photoinitiator was prepared as a stock in distilled water at aconcentration of 50 mg / mL and then added to the 50 mL tube containing the resin. Next, 600 (1L of each resin with varied DP were pipetted in the middle of the 3D DLP printer resin vat and exposed under UV light for 2 minutes on the printer.t Following UV exposure, the resin drops were lightly scraped to see if they held their shapes. A representative procedure for preparation of DP 250 DAAm resin is as follows: to a 50-mL tube, 1 g difunctional PEG macro-CTA (0.5 g, 0.063 mmoles DCT), DAAm (2.66 g, 15.8 mmoles), and distilled water (4.74 g) were added and vortexed. Next, 316 pL of a 50 mg / mL LAP stock in water was added to the resin and vortexed.[000105] Fig. 4 shows that all resins successfully underwent PISA when exposed to UV light as evidenced by the increase in opacity with increasing DP. Resins were lightly scraped following 2- minute UV exposure. Although the DP 250 resin slightly gelled, it failed to hold its shape following exposure which indicates little if any physical crosslinking. DP 500, 750 and 1000 resins showed little, if any, evidence of gelation and were very fluid. These studies show the use of multi-functional RAFT agents promoted the physical crosslinking necessary for the exposed resin to cure and hold its shape during 3D DLP printing.5. PISA DLP Printing of Crosslinked and Uncrosslinked Resins Using Difunctional PEG Macro- CTA[000106] To synthesize 3D DLP PISA resins, the CTA density per gram polymer (moles DCT / g PEG macro-CTA) was used to target a degree of polymerization for the PISA 3D printing resin. This value was 0.139 mmoles DCT / g polymer (75% theoretical). In terms of resin formulation, hydrophilic difunctional PEG macro-CTA was blocked either with DAAm under aqueous conditions or with acrylic acid and DMAPS in acetic acid. DAAm monomer is soluble in water, but its homopolymer is not. The target degree of polymerization for this PISA was 500 as a total solids concentration of 40 wt. %. The target degree of polymerization (DP) of 500 is based on the total number of CTAs present in the polymer (DP 500 from both arms of the RAFT agent). The CTA graft density was determined via UV-Vis. LAP was employed as a water-soluble photoinitiator at a concentration of 0.25 wt. % with respect to solids. Phenol red was additionally employed as a photoabsorber at a concentration of 0.01 wt. % with respect to solids. Two resins were prepared and 3D-printed under PISA conditions: one with and without inclusion of MBAc crosslinker. In the case of the MBAc-containing crosslinker, MBAc was included at a concentration of 2.5 wt% with respect to solids.[000107] Similarly, PISA resins were formulated by blocking AA and DMAPS to difunctional PEG macro-CTA in acetic acid. The DMAPS monomer is soluble in acetic acid, but its polymer is not. However, DMAPS alone was slow to block and formed a very sticky print that would get stuck to the resin vat. Addition of AA seemed to speed up curing and reduce stickiness of the cured parts whileenough DMAPS was still present in the formulation to promote self-assembly. In this case, the target degree of polymerization for the AA was 550 and for the DMAPS was 300, all at a total solids concentration of 35 wt. %. TPO was employed as the photoinitiator at a concentration of 0.75 wt. % with respect to solids. Phenol red, sparingly soluble in acetic acid, was still employed as the photoabsorber at a concentration of 0.01 wt. % with respect to solids, though the phenol red was more suspended than dissolved. Much like with the DAAm formulation, two resins were prepared: one with and without MB Ac crosslinker in a manner similar to what was described previously.[000108] Resins were filtered through a fine mesh into the resin vat. ChituBox slicing software was used to set printing parameters and prepare the file for printing on the AnyCubic Photon Mono DLP printer. DAAm PISA printing parameters included 100 pm layer thickness, a bottom exposure time of 45 s per layer and a normal exposure time of 40 s per layer. Acrylic acid-co-DMAPS PISA printing parameters included a layer thickness of 100 pm, a bottom exposure time of 50 s per layer, and a normal exposure time of 45 s per layer. Prints included tree frogs for DAAm and acrylic acid-co- DMAPS resins in addition to an ASTM D638 Type V dogbone for DAAm resins. A representative procedure for DAAm PISA resin preparation without crosslinker is as follows: to a 50-mL conical tube, difunctional PEG macro-CTA (1 g, 0.139 mmoles DCT), DAAm (11.7 g, 69.3 mmoles), LAP (31.8 mg, 0.108 mmoles), and phenol red (1.27 mg, 3.59 pmoles) were dissolved homogeneously in distilled water (19.1 g). A representative procedure for acrylic acid-co-DMAPS PISA resin preparation without crosslinker is as follows: to a 50-mL conical tube, difunctional PEG macro-CTA (1 g, 0.139 mmoles DCT), acrylic acid (5.50 g, 76.3 mmoles), DMAPS (13.44 g DMAPS, 48.2 mmoles), and TPO (150 mg, 0.357 mmoles) were dissolved in acetic acid (37.0 g). Phenol red (1.99 mg, 5.63 pmoles) was additionally added but stayed suspended in acetic acid.6. Dissolution Studies of 3D PISA Prints[000109] Following 3D printing of PISA resins with and without crosslinker, PIS A-printed tree frogs using DAAm were placed into DMF for dissolution studies. DMF was chosen since it should solubilize both PEG and DAAm blocks of the PISA polymer. The printed tree frog without crosslinker and printed tree frog containing MB Ac crosslinker were placed in separate 100 mL beakers containing 50 mL of DMF. Dissolution (or lack thereof) was documented for 4 hours. Additionally, PISA printed tree frogs using AA and DMAPS in acetic acid were placed into 0.5 M NaCl aqueous solution for dissolution studies. The salt solution was chosen as it should solubilize PEG, acrylic acid, and DMAPS. Frogs were placed into 50-mL salt solutions, and dissolution was followed for two to four hours.[000110] Fig. 5 shows that the DAAm PISA frog without MBAc crosslinker dissolved in DMF following 3D printing, thus indicating physical-crosslinking of the part. Fig. 6 shows that the DAAm PISA frog with MBAc crosslinker did not dissolve following 3D printing but did swell.7. Characterization of 3D Printed PISA polymers[000111] PISA polymers were characterized via 'H Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Gel Permeation Chromatography (GPC), and Atomic Force Microscopy (AFM). H NMR of the starting resins of DAAm and AA-co-DMAPS that contained no MBAc crosslinker were measured in D2O. After dissolution of the frogs for both DAAm PISA (in DMF) and AA-co-DMAPS PISA (in aqueous brine solution),]H NMR of the dissolved solutions of DAAm frogs and acrylic acid-co-DMAPs frogs were taken in CDCh and D2O, respectively. In doing so, conversion of the monomer in the post-printed part could be determined by measuring the disappearance of the vinyl resonances (5.5 - 6.5 ppm depending on the monomer) with respect to the methylene protons in the PEG backbone (OCH2CH2, ~3.6 ppm). Additionally,1H NMR of lyophilized, uncrosslinked PISA polymers for both DAAm and AA-co-DMAPS were measured in CDCI3 and D2O, respectively.1H NMR of the pure materials helped to estimate composition and degree of polymerization for the blocked polymer, which was later confirmed by GPC. SEM imaging of the lyophilized DAAm PISA 3D printed part was performed by first sputter coating the fractured surface with Au using a Denton sputter coater. The microstructure of the coated surface was then imaged on the PRISMA E SEM at a voltage of 20 kV. GPC of DAAm dissolved frogs samples were measured using DMF + 0. 1 wt% LiBr as the mobile phase and PS as the calibration standards. GPC of AA-co-DMAPS dissolved frogs was not measured due to lack of a suitable mobile phase for both PISA blocks. GPC results of the postprinted dissolved DAAm uncrosslinked frog are shown in Fig. 7. AFM was performed on a Dimension Icon system (Bruker) using the Scanasyst air mode. To prepare the samples, 10 uL of the freshly prepared polymer resin was deposited onto a freshly cleaved mica surface and cured under UV light for 1 minute, then drying for another 30 minutes. The Scanasyst mode with a scan rate of 0.8 Hz was used to determine the surface profiles of the resins with ultrasharp 14 series (NSC 14) tips purchased from Nanoandmore.8. Mechanical Properties of 3D-printed PISA Dogbones[000112] DAAm PISA resins with and without crosslinker were cast into a plastic ASTM D638 Type V dogbone mold and cured for 2 minutes under UV light. After demolding, the parts were immediately loaded onto the Shimadzu EZ-LX series tensile tester using 5kN load cell tensile grips. Stroke was set to a value of 10 mm / min, and parts were placed under tension until failure. Modulus of elasticity forthe materials was determined by taking the slope of the linear portion of the stress-strain curve that intersects the origin. The % elongation was determined using the displacement of the dogbone gauge length relative to its initial gauge length. Results of mechanical properties are summarized in Table 1 and Figs. 8 and 9. Referring to Fig. 8, the left graph provides results for dogbones cured from DAAm PISA resins containing 2.5 wt. % MB Ac crosslinker (i.e., chemically -crosslinked), and the right graph shows results for dogbones cured from DAAm PISA resin containing no MB Ac crosslinker (i.e., physically-crosslinked). Referring to Fig. 9, the left graph shows results for dogbones cured from AA- co-DMAPS resins containing 2.5 wt. % MBAc crosslinker (i.e., chemically-crosslinked), while the right graph provides results for dogbones cured from AA-co-DMAPS PISA resin containing no MBAc crosslinker (i.e., physically-crosslinked).Table 1. Mechanical Properties for DAAm Resins With and Without Crosslinker[000113] AA-co-DMAPS PISA resins with and without crosslinker were also cast into dogbones, dialyzed against isopropanol to remove the acetic acid, and measured. While the results were reported, the large inconsistencies that resulted for the uncrosslinked parts were attributed to the rapid drying of the isopropanol in the part as it was being measured. Due to the rapid drying, the part became stiffer during measurement. Nonetheless, this results still show a general trend.9. Controlled Dissolution Studies of 3D Printed PISA P Scaffolds[000114] DAAm PISA resins with and without crosslinker were prepared as described previously. Two separate parts (CAD design shown in Fig. 10) incorporating DAAm resins with and without crosslinker were printed to test controlled dissolution of the part architecture. In the case of theplatform and pillar scaffold design (top half of Fig. 10), the DAAm PISA resin containing crosslinker was used to print the platforms while the resin containing no crosslinker was used to print the pillars. In the case of the platform-cylinder design (bottom half of Fig. 10), the resin containing crosslinker was used to print the platform while the one without crosslinker was used to print the cylinders. ChituBox slicing software was used to determine the slices at which the design transitioned from a platform to pillar, which indicated the slice at which the resin needed to be swapped from the resin containing crosslinker to the one without crosslinker. This was repeated multiple times by stopping the print at the appropriate layer, cleaning the vat to avoid contamination and switching out the resin before finally resuming the print. The same process was repeated with the platform-cylinder design. Following printing, the parts were washed with distilled water and fully submerged in DMF for dissolution. Dissolution of the pillars and cylinder followed, while the platforms remained intact. Fig. 1 1 shows the printed platform and pillar scaffold before DMF submersion (left) and the dissolution of the pillars upon submersion (center). The top right portion of Fig. 11 shows the printed platformcylinder design before DMF submersion, while the bottom right portion of Fig. 11 shows the dissolution of the cylinders after submersion.10. Conclusion[000115] In summary, soluble 3D printed objects can be created using the PISA process to induce gelation. The resultant parts are mechanically stable, but they are not chemically crosslinked. This allows them to dissolve or swell when immersed in different solvents. Based on these findings, the PISA process can be used as a relatively rapid method of physically crosslinking multi-functional polymers during the 3D printing process without the need for chemical crosslinkers. While the crosslinked polymer may have a slight mechanical advantage in terms of its higher elastic modulus, it is limited by its lack of solubility due to the presence of the chemical crosslinks. Further, it should be possible to tune both the solubility and microstructure of the resultant objects by targeting different core-forming segment DPs with or without asymmetric crosslinking agents. Difunctional macro-CTAs are likely the simplest multi-functional polymers that can be used to 3D print mechanically robust objects. However, PISA P from macromolecules / nanoparticles with higher RAFT CTA functionality could yield materials with new and interesting morphologies and properties.EXAMPLE 2Printing DAAm withPoly(DMA-co-HEAm) Macro-CTA1. Materials[000116] N'N-Dimethylacrylamide (DMA, 99%) was obtained from Sigma-Aldrich.[000117] N-(2-Hydroxyethyl)acrylamide (HEAm, >98%), trimethylamine (TEA, >99%), tetrabromofluorescein (eosin Y, EY, >95%), diacetone acrylamide (DAAm, >98%), 2-butanone (MEK, >99%), and ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (>95%) were obtained from TCI America.[000118] 2-Butylthiocarbonothioylthio)propanoic acid (BTP, 95%), 4-((((2- carboxyethyl)thio)- carbonothioyl)thio)-4-cyanopentanoic acid (CCC, 95%), and 4-cyano-4-(((dodecylthio)carbono- thioyl)thio) pentanoic acid (DCT, 97%) were obtained from Boron Molecular.[000119] Lithium bromide (LiBr, >99%), dichloromethane (CH2CI2, >99.5%), N'N- dimethylformamide (DMF, >99%), 4-dimethylaminopyridine (DMAP, >99%), and 3-(3- dimethylaminopropyl)-l-ethyl-carbodiimide hydrochloride (EDC, >98%) were obtained from Chem Impex Int.2. Synthesis of Lithium Phenyl-2,4,6-Trimethylbenzoylphosphinate (LAP) Photoinitiator[000120] To a 250-mL beaker containing 100 mL of 2-butanone, ethyl phenyl(2,4,6- trimethylbenzoyl)phosphinate (7 g, 22.1 mmol) and lithium bromide (7.69 g, 88.4 mmol) were added and stirred into solution. Once dissolved, the mixture was heated in a 60°C water bath for 24 hours. The precipitated product was vacuum-filtered, washed six times with 2-butanone, and vacuumed dry to obtain the pure white solid (5.53 g, ~85% yield).3. Synthesis of Poly(DMA-co-HEAm) Macro-CTA via PET RAFT[000121] RAFT copolymerizations of DMA and HEAm (molar ratio 9:1, respectively) were conducted under aqueous conditions at an initial comonomer concentration of 2.5 M (~20 wt%), targeting a degree of polymerization ([M]o / [CTA]o) of 100, 250, 500, 1,000, 5,000 or 10,000. A type II photoinitiating system based on eosin Y and TEA was employed in these polymerizations using a [TEA]o / [EY]o ratio of 100. [CTA]o / [EY]o ratios of 20, 15, 10, 5, 5, and 5 were used for DP targets 100, 250, 500, 1,000, 5,000 and 10,000, respectively. A 0.1 molar equivalent DMF spike with respect to total comonomer concentration was used an internal NMR reference to determine polymer conversion. ' H NMR samples in D2O were measured before and after polymerization, and conversion was determined by integrating the reduction in the area of the vinyl peaks of DMA / HEAm (~5.5-6.5 ppm) with respect to the DMF amide peak (~8.02 ppm).[000122] Polymerizations were carried out in 500-mL beakers using a GLW 30 W LED green light (550 nm) at a distance of 6” from the light source (~1450 lux as determined by the MT-912 light meter). Once placed under the light, polymerization was carried out for 48 hours followed bydetermining polymer conversion via NMR. Polymer solutions were then diluted with DI water (1:1 v / v) and placed in SpectrPor regenerated cellulose dialysis membranes (12-14 kDa) cutoff. Polymers were dialyzed first against methanol (3x over 3 days) to remove unreacted monomer and excess eosin Y followed by dialysis against water (3x over 2 days) to remove the methanol. Polymers were then frozen and lyophilized to obtain the final product. A representative procedure for macro-CTA synthesis for DP 10,000 is as follows: to a 500-mL beaker, DMA (45.0 g, 454 mmol), HEAm (5.81 g, 50.4 mmol), 310 pL of a 50 mg / mL CCC stock in methanol (15.5 mg, 50.4 pmol), 262 pL of a 25 mg / mL eosin Y stock in methanol (6.55 mg, 10.1 pmol), 140 pL TEA (0.102 g, 1.01 mmol) and DMF (3.68 g, 50.4 mmol) were added and mixed homogeneously. The solution was then diluted with 202 mL of distilled water to a final comonomer concentration of ~2.5 M (~20 wt%).4. Post-Polymerization Esterification of Poly(DMA-co-HEAm) Macro-CTAs ( CFS synthesis)' [000123] Following isolation, BTP RAFT agents were functionalized by grafting the polymers with varying densities of CTAs, in this case BTP. Two scaffolds were chosen for grafting and subsequent studies: DP 500 and DP 10,000. These two DPs result in drastically different viscosities in water (the basis for the 3D PISA printing resin) which was hypothesized to affect ease of printing as well as print resolution. BTP CTA was grafted onto the hydroxyl residues of the HEAm units of the poly(DMA- co-HEAm) macro-CTA via Steiglich esterification. For the DP 10,000, the grafting densities were 1 %, 2.5%, 5%, and 10% of HEAm units. For the DP 500 scaffold, grafting densities were 4%, 10%, 20%, 50%, and 100% of HEAm units. For these esterifications, DMAP was employed as the catalyst, and EDC was employed as the carhodiimide coupling reagent. Since HEAm only makes up 10% of the DP 10,000 CFS polymer, this means that no more than 100 BTP RAFT agents will be esterified to any one polymer chain.[000124] To begin, lyophilized CFS was dissolved into dichloromethane at a concentration of 10 wt. % for ~2 hours. Following complete dissolution, BTP and DMAP, respectively, were added into the solution. Lastly, EDC was slowly added to the solution in small increments. As the EDC reacted, the solution color changed in appearance from a bright yellow to a dark orange-red and back again. The solution was covered and left to react for 18 hours on a magnetic stir plate. For purification, the grafted solution were dialyzed against methanol (3x for 3 days) to remove any unreacted BTP in addition to DMAP and EDC. This was followed by dialysis against water, freezing and lyophilization to obtain the final large molecular weight, functionalized polymers (CFSs). A representative procedure for the 10% BTP grafted poly(DMA-co-HEAm) macro-CTA is as follows: to a 100-mL beaker, 10 g of poly(DMA-co-HEAm) macro-CTA (1.14 g HEAm, 9.90 mmol R-OH) were dissolved in 68 mL of dichloromethane. This was followed by the addition of BTP (0.236 g, 0.991 mmol) and DMAP (0.181g, 1.49 mmol). EDC (0.284 g, 1.49 mmol) was then slowly added into the solution and allowed to react overnight. An additional batch of poly(DMA-co-HEAm) macro-CTA was grafted with 10% DCT instead of BTP so that experiments could be carried out with methacrylate monomers.5. Characterization of CFSs[000125] CFSs were characterized by dynamic light scattering (DLS), gel permeation chromatography (GPC),1H nuclear magnetic resonance (NMR), and UV-visible spectrophotometry (UV-Vis). In more detail, 1 mg / mL samples of CFS in DT water were prepared, and 1 mL was pipetted into a 1.25 x 1.25 cm polystyrene cuvette. Polymer size was measured on the Malvern dynamic light scattering system. NMR of the purified DP 10,000 poly(DMA-co-HEAm) and 10% grafted CFS were measured in CDCh, and 5 mg / mL samples of CFS in DMF were measured at a flow rate of 0.5 mL / min on the Agilent Infinity II series GPC. Number average molecular weight values (Mn) for the CFS were determined using a PMMA calibration curve. UV-Vis was used to determine moles of BTP per gram of polymer. This was done by preparing a 10 mg / mL in DI water and measuring the absorbance on the TECAN infinite M nano-i- UV-Visible spectrophotometer and comparing to a BTP standard curve using Beer’s law. The 10% DCT grafted polymer was quantified in the same manner, using a DCT standard curve instead. To account for the absorbance of any residual eosin Y within the CFS, the ungrafted and purified poly(DMA-co-HEAm) macro-CTA (concentration) were used as an absorbance blank that was subtracted from the CFS sample absorbance. GPC traces are shown in Fig. 12, summarized molecular weight / molar mass dispersity values are provided in Table 2, a DLS trace graph is provided in Fig. 13, and NMR spectra can be found in Fig. 14.Table 2 - Summarized Molecular Weights and PDI Values for Additional Varying Poly(DMA-co- HEAm) Target DPs[000126] UV-Vis spectra can be found in Fig. 15, where the blank is solvent only (91 % isopropanol). The absorbance value at 325 nm was used to determine the CTA concentration per gram of polymer via a BTP standard curve in 91% isopropanol. Since there is a slight difference in absorbance between the ungrafted CTS sample and blank at this wavelength, this absorbance was taken into account when determining BTP concentration.6. 3D DLP Printing of Aqueous CFS PISA Resins[000127] For 3D DLP printing studies, the 10% BTP-grafted multifunctional CFS macro-CTA was utilized as the stabilizer block with DAAm serving as the solvophobic / PISA block in the aqueous based PISA system. A target DP ([M]o / [CTA]o) of 500 was chosen to formulate the resin. The DP calculation was determined based on the CTA value of the CFS polymer as determined by UV-Vis, and 0.5 wt. % LAP photoinitiator and 0.005 wt. % phenol red photoabsorber with respect solids were the other two components added to the system. Due to the high molecular weight of the CFS (~ 1 MDa), curing trials were first conducted in 24-well plates to find a solids content that would result in a workable viscosity for DLP printing. From these trials, it was determined that 30 wt. % would be chosen to formulate the final DLP resins.[000128] To make the resin, CFS was dissolved in distilled water and stirred into solution followed by the DAAm. The appropriate amounts of LAP and phenol red stocks in water were then added to the solution and mixed homogeneously. Resins were used to a print a treefrog model at three different normal exposure times: 5 s, 10 s, and 15 s per layer. Fig. 16 shows three views of a treefrog formed with 10% BTP-grafted DP 10,000 CFS DAAm PISA resin printed at a normal exposure time of 10 s per layer. Additionally, a “S&T” moniker (Fig. 17) was also printed to evaluate the resolution of these resins and whether they were subject to significant overcuring by comparing the DP 10,000 to a 3Dprinted part using the DP 500 grafted CFS (10%, target DAAm DP of 500). Photoabsorber and photoinitiator concentrations were kept constant for the DP 500 CFS print. Lastly, a lattice cube (Fig. 18) was also printed with DP 500 CFS PISA system. S&T logo and lattice cube parts were printed using bottom and normal exposure times of 20 s per layer with the less viscous DP 500 scaffold. All parts were printed on the Phrozen Sonic Mini 8K DLP printer (1.60 mW cm-2, 405 nm, resolution = 22 pm) using a layer thickness of 50 pm.[000129] A representative procedure for CFS DAAm PISA resin is as follows: to a 100-mL beaker, 10% BTP grafted CFS (2.50 g, 0.183 mmol BTP) and DAAm (15.5 g, 91.6 mmol) were dissolved in 42.0 g of distilled water by hand-stirring. Next, 1.79 g of a 50 mg / g LAP stock and 0.359 g of a 2.5 mg / g phenol red stock were added to complete the resin. An additional PISA resin for a methacrylate- based system was formulated using N-(2-hydroxypropyl)methacrylamide (HPMA) and the 10% DCT grafted CFS to show that multiple monomer systems could be cured via this PISA mechanism.7. Characterization of 3D DLP Printed CFS PISA Parts[000130] Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to evaluate the nanostructural and microstructural features of PISA-printed parts. For these studies, the 10% BTP-grafted CFS PISA resin with DAAm (target DP of 500) was utilized. For AFM, parts were prepared by pipetting a small amount of resin onto a metal substrate and curing under UV light for 2 minutes. For SEM, resins were cured under a 30 W UV light (405 nm) in a 12-well plate for 2 minutes. After removal, the cured parts were dialyzed against distilled water for one day to remove any residual monomer. They were then frozen and lyophilized. The resulting part was fractured and coated with Au on the Denton Sputter coater before being imaged on the PRISMA E SEM (25 kV).[000131] Referring to Fig. 19, the SEM images show a highly porous and web-like nanostructure at the lowest magnification (left). At the highest magnification (right), there appears to be bubble or popcorn-like structures on the surfaces of each web. The roughness on the surface also appears to consist of nanoporosity in between these surface structures. The structures themselves may be the result of self- assembled nanostructures that were produced via PISA in the 3D printing process. However, since the resolution was lacking at this high magnification, further investigation of the structure on the parts was studied via AFM. Referring to Fig. 20, the top left image shows the AFM topography, while the top middle image shows the corresponding peak force error image. The top right and bottom left and middle images are 2D roughness images, while the bottom right image includes height information. As the images of Fig. 20 show, the morphology of the PISA printed nano-objects was predominately spherical with some irregular spheres. This result contrasts sharply with that of a difunctional PEG scaffold and a hyperbranched scaffold (Example 1), in which a combination of well-defined spheres and worms were observed. It is possible that the high molecular weights of the CFSs disrupted the formation of highly uniform morphologies.[000132] This Example 2 showed that reducing the exposure time to 10 seconds was sufficient for successful 3D printing of detailed treefrog models without noticeable defects (Fig. 16). The printed frogs displayed distinct features, such as individual digits and body ribbing. Notably, the frogs exhibited a yellow color due to the pH-sensitive phenol red photoabsorber, alongside a bluish-white hue near the legs and feet, attributed to light scattering from nanostructures formed during polymerization or UV curing, indicative of PISA activity. Compared to Example 1 , which employed a linear difunctional PEG macro-CTA, the curing times were reduced from 45 s / layer to just 10 s / layer in this Example 2. This significant improvement in reducing cure time was attributed to the higher density of anchor points or CTAs per chain (higher functionality), which allowed the material to gel at lower conversions when compared to the difunctional system.[000133] Printing with a 15-second exposure time was successful, although it led to overcuring, especially noticeable on the frog’s feet. Conversely, reducing the exposure time to 5 seconds resulted in part failure and defects, with the shorter exposure insufficiently curing the slices for the arms, causing the frog’s front feet to detach. This printing displayed a more pronounced blue color near the arms and feet, indicating a lower monomer conversion of the solvophobic block during UV exposure. This likely stemmed from reduced polymerization, resulting in smaller nanostructures and increased light scattering. The viscosity of this resin, particularly the DP 10,000 CFS PISA-based resin, may also impact the resolution, degree of overcuring, and printing difficulty. Resolution could potentially be improved with increased photoabsorber concentrations. However, this comes with the drawback of increased cure times.[000134] To evaluate the potential detail of CFS resins, a standard 20-second exposure was used to print a lattice cube model and S&T logo with the less viscous DP 500 scaffold. Longer cure times were required as this was a slower curing resin at the same LAP and phenol red concentrations when compared to the DP 10,000 scaffold. The resulting lattice cube model (2B) showed high detail but some overcuring, possibly due to resin getting trapped in the lattice holes and overcuring in subsequent layers.[000135] The 3D printed “S&T” logo had clear lettering with minor overcuring, not significantly affecting print quality. This was contrasted with a logo printed with the more viscous DP 10,000 CFS where more significant overcuring was noted. The letters were discernible under light, but overcuring obscured the gaps between them. Overall, PISA printing can effectively produce complex structures when using suitable scaffolds for resin preparation.8. Dissolution Studies for Cured CFS PISA Resins[000136] Dissolution studies were performed for BTP and DCT grafted CFS resins to see how DP, graft density, and monomer may affect the dissolution of parts following curing / printing. Due to the viscosity limitations associated with the 1% BTP grafted CFS resin formulations, all dissolution study resins were fixed at a solids content of 25 wt. %. Five different DP targeted resins (100, 250, 500, 750, 1,000) for each BTP graft density for both DP 10,000 and DP 500 CFS grafted scaffolds were prepared in a manner similar to that described previously. Next, 1 g of reach resin was pipetted into a 24-well plate and exposed to UV light for 2 minutes on the Phrozen Sonic Mini 8K DLP printer. The cured parts were then placed in DMF, and dissolution (or lack thereof) was monitored over time. DMF should solubilize both the poly (DMA-co-HEAm) and DAAm blocks of the polymer. Fig. 21 provides photos of these dissolution studies. All samples marked by a checkmark indicate full dissolution of the parts following curing. Samples marked by an “X” either did not dissolve at all or only partially dissolved after 24 hours in DMF.[000137] Similarly, a DP study of dissolution was also conducted for the 10% DCT grafted CFS with HPMA at a solids content of 25 wt. %. In this case, DPs of 50, 100, 175, 250, and 500 were targeted, and the resin was cured for 5 minutes under U V light due to the slower polymerization rates of HPMA. Fig. 22 shows that the target DPs of 250 or less for HPMA led to dissolution of the part while the DP 500 swelled but did not dissolve.[000138] Additional dissolution studies were carried out on these resins with free RAFT agent. Free CCC RAFT agent was added at different concentrations to the 5% BTP grafted CFS DAAm resin to see if increasing free CTA may promote dissolution. CCC molar equivalents of 0.25, 0.5, 1, 2, 3.5, 5, and 10 with respect to grafted BTP concentration were added to the resins and cured in the same manner as previously described for dissolution studies. Curing times were 5 minutes in these studies. After curing, parts were placed in DMF to monitor dissolution. Fig. 23 shows that increasing free CCC concentration with respect to BTP promoted dissolution in DMF.[000139] In Example 1 , a difunctional PEG macro-CTA combined to 3D print DAAm was used. The resulting 3D printed parts were soluble in DMF, confirming the absence of chemical crosslinks. Example 1 also showed that the PISA printing formulations could be assembled in isopropanol to yield parts with controllable aqueous dissolution kinetics.[000140] In this Example 2, parts grafted with a 1% BTP concentration successfully retained their shape at lower DPs (e.g., 100 and 250) although they exhibited a gel-like appearance. However, at higher DPs (e.g., 500, 750, 1 ,000), these parts formed stable, well-defined shapes, despite their inherent fragility. For parts with 1% BTP grafting, dissolution in DMF occurred within hours, irrespective of their DP. Notably, parts with a higher DP of 1,000 and 1% graft exhibited prolonged dissolution times,approximately 1-2 hours, indicating a degree of DP dependency in dissolution. In contrast, parts with lower target DPs dissolved more rapidly, typically within 15-30 minutes.[000141] In samples with a 2.5% graft density, the parts did not completely dissolve in DMF, but rather disintegrated into gel-like fragments over several hours. These fragments continued to break down over a week but did not achieve total dissolution. Parts with 5% and 10% graft densities did not dissolve or disintegrate but instead showed significant swelling during the same period. This pattern suggests that the target DP does not substantially influence the solubility of PISA printed parts across different CTA graft densities. The complete dissolution of all parts at 1 % graft density, contrasted with the lack of dissolution at higher graft densities (2.5%, 5%, and 10%), implies the existence of a CTA graft threshold above which parts do not dissolve. The increase in the number of CTA groups per scaffold might lead to crosslinking via termination by coupling. Additionally, the brush architecture of the CTA-functionalized scaffolds used in these experiments likely affects the frequency of these chain coupling reactions. Hyperbranched scaffolds that have a high number of CTA groups / scaffold did yield soluble parts suggesting that the scaffold architecture does play an important role.[000142] As mentioned previously, HPMA was polymerized from the 10% CFS, targeting a range of DPs. Because of the slower polymerization rates of HPMA relative to DAAm, the cure times per increased to 5 minutes per layer. Almost all parts from the HPMA system dissolved except for those with a DP of 500. This testing employed scaffolds grafted with 4-cyano-4- (((dodecylthio)carbonothioyl)thio)pentanoic acid (DCT) rather than BTP in order to provide a more appropriate R group for the methacrylate monomer. Additionally, the dissolution process in DMF was slow, taking one day for DP 50, a few days for DP 100, and up to a week for DPs 175 and 250, as shown in Fig. 22.[000143] As described above, additional experiments were conducted in order to probe the ability of free CTA to suppress crosslinking reactions leading to soluble 3D printed parts (Fig. 23). DAAm was polymerized in the presence of the 5% BTP-grafted CFS with the addition of free trithiocarbonate- based CTA (CCC). These experiments showed that PISA prints conducted with two or more equivalents of free CTA relative to CFS CTA groups were completely soluble in DMF. In contrast, PISA prints conduct at a free CTA to CFS CTA ratio of one and below resulted in substantial swelling (>5 times their original weight), but did not dissolve.9. Mechanical Property Studies for Cured CFS PISA Resins[000144] Mechanical properties for the BTP-grafted CFS PISA resin with DAAm were measured and evaluated as a function of increasing target DP (degree of polymerization), increasing BTP graft density, and increasing solids concentration. In DP studies, the DP was varied (100, 250, 500, 750, and1,000) while graft density (10%) and solids content (25 wt.%) were kept fixed. In graft density studies, BTP grafts with respect to hydroxyls (1, 2.5, 5, and 10%) were varied while DP (1,000) and solids content (25 wt. %) were kept fixed. For solids content studies, the solids were varied (12.5, 25, and 40 wt. %) while the graft density (10%) and DP (500) were fixed.[000145] Additionally, mechanical properties for the 10% DCT grafted CFS PISA resin with HPMA were measured using a target DP of 250 and solids content of 25 wt. %. The modulus was determined from the slope of the stress-strain curve within the linear elastic range. Strain-to-break was calculated by measuring the change in length relative to the initial gauge length. The toughness was estimated from the energy derived from the area under the stress-strain curve.[000146] To perform these studies, the various resins were pipetted into a silicone-coated ASTM D638 Type V dogbone mold (3 samples per set of conditions) and were cured for 2 minutes (DAAm) or for 5 minutes (HPMA) under UV light (405 nm). Following removal, samples were tested on the Shimadzu EZ-LX tensile tester using a 5 kN load cell and a stroke of 10 mm / min. Mechanical properties were not measured for the DP 500 scaffold.[000147] Figs. 24-26 and Table 3 provide these results.Table 3. Mechanical Property Values for 10% DCT-grafted LFP HPMA PISA resin system (DP 250 HPMA, 25 wt. % solids)[000148] The modulus was observed to increase until it reached a maximum value of 50.9 ± 3.30 kPa at DP 500, after which it began to decrease with rising DP. Strain-to-break diminished from approximately 1034 ± 1 17% at the lowest DP of 100 to merely 202 ± 21 .2% at the highest DP of 1 ,000. The combined influence of these two factors on the energy derived from the area under the stressstrain curve culminated in a peak toughness of 1853 ± 700 kJ / m3at DP 250, followed by a sharp decline at higher DPs (<274 ± 23.2 kJ / m3). The large error bar for this measurement seems to be attributable to the larger error associated with the strain-to-break of these parts.[000149] Given the high graft density of the 10% BTP-grafted CFS, the DAAm monomer composes most of the resin solids content (since target DP is based on moles of CTA). As DP increases, so does the proportion of monomer in the resin system. DAAm is a highly crystalline material that exhibitsstrong hydrogen bonding and a high Tg. Therefore, it was expected that increasing the DAAm should result in a higher modulus, which is what was observed up to DP 500. However, at higher target DPs, the modulus began to decrease. The relative proportions of monomer and stabilizer in the system can be used to explain this decrease. For the 10% grafted system at high target DPs (>750), the DAAm monomer constituted >90% of the total solids with small amounts of the CFS stabilizing the large amounts of phase-separated domains. In other words, the sample may have been behaving more like a bulk DAAm part since there was little stabilizer in the system. As its name suggest, the CFS or stabilizing segment is important for keeping the hydrophobic core-forming block and the overall part stable under aqueous conditions. Too little stabilizer and the hydrophobic chains will not be stabilized effectively. The higher target DP parts are thus mostly held together by self-assembled chains that are quite hydrophobic. In the absence of any chemical crosslinker, these high DP DAAm parts with little stabilizer should start to become weaker at high concentrations of core-forming block or DAAm monomer, which is what was observed with the decrease after DP 500. Resins targeting lower DPs with larger proportions of CFS yielded parts that were rubbery and compliant.[000150] Similarly, this relationship between monomer concentration and stabilizer can be expanded to explain the trends of strain-to-break and toughness. The mass ratio of DAAm-to-stabilizer is 1.2 for DP 100 (1034%) at the experimental 10% graft density, which showed the highest strain-to-break. Compare that to a ratio of 3 for the DP 250 (973%) and ratio of 6 for DP 500 (349%), where the strain- to-break dropped off significantly. As the stabilizer in the system decreases, it reaches a point where the brittle DAAm blocks make up most of the system (>86% at DP 500). We would expect an increase in the brittle core-forming block to see a reduction in strain-to-break values, which is what was observed across all DPs. It appears that there is some critical concentration of DAAm with respect to stabilizer (>80%) in which the bulk properties begin to reflect those of poly(DAAm) in water without crosslinker, which would explain both the loss in strain-to-break and modulus values. Bulk poly(DAAm) is unstable in water and cannot hold its shape. The small addition of CFS allowed it to hold its shape via physical crosslinking formed by PISA printing. Since toughness is contributed to by strain-to-break and modulus, it makes sense the energy under the curve would be significantly less in DPs 500-1000 given the low strain-to-break.[000151] For graft density studies, the targeted DP for all cured resins was kept fixed at a value of 1 ,000 with a fixed total solids content of 25 wt. %. As shown in Fig. 25, the modulus of the material increased nearly linearly from a minimum value of 2.80 ± 0.625 kPa to a maximum of 44.76 ± 5.27 kPa with increasing graft density. Strain-to-break remained nearly constant (or slightly increased) up to a maximum (1085 ± 133%) at a graft density of 5% before falling off considerably at a graft density of 10%. The contribution of both modulus and strain to energy and therefore toughness resulted inincreasing toughness with graft density up to a peak toughness at 5% graft density (1280 ± 163 kJ / m3). Considering the sharp falloff in strain-to-break at the 10% graft density, it makes sense that the resulting toughness for this graft density was considerably lower than the graft densities at 2.5 and 5% and did not follow the increasing toughness with graft density trend that the others showed. In fact, this 10% graft density targeting a DP of 1 ,000 was in good agreement with the previous results obtained in the DP studies of mechanical properties. Increasing modulus for these systems can be explained by the increasing density of physical crosslinks within the cured part with increasing CTA graft density. This means higher modulus or stiffness may be associated with the increased number of chain entanglements per unit volume. The sharp decrease in strain-to-break may be explained by the same phenomenon that was observed in the DP studies. While the relative amount of DAAm-to-scaffold in the 10% grafted PISA resin is high (meaning little stabilizer), there is much more scaffold present relative to DAAm in the 1, 2.5, and 5% graft densities at the same targeted DP. As mentioned previously, increasing amounts of CFS relative to DAAm leads to more compliant and rubbery parts, which explains the high strain-to-break values and toughness values associated with these two densities. On the opposite end, the 1% graft density has little monomer relative to the scaffold and few chain entanglements per unit volume because of the low graft density. The parts themselves were observed to be weak and barely hold their shape during dogbone mold removal, which may explain the low toughness associated with the 1% graft density.[000152] Finally, the total solids content was varied for the 10% BTP graft density scaffolds using a DAAm target DP of 500. As shown in Fig. 26, modulus increased with increasing solids content to a maximum of 126 ± 4.77 kPa at a solids content of 40 wt. %. These same trends were observed with strain-to-break (maximum of 557 ± 164% at 40 wt. %) and toughness (maximum of 1396 ± 596 kJ / m3at 40 wt. %). At just 12.5 wt. % solids, parts were barely being held together and were made of almost 90 wt. % water. In contrast, the 40 wt. % part held its shape well and could be handled roughly without any issue. Since the part was only 60 wt. % water, there was much more solids present per unit volume, resulting in tougher and stiffer parts. The higher solids parts, while mechanically stronger, will experience a less open or porous structure following drying which may be disadvantageous for applications such as tissue engineering and cell culture, if gelatin is incorporated. A combination of mechanically-strong and porous materials could be selectively developed by targeting a solids content somewhere between 25 and 40 wt. %, especially if these materials are targeted for cell culture and tissue engineering applications.[000153] In comparison to Example 1 , which employed a difunctional PEG macro-CTA stabilizer, the Example 2 system displayed notable improvements in both curing rate and mechanical properties. CFS resins, targeting a DP of 500 at a solids content of 40 wt. %, exhibited higher overall toughness(1396 kJ / m3, >50% higher) than the PEG system (910 kJ / m3). The stiffness of the CFS system (225 kPa) was lower than that of the PEG system (390 kPa), which can be attributed to the higher DAAm- to-grafted polymer ratios in the PEG system. The strain values for many of the CFS compositions were higher, indicating greater stretchability compared to the PEG system. Additionally, toughness values for several CFS compositions surpassed those of the PEG system, with some formulations exhibiting over double the toughness value. For instance, the DP 250-targeted 10% graft system had a toughness value of 1853 kJ / m3, more than twice that of the PEG system.[000154] To put these results into context, they were compared to the previous linear difunctional PEG PISA system. In those studies, the DAAm PEG resins were cured using a target DP of 500 and a solids content of 40 wt. %. Resulting cured parts had modest mechanical stiffness (390 kPa), strain (~650%), and toughness (910 kJ / m3). These values were compared to mechanical property values in the 40 wt. % system with a target DP of 500, conditions which mirror those used in the PEG resins. While the stiffness (225 kPa) was lower and the strain (557%) was comparable for the CFS system when compared to the PEG system, the energy calculated under the stress-strain curve resulted in a higher overall toughness (1396 kJ / m3, >50% higher) for these CFS materials / architectures.EXAMPLE 3PISA Printing of Microneedles / . Materials[000155] N-(2-Hydroxyethyl)acrylamide (HEAm, >98%), N’N-Dimethylacrylamide (DMA, >99%), Acrylamide (Am, >98%), N-(butoxymethyl)acrylamide (BAm, >96%), and diphenyl(2,4,6- trimethylbenzoyl)phosphine Oxide (TPO, >98%) were obtained from TCI America.[000156] 4-Dimethylaminopyridine (DMAP, >99%), 3-(3-Dimethylaminopropyl)-l-ethyl- carbodiimide hydrochloride (EDC, >98%), N’N-dimethylformamide (DMF, >99%), and 10- hydroxycamptothecin (10CAM, >99.5%) were obtained from Chem Impex.[000157] Methylene Chloride (>99.5%) was obtained from Fisher Scientific. 2- (Butylthiocarbonothioylthio)propanoic acid (BTP, 95%) was obtained from Boron Molecular.[000158] 4,4'-Azobis(4-cyanovaleric acid) (ABCVA, >75%) and Phenol Red were obtained from Sigma.[000159] N’NMethylene(bisacrylamide) (MBAc, >96%) was obtained from Alfa Aesar. Methylene blue trihydrate was obtained from Fisher Scientific. Fetal Bovine Serum (FBS) was obtained from Cytiva.2. Synthesis of BTP Monomer (Transmer)[000160] In a 50-mL conical tube, BTP (2.50 g, 10.5 mmoles), HEAm (1.45 g, 12.6 mmoles), and DMAP (1.53 g, 12.6 mmoles) were dissolved in 15 mL of methylene chloride. Once dissolved, EDC (2.41 g, 12.6 mmoles) was slowly added in increments until fully dissolved. The tube was sealed and allowed to react overnight (~16 hours). The solution was washed thrice with 0.6 M sodium bicarbonate wash followed by two DI water washes. The solution was then filtered over MgSO4 and concentrated via rotary evaporation to obtain the viscous orange product. Synthesis was confirmed by peak integrations via 'H NMR in CDCh.3. Synthesis of BTP Radiant Star Scaffolds (RSS)[000161] To a 25-mL round bottom flask, BTP transmer (2.50 g, 7.45 mmoles) was dissolved in DMF (4.64 g) followed by addition of ABCVA (0.208 g, 0.745 mmoles) at a [transmer]o / [I]o ratio of 10. The solution was sealed with a rubber septum and parafilm and was purged under Argon for 30 minutes. The sealed flask was placed in a pre-heated water bath at 70°C for 18 hours. ' H NMR in CDCh confirmed complete disappearance of the vinyl protons (3H, 5.5 - 6.5 ppm), indicating complete conversion of all transmer. The polymerization solution was then precipitated into distilled water, washed three times, and freeze-dried to obtain the final sticky product.4. Synthesis ofPoly(DMA ) RSS Macro-CTA[000162] To a 50-mL round bottom flask, DMA (5.00 g, 50.5 mmoles) and BTP RSS (0.169 g, 0.504 mmoles) were dissolved in DMF (19.86 g) at a [M]o / [CTA]o ratio of 100. This was followed by a 0.14 g addition of a 50 mg / g ABCVA stock in DMF using a [CTA]o / [I]o ratio of 20. The solution was sealed with a rubber septum and parafilm and was purged under Argon for 30 minutes. The sealed flask was placed in a pre-heated water bath at 70°C for 24 hours, ' l l NMR in CDCh confirmed complete disappearance of the vinyl protons (3H, 5.5 - 6.5 ppm) with respect to DMA methyl peaks (6H, 2.65 ppm), indicating complete conversion. The polymer was dialyzed in SpectraPor regenerated cellulose dialysis membranes (12 - 14 kDa cutoff) against water for two days with the distilled water being changed three times. The solution was then freeze-dried to obtain the final polymer. A similar process was also used to prepare a target DP 250 ([M]o / [CTA]o = 250) DMA RSS.[000163] GPC analysis of the homopolymerized transmer and the corresponding poly(DMA) RSS indicated broad molecular weight distributions and relatively low molecular weights. The molecular weight and molar mass dispersity of the poly(DMA) RSS were determined to be 28,443 g / mol and 2.00, respectively. The homopolymerized transmer molecular weight was determined to be approximately 3,000 Da; however, the broad multimodal distribution complicated the determination of the molecular weight. Due to the highly branched nature of these polymers, the molecular weights,which are based on linear polystyrene standards, likely underestimate their true values. For this reason, the CTA concentration for subsequent PISA printing experiments was determined via UV vis spectroscopy at 325 nm based on the extinction coefficient of the starting CTA (Fig. 27).5. Synthesis of Poly(DMA-co-l OCAM) RSS macro-CTA for Drug Release Studies[000164] To a 5-mL round bottom flask, DMA (0.5 g, 5.04 mmoles) and 10-hydroxycamptothecin (10CAM; 0.14, 0.252 mmoles) were dissolved in DMF (2.15 g). Next, 0.33 g of a 50 mg / g BTP RSS stock in DMF was dripped in, followed by a 71 pl. addition of a 10 mg / mL ABCVA stock in DMF. The mixture was then sealed with a rubber septum and parafilm and was purged under Argon for 20 minutes. The solution was then placed in a pre-heated water bath (70°C) for 24 hours.]H NMR in CDCh confirmed full conversion of both monomers by observing the disappearance of the methacrylate and acrylamide vinyl proton peaks (5.5 - 6.5 ppm). The solution was dialyzed against water for 2 days in the fridge (4 °C). The solution was then freeze-dried and stored out of light.6. Characterization[000165] Materials were characterized via1H Nuclear Magnetic Resonance Imaging (1H NMR), Gel Permeation Chromatography (GPC), and UV-Visible Spectrophotometry (UV-Vis). Purified BTP transmer, BTP RSS, and DMA RSSs were measured on the Bruker 400MHz]H NMR in CDCh (10 mg / mL) to determine synthesis and composition. Molecular weights for BTP RSS and DMA RSS were determined via GPC using PS standards. Samples for GPC were prepared at a concentration of 5 mg / mL in DMF + 1% LiBr. CTA concentration of the RSS macro-CTA was determined via UV-Vis using a BTP standard curve in 91% isopropanol.7. Dissolution of PISA-Based RSS Resins as Function of Composition and Degree of Polymerization[000166] Organic -based PISA resins for DLP printing were formulated in 91% isopropanol using acrylamide (Am) and butoxymethyl acrylamide (BAm) monomers. To study how dissolution rates of PISA-cured microneedle resins in water could be controlled, varying molar concentrations of BAm (0 - 20 mole %) were introduced into the core-forming Am block at a fixed DP of 1,000. PISA resins were prepared by mixing DP 100 DMA RSS, Am, and BAm monomers and TPO photoinitiator (0.125 wt. % with respect to solids) at an overall solids concentration of 40 wt. % in 91% isopropanol. Three samples of each resin composition (~ 1.5 g per sample) were cured in a 12-well plate using a 30W handheld UV lamp (405 nm) for 5 minutes and then weighed. Each sample was placed in lx PBS Buffer (~60 g), and time to full dissolution was recorded. A representative procedure for 100 mole %Am target composition (fixed DP 1,000) is as follows: to a 50-mL tube, DP 100 DMA RSS (0.25 g, -25.2 pmoles BTP), and Am monomer (1.79 g, 25.2 mmoles) were dissolved in 91 % isopropanol (3.06 g). Next, 51 pL of a 50 mg / mL TPO stock (2.55 mg, 7.17 pmoles) in 91% IPA were then added to complete the resin.[000167] Fig. 28 shows that the introduction of only 5 mol % BAM to AM yielded a 50% reduction in the aqueous dissolution kinetics. When the BAM content was increased to 12.5 mol %, the dissolution rate further decreased to one-fourth that of the pure AM samples. Further increases in the BAM content to 15 mol % yielded samples that did not completely dissolve but did swell and break up into pieces. These studies collectively occurred over a period of 1-1.5 h for these sample sizes. When part size (mass) was approximately doubled for all compositions, the dissolution rate was extended up to 3-3.5 h in some cases. However, the average mass loss rate for the larger-scale studies closely matched the values shown for small-scales studies.[000168] Similarly, dissolution as a function of the target DP for the core-forming block at a fixed core composition of 95 Am - 5 BAm (mole %) was studied. Samples were prepared in a similar manner (40 wt. % solids and 0.125 wt. % TPO with respect to solids). A representative procedure for target DP 1,000 at a fixed composition of 95 Am - 5 BAm (mole %) is as follows: to a 50-mL conical tube, DP 100 DMA RSS (0.25 g, -25.2 pmoles BTP), Am monomer (1.70 g, 23.7 mmoles), and BAm monomer (0.197 g, 1.26 mmoles) were dissolved in 91% IPA (3.22 g). Then, 54 pL of a 50 mg-mL-1 TPO stock (7.70 pmoles) were added to complete the resin.[000169] Referring to Fig. 29, the dissolution rates of samples with a fixed comonomer composition of 95 mol % AM and 5 mol % BAM were plotted against various target DPs. For the sample with a target DP of 100, the dissolution rate was the highest, estimated to be around 27 mg of mass loss per minute. At a target DP of 500, the dissolution rate noticeably decreased to roughly 6 mg / min. The most significant reduction in the dissolution rate was observed for the sample with a DP of 1 ,500, where the rate was approximately 2.5 mg / min. This trend underscores the inverse relationship between the target DP and the dissolution rate, emphasizing the importance of the polymer chain length in controlling the aqueous dissolution behavior of the material. The photopolymerized samples also show a distinct difference in their appearance as a function of both the target DP as well as the molar feed ratio of AM and BAM (Figs. 28-29). Here, a transition from white to blue was observed as the composition changed completely from AM to 15 mol % BAM. This is not surprising given the solubility of BAM and its corresponding polymer in isopropanol. Similarly, a color change from clear to blue was observed as a function of target DP at a molar feed ratio of 95 mol % AM:5 mol % BAM. For example, samples cured at this position targeting a DP of 100 appeared almost clear while samples prepared targeting a DP of 1,500 appeared blue.8. DLP Printing of Microneedle Scaffolds Using PISA-Based RSS Resins[000170] Using dissolution studies as a guide, resin formulations employing 87.5 Am - 12.5 BAm, 90 Am - 10 Bam, or 95 Am - 5 BAm (mole %) were chosen for the core-forming block (fixed DP of 1,250) along with DP 100 DMA RSS macro-CTA for printing of microneedles. Microneedle platform supports were printed with resins formulated using 100 mole % Am for the core-forming block (target DP of 1,000) and the DP 250 DMA RSS macro-CTA. The higher DP RSS was observed to produce a rubbery platform, designed to make removal from the build plate easier. DP 100 DMA RSS can also be used to formulate the platform resin as well, though the part will need to be dried on the build plate to be removed. The 90 Am - 10 BAm microneedle resin composition was used for microneedle dissolution studies (composition results in slower dissolution in water) while the 95 Am - 5 BAm was used for SEM and AFM imaging (composition produced highest resolution).[000171] Alternatively, microneedles for platform dissolution studies were also printed with a resin containing a small amount of methylene bisacrylamide (MBAc) crosslinker. All resins were formulated in 91% isopropanol using a total solids content of 40 wt. %, a TPO (photoinitiator) content of 0.5 - 0.6 wt. % with respect to solids, and a phenol red (photoabsorber) content of 0.01 - 0.02 wt. % with respect to solids. A small amount of REMA (Rhodamine B methacrylate) monomer (0.0125 wt. % with respect to solids) was also added to the microneedle resin to fluoresce the needles in solution following dissolution of the platform, making them easier to observe when illuminated under UV exposure.[000172] Microneedle scaffolds were designed in Windows 3D Builder and were sliced in ChituBox slicing software. The scaffolds were printed at various sizes on the Phrozen Sonic Mini 8K DLP printer using a layer thickness of 25 pm and bottom / normal exposure times per layer of 45 - 65 seconds with longer times yielding better results. The 100% Am platform resin was used to start the print until it reached the layers corresponding to the needles themselves. At this point, the print was stopped, and the resin was switched over to the Am - BAm resins before continuing. Following printing, the part was washed on the build plate with 91% IPA. It was then either scraped off directly or placed in a 60°C oven overnight to dry, after which the part could easily be popped off the plate. The microneedle parts were then either sent for SEM imaging and AFM imaging or used for dissolution studies.[000173] Microneedle parts for dissolution studies were submerged in 100 g of lx PBS at 37°C to monitor the rapid dissolution of the platform and the delayed or slower dissolution of the needles. The platforms were observed to dissolve in approximately 15 min, leaving behind the microneedle tips.[000174] Fig. 30, which includes a penny for reference, shows the microneedles printed under these conditions with a PISA resin based on 100% AM DP 1000 PISA block. The platforms, printed in theabsence of the rhodamine B methacrylate, appeared yellow, while the tips, which included the fluorescent monomer, appeared pink. The all-pink microneedle scaffolds shown in Fig. 31 were printed fully with a targeted composition of 95 mol % AM and 5 mol % BAM and were used for SEM imaging. Following the dissolution of the bases, the tips could be observed (Fig. 32). The printed microneedle scaffold dimensions closely matched those of the CAD design, and the features were nearly identical to those in the CAD file.[000175] The tips dissolved shortly after, within an hour. It was, however, also possible to PISA print tips that swelled hut did not dissolve with the incorporation of a small amount of N'N- methylenebis (acrylamide) (e.g., 1.5 wt %) cross-linker or by adjusting the composition to 85 mol % AM and 15 mol % BAM. At this target compositional ratio, the PISA resins swelled but did not dissolve. Microneedles with cross-linker will remain intact indefinitely unless broken down, which can happen in the case of enzymatic degradation via proteases in the body. Compositions of 15 mol % or greater BAM did not seem to break down further in subsequent weeks and were quite stable. Since there were no chemical cross-links that could be broken down via enzymatic degradation, these parts would likely remain intact.9. SEM and AFM Imaging of PISA-printed Microneedle Scaffolds[000176] Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to image the micro and nanostructural features, respectively, for printed microneedles. SEM was performed on the PRISMA E SEM at an accelerating voltage of 5 kV to capture the individual print layers and the size of microneedle tips diameters. Samples were prepared for SEM by applying a conductive coating onto the sample via the Denton sputter coater. To prepare the samples, 20 pL of freshly synthesized PISA printing resin was applied onto a freshly cleaved mica surface. The resin was then exposed to UV light for 1 minute to initiate the self-assembly process. Following this, the samples were allowed to be dried in air for 60 minutes. The resulting deposited samples were subsequently examined using Atomic Force Microscopy (AFM) (Dimension Icon system, Bruker), operating in Scanasyst air mode with a scan rate of 0.996 Hz. HQ:NSC14 / Cr-Au BS probes purchased from Nanoandmore, featuring a resonance frequency of 160 kHz and a nominal spring constant of 5 N / m, were used in this analysis.[000177] Fig. 33 displays SEM images of microneedles in a horizontal / vertical arrangement, with the middle image of Fig. 33 focusing on a microneedle with a larger intended dimension. Fig. 34, on the other hand, illustrate microneedles arranged diagonally, with the middle image Fig. 34 highlighting a microneedle of a smaller intended size. The 25-pm print layers are visible as lines on the sides of the microneedles (Figs. 33 (left) and 34 (left)) and as concentric circles when viewed from the top (Figs.33 (right) and 34 (right)). Microneedles with larger dimensions (Fig. 33, left) display more uniform layering and smoother surfaces than the smaller ones (Fig. 33, middle), which exhibit some inconsistencies on their surfaces, particularly on the diagonal of the cone. Some microneedles, as seen in the middle images of Figs. 33 and 34, also show microcracks, which may have been caused by stresses from the swift evaporation of isopropanol.[000178] Analysis using ImageJ software indicated that microneedles in the horizontal / vertical configuration had an average length of 1.17 ± 0.023 mm, a base diameter of 375 ± 3.71 pm, and a tip diameter of 34 + 1.8 pm. In contrast, the diagonally arranged microneedles have a length of 927 ± 12.2 pm, a base diameter of 290 ± 2.5 pm, and a tip diameter of 27 ± 3.5 pm. It is noteworthy that the tip diameters aligned well with the XY resolution limit of the Phrozen Sonic Mini 8K printer, which is 22 pm. When compared with conventional hypodermic needles, these microneedle tips have narrower widths, indicating their suitability for skin penetration.[000179] AFM measurements (Fig. 35 - Scale bar: 150 nm) revealed roughness, and topographical imaging of the part surface reveals the presence of wormlike particles, spherical particles, and / or phase-separated domains, which may be a direct consequence of the self-assembly process during printing / curing. These observations are consistent with the proposed mechanism for PISA printing.10. Drug Release Studies for PISA-Cured Microneedle Resins[000180] Drug release studies from cured PISA-based resins were performed using two separate drugs: 10-hydroxycamptothecin (10CAM) and methylene blue trihydrate (MBT). PISA-based resins mimicking those used to print microneedles were cured in 24 well plates under a handheld 30W UV light (405 nm). Since the 10C AM monomer was chemically bound to the polymer scaffold, a small amount of MB Ac crosslinker was added so that dissolution of the 10CAM -containing polymer would not artificially represent the release kinetics when absorbance was measured at various time points. The inclusion of crosslinker would ensure that any absorbance change should result from hydrolysis of the 10C AM phenyl ester linkage and release into the surrounding serum. For MBT, release studies were performed both with and without MBAc crosslinker since the MBT was not chemically bound to the structure but instead was encapsulated within the microneedles. The 10C AM approach leads to polymeric prodrugs, wherein the drug is anchored to the polymer scaffold through a hydrolytically cleavable phenyl ester. Post-dissolution of the PISA-printed needle tips within the body, the polymer then gradually releases the covalently attached drug. In the encapsulation approach, MBT is physically confined within the PISA-printed tip, facilitating its swift release upon needle tip dissolution.[000181] For resin preparation of 10C AM drug release, DMA-co-lOCAM RSS macro-CTA was chain extended with a DP 1250 block of 95 Am - 5 BAm (mole %) in 91% IPA in the presence of DP 50 MBAc crosslinker (-8.5 wt. % with respect to solids).[000182] Resin preparation for MBT drug release used a target DP 1250 block of 95 Am - 5 BAm in the presence of DMA RSS macro-CTA with or without the addition of 1.5 wt. % MBAc crosslinker (with respect to solids, DP 10 target) and 0.25 wt. % MBT with respect to solids was used as well.[000183] All resins were formulated using 0. 125 wt. % TPO with respect to solids. Once resins were prepared, three samples for each time point were cured in a 24 well plate for 5 minutes and were then dried overnight. 10CAM samples were placed into 5 g of 100% Fetal Bovine Serum at 37°C, and 200- pL aliquots were taken from the sample solutions at various time points. MBT samples were placed into 10 g of lx PBS at 37°C, and aliquots were similarly taken. Absorbance of the collected aliquots were measured at 366 nm for 10CAM and 665 nm for MBT. Using 10CAM and MBT standard curves, drug release for each case was determined.[000184] Microneedles containing 10CAM residues released 6% of the drug over a period of 8 h (Fig. 36). These kinetics are consistent with our previous studies of this monomer. In comparison, 22% of MBT was released into the surrounding PBS over a period of 4 h (Fig. 37). Microneedles PISA printed in the absence of the cross-linker showed nearly instantaneous release of the encapsulated MBT (Fig. 38). Here, the drug release rates closely follow the dissolution rate of the microneedle at the 95 mol % AM and 5 mol % BAM composition employed (Figs. 28-29).EXAMPLE 4Printing Acrylic-Acid-Based PISA Resins Using Multi-CTA-Functionalized PDMS Scaffold1. Synthesis of Multi-CTA-Functionalized PDMS Scaffold[000185] A 50-mL tube was charged with 10 g of [3-4% (epoxycyclohexylethyl)methylsiloxane]- dimethyl siloxane copolymer (E-PDMS; 0.53 mmol epoxide), 0.625 g of 2- (butylthiocarbonothioylthio)propanoic acid) (BTP; 0.53 mmol; RAFT CTA), and 0.34 g of N'N- diisopropylethylamine (DIPEA; 0.53 mmol; amine base). To this mixture, 20 g of toluene were added, and the contents were vortexed until a homogeneous solution formed. The tube was then sealed with parafilm and placed in a pre-heated water bath at 80°C for 24 hours. Afterward, the reaction tube was removed from the water bath, and the product was precipitated three times in acetone, each time using a centrifuge to spin down the product before re-dispersing it in fresh toluene. A final precipitation into acetone followed, after which the solvent was decanted as completely as possible. The tube was leftopen to air in a fume hood overnight to allow the product to fully dry, yielding the final multi-CTA- functionalized PDMS scaffold.[000186] During this reaction, the ring-opening reactivity of the epoxy groups on E-PDMS causes the epoxy groups to react with the carboxylic acid-terminated RAFT agents in the presence of the base. The amine base deprotonates the RAFT agent, thereby activating the epoxide site for nucleophilic attack and forming a covalent bond between PDMS and the CTA. Scheme A depicts this reaction.[000187] Because multiple CTAs are grafted onto each PDMS chain, the system generates numerous polymer growth points during polymerization-induced self-assembly. This yields more robust physical crosslinks that enhance mechanical stability within the phase-separated nanostructures formed during printing. The resulting multi-CTA PDMS scaffold supports polymerization-induced self-assembly in non-polar solvents, enabling the fabrication of physically crosslinked, reversibly dissolvable, 3D- printed objects.2. 3D Printing of Acrylic-Acid-Based PISA Resins[000188] To demonstrate the adaptability of the multi-CTA-functionalized PDMS scaffold prepared in Part 1 of this Example, PDMS-poly(acrylic acid) hybrids were synthesized by growing acrylic acid from the PDMS precursor in toluene. This RAFT PISA resin was prepared at a target monomer-to- CTA ratio [M]o / [CTA]o=55. Diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) was used as the photoinitiator at a level of 0.85 wt.% relative to total solids, and an Oil Red O was used as the photoabsorber at a level of 0.015 wt.% relative to solids. Specifically, 10 g of acrylic acid (AA; 0.14 mol) and 5 g of multi-CTA-functionalized PDMS scaffold prepared in Part 1 of this Example (provided 2.6 mmol of CTA) were combined in a 50 mL tube. Next, 0.13 g of TPO (0.37 mmol) was added, followed by 22.5 g of toluene to achieve a final solids concentration of 40 wt.%. A 5 mg / g solution of Oil Red O in toluene (0.45 g, 5.5 mol ) was then introduced. The tube’s contents were vortexed until fully homogeneous.[000189] The resin was printed on a Phrozen Sonic Mini 8KS DLP printer using a 50- m layer thickness. Both the normal and bottom exposure times were set to 90 seconds. A Missouri University of Science and Technology “S&T” logo served as a test print. The logo was designed in Windows 3D Builder and sliced with ChituBox 3D slicing software.[000190] PDMS and the newly formed polymer segments remained covalently linked; however, the poly(acrylic acid) domains became incompatible with the highly hydrophobic solvent, promoting phase separation. As a result, PDMS stabilized the nanodomains, combining the oxygen permeability of PDMS with the hydrophilic characteristics of poly(acrylic acid). This approach is beneficial for applications such as contact lenses, where high oxygen transmission and surface wettability are crucial for clinical performance. Beyond acrylic acid, other monomers can be similarly integrated into the PISA process. For instance, polymerizing methyl methacrylate (MMA) in a non-polar medium containing PDMS can generate PDMS-PMMA composites with improved mechanical strength and optical properties, all while retaining PDMS’s flexibility and oxygen permeability. Critically, these materials rely on reversible, noncovalent assembly rather than permanent chemical crosslinks, offering greater control over mechanical properties, dissolution behavior, and potential post-print modifications.EXAMPLE 5One-Pot Synthesis of Multi-Functional N'N-Dimethylacrylamide Macro-CTA[000191] RAFT homopolymerizations of N'N-dimethylacrylamide (DMA) were conducted in water or ethanol, using monomer-to-CTA ratios [M]o / [CTA]o= 100 and CTA-to-initiator ratios [CTA]o / [I]o = 20. All polymerizations were carried out at 40 wt.% solids in ethanol or 50 wt.% in water, with acrosslinker-to-CTA ratio [CL]o / [CTA]o = 0.7. This crosslinking lightly connects polymer chains, resulting in a multi-functional scaffold bearing multiple CTA sites. Solutions were purged under argon for 30 minutes to remove oxygen and then placed in a 60°C water bath for 24 hours.[000192] In more detail, 15 g of DMA (0.151 mol) were first combined with 0.465 g of 4-((((2- carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (CCC, used as CTA; 1.51 mmol) and 0.163 g of N'N-methylene bisacrylamide (MBAC, used as crosslinking agent; 1.06 mmol) in a 50 mL round-bottom flask. The mixture was vortexed until the CCC and MBAC dissolved. Then, 22 mg of 4,4'-azobis(4-cyanovaleric acid (ABCVA, used as free radical initiator; 75.7 pmol) were introduced and vortexed until fully dissolved. Finally, 15 g of water was added, and the flask was sealed with a rubber septum and parafilm before purging under argon for 30 minutes. The flask was then placed in a pre-heated 60°C water bath overnight. The CTA concentration in the resulting polymer was determined by UV-vis spectrophotometry at 325 nm using a CCC standard curve.EXAMPLE 63D Printing of DMA, One-Pot-Based PISA Resins[000193] All 3D printing PISA resins employed either the ethanol- or aqueous-based DMA one-pot macro-CTA of Example 5 as the stabilizing block. The self-assembling block (core- forming segment) in these resins included one of the following:1. Diacetone acrylamide (D AAM) in water;2. A 50 / 50 (by mole) acrylamide / 2 -hydroxyethyl acrylamide (AM / HEAM) mixture in ethanol; or3. Isobomyl acrylate (IB A) in an 85 / 15 (by weight) ethanol / water mixture.[000194] Exposure and thickness settings varied by resin. Typical normal and bottom layer exposure times were approximately 30 s for DAAM, 60 s for AM / HEAM, and 90 s for IBA, while layer thickness ranged from 25 pm to 100 pm. Photoinitiator loading was 0.85 wt.% with respect to total solids. Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) served as the initiator for DAAM, whereas TPO was used for AM / HEAM and IBA. Phenol red was introduced as a photoabsorber at 0.015 wt.% with respect to solids. The final solids content was held at 40 wt.% in each resin, and monomer-to-CTA feed ratios [M]o / [CTA]o of 250 (DAAM), 500 (AM / HEAM), or 125 (IBA) were utilized. All resins were printed on the Phrozen Sonic Mini 8KS DLP printer.[000195] An exemplary DAAM procedure is: In a 50 mL tube, 5 g of 50 wt.% DMA one-pot polymer (25.5 mmol DMA, 0.252 mmol CTA) (prepared in Example 3) in water was combined with 10.66 g of DAAM (63.0 mmol). Then, 17.22 g of water was added, and the tube was sealed and vortexed until the DAAM dissolved. Next, 0.112 g of LAP (0.379 mmol) and 0.395 g of a 5 mg / g phenol red solutionin Dimethyl sulfoxide (DMSO; 5.58 u mol) were introduced. The resin was vortexed until homogeneous and kept covered with foil until ready for printing.[000196] Various samples were printed and are shown in Figs. 39-41. Fig. 39 shows AM / HEAM dragonflies (DP 250 AM / DP250 HEAM and DMA one-pot method in ethanol). A cylinder of the IB A resin was printed followed by switching the resin to Am / HEAM to print the dragonfly on top of it. The parts were then submerged in water. The AM / HEAM resin is soluble in water but the IB A resin is not. So, the AM / HEAM dragonfly dissolved while the IBA cylinder is not and stays in tact. The top photo shows the parts after printing while the bottom ones show the parts after some time in submerged in water. In Fig 40, the cylinder was printed once again with IBA resin, followed by switching to the DAAM resin to print the dragonfly. The parts were then submerged in ethanol. The DAAM resin is soluble in ethanol but the IBA is not. So, the DAAM dragonflies dissolve but the IBA cylinders do not and remain intact. The top photo shows the parts after printing while the bottom ones show the parts after some time in submerged in ethanol. Lastly, in Fig 41, the AM / HEAM resin was used to print the cylinder followed by switching to the IBA resin to print the dragonfly on top of the cylinder. The part was then submerged in THF (tetrahydrofuran). The IBA resin is soluble in this solvent but the AM / HEAM resin is not. So they IBA dragonflies dissolved but the AM / HEAM cylinders are left intact. The top photo shows the parts after printing while the bottom ones show the parts after some time in submerged in THF.[000197] Fig. 42 provides optical images of 3D printed blood vessels using AM and DAAM based resins. As shown, the blood vessels were printed with a high degree of resolution with almost no defects. The smallest channels of these as-printed vessels were on the order of 100-150 pm.EXAMPLE 7 Printing Diacetone Acrylamide with Gelatin Macro-CTA1. Synthesis of Gelatin Macro-CTA[000198] In a 50-mL conical tube, 2-(butylthiocarbonothioylthio)propanoic acid (BTP, 1.5 g, 0.00629 mol, Boron Molecular), N-hydroxy succinimide (NHS, 0.724 g, 0.00629 mol, Chem-Impex), and dimethyl sulfoxide (DMSO, 13.72 g, Chem-Impex) were added and vortexed until homogeneous. Next, N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC, 1.21 g, 0.00629 mol, Chem-Impex) was slowly added and vortexed until all the EDC dissolved. The reaction tube was then reacted for five hours. In a separate 500-mL beaker containing 200 mL of 100-mM sodium bicarbonate buffer and 100 mL of DMSO), the solution was heated to 50°C and 30 g of gelatin (Sigma AldrichG6650) were slowly added until the solution became a clear light brown color. The stir speed inside the gelatin solution was 1 , 100 rpm. Subsequently, the unpurified NHS ester solution was added slowly and the solution was allowed to react for two hours. Once the reaction was complete, the grafted gelatin was precipitated with ethanol by mixing 15 mL of the gelatin solution and 35 mL of the ethanol and shaken vigorously. The shaken solution was centrifuged in a Thermo Fisher Scientific Sorvall Centrifuge at a speed of 2,000 rpm for 5 minutes. The precipitated gelatin was dissolved in distilled water and placed inside a 10-12K dialysis tubing (Innovating Science) for three days at 40°C. Lastly, the gelatin solution was frozen and lyophilized on a freeze dryer (LabConco) for three days.2. 3D DLP Printing of Resins[000199] The gelatin-BTP (1.5 g) prepared in Part 1 of this Example and diacetone acrylamide (6.05 g, 0.036 mol, TCI) were added to water (27.2 g) and then vortexed until homogeneous. A LAP stock solution (2.52 g, 45 mg / g in water) and tartrazine stock solution (0.50 g, 15 mg / g in water, photoabsorber from TCI) were then added. Lastly, the solution was vortexed until homogeneous, and the resin was centrifuged to remove any trapped air bubbles. This process is vital to preventing the formation of air bubbles while printing.

Claims

CLAIMS1. A method of forming a structure, said method comprising:(i) exposing a first printing ink to light so as to form a first printed layer, wherein: said first printing ink comprises a polymer scaffold, a phase-separating monomer, and a photoinitiator dispersed or dissolved in a solvent system; and said polymer scaffold comprises a polymer having at least two chain transfer agents;(ii) exposing a second printing ink to light so as to form a second printed layer against said first printed layer, wherein said first and second printing inks can be chemically the same as, or chemically different from, one another; and(iii) repeating exposing (ii) one or more times with one or more further printing inks so as to form one or more additional printed layers, wherein said one or more further printing inks can be chemically the same as one or both of the first and second printing inks or chemically different from one or both of the first and second printing inks, wherein (i), (ii), and (iii) result in the formation of said structure.

2. The method of claim 1 , wherein said printing ink does not contain a crosslinking agent.

3. The method of claim 1 , wherein said first printed layer lacks chemical crosslinking.

4. The method of claim 1 , wherein said first printed layer has a chemical crosslink density of less than about 1 mol / nm3.

5. The method of any of claims 1 to 4, wherein said polymer is chosen from one or more of:(a) polyethylene glycol, [epoxycyclohexylethyl)methylsiloxane]-dimethylsiloxane copolymer, biopolymers, polymeric drugs, or combinations of the foregoing; or(b) polymers comprising monomers chosen from one or more of N’N-dimethylacrylamide, N-(2-hydroxyethyl)acrylamide, benzyl methacrylate benzyl acrylate, mono-2- (methacryloyloxy)ethyl succinate 2-carboxyethyl acrylate 2-carboxyethyl acrylate oligomers, styrene, methyl methacrylate, ethyl acrylate, propyl acrylate, methyl acrylate, or combinations of the foregoing.

6. The method of any of claims 1 to 4, wherein said chain transfer agents are chosen fromone or more of 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid (DCT), 2- butylthiocarbonothioylthio)propanoic acid (BTP), 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4- cyanopentanoic acid (CCC), dibenzyl trithiocarbonate, 3-((((l- carboxyethyl)thio)carbonothioyl)thio)propanoic acid, 2-(((dodecylthio)carbonothioyl)thio)propanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, 4-((((2- carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, cyanomethyl methyl(phenyl)carbamodithioate, 2-cyanobutan-2-yl dodecyl carbonotrithioate, bis(dodecylsulfanyl thiocarbonyl)disulfide, methyl 4-cyano-4-(dodecylthiocarbonothioylthio)pentanoate, 2-cyanobutan-2- yl methyl(piridin-4-yl)carbamodithioate, bis(carboxyethylsulfanyl thiocarbonyl)disulfide, bis(methyl- pyridin-4-yl-amino-thiocarbonyl)disulfide, cyanomethyl (3,5-dimethyl-lH-pyrazole)-carbodithioate, benzyl 3,5-dimethyl- IH-pyrazole- 1 -carbodithioate, bis(3,5-dimethyl- IH-pyrazol- 1 - ylthiocarbonyl)disulfide, 2-cyanobutanyl-2-yl 3, 5 -dimethyl- 1 H-pyrazole- 1 -carbodithioate, bis(4- chloro-3,5-dimethyl-lH-pyrazolesulfanylthiocarbonyl)disulfide, 2-cyanobutan-2-yl 4-chloro-3,5- dimethyl- 1 H-pyrazole- 1 -carbodithioate, 2-(butylthiocarbonothioylthio)propanoic acid, 4-cy ano-4- (((dodecylthio)carbonothioyl)thio)pentanoic acid, 2-cyano-5-hydroxypentan-2-yl dodecyl trithiocarbonate, 1 ,4-phenylenebis(methylene) didodecyl dicarbonotrithioate, 4-cyano-4- (phenylcarbonothioylthio)pentanoic acid, 2,2'-[carbonothioylbis(thio)]bis [2-methylpropanoic acid] , methyl 3-((l-methoxy-l-oxopropan-2-ylthio)carbonothioylthio)propanoate, benzyl butyl carbonotrithioate, 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, 4-cyano-4- (((dodecylthio)carbonothioyl)thio)pentanoic acid, methyl 4-cyano-4-(dodecylthiocarbonothioylthio)pentanoate, or combinations of the foregoing.

7. The method of any of claims 1 to 4, wherein said phase separating monomer is chosen from one or more of diacetone acrylamide, acrylic acid, [2-(methacryloyloxy)ethyl]dimethyl-(3- sulfopropyl)ammonium hydroxide, hydroxypropyl methacrylate, acrylamide, 2-hydroxyethyl acrylamide, isobornyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, or combinations of the foregoing.

8. The method of any of claims 1 to 4, wherein said photoinitiator is chosen from one or more of lithium phenyl-2,4,6-trimethylbenzoylphosphinate, diphenyl(2,4,6-trimethylbenzoyl)- phosphine oxide, benzoyl peroxide, bisacylphosphine oxide, benzophenone, phenanthrenequinone, 1- phenyl-1,2 propanodione, or combinations of the foregoing.

9. The method of claim 1, wherein the molar ratio of phase-separating monomer to chain transfer agent of about 25:1 to about 2,000: 1.

10. The method of claim 1 or 9, wherein: said polymer is chosen from one or more of:(a) polyethylene glycol, [epoxycyclohexylethyl)methylsiloxane]-dimethylsiloxane copolymer, biopolymers, polymeric drugs, or combinations of the foregoing; or(b) polymers comprising monomers chosen from one or more of N’N-dimethylacrylamide,N-(2-hydroxyethyl)acrylamide, benzyl methacrylate benzyl acrylate, mono-2-(methacryloyloxy)ethyl succinate 2-carboxyethyl acrylate 2-carboxyethyl acrylate oligomers, styrene, methyl methacrylate, ethyl acrylate, propyl acrylate, methyl acrylate, or combinations of the foregoing; said chain transfer agents are chosen from one or more of 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid (DCT),butylthiocarbonothioylthio)propanoic acid (BTP), 4-((((2- carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (CCC), dibenzyl trithiocarbonate, 3-((((l-carboxyethyl)thio)carbonothioyl)thio)propanoic acid, 2-(((dodecylthio)carbonothioyl)thio)propanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, 4-((((2- carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, cyanomethyl methyl(phenyl)carbamodithioate, 2-cyanobutan-2-yl dodecyl carbonotrithioate, bis(dodecylsulfanyl thiocarbonyl)disulfide , methyl 4-cyano-4-(dodecylthiocarbonothioylthio)pentanoate, 2-cyanobutan-2-yl methyl(piridin-4- yl)carbamodithioate, bis(carboxyethylsulfanyl thiocarbonyl)disulfide, bis(methyl-pyridin-4- yl-amino-thiocarbonyl)disulfide, cyanomethyl (3,5-dimethyl- lH-pyrazole)-carbodi thioate, benzyl 3 ,5-dimethyl- IH-pyrazole- 1 -carbodithioate, bis(3,5-dimethyl- 1 H-pyrazol- 1 - ylthiocarbonyl)disulfide, 2-cyanobutanyl-2-yl 3,5-dimethyl-lH-pyrazole-l -carbodithioate, bis(4-chloro-3, 5 -dimethyl- lH-pyrazolesulfanylthiocarbonyl)disulfide, 2-cyanobutan-2-yl 4- chloro-3,5-dimethyl- IH-pyrazole- 1 -carbodithioate, 2-(butylthiocarbonothioylthio)propanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, 2-cyano-5-hydroxypentan- 2-yl dodecyl trithiocarbonate , 1 ,4-phenylenebis(methylene) didodecyl dicarbonotrithioate, 4- cyano-4-(phenylcarbonothioylthio)pentanoic acid, 2,2'-[carbonothioylbis(thio)]bis[2- methylpropanoic acid], methyl 3 -((1 -methoxy- l-oxopropan-2- ylthio)carbonothioylthio)propanoate, benzyl butyl carbonotrithioate, 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, methyl 4-cyano-4- (dodecylthiocarbonothioylthio)pentanoate, or combinations of the foregoing; and said phase separating monomer is chosen from one or more of diacetone acrylamide, acrylic acid, [2- (methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, hydroxypropyl methacrylate, acrylamide, 2-hydroxyethyl acrylamide, isobomyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, or combinations of the foregoing.

11. The method of claim 1, wherein one, two, or all of said first printing ink, said second printing ink, and said further printing inks comprises a photoabsorber.

12. The method of claim 1 , wherein said first printing ink is flowable and said first printed layer is nonflowable.

13. The method of claim 1, wherein said light has a wavelength of about 100 nm to about 700 nm.

14. The method of any of claims 1 to 4 or 11-13, wherein each of said exposing (i), said exposing (ii), and said repeating (iii) is individually carried out for less than about 60 seconds.

15. The method of claims 10, wherein each of said exposing (i), said exposing (ii), and said repeating (iii) is individually carried out for less than about 60 seconds.

16. The method of any of the foregoing claims, wherein said structure has an elastic modulus of about 50 kPa to about 400 kPa.

17. The method of any of the foregoing claims, wherein said structure has a strain-to-break of about 200% to about 1,200%.

18. The method of any of the foregoing claims, wherein said structure has a toughness of about 100 kJ / m3to about 1,300 kJ / m3.

19. The method of any of the foregoing claims, wherein said structure has a dissolution rate of about 4 mg / min to about 28 mg / min.

20. The method of claim 1, wherein each of said exposing (i), said exposing (ii), and said repeating (iii) is carried out by digital light processing.

21. The method of claim 1 , wherein said polymer scaffold further comprises a drug bonded with said polymer.

22. The method of claim 1 , wherein said first printed layer comprises a pattern.

23. A three-dimensional structure formed according to the method of any of the foregoing claims.

24. The use of the three-dimensional structure of claim 23 for tissue engineering, drug delivery, development of vascularized structures, fugitive scaffolds, dissolvable microneedles, and / or microfluidic devices.

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