Transparent, high-resolution 3D printing with siloxane-based polymers

Abstract

A photocurable composition includes a reactive polymer portion including a first polymer component including one or more alkenyl-functional siloxane polymers, a second polymer component including one or more thiol-functional siloxane polymers, a photoabsorber system and a photoinitiator system, each of which exhibits high absorbance at wavelengths in the range of ± 5nm from a wavelength at which photocuring occurs and low absorbance at wavelengths in the range of 420-680nm. A combination of the photoinitiator system and photoabsorber system exhibits a cumulative absorbance at wavelengths in the range of ± 5nm of the wavelength at which photocuring occurs that is at least 1000 times greater than the maximum absorbance at wavelengths in the range of 420-680 nm. The composition includes no solvent and has an upper critical solution temperature below 20 °C and a lower critical solution temperature above 60 °C. The composition is photocurable to form a transparent material.

Description

Atty. Docket No.25-024PCT Transparent, High-Resolution 3D Printing with Siloxane-based Polymers CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Patent Application Serial No.63 / 694,526, filed September 13, 2024, the disclosure of which is incorporated herein by reference. STATEMENT OF GOVERNMENT INTEREST

[0002] This invention was made with government support under grant number 2138923 awarded by the National Science Foundation. The government has certain rights in the invention. BACKGROUND ART

[0003] The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.

[0004] Additive manufacturing (for example, 3D printing, lithography, etc.) is a promising modality for enabling the rapid prototyping of novel geometries beyond what is possible with manufacturing processes such as injection molding. In general, additive manufacturing is a process which builds a three-dimensional article by adding material in successive layers. The process may, for example, be guided by a digital design file.

[0005] Over the past decade, 3D printing using fused deposition of thermoplastic polymer resins and stereolithography of thermoset polymer resins has become widely adopted. However, the range of commercially available materials is limited, especially for transparent, biocompatible, and elastomeric materials that can be printed at high resolution. This gap in the materials market precludes the adoption of 3D printing for applications that would otherwise benefit from rapid prototyping, including, but not limited to, microfluidics and bioprinting. In other words, additive manufacturing or 3D printing of flexible structures for microfluidics and bioprinting can be challenging as a result of a gap in commercially available materials that satisfy biocompatibility and imaging criterion. Additionally, the field of microfluidics commonly uses soft lithographic manufacturing with siloxane elastomers toAtty. Docket No.25-024PCT create devices with micron-scale features and channels, which can require costly cleanroom fabrication equipment and time-consuming manual processes.

[0006] Various siloxane resins have been previously evaluated for additive manufacturing using (meth)acrylate and thiol-ene chemistries. See, for example, U.S. Patent No. 12,286,512, U.S. Patent Application Publication Nos.2020 / 0032062, 2020 / 0071525, and 2023 / 0250288, Battacharjee, N., et al., Desktop-Stereolithography 3D-Printing of Poly(dimethylsiloxane)-Based Material with Sylgard-184 Properties, Advanced Materials, 20, 1800001 (2018), Fleck, E., et al., Low-Viscosity Polydimethylsiloxane Resing for Facile 2E Printing of Elastomeric Microfluidics, Micromachines, 14, 1773 (2023), and Wallin, T.J., et al., Click Chemistry Stereolithography for Soft Robots that Self-heal, J. Mater. Chem. B., 5, 6429 (2017). Varying degrees of success have been achieved with such materials in creating 3D printed materials which are transparent, biocompatible, and / or elastomeric. For example, a number of such formulations exhibited relatively low transmittance in the visible light spectrum (that is, they lacked suitable transparency). Moreover, in a number of such formulations, significant and time-consuming post-printing processing was required to increase transmittance in the visible light spectrum.

[0007] To address the aforementioned and other challenges, it is desirable to develop materials such as monomers, oligomers, polymers, and additives for improving the 3D printing resolution while maintaining transparency of the material and, in some cases, providing biocompatibility. SUMMARY OF THE INVENTION

[0008] A composition, which is photocurable to produce a transparent material, includes a reactive polymer portion including a first polymer component including one or more siloxane polymers, each of which includes a plurality of alkenyl functional groups, and which are reactive in a thiol-ene reaction, and a second polymer component including one or more siloxane polymers, each of which comprises a plurality of thiol functional groups, and which are reactive in a thiol-ene reaction. The composition also includes a photoabsorber system including one or more photoabsorbers and a photoinitiator system including one or more photoinitiators. Each of the photoabsorber system and the photoinitiator system exhibits high absorbance at wavelengths in the range of ± 5nm from a wavelength at which photocuring occurs and low absorbance in wavelength range of 420-680nm. A combination of the photoinitiator system and photoabsorber system exhibits a cumulative absorbance at wavelengths in the range of ± 5nm of the wavelength at which photocuring occurs that is at least 1000 times greater than the maximum absorbance at wavelengths in the range of 420-Atty. Docket No.25-024PCT 680 nm. The composition includes no solvent and has an upper critical solution temperature below 20 °C and a lower critical solution temperature above 60 °C. Each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of all others of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component. Further, each of the one or more photoabsorbers and each of the one or more photoinitiators at least one of (i) has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component and (ii) is present in a weight % less than 5% and is soluble within the composition.

[0009] At least one of the first polymer component and the second polymer component may include one or more branched siloxane polymers. At least one of the one or more siloxane polymers of the first polymer component may be an MDTQ siloxane polymer including a plurality of alkenyl functional groups. At least one of the one or more siloxane polymers of the second polymer component may be an MDTQ siloxane polymer comprising a plurality of thiol functional groups. In a number of embodiments, each of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component independently has a weight average molecular weight in the range 100 g / mol to 10,000,000 g / mol, optionally in the range of 100 g / mol to 500,000 g / mol, and further optionally in the range of 100 g / mol to 100,000 g / mol. In a number of embodiments, a ratio of thiol functional groups to alkenyl functional groups in the reactive polymer portion is in the range of 1:1 to 4:1, optionally in the range of 1:1 to 2.5:1, and further optionally in the range of 1:1 to 1.5:1.

[0010] At least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component may include at least one of a plurality of aryl groups and a plurality of heteroaryl groups. At least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component may include 0.01 to 60 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups andAtty. Docket No.25-024PCT the plurality of heteroaryl groups. In a number of embodiments, the aryl groups are phenyl groups.

[0011] Each of one of the one or more siloxane polymers of the first component and each of the one or more siloxane polymers of the second component may include at least one of a plurality of aryl groups and a plurality of heteroaryl groups. In a number of embodiments, each of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes 0.01 to 60 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups. In a number of embodiments, the aryl groups are phenyl groups.

[0012] The composition may further include a nonreactive reinforcing filler, wherein the nonreactive reinforcing filler has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component. The nonreactive reinforcing filler may include an MDTQ siloxane polymer or a silica. In a number of embodiments, the nonreactive reinforcing filler includes fumed silica. A surface of the fumed silica may be modified to improve dispersibility. The fumed silica is present in a weight % in the range of 2 to 20 weight% of the composition in a number of embodiments.

[0013] In a number of embodiments, the nonreactive reinforcing filler includes an MDTQ siloxane polymer. The MDTQ siloxane polymer may, for example, be present in a weight % in the range of 0 to 20 weight % of the composition.

[0014] In a number of embodiments, the photoinitiator system includes at least one of ethyl phenyl(2,4,6-trimethylbenzoyl) phosphinate, lithium phenyl-2,4,6- trimethylbenzoylphosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP), 2-Hydroxy- -(2-hydroxyethoxy)-2-methylpropiophenone, 2-Benzyl-2-(dimethylamino)-1-[4-(morpholinyl) phenyl]-1-butanone, 1-Hydroxycyclohexyl phenyl ketone), 2,2-dimethoxy-2-phenylacetophenone, 1-[4- (Phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime), 2,3-bornanedione (Camphorquinone), Bis(4-methoxybenzoyl)diethylgermanium, and derivatives thereof. In a number of embodiments, the photoinitiator system includes at least one of ethylAtty. Docket No.25-024PCT phenyl(2,4,6-trimethylbenzoyl) phosphinate and lithium phenyl-2,4,6- trimethylbenzoylphosphinate.

[0015] In a number of embodiments, the photoabsorber system includes at least one of 2- isopropylthioxanthone, 2,4-diethylthioxanthone, avobenzone, octocrylene, bisoctrizole, drometrizole, bumetrizole, octavenzone, bemotrizinol, titanium dioxide nanoparticles, zinc oxide nanoparticles, and derivatives thereof. In a number of embodiments, the photoabsorber system includes at least one of 2-isopropylthioxanthone, and 2,4- diethylthioxanthone, and optionally wherein the photoabsorber system includes 2- isopropylthioxanthone and 2,4-diethylthioxanthone.

[0016] In a number of embodiments, the composition is transparent before photocuring. The composition may, for example, have a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99% in the range of 420 to 680 nm and has less than 5 NTU turbidity, optionally less than 1NTU, and further optionally less than 0.3 NTU.

[0017] In a number of embodiments, the transparent material has a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99%, in the range of 420 to 680 nm and has less than 5% haze, optionally less than 2% haze, and further optionally less than 1% haze.

[0018] In a number of embodiments of the composition, a combination of the photoinitiator system and the photoabsorber system exhibits a cumulative absorbance greater than 3 OD, optionally greater than 4 OD, and further optionally greater than 5 OD in a range of wavelengths within ± 5nm of the particular wavelength at which photocuring occurs.

[0019] A method of forming a three-dimensional article, which is transparent, includes a) exposing a first layer of the composition hereof (as, for example, described above) to electromagnetic radiation to react at least a portion of the reactive polymer component to form a first polymerized layer, b) optionally forming a second polymerized layer by disposing a second layer of the composition of claim 1 on at least a portion of the first polymerized layer and exposing the second layer to electromagnetic radiation to react at least a portion of the reactive polymer component thereof to form the second polymerized layer, and c) optionally repeating the actions of b) a determined number of times.

[0020] A three-dimensional article, which is transparent, may be formed by the method set forth herein. The three-dimensional article may, for example, have a Young’s modulus below 10 MPa and an elongation at break of at least 50%. In a number of embodiments, the three- dimensional article has an elongation at break of at least 100%. The three dimensionalAtty. Docket No.25-024PCT article may, for example, have a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99%, in the range of 420 to 680 nm and has less than 5% haze, optionally less than 2% haze, and further optionally less than 1% haze.

[0021] The present devices, systems, and methods, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG.1 illustrates the results of absorbance testing in a representative study hereof using a commercially available and transparent siloxane-based resin with five different formulations of UV photoabsorbing additives.

[0023] FIG.2 illustrates the results of tensile testing in a representative study using ASTM D412-C (Specimen cutting die) specimens.

[0024] FIG.3 illustrates the results of tear strength testing in a representative study using ASTM 624-C specimens.

[0025] FIG.4A illustrates a forward isometric view of a representative embodiment of a 3D printed model or part hereof including internal channels of different dimensions and with overhangs of different thicknesses.

[0026] FIG.4B illustrates another, rearward isometric view of the 3D printed article of FIG. 4A.

[0027] FIG.4C illustrates a side view photograph of a 3D printed article hereof including channels of various dimension.

[0028] FIG.4D illustrates a top view photograph of a 3D printed article hereof in which open channels are visible as translucent white strips.

[0029] FIG.4E illustrates a top view photograph of the 3D printed article hereof demonstrating the transparency thereof, wherein the marking lines of an underlying ruler are visible through the printed article.

[0030] FIG.5 illustrates mechanical tensile test data for representative transparent silicone resins hereof containing vinyl-functional Q-resins, wherein specimen VQ-2 contains SMS-022 as a chain extender with increased failure strain and reduced modulus compared to specimen VQ-1, which contains no SMS-022.

[0031] FIG.6 illustrates photomicrographs demonstrating the results of biocompatibility testing of samples of SYLGARD 184 PDMS (panel a) and the VQ-1 photocured silicone resin hereof (panel b), wherein the testing was conducted by culturing C2C12 cells in vitro.Atty. Docket No.25-024PCT

[0032] FIG.7 illustrates a structure of a representative copolymer of a thiol-functionalized MTQ resin and a dialkyl-diaryl (dimethyl-diphenyl) siloxane resin.

[0033] FIG.8 illustrates a structure of a representative MDTQ silicone resin containing thiol, aryl and / or alkyl moieties.

[0034] FIG.9 illustrates a structure of a representative example of a silicone-organic- silicone network hereof, formed with an organic bridge (X) between an MTQ silicone resin and an MD silicone resin, and containing thiol, aryl, and / or alkyl moieties.

[0035] FIG.10 illustrates representative examples of surface modifications to fumed silica with surface silanol groups, wherein panel a) illustrates hydrophilic silica with exposed silanol moieties, panel b) illustrates grafted dialkyl / diaryl silicone onto the surface of fumed silica, panel c) illustrates grafted dialkyl / diaryl silicone and silanized moieties on fumed silica, and panel d) illustrates grafted dialkyl / diaryl silicone onto fumed silica, where the silicone is silanized.

[0036] FIG.11 illustrates data of mechanical tensile testing of photocured, transparent silicone resins with fumed silica, wherein modifying the fumed silica by grafting dimethyl / diphenyl silicone onto the silica surface increased the elongation of silicone resins compared to unmodified fumed silica.

[0037] FIG.12 illustrates a representative example of a transparent photocured silicone resin sample including 10% fumed silica by weight (3mm thick) overlaid on a 1951 USAF resolution test chart. DESCRIPTION

[0038] It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described representative embodiments. Thus, the following more detailed description of the representative embodiments, as illustrated in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely illustrative of representative embodiments.

[0039] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.Atty. Docket No.25-024PCT

[0040] Furthermore, described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, et cetera. In other instances, well known structures, materials, or operations are not shown or described in detail to avoid obfuscation.

[0041] As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a photoabsorber” includes a plurality of such photoabsorbers and equivalents thereof known to those skilled in the art, and so forth, and reference to “the photoabsorber” is a reference to one or more such photoabsorbers and equivalents thereof known to those skilled in the art, and so forth. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each separate value, as well as intermediate ranges, are incorporated into the specification as if individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contraindicated by the text.

[0042] As used herein, the term “polymer” refers to a chemical compound that is made of a plurality of small molecules or monomers that are arranged in a repeating structure to form a larger molecule. Thus, a polymer is a compound having multiple repeat units (or monomer units) and includes the term “oligomer,” which is a polymer that has only a few repeat units. The term “copolymer” refers to a polymer including two or more dissimilar repeat units (including terpolymers - comprising three dissimilar repeat units - etc.). Polymers may occur naturally or be formed synthetically. The use of the term “polymer” encompasses homopolymers (having a single repeat unit) as well as copolymers. The term “copolymer” is used herein to include any polymer having two or more different monomers. Copolymers may, for example, include alternating copolymers, periodic copolymers, statistical copolymers, random copolymers, block copolymers, graft copolymers etc.

[0043] As used herein, the terms “alkyl,” “aryl” and / or other groups refer generally to both unsubstituted and substituted groups unless specified to the contrary. Unless otherwise specified, alkyl groups are hydrocarbon groups and are preferably C1 to C20 (that is, having 1 to 20 carbon atoms) alkyl groups, saturated or unsaturated (that is containing double bonds or not), and can be branched or unbranched, acyclic or cyclic. The above definition ofAtty. Docket No.25-024PCT an alkyl group and other definitions apply also when the group is a substituent on another group (for example, an alkyl group as a substituent of an alkylamino group or a dialkylamino group). The term “aromatic” refers to cyclic or polycyclic groups which are conjugated. The term “aryl” refers to cyclic or polycyclic groups including delocalized pi electrons which are derived from an aromatic hydrocarbon via the removal of a hydrogen atom. Aryl groups hereof include 6 to 14 carbon atoms in one or more fused rings thereof. Aryl groups include, for example, phenyl, naphthyl, or anthryl. Heteroaryl groups or heteroaromatic groups may contain one or more heteroatoms (an atom other than carbon) such as N, O, S and P in the ring structure.

[0044] The term “amine” refers to the group -NRaRb, wherein Raand Rbare for example, independently hydrogen, an alkyl group, and / or an aryl group. The term “carboxyl” refers to the group -COOH. The term “sulfone” refers to the group -SO2. The term “hydroxyl” refers to the group -OH.

[0045] As used herein, the term “approximately” when used in connection with a value means within 5%, within 2%, or within 1% of the value unless otherwise indicated herein or otherwise clearly contraindicated by the text. As used herein the term “and / or” means one of or both of an entity. Thus, A and / or B means A or B, or both A and B. As used herein, the term “biocompatible” refers to a material performing its intended function in contact with a living biological system without eliciting a significantly harmful or inappropriate response. Biocompatibility may be determined by measuring the cytotoxicity of the material in contact with living cells cultured in vitro as determined through ISO 10993-5:2009 compliant protocols using live / dead assays. Quantitatively, the ISO 10993-5:2009 (Biological evaluation of medical devices) standard indicates that the reduction of cell viability by more than 30% (that is, the death of more than 30% of cells) is considered a cytotoxic effect. As used herein, the term “transparent,” when used in connection with a solid sample, refers to a material having a transmittance of at least 90 % in the range of 420 to 680 nm and having less than 5% haze for a solid, 1mm-thick material sample. As used herein, the term “transparent,” when used in connection with a liquid sample, refers to a material having a transmittance of at least 90 % in the range of 420 to 680 nm and having less than 5 NTU turbidity for a liquid, 1mm-thick material sample. In general, and in the examples described herein, transmittance in the range of 420 to 680nm is desirably greater than 90%, more desirably greater than 95%, and even more desirably greater than 99%. Haze for a solid 1mm-thick sample is desirably < 5%, more desirably < 2%, and even more desirably <1% as measured following the standard ASTM D1003 (Haze and luminous transmittance of transparent plastics).Atty. Docket No.25-024PCT Turbidity for a 1mm thick liquid sample is desirably <5 NTU, more desirably <1NTU, and even more desirably < 0.3 NTU following ASTM D6855 (Standard test method for the determination of turbidity below 5 NTU in static mode). As used herein, the term “elastomeric” (when, for example, used in connection with additive manufactured articles hereof) refers to a material exhibiting reversible elongation, a Young’s modulus below 10 MPa, and an elongation at break of least 100%.

[0046] The adoption of ultraviolet (UV) stereolithographic 3D printers, along with suitable materials, may significantly reduce engineering effort and prototyping time (for example in areas including, but not limited to, microfluidics). Properties for materials for use in areas such as microfluidics should ideally include being optically transparent to enable imaging, being printable at high resolution to create micron-scale features, being biocompatible to avoid significantly negatively impacting living cells, and being gas permeable to enable gas exchange for cell metabolisms. Suitable materials may, for example, serve as a drop-in substitute for materials conventionally used in soft lithography such as SYLGARD 184, a polydimethylsiloxane (PDMS) elastomer. SYLGARD 184 is a curable silicone elastomer available from DOW Chemical Company of Midland, MI USA, which is considered to be biocompatible and is used in a number of biomedical applications. PDMS and other silicone rubbers are well known for their usage in medical devices due to their biocompatibility and uniquely high gas permeability. As a result, 3D printable silicone resins are a promising candidate for satisfying criterion for microfluidic devices and bioprinting. In general, siloxanes are molecules which include one or more siloxane functional groups (Si-O-Si). Silicones are polymeric materials including a plurality of siloxane functional groups through the structure thereof (that is, polysiloxanes or siloxane-based resins or polymers).

[0047] In a number of embodiments hereof, siloxane-based or silicone resins are photocured in an additive manufacturing process (for example, a 3D printing process or a photoresist lithography process) using thiol-ene chemistry. In thiol-ene chemistry, which may be photoinitiated, a thiol-functional compound reacts with an alkenyl-functional compound to form an alkyl sulfide. The reaction is exothermic, proceeds rapidly, and provides high yield. Thiol-ene reactions are thus regarded as a form of “click chemistry.”

[0048] The formulations or compositions described herein may, for example, include siloxane-based polymers or resins in a polymer component or portion thereof. The polymer portion includes a first polymer component including one or more alkenyl-functional siloxane polymers. A second polymer component of polymer portion hereof includes one or more mercapto-or thiol- functional (-SH functional) siloxane polymers. The siloxaneAtty. Docket No.25-024PCT polymers of the first polymer component and the siloxane polymers of the second polymer component may or may not be transparent in the liquid state, but photocured to provide a transparent article. Siloxane polymers hereof may be homopolymers or copolymers. It is, however, desirable that the first component polymer(s) and the second component polymer(s) of the reactive polymer portion hereof be transparent in the liquid state (before photocuring).

[0049] The formulations further include a photoinitiator system including one or more photoinitiators and a photoabsorber system including one or more photoabsorbers. In a number of embodiments, the compositions or formulations hereof are 3D printable to form objects or articles that are flexible, elastomeric, and / or visibly transparent. Transparency may be achieved in the articles hereof without post-processing. Further, the compositions hereof may desirably be solvent-free. In a number of embodiments, the additive manufactured (for example, 3D printed) articles hereof are also biocompatible.

[0050] Alkenyl-functional siloxane polymers hereof may include a plurality of alkenyl groups, which are groups that include a carbon double bond and can undergo an alkyl hydrothiolation reaction. Examples of alkenyl groups include, but are not limited to, vinyl groups, norbornene groups, acrylate groups, and methacrylate groups. Alkenyl groups of alkenyl-functional siloxane polymers hereof may, for example, be terminal groups, pendant groups or a combination thereof. The alkenyl-functional siloxane polymers may be linear or branched. Alkenyl-functional siloxane polymers hereof may, for example, desirably include 2 to 1000 alkenyl groups, more desirably include 2 to 50 alkenyl groups, or even more desirably include 2 to 10 alkenyl groups. The alkenyl group may be present in a random distribution, be present in an ordered or partially ordered distribution on individual siloxane polymer chains. The weight percentage of alkenyl groups may vary widely in the alkenyl- functional siloxane polymers herein. For example, alkenyl-functional siloxanes may desirably include 0.01 to 30 weight % alkenyl groups, more desirably include 0.01 to 20% weight % alkenyl groups, or even more desirably include 0.05 to 10 weight % alkenyl groups. In a number of embodiments, alkenyl-functional polymers hereof may have a molecular weight (referring to weight average molecular weight or Mw) of desirably 100 to 10,000,000 g / mol, more desirably 100 to 500,000 g / mol or even more desirably 100 to 100,000 g / mol. The polymers hereof may desirably have a viscosity of 0.5 to 100,000 cP, more desirably 0.5 to 6,000 cP, or even more desirably 0.5 to 3,000 cP. Representative examples of commercially available alkenyl-functional polymers are disclosed in representative studies hereof. However, many other suitable alkenyl-functions polymers are commercially available and / orAtty. Docket No.25-024PCT may be made using synthetic methods known in the art. In a number of embodiments, the alkenyl-functional siloxane polymer hereof may include a plurality of aryl or heteroaryl groups (for, example, phenyl groups, naphthyl groups, anthryl groups, benzothiophene groups, etc.). As known in the art, phenyl groups are functional groups that include an aromatic ring of 6 carbon atoms. Naphthyl groups contain 10 carbon atoms forming two fused benzene rings. Anthryl groups contain 14 carbon atoms forming three fused benzene rings. Thiophene groups contain 4 carbon atoms and one sulfur atom forming an aromatic ring. Benzothiophene groups contain 8 carbons atoms and one sulfur atom forming fused heteroaromatic rings. The inclusion of aryl groups such as phenyl groups or heteroaryl groups may increase the refractive index of the siloxane polymer and thus be used in matching refractive induces of components of composition hereof. In general, the presence of aromatic groups such as aryl groups and / or heteroaryl groups may be used to adjust solubility of components, to adjust dispersibility of components, or to adjust refractive index. In a number of embodiments, alkenyl-functional polymers hereof may desirably include 0.01 to 60 weight % aryl and / or heteroaryl groups, more desirably include 0.01 to 50 weight % aryl and / or heteroaryl groups, or even more desirably include 10 to 50 weight % aryl and / or heteroaryl groups. In a number of embodiments, the aryl groups are phenyl groups, and polymers hereof may desirably include 0.01 to 60 weight % phenyl groups, more desirably include 0.01 to 50 weight % phenyl groups, or even more desirably include 10 to 50 weight % phenyl.

[0051] Thiol-functional siloxane polymers hereof may include a plurality of thiol groups. The thiol groups may be terminal groups, pendant groups or a combination thereof. The thiol- functional groups can undergo an alkyl hydrothiolation reaction. In a number of embodiments, the thiol-functional siloxane polymer component has desirably 2 to 1000 thiol groups, more desirably 2 to 100 thiol groups, or even more desirably 2 to 10 thiol groups. In a number of embodiments hereof, alkenyl functionality and thiol functionality of the siloxane polymers of the reactive polymer portion hereof are selected to achieve a desired degree of crosslinking in a resultant photocured, three-dimensional article.

[0052] Thiol groups of thiol-functional siloxane polymers hereof may be present in a random distribution, a partially ordered distribution, or an ordered distribution on the chains of the siloxane polymers. The thiol-functional siloxane polymers may be linear or branched. In a number of embodiments, the thiol-functional siloxane polymers hereof desirably have a molecular weight (Mw) of 150 g / mol to 10,000,000 g / mol, more desirably a molecular weight (Mw) of 150 g / mol to 1,000 g / mol, or even more desirably a molecularAtty. Docket No.25-024PCT weight (Mw) of 150 g / mol to 10,000 g / mol. The thiol-functional polymers hereof may have a viscosity of desirably 0.5 to 100,000 cP, more desirably 0.5 to 6,000 cP, and even more desirably 0.5 to 3,000 cP. Representative examples of commercially available thiol-functional siloxane polymers were used in studies hereof. Those skilled in the art will appreciate that the formulations hereof can include other commercially available thiol-functional siloxane polymers and / or can include thiol-functions siloxane polymers synthesized using synthetic methods known in the art. A number of representative examples of suitable alkenyl- functional siloxane polymers and thiol-functional siloxane polymers for use the polymer portion hereof are described, for example, in U.S. Patent Application Publication Nos. 2020 / 0032062 and 2020 / 0071525.

[0053] The amount of thiol groups may vary widely in thiol-functional siloxane polymers hereof. For example, in a number of representative examples, thiol-functional siloxane polymers hereof include desirably 0.01 to 35 weight % thiol groups, more desirably 0.01 to 25 weight % thiol groups, or even more desirably 0.01 to 15 weight % thiol groups. Depending upon the desired mechanical properties of the printed article, part or object, the first polymer component and the second polymer component may be added or mixed to, for example, achieve between a 1:1 to 4:1 stoichiometric ratio of thiol functional groups to alkenyl functional groups In a number of embodiments, the thiol-functional siloxane polymers hereof may include a plurality of phenyl groups. In a number of embodiments, thiol-functional polymers hereof may desirably include 0.01 to 60 weight % aryl and / or heteroaryl (for example, phenyl groups, more desirably include 0.01 to 50 weight % and and / or heteroaryl groups, or even more desirably include 10 to 50 weight % aryl and / or heteroaryl groups. In a number of embodiments, the aryl group are phenyl groups, and the thiol-functional siloxane polymers hereof may desirably include 0.01 to 60 weight % phenyl groups, more desirably include 0.01 to 50 weight % phenyl groups, or even more desirably include 10 to 50 weight % phenyl groups.

[0054] In a number of embodiments hereof, one or more of the siloxane polymers of the reactive polymer portion hereof include both alkyl groups and at least one of aryl and heteroaryl group. In a number of embodiments, one or more of the siloxane polymers of the reactive polymer portion hereof include methyl groups and phenyl groups.

[0055] As described above, the alkenyl-functional siloxane polymer(s) of the first polymer component and the thiol-functional siloxane polymer(s) of the second polymer component may include linear and / or branched siloxane polymers. Using relationships known in the polymer arts, and particularly the polysiloxane polymer art, mechanical properties of the 3DAtty. Docket No.25-024PCT printed articles formed from compositions hereof may be readily adjusted through choice of the siloxane polymers of the first polymer component and the second polymer component. For example, the degree of crosslinking can be readily adjusted through choice of functionality, the linear or branched nature of the polymers, alkenyl group-thiol group ratio, and polymer molecular weight as known in the art. Various combinations of first and second polymer components can be used to achieve a wide variety of properties, including mechanical properties. As described further below, various additives (such as reinforcing agents and / or fillers) may also be used to achieve desired properties, including mechanical properties.

[0056] The photocurable compositions hereof further include, a photoinitiator system including one or more photoinitiators and a photoabsorber system including one or more photoabsorbers. To achieve improved transparency (without requiring post-processing, such as extraction) in formulations or compositions of siloxane-based 3D printable resin materials hereof, the first polymer component, the second polymer component, the one or more photoabsorbing agents, and the one or more photoinitiators are selected to achieve a determined transparency.

[0057] Transparency of additive manufactured or 3D printed articles hereof may be achieved through selection (or modification) of components (including siloxane polymer components, photoabsorbers, photoinitiators, reinforcing agents, fillers etc.) to achieve solubility and / or refractive index matching depending upon, for example, the nature of and the amount of a particular component in the composition. In a number of embodiments, the polymer components are matched in refractive indices with a difference in refractive index, 0.050, less than 0.030, less than 0.010, or less than 0.002. In a number of embodiments, the polymer components, photoinitiator system, and photoabsorber system are selected to form a transparent single phase liquid system. Transparency of this liquid system is desirably maintained through a temperature range of 20-60°C (which includes the range of temperatures at which additive manufacturing or 3D printing typically occurs). The lower critical solution temperature (LCST) is desirably above 60°C and the upper critical solution temperature (UCST) is desirably below 20°C.

[0058] In general, it is desirable for the liquid, photocurable compositions hereof to be transparent under the conditions of photocuring (for example, in additive manufacturing of three-dimensional articles hereof). For example, the scattering of light in a turbid liquid may lead to reduced printing resolution in a 3D printing process (for example, blurred edges instead of sharp edges). Further, the photocurable compositions hereof should result inAtty. Docket No.25-024PCT transparent, solid, three-dimensional articles after photocuring (for example, upon completion of an additive manufacturing process).

[0059] Photoabsorbing agents or photoabsorbers are materials which may be added to photopolymer resins to improve printing precision by absorbing stray or scattered light during 3D printing processes. In general, photoabsorbing agents or photoabsorbers for use herein may, for example, exhibit high absorbance in the UVA and violet spectrum (wavelengths of 360-410nm) and low absorbance in the visible spectrum (420-680nm). Common 3D printing wavelengths include 365nm, 385nm, 395nm, or 405nm. It is desirable that photoabsorbers exhibit high absorbance in a range of wavelengths within ± 5nm of a particular wavelength at which photocuring occurs (for example, in a 3D printer). For example, in a 3D printer using a 385nm light source, the photoabsorber should exhibit high absorbance between 380 to 390nm. As used herein, the term “high absorbance” refers to a material having a transmittance no more than 0.1% at a specified wavelength or range of spectral wavelengths for a 1mm-thick material sample. As used herein, the term “low absorbance” refers to a material having a transmittance of at least 90% at a specified wavelength or range of spectral wavelengths for a 1mm-thick material sample.

[0060] Photoinitiators are light-sensitive molecules which may be used to initiate the photopolymerization process. Photoinitiators, when exposed to a specific wavelength of light, may undergo a chemical reaction that generates reactive species (for example, radicals or ions) that trigger the polymerization of monomers or oligomers of the 3D printable resin. Photoinitiators for use herein may, for example, be Type I or Type II photoinitiators. Similar to photoabsorbers hereof, photoinitiators may exhibit high absorbance in the UVA and violet spectrum (specifically at the printing wavelengths 360-410nm) and low absorbance in the visible spectrum (420-680nm). It is desirable that photoinitiators exhibit high absorbance in a range of wavelengths within ± 5nm of a particular wavelength at which photocuring occurs. Photoinitiators for use herein should be sufficiently soluble in the formulations hereof to initiate photopolymerization.

[0061] Cumulatively, the combined photoinitiator / photoabsorber systems hereof should have an absorbance in a range of wavelengths within ± 5nm of a particular wavelength at which photocuring occurs that is at least three orders of magnitude higher (1000x or more) compared to the maximum absorbance at all wavelengths in the visible spectrum. Such formulations enable high-resolution and transparent printing. As used herein, the term “maximum absorbance” refers to the maximum value of absorbance in the absorption spectrum of a material, where the maximum value of absorbance corresponds to aAtty. Docket No.25-024PCT wavelength within a range of spectral wavelengths. As used herein, absorbance (A) is related to transmittance (T) through the Beer-Lambert Law, = log , where absorbance ismeasured in units of optical density (OD). As used herein, a difference of three units of optical density (OD) corresponds to three orders of magnitude (1000x) of absorbance. As used herein, transmittance (T) is defined as = / , where Io is the incident light fluxreceived by a surface and Itis the light flux transmitted through a surface to the opposite side from the incident light flux. As used herein, the term “cumulative absorbance” refers to the absorption spectrum of a material containing one or more photoinitiator systems and / or one or more photoabsorber systems. The combined photoinitiator / photoabsorber systems hereof may have a cumulative absorbance desirably greater than 3 OD, more desirably greater than 4 OD, or even more desirably greater than 5 OD in a range of wavelengths within ± 5nm of a particular wavelength at which photocuring occurs.

[0062] The desired wavelength requirements of photoabsorbers hereof generally overlaps with UVA-blocking polymer additives and / or sunscreen ingredients. Such photoabsorbers include, but are not limited to, organic compounds like 2-Isopropylthioxanthone( ITX), 2,4- diethylthioxanthone (DETX), avobenzone, octocrylene, bisoctrizole, drometrizole, bumetrizole, octavenzone, bemotrizinol, or other benzotriazole-based photoabsorbers such as TINUVIN® CarboProtect (available from BASF of Florham Park, New Jersey USA). Photoabsorbers hereof may also include UVA-absorbing particles such as titanium dioxide nanoparticles or zinc oxide nanoparticles. Particles may be surface modified to adjust their solubility, to adjust their dispersibility, or to adjust their refractive index.

[0063] In a number of representative studies, ethyl phenyl(2,4,6-trimethylbenzoyl) phosphinate (TPO-L) was used as a photoinitiator. UV-absorbing additives such as ITX and DETX were also used in a number of studied representative embodiments. Other representative examples of photoinitiators for use herein include, but are not limited to, 2,4,5–trimethylbenzoyldiphenylphosphine oxide (TPO), phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide (BAPO), lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP), 2-Hydroxy- -(2-hydroxyethoxy)-2-methylpropiophenone, 2-Benzyl-2-(dimethylamino)-1-[4-(morpholinyl) phenyl]-1-butanone, 1-Hydroxycyclohexyl phenyl ketone), 2,2-dimethoxy-2-phenylacetophenone, 1-[4- (Phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime), 2,3-bornanedione (Camphorquinone) or Bis(4-methoxybenzoyl)diethylgermanium.

[0064] Although certain additives such as photoinitiators, photoabsorbers, etc. may not be matched in refractive index to other components of the compositions hereof, transparencyAtty. Docket No.25-024PCT may be achieved if such an additive is present in low quantities and / or if such an additive has suitable solubility in the compositions hereof. In general, when an additive such as a photoinitiator or a photoabsorber is present in a weight % less than 5% and is soluble within the composition, transparency may be achieved even if the additive is not matched in refractive index to other components of the compositions hereof. Various additives are readily tested for refractive index, solubility and / or biocompatibility.

[0065] Representative studies hereof have demonstrated that addition of DETX to ITX and / or TPO-L may, for example, increase the optical absorbance of the photocurable formulations hereof. The combination of additives described herein may produce comparable absorbance results in a variety of siloxane-based (for example, polydimethylsiloxane-based) resins. In a number of embodiments, siloxane-based resins hereof may be transparent and elastomeric as described above. Further, the resins and additives hereof desirably enable 3D printing of channels with side dimensions including, but not limited to approximately 0.25mm or 250 microns.

[0066] The amount of vinyl polymer component(s) and thiol polymer component(s) in the polymer portion of the compositions hereof can vary significantly. The individual polymer components can be present in the range of 0.5% to 99.5% by weight (of the polymer component). In a number of embodiments, the alkenyl-functional siloxane polymer(s) of the first polymer component are present at 40.0% to 96.0% by weight. The thiol-functional polymer(s) of the second polymer component may, for example, be present in the range of 4.0% to 60.0% by weight. A desirable range in the compositions hereof of the reactive polymer component, that is, the combination of the alkenyl-functional siloxane polymer and the thiol-functional polymer, is 70.0 to 99.9 % by weight, or more desirably in the range of 75.0 to 98.0% by weight. In the representative examples hereof, the stoichiometric ratio of thiol groups to alkenyl groups in the studied polymer compositions hereof was varied between 1.5:1 to 2.5:1. In a number of studies, the ratio was 1:1. However, the stoichiometric ratio of thiol groups to alkenyl groups in the polymer compositions hereof may range broadly from, for example, from 1:1 to 4:1 of thiol groups to alkenyl groups. Varying the ratio of thiol groups to alkenyl groups may be used to vary mechanical properties by affecting, for example, the crosslink density, distance between crosslinks, and degree of polymerization for the printed articles hereof.

[0067] Photoinitiator(s) of the photoinitiator system hereof may be present in the composition hereof in the range of desirably 0.01 to 5 % by weight, more desirably 0.01 to 2 % by weight, or even more desirably 0.10 to 2 % by weight. Photoabsorber(s) of theAtty. Docket No.25-024PCT photoabsorber system hereof may, for example, be present in the range of desirably 0.01 to 5 % by weight, more desirably 0.01 to 2 % by weight, or even more desirably 0.10 to 2 % by weight.

[0068] Photocurable 3D printing resins formulated using vinyl-functional and mercapto- or thiol- (-SH) functional siloxane may provide economic advantages, for example, when compared with (meth)acrylated siloxane resins. Photosensitive UV-absorbing additives may be evaluated to improve the 3D printing resolution of the material using methodologies as described herein. Further, the material’s tensile and tear strengths may be characterized on a materials testing system as described herein, and then the material may be 3D printed to identify the minimum printable resolution of enclosed channels as further described herein.

[0069] High optical absorbance at 3D printing wavelengths may enable high-resolution printing by preventing excessive curing from scattered light in the XY axes and to prevent excessive curing depth in the Z axis. High-resolution printing can create sub-millimeter scale features such as pillars on the external facing sides of printed parts, as well as sub-millimeter scale features such as tunnels or cavities in the internal volume of printed parts. Wavelengths of light commonly used in 3D printing include 365, 385 and 405nm. TPO-L and ITX have previously been used as UV photoabsorbers in formulations printed with 385nm and 405nm light because of their low yellowing effect. DETX is a thioxanthone similar to ITX but with greater UV absorbance in formulations. To compare the absorbance of formulations including TPO-L, ITX, and DETX in representative studies hereof, multiple combinations of the additives were mixed with DMS-V21 resin and pipetted into a 48-well plate for UV-Vis spectrophotometry. DMS-V21 is a vinyl terminated polydimethylsiloxane available from Gelest Inc. of Morrisville, PA USA.

[0070] In a representative experiment, UV-Vis spectrophotometry revealed significant differences in absorbance between the 385nm and 405nm wavelengths for various formulations containing ITX and DETX. FIG.1 illustrates the results of such studies, showing absorbance readings of siloxane-based resins with five different formulations of UV photo absorbing additives. The studied formulations of additives in FIG.1 included: TPO-L, ITX, DETX, ITX and TPO-L, ITX and DETX, and ITX, DETX and TPO-L. Common vat polymerization wavelengths of 385mm and 405mm are highlighted in FIG.1.

[0071] While the optical density (OD) at 405nm was lower than 0.3 for all tested formulations, the optical density at 385nm was greater than 3.7 for all tested formulations other than the sample containing only TPO-L. Formulations containing DETX saturated the spectrophotometer at the maximum OD limit of 4. Comparing the formulations with andAtty. Docket No.25-024PCT without DETX at 390nm shows a difference of more than 1.3 OD, where the sample of ITX / DETX / TPO-L has an OD of 3.2 and the sample of ITX / TPO-L has an OD of 1.9. Considering that OD uses a logarithmic scale for evaluating light absorbance, a difference in 1.3 OD corresponds to an approximately 20 times lesser transmittance of light at the 390nm wavelength.

[0072] These absorbance results support an expectation that higher resolution 3D printing may be achieved using, for example, a 385nm light source compared to a 405nm light source. Furthermore, formulations containing both ITX and DETX may result in higher resolution 3D printing than formulations containing solely combinations of ITX and TPO-L, assuming equivalent loadings of each photosensitive additive. A wavelength of electromagnetic energy / light may readily be optimized for a particular formulation by those skilled in the art using the methodologies describe herein and knowledge in the art.

[0073] In a number of representative studied embodiments, vinyl-functional and mercapto- or thiol-functional (SMS-022, SMS-042; Gelest) siloxane resins were combined in a ratio of 56.2% DMS-V21, 29.2% SMS-022, and 14.6% SMS-042 by weight to achieve a 1:1 stoichiometric ratio between vinyl and thiol functional groups. The weight percents are those for silicone-based polymer or the polymer portion of the composition, and do not include the photoinitiators or photoabsorbers. TPO-L was used as a photoinitiator. UV- absorbing additives ITX and DETX were dissolved in the resins using an ultrasonic homogenizer. Studied embodiments included 0.6 % by weight TPO-L, 0.4 % by weight ITX, and 0.2 % by weight DETX. Mechanical testing specimens were 3D printed on a Phrozen Sonic Mini 8K printer using 405nm light with a light intensity of 1.2mW / cm2, while resolution test specimens were 3D printed on an Asiga Pico 2 printer using 385nm light with a light intensity of 1.2mW / cm2. Specimens for the Phrozen Sonic Mini 8K printer were prepared by creating the geometry in STL file format and slicing the geometry into 50 micron thick layers along the Z axis using Lychee Slicer. Specimens for the Asiga Pico 2 printer were prepared by creating the geometry in STL file format and slicing the geometry into 50 micron thick layers along the Z axis using Asiga Composer. Factors affecting the photocuring time of the resin during 3D printing include the absorbance of the photoinitiator system, the absorbance of the photoabsorber system, the viscosity of the silicone resin formulation, and / or the crosslinking density. For the examples described herein, photocuring times ranged between 5 to 45 seconds for 50 micron thick layers along the Z axis.

[0074] In representative studies of mechanical properties, the prepared silicone resin formulation demonstrated a 195% failure strain, which exceeds the 100% failure strain ofAtty. Docket No.25-024PCT SYLGARD 184 when mixed with a 10:1 base:curing agent ratio as described in the SYLGARD 184 datasheet. FIG.2 shows the results of a representative study, which included a tensile test of ASTM D412C specimens (n=2) at 50% scale. The average tensile strength was 51.2 kPa and the average strain to failure was 195%. The average modulus was 31.1 kPa measured at 100% strain. The formulation’s tensile strength of 31.1 kPa was significantly lower than that of SYLGARD 184 (6200 kPa).

[0075] FIG.3 shows the results of a representative study including a tear strength test of ASTM 624C specimens (n=2) 3D printed at 50% scale. The average tear strength was 0.153 N / mm. The 0.153 N / mm tear strength of the 3D printed formulation was approximately one order of magnitude lower than that of SYLGARD 184 (2.6 N / mm).

[0076] FIGS.4A-4E illustrate representative examples of 3D printed test blocks using the representative siloxane-based composition described above with internal channels of different dimensions and with overhangs of different thicknesses. FIGS.4A and 4B illustrate diagrams of a test block including sets of channels and overhangs. FIG.4A shows a forward isometric view showing stepped overhangs and open channels. FIG.4B shows a back or rearward isometric view showing channels with nominal widths ranging from, in an example experiment, 0.1mm to 1mm and heights ranging from 0.05mm to 1mm.

[0077] In a number of studies, the smallest printable channel formed was 0.25mm wide and 0.25mm tall, as seen in FIG.4C (see arrow). Further optimization of 3D printable compositions hereof will enable even smaller printable dimensions. FIG.4C illustrates a side view of the printed part. Channels with wider widths and taller heights were also printable. In the studied example of FIG.4C, the square channel with side length of 1mm did not fully print (see right side of photograph). That result may have been due to excessive peeling or suction forces during the printing process and the relatively low mechanical strength of the formulation.

[0078] As illustrated in FIGS.4D and 4E, the 3D printed materials hereof were noticeably transparent. For example, FIG.4D shows a top view of a printed part, with open channels visible as translucent white strips. FIG.4E shows a top view of a printed part showing the transparency of the material, as the marking lines of the underlying ruler were visible through the test block, which was up to 1.6mm thick at the tallest overhang. As the siloxane- based resins were composed primarily of dimethylsiloxane units, similar transparency and high-resolution printing is expected in other embodiments, which may include dimethylsiloxane-based 3D printing resins that may be alternatively functionalized with, but not limited to, methacrylate or acrylate groups.Atty. Docket No.25-024PCT

[0079] Formulations hereof may, for example, include polymer and / or other components selected to improve mechanical properties and / or increase the range of complex geometries (for example, channels, overhangs, etc.) that may be 3D printed. Examples of such components include, but are not limited to, reinforcing resins and fillers such as fumed silica. Representative examples of such components may be the same as or similar to those found in liquid silicone rubbers.

[0080] In general, resins such as MDTQ polysiloxane resins for use in 3D printing are high- performance, specialized resins which may be designed for specific applications. Such resins may offer unique mechanical properties, biocompatibility, or other characteristics not typically found in general-purpose resins. MDTQ resins in formulation hereof may be present as reactive components (that is, be alkenyl-functionalize or thiol-functionalized) or be present as a filler (that is, a non-reactive component) to achieve desired mechanical and / or optical properties. Fumed silica, which is also known as pyogenic silica, is a powder formed of amorphous silica particles having high surface area which may be used as a filler herein. Such components may be used in formulations hereof which are biocompatible, making them suitable for applications including, but not limited to, microfluidics and / or bioprinting as described above. Formulations may maintain transparency while excluding cytotoxic solvents such as ethanol, acetone, isopropanol, toluene, chloroform, dichloromethane, tetrahydrofuran, hexane, or dimethyl sulfoxide.

[0081] As discussed above, mechanical performance may be controlled (for example, enhanced) with the addition of various siloxane resins which function as reinforcing agents such as various MDTQ resins. MDTQ resins are a type of silicone or polysiloxane resin including the presence of four distinct structural units within the molecular structure thereof. M or monofunctional represent R3SiO as a chain terminating unit. D or difunctional represents R2SiO2as a chain extending unit. T or trifunctional represents RSiO3, as a crosslinking unit. Q or quadrifunctional represents SiO4, a strong crosslinking unit which forms a reticulated, silica-like core. As used herein, the term “MDTQ resin” refers to a resin which may include the M, D, T, and Q structure units, one or more of any one of those structure units, or any combination of subsets thereof. Siloxane-based or silicone resins may, for example, be composed of a subset combination of structural units such as DT, MQ, MDT, or MTQ resins. Mechanical performance may be alternatively or additionally enhanced using various fillers such as fumed silica powders. Silicone MDTQ resins or fillers that are functionalized with alkenyl groups may be used to substitute for at least a portion of alkenyl- functional silicone polymers in the formulation. Silicone MDTQ resins or fillers that areAtty. Docket No.25-024PCT functionalized with thiol groups may be used to substitute for at least a portion of thiol- functional silicone polymers in the formulation.

[0082] In a number of representative embodiments of compositions or formulations hereof, introduction of reinforcing agents, including, but not limited to, MDTQ-resins and / or silica fillers, was found to significantly improve the mechanical properties of the formulation. In a number of representative studies, transparent, photocurable silicone resins utilizing MDTQ-resins and fumed silica fillers were used to form 3D printed models or parts. Biocompatibility was also demonstrated for a representative resin formulation when cultured with in vitro C2C12 muscle cells. Transparency was maintained through matching optical refractive indices and maintaining soluble liquid phases of formulation ingredients. For example, formulations may include an alkenyl-functional silicone polymer and a thiol- functional silicone polymer with a relative difference in refractive index, n, desirably less than 0.050, more desirably 0.020, more desirably less than 0.010, or even more desirably less than 0.002. In another example, formulations may include the aforementioned silicone polymers along with a fumed silica filler with a relative difference in refractive index, n, desirably less than 0.050, more desirably less than 0.020, more desirably less than 0.010, or even more desirably less than 0.002.

[0083] In such representative formulations, the photoinitiator system and photoabsorber system were chosen for their solubility in the silicone polymers to maintain a single liquid phase. The concentrations of the photoinitiator system and the photoabsorber system may impact the LCST and UCST of the liquid formulation. For additive manufacturing, the LCST should be above the highest anticipated temperature observed during manufacturing and the UCST should be below the lowest anticipated temperature observed during manufacturing. For the examples described herein, the LCST was above 100°C and the UCST was below 20°C. In example formulations, the LCST is desirably above 20°C , more desirably above 60°C, and even more desirably above 100°C. The UCST is desirably below 20°C , more desirably below 0°C , and even more desirably below -80°C. Higher concentrations of the photoinitiator system or photoabsorber system than herein described can lead to precipitation into a multi-phase liquid with reduced transparency. Careful selection of the silicone polymers may increase the solubility of the photoinitiator system or photoabsorber system and enable higher concentrations of the photoinitiator system or photoabsorber system within the formulation while maintaining transparency within the desirable UCST and LCST thresholds. Many of the aforementioned example photoinitiators or photoabsorbers include one or more aryl groups such as phenyl groups. The inclusion of aromatic moietiesAtty. Docket No.25-024PCT (for example, aryl moieties such as phenyl moieties) in an alkenyl-functional silicone polymer, a thiol-functional silicone polymer, a silicone MDTQ resin, and / or a fumed silica filler are example methods of increasing the solubility or dispersibility of additives such as the photoinitiator system, the photoabsorber system, and / or a filler. Without limitation to any mechanism, increasing solubility or dispersibility may be a result of hydrophobic and / or pi-pi interaction between components of the compositions hereof.

[0084] Q-resins can act as reinforcing constituents in silicone resin formulations while maintaining transparency. In a number of studied embodiments, thiol-ene reactive Q-resins were incorporated into a photocurable formulation with a refractive index of 1.40-1.42 through a blend of a vinyl-functional Q-resin diluted in a vinyl-functional silicone (Siltech Corporation, Silmer G-180). The composition of a representative example of a transparent silicone resin formulation was 48.9% SMS-042, 39.5% G-180, and 11.6% DMS-V21 by weight. SMS-042 is a 4-6% (mercaptopropyl)methylsiloxane)-dimethylsiloxane copolymer available from Gelest Inc. Silmer® G-180 is a vinyl-functional Q-resin diluted in vinyl silicone available from Siltech Corporation of Toronto, Ontario Canada. DMS-V21 is a vinyl-terminated polydimethylsiloxane available from Gelest Inc. as described above.

[0085] Mechanical testing revealed the strength of formulations reinforced with Q-resins to be over 18x higher than unreinforced formulations. The modulus, elongation, and strength are further tunable through the addition of chain extenders such as SMS-022. SMS-022 is a 2-3%(mercaptopropyl)methylsiloxane-dimethylsiloxane copolymer. FIG.5 illustrates mechanical tensile test data for representative transparent silicone resins hereof containing vinyl-functional Q-resins. In FIG.5, specimen VQ-2 contains SMS-022 as a chain extender and demonstrated increased failure strain and reduced modulus compared to specimen VQ-1, which contained no SMS-022. The formulation containing the chain extender was 36.3% SMS-042, 33.5% G-180, 20.4% SMS-022, and 9.9% DMS-V21 by weight.. The formulation containing no chain extender exhibited a tensile strength of 569 kPa and a failure strain of 62%. The formulation containing chain extender exhibited a tensile strength of 449 kPa and failure strain of 71%. Both the VQ-1 and VQ-2 formulations contained 0.6% by weight TPO-L and 0.5% by weight ITX. Inclusion of additional chain extender into the formulation and / or other modifications may be used to achieve elastomeric failure strains above 100% if desired for a particular use.

[0086] The cytotoxicity of the silicone resin formulation of FIG.5, which included vinyl- functional Q-resin and no chain extender (VQ-1) (panel b), was evaluated using a live-dead assay with C2C12 myoblasts over 72 hours. Photocured discs of the silicone resinAtty. Docket No.25-024PCT formulation (6mm diameter, 3mm tall, n=5) were washed in ethanol and then washed in phosphate-buffered saline prior to being placed in sterile well plates and seeded with C2C12 cells. Discs of Dow SYLGARDTM184 PDMS (panel a) were used as control specimens in separate sterile wells that were also washed in ethanol and phosphate-buffered saline prior to seeding C212 cells. After culturing the cells for 72 hours, live-dead staining revealed comparable live cell activity (represented by green in the colored version of the photomicrographs) between the samples of photocured silicone resin and the samples of SYLGARD 184. The similar qualitative distribution of live cells (green) and dead cells (red) between the two samples indicated that the photocured silicone resin hereof is biocompatible and non-cytotoxic.

[0087] Fumed silica is a common reinforcing filler for silicone rubbers, typically increasing the tensile strength, elongation, modulus, and / or compressive strength. Hydrophilic and hydrophobic variants of fumed silica contribute differently to the thixotropic thickening and shear thinning of silicone rubbers, with hydrophilic silica typically increasing the viscosity of silicone rubbers more than hydrophobic silica at comparable loadings by weight %.

[0088] Fumed silica typically exhibits a refractive index of 1.45-1.47, and the inclusion of fumed silica in silicone rubber formulations with mismatched refractive indices can cause haziness. See, for example, Ford et al., 3D Printing of Transparent Silicone Elastomers, Advanced Materials Technology, 7:5, 2100974 (2021). Even in closely refractive index- matched formulations, there may be turbidity or polychromatic sheen attributed to the thermochromic effect.

[0089] Studies hereof demonstrated that the representative filler, fumed silica, could be included in a refractive index matched silicone resin formulation hereof to create transparent, photocurable silicone resins without exhibiting excessive turbidity or the thermochromic effect. Photocured samples of the resin also did not display excessive haziness or the thermochromic effect. As the addition of aryl (phenyl) and sulfur-inclusive moieties are known to increase the refractive indices of materials, thiol-ene chemistry was used for the silicone resin formulation with a vinyl-functional dimethyl-diphenyl siloxane and a thiol-phenyl-functional MDTQ-resin. The vinyl-functional dimethyl-diphenyl siloxane (PDV- 1625) has a refractive index of 1.47. PDV-1625 is a vinyl terminated (15-17% diphenylsiloxane)-dimethylsiloxane copolymer available from Gelest. The thiol-phenyl- functional MDTQ-resin had a refractive index of 1.46. A studied embodiment of the thiol- phenyl-functional MDTQ-resin contained 6.5% thiol and 15.1% phenyl by weight. The thiol- phenyl-functional MDTQ-resin may be created by using an organic bridge between a MTQ-Atty. Docket No.25-024PCT resin and a MD-resin to form a silicone-organic-silicone network. In one embodiment, the thiol-phenyl functional MDTQ-resin is a copolymer of a thiol-functional MTQ-resin and an alkenyl-functional dimethyl-diphenyl siloxane.

[0090] FIG.7 illustrates a structure of a representative copolymer of a thiol-functionalized MTQ resin and an alkenyl-functional dimethyl-diphenyl siloxane resin. FIG.8 illustrates a structure of a representative example of a MDTQ resin including thiol and phenyl moieties. FIG.9 illustrates a representative example of a silicone-organic-silicone network formed with an organic bridge (X) between an MTQ silicone resin and an MD silicone resin, containing thiol and phenyl moieties. Those skilled in the art will appreciate that the structure of the organic bridge can vary significantly. Those skilled in the art will also appreciate that the vinyl-functional dimethyl-diphenyl siloxane resin may be functionalized with additional or alternative moieties including, but not limited to, alkenyl or carbon double-bond groups such as norbornene, acrylate, or methacrylate without affecting usage thereof in formulations hereof.

[0091] The vinyl-functional dimethyl-diphenyl siloxane used in compositions hereof may be substituted with other vinyl-functional MDTQ silicone resins with different compositions of M, D, T, and Q groups without affecting the usage of the vinyl-functional siloxane. The vinyl- functional dimethyl-diphenyl siloxane may be functionalized with alternative or additional moieties such as one or more hydroxyl groups, carboxyl groups, alkane groups, phenyl groups, naphthalene groups, thiophene groups, or sulfone groups without affecting functionality thereof in the formulations hereof. The representative grafted dimethyl- diphenyl siloxane moieties may, for example, include different compositions of methyl and aryl groups, such as dimethyl-methylaryl (dimethyl-methylphenyl) or diaryl-methylaryl (diphenyl-methylphenyl) compositions. Phenyl groups may, for example, be replaced with aryl or heteroaryl moieties such as thiophene, naphthalene, anthracene, or benzothiophene.

[0092] Further, the thiol-functional MTQ-resin may be substituted with other thiol- functional MDTQ silicone resins with different compositions of M, D, T, and Q groups without affecting the usage of the resin. The thiol-functional copolymer may, for example, be substituted with a thiol-functional and aryl- and / or heteroaryl-functional (for example, phenyl-functional) MDTQ resin eliminating the thiol-ene bridge in the copolymer. The thiol- functional silicone polymer, the thiol-functional MTQ-resin, the derived copolymer, or the thiol-aryl-functional MDTQ resin may include additional moieties such as hydroxyl, carboxyl, alkane, amine, or sulfone without affecting functionality. The dimethyl-diphenyl siloxane and / or copolymer may utilize different compositions of methyl (and / or other alkyl) and arylAtty. Docket No.25-024PCT groups, such as dimethyl-methylaryl (dimethyl-methylphenyl) or diaryl-methylaryl (diphenyl- methylphenyl) compositions. Dimethyl-diaryl siloxane and / or the derived copolymer may utilize different compositions of M, D, T, and Q groups without affecting the usage of the siloxane or copolymer in the formulations hereof.

[0093] Refractive index matching can be accomplished with silicone resins of different molecular weights than described herein. Moreover, adjustments to the weight % of sulfur- inclusive moieties and aromatic moieties may be used to match refractive indices outside of the range of 1.45-1.47 of the present studies.

[0094] A number of studies were performed to demonstrate the mechanical properties and transparency of formulations hereof after adding a variety of fumed silicas with different surface modifications. FIG.10 illustrates representative examples of surface modifications to fumed silica with surface silanol groups. Panel a) illustrates hydrophilic silica with exposed silanol moieties. Panel b) illustrates grafted dimethyl / diphenyl silicone onto the surface of fumed silica. Panel c) illustrates grafted dimethyl / diphenyl silicone and silanized moieties on fumed silica. Panel d) illustrates grafted dimethyl / diphenyl silicone onto fumed silica, where the silicone is silanized. As discussed further below, grafting silicone resins with, for example, phenyl moieties, as well as silanization using hexamethyldisilazane, can increase the weight % of fumed silica that can be added to silicone resin formulations while maintaining transparency.

[0095] For such studies, fumed silica was added to a representative example of a silicone resin formulation containing 80.4% PDV-1625 and 19.6% thiol-phenyl-functional MDTQ-resin by weight, and 0.6% by weight TPO-L and 0.5% by weight ITX.

[0096] In a number of representative studies, up to 3% by weight of a hydrophilic fumed silica (CAB-O-SIL® EH-5 or EH-5) was incorporated into the formulation while maintaining transparency and without exhibiting the thermochromic effect. Cabot CAB-O-SIL EH-5 is a very high surface area fumed silica available from Cabot of Billerica, MA USA. Further studies demonstrated that the loading of fumed silica can be further increased to 13% by weight using hydrophobic fumed silica (CAB-O-SIL TS-530 or TS-530). CAB-O-SIL TS-530 is a high surface area fumed silica having a surface modified with hexamethyldisilazane, exhibiting a hydrophobic surface, which is available from Cabot. Further representative studies demonstrated that hydrophilic silica can be surface treated to enable higher loading by weight while maintaining transparency and without exhibiting turbidity or the thermochromic effect. Surface treatments may, for example, include the grafting of dimethyl-diphenyl siloxane onto the surface of fumed silica and silanization usingAtty. Docket No.25-024PCT hexamethyldisilazane. In one example of a surface treatment, 25% dimethyl-diphenyl siloxane by weight was grafted onto the surface of EH-5, followed by silanization using 40% hexamethyldisilazane by weight, to enable up to 19% by weight of the treated silica to be added to the silicone resin formulation. Mechanical elongation was increased using surface modified fumed silica by grafting 50% dimethyl / diphenyl siloxane onto the surface of TS- 530. A formulation utilizing 13% by weight of the modified TS-530 silica exhibited a tensile strength of 565kPa and a failure strain of 101%, whereas an identical formulation utilizing unmodified TS-530 exhibited a tensile strength of 596kPa and a failure strain of 68%. FIG.11 illustrates mechanical tensile testing of the photocured, transparent silicone resins for formulations including ungrafted fumed silica and for formulations including fumed silica grafted with dimethyl / diphenyl siloxane, demonstrating that modifying fumed silica by grafting dimethyl / diphenyl silicone onto the silica surface increases the elongation of silicone resins compared to unmodified fumed silica. Without limitation to any mechanism, it is believed that surface modifications of silica hereof improve dispersibility of the silica in the compositions hereof to enable increased loading rates while maintaining transparency. Without limitation to any mechanism, increased dispersibility may, for example, be achieved using surface modifying groups with favorable interactions with components of the composition (for example, via hydrophobic interactions and / or via pi-pi interactions).

[0097] The LCST and UCST of silicone resin formulations were evaluated by depositing 10mL of the resin formulation within 20mL borosilicate vials and monitoring the transparency of the formulation across a range of temperatures. Formulations were first heated to 100°C to evaluate the LCST and then allowed to cool to 20°C to evaluate the UCST. An example transparent silicone resin formulation containing 56.2% DMS-V21, 29.2% SMS-022, and 14.6% SMS-042 by weight and 0.6% by weight TPO-L and 0.5% by weight ITX demonstrated a LCST above 100°C and a UCST above 30°C. An example transparent silicone resin formulation containing 80.4% PDV-1625 and 19.6% thiol-functional MDTQ-resin by weight and 0.6% by weight TPO-L and 0.5% by weight ITX demonstrated a LCST above 100°C and a UCST below 20°C. These examples indicate that the introduction of silicone polymers with aryl groups such as phenyl groups improved the soluble concentration of the photoabsorber system while maintaining transparency at the desired temperature ranges for additive manufacturing.

[0098] Fumed silica used in compositions hereof may be functionalized with alternative or additional moieties such as one or more hydroxyl groups, carboxyl groups, alkane groups, phenyl groups, naphthalene groups, thiophene groups, or sulfone groups without affectingAtty. Docket No.25-024PCT functionality thereof in the formulations hereof. The representative grafted dimethyl- diphenyl siloxane moieties may, for example, include different compositions of alkyl (for example, methyl) groups and aryl (for example, phenyl) groups, such as dimethyl-methylaryl (dimethyl-methylphenyl) or diaryl-methylaryl (diphenyl-methylphenyl) compositions. Phenyl groups may, for example, be replaced with aryl or heteroaryl moieties such as thiophene, naphthalene, anthracene, or benzothiophene.

[0099] Refractive index matching can be accomplished with fumed silicas of different surface energy, different molecular weights, different surface areas, different weight % of grafted surface modifiers, or with different weight % of silica in the silicone resin formulation. Modifying the surface of fumed silica can change the refractive index of the fumed silica to either a higher or lower refractive index than the representative 1.45-1.47 range specified in representative examples hereof. Other components of the transparent silicone resins hereof, such as the thiol-functionalized copolymer, the thiol-phenyl-functional MDTQ resin, or the dimethyl-diphenyl siloxane resin, may also be modified to match such refractive indices when outside of the representative 1.45-1.47 range discussed herein.

[0100] FIG.12 illustrates a representative study demonstrating the transparency of a transparent photocured silicone resin sample including 10% fumed silica by weight (3mm thick). In FIG.12, the sample is overlaid on a 1951 USAF resolution test chart.

[0101] Studies hereof have demonstrated that mechanical properties of three-dimensional, photocured articles hereof can be varied over a wind range using factors such as chain flexibility, chain length, crosslinking density, reinforcing filler content, etc. (as known in the polymer arts) while achieving transparency. Representative examples of photocured articles hereof may, for example, exhibit elastic moduli or Young’s moduli in the range of 0.02 to 3.0 MPa, a tensile strength in the range of 0.02 to 6.0 MPa, and elongations at break in the range of 10 % to 250 %. Such ranges may be readily extended via selection of the components of the compositions hereof as known, for example, in the polymer arts. In a number of embodiments, the three-dimensional, photocured articles hereof are elastomeric (that is, exhibiting reversible elongation, a Young’s modulus below 10 MPa, and an elongation at break of least 100%).

[0102] The photocurable (that is, curable upon application of electromagnetic energy in a determined wavelength typically between 350 to 410 nm) compositions hereof are well suited for use in additive manufacturing procedures such as 3D printing, but may be used in many processes. In additive manufacturing procedures, an object or article is built a layer at a time. In additive manufacturing, a digital design for an article is typically first created using,Atty. Docket No.25-024PCT for example, computer aided design or CAD software or by scanning on object or article to be printed. The design is then translated into a layer-by-layer framework. The layer-by-layer framework is used by an additive manufacturing machine such as a 3D printer to form the article one layer at a time.

[0103] An additive manufacturing process using a photocurable composition hereof may, for example, include exposing a first layer of the photocurable composition to electromagnetic radiation to react at least a portion of the reactive polymer component (via thiol-ene chemistry) to form a first polymerized layer. A second polymerized layer may be formed by disposing a second layer of the photocurable polymer composition on a least a portion of the first polymerized layer and exposing the second layer to electromagnetic radiation to react at least a portion of the reactive polymer component for form the second polymerized layer. Such actions may be repeated a determined number of times to form additional polymerized layers.

[0104] Experimental.

[0105] Materials and Methods.

[0106] Material Preparation. In a number of representative studied embodiments, vinyl- functional (DMS-V21; Gelest) and mercapto-functional (SMS-022, SMS-042; Gelest) siloxane resins were combined in a ratio of 56.2% DMS-V21, 29.2% SMS-022, and 14.6% SMS-042 by weight to reach a stoichiometric ratio between vinyl and mercapto functional groups. In a number of studied embodiments, ethyl phenyl(2,4,6-trimethylbenzoyl) phosphinate (TPO-L; Esstech) was used as a photoinitiator. UV-absorbing additives such as 2- Isopropylthioxanthone (ITX; Sigma-Aldrich) and 2,4-diethylthioxanthone (DETX; Sigma- Aldrich) may be dissolved in the resins using an ultrasonic homogenizer (Sonics VCX-750) for 5 minutes at 20% amplitude with a 1 / 16” microtip, followed by mixing in a centrifugal planetary mixer (Thinky AR100) for 2 minutes.

[0107] Mechanical Testing. The tensile strength and strain of the silicone may, for example, be evaluated with ASTM D412C specimens 3D printed at 50% scale in the XY axes with 3mm thickness in the Z axis (n=2). The tear strength may be evaluated using ASTM D624C specimens 3D printed at 50% XY scale with 3mm Z-thickness (n=2). Specimens may, for example, be tested in a tensile testing machine (MTS Criterion Model 42) with a 50N load cell and displaced at a rate of 500 mm / min.

[0108] 3D Printing. Mechanical testing specimens may be 3D printed on a Phrozen Sonic Mini 8K printer using 405nm light, while resolution test specimens may be 3D printed on an Asiga Pico 2 printer using 385nm light. Mechanical testing specimens and printing resolutionAtty. Docket No.25-024PCT specimens may be printed using a formulation with, for example, 0.6% TPO-L, 0.4% ITX, and 0.2% DETX by weight. The 3D printing exposure times for each printer may be tuned by identifying the gelation time of 10mm discs when exposed to each wavelength at a 1.2mW / cm2intensity in increments of 2 seconds. Suitable light intensity and exposure time for use in photocuring can vary significantly as it depends, for example, on the crosslinking density. Such parameters are readily determined for a particular composition and configuration by those skilled in the art.

[0109] The minimum printable resolution of the formulated resin may be evaluated using a test block containing 4 sets of channels including varying widths and heights as well as overhangs of varying thicknesses. For example, three sets of channels may include widths of either 0.1mm, 0.25mm, or 0.5mm. Within each set, 5 channels may be modeled with heights including 0.05mm, 0.1mm, 0.25mm, 0.5mm, and 1mm. The fourth set of channels may be square with side lengths including 0.05mm, 0.1mm, 0.25mm, 0.5mm, and 1mm. Overhangs forming the roof of each channel may be progressively reduced in thickness from 0.3mm in increments of 0.1mm until becoming open-faced. Images of the test block may be captured using an AmScope SM-1T optical microscope.

[0110] The foregoing description and accompanying drawings set forth a number of representative embodiments at the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope hereof, which is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

Atty. Docket No.25-024PCT Claims 1. A composition, which is photocurable to produce a transparent material, comprising: a reactive polymer portion comprising, a first polymer component comprising one or more siloxane polymers, each of which comprises a plurality of alkenyl functional groups, which are reactive in a thiol-ene reaction, and a second polymer component comprising one or more siloxane polymers, each of which comprises a plurality of thiol functional groups, which are reactive in a thiol-ene reaction, a photoabsorber system comprising one or more photoabsorbers, and a photoinitiator system comprising one or more photoinitiators, wherein each of the photoabsorber system and the photoinitiator system exhibit high absorbance at wavelengths in the range of ± 5nm from a wavelength at which photocuring occurs and low absorbance in a wavelength range of 420-680nm, and wherein a combination of the photoinitiator system and photoabsorber system exhibits a cumulative absorbance at wavelengths in the range of ± 5nm of the wavelength at which photocuring occurs that is at least 1000 times greater than the maximum absorbance at wavelengths in the range of 420-680 nm, wherein the composition comprises no solvent and has an upper critical solution temperature below 20 °C and a lower critical solution temperature above 60 °C, wherein each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of all others of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component, and further wherein each of the one or more photoabsorbers and each of the one or more photoinitiators at least one of (i) has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component and (ii) is present in a weight % less than 5% and is soluble within the composition.Atty. Docket No.25-024PCT 2. The composition of claim 1 wherein at least one of the first polymer component and the second polymer component includes one or more branched siloxane polymers.

3. The composition of claim 1 wherein at least one of the one or more siloxane polymers of the first polymer component is an MDTQ siloxane polymer comprising a plurality of alkenyl functional groups.

4. The composition of claim 1 wherein at least one of the one or more siloxane polymers of the second polymer component is an MDTQ siloxane polymer comprising a plurality of thiol functional groups.

5. The composition of claim 1 wherein each of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component independently has a weight average molecular weight in the range of 100 g / mol to 10,000,000 g / mol, optionally in the range of 100 g / mol to 500,000 g / mol, and further optionally in the range of 100 g / mol to 100,000 g / mol.

6. The composition of claim 1 wherein a ratio of thiol functional groups to alkenyl functional groups in the reactive polymer portion is in the range of 1:1 to 4:1, optionally in the range of 1:1 to 2.5:1, and further optionally in the range of 1:1 to 1.5:

1.

7. The composition of claim 1 wherein at least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes at least one of a plurality of aryl groups and a plurality of heteroaryl groups.

8. The composition of claim 7 wherein at least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes 0.01 to 60 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups.

9. The composition of claim 7 wherein the aryl groups are phenyl groups.

10. The composition of claim 1 wherein each of one of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component comprise at least one of a plurality of aryl groups and a plurality of heteroaryl groups.

11. The composition of claim 10 wherein each of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes 0.01 to 60 weight % of at least one of the plurality of aryl groups andAtty. Docket No.25-024PCT the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups.

12. The composition of claim 10 wherein the aryl groups are phenyl groups.

13. The composition of any one of claims 1 through 12 further comprising a nonreactive reinforcing filler, wherein the nonreactive reinforcing filler has a refractive index within 0.050, optionally within 0.020, optionally within 0.010, and further optionally within 0.002, of each of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component.

14. The composition of claim 13 wherein the nonreactive reinforcing filler comprises an MDTQ siloxane polymer or a silica.

15. The composition of claim 14 wherein the nonreactive reinforcing filler comprises fumed silica.

16. The composition of claim 15 wherein a surface of the fumed silica is modified to improve dispersibility.

17. The composition of claim 16 wherein the fumed silica is present in a weight % in the range of 2 to 20 weight% of the composition.

18. The composition of claim 14 wherein the nonreactive reinforcing filler comprises an MDTQ siloxane polymer.

19. The composition of claim 18 wherein the MDTQ siloxane polymer is present in a weight % in the range of 0 to 20 weight % of the composition.

20. The composition of claim 13 wherein at least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component comprise at least one of a plurality of aryl groups and a plurality of heteroaryl groups and the nonreactive reinforcing filler includes at least one of a plurality of aryl groups and a plurality of heteroaryl groups.

21. The composition of claim 20 wherein the at least one of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes 0.01 to 60 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups.

22. The composition of claim 20 wherein the aryl groups are phenyl groups.Atty. Docket No.25-024PCT 23. The composition of claim 13 wherein each of the one of the one or more siloxane polymers of the first polymer component and each of the one or more siloxane polymers of the second polymer component comprise at least one of a plurality of aryl groups and a plurality of heteroaryl groups.

24. The composition of claim 23 wherein each of the one or more siloxane polymers of the first polymer component and the one or more siloxane polymers of the second polymer component includes 0.01 to 60 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, optionally 0.01 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups, and further optionally 10 to 50 weight % of at least one of the plurality of aryl groups and the plurality of heteroaryl groups.

25. The composition of claim 23 wherein the aryl groups are phenyl groups.

26. The composition of claim 1 wherein the photoinitiator system includes at least one of ethyl phenyl(2,4,6-trimethylbenzoyl) phosphinate, lithium phenyl-2,4,6- trimethylbenzoylphosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, lithium phenyl-2,4,6- trimethylbenzoylphosphinate (LAP), 2-Hydroxy- -(2-hydroxyethoxy)-2-methylpropiophenone, 2-Benzyl-2-(dimethylamino)-1-[4-(morpholinyl) phenyl]-1-butanone, 1-Hydroxycyclohexyl phenyl ketone), 2,2-dimethoxy-2-phenylacetophenone, 1-[4- (Phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime), 2,3-bornanedione (Camphorquinone), Bis(4-methoxybenzoyl)diethylgermanium, and derivatives thereof.

27. The composition of claim 1 wherein the photoinitiator system includes at least one of ethyl phenyl(2,4,6-trimethylbenzoyl) phosphinate and lithium phenyl-2,4,6- trimethylbenzoylphosphinate.

28. The composition of claim 1 wherein the photoabsorber system includes at least one of 2- isopropylthioxanthone, 2,4-diethylthioxanthone, avobenzone, octocrylene, bisoctrizole, drometrizole, bumetrizole, octavenzone, bemotrizinol, titanium dioxide nanoparticles, zinc oxide nanoparticles, and derivatives thereof.

29. The composition of claim 1 wherein the photoabsorber system includes at least one of 2- isopropylthioxanthone, and 2,4-diethylthioxanthone, and optionally wherein the photoabsorber system includes 2-isopropylthioxanthone and 2,4-diethylthioxanthone.

30. The composition of any one of claims 1 through 12 wherein the composition is transparent before photocuring.

31. The composition of claim 30 wherein the composition has a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99% in the range of 420 to 680 nmAtty. Docket No.25-024PCT and has less than 5 NTU turbidity, optionally less than 1NTU, and further optionally less than 0.3 NTU.

32. The composition of claim 13 wherein the composition has a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99%, in the range of 420 to 680 nm and has less than 5 NTU turbidity, optionally less than 1NTU, and further optionally less than 0.3 NTU.

33. The composition of claim 1 wherein the transparent material has a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99%, in the range of 420 to 680 nm and has less than 5% haze, optionally less than 2% haze, and further optionally less than 1% haze.

34. The composition of any one of claims 1 through 12 wherein a combination of the photoinitiator system and the photoabsorber system exhibits a cumulative absorbance greater than 3 OD, optionally greater than 4 OD, and further optionally greater than 5 OD in a range of wavelengths within ± 5nm of the particular wavelength at which photocuring occurs.

35. A method of forming a three-dimensional article, which is transparent, comprising: a) exposing a first layer of the composition of claim 1 to electromagnetic radiation to react at least a portion of the reactive polymer component to form a first polymerized layer, b) optionally forming a second polymerized layer by disposing a second layer of the composition of claim 1 on at least a portion of the first polymerized layer and exposing the second layer to electromagnetic radiation to react at least a portion of the reactive polymer component thereof to form the second polymerized layer, and c) optionally repeating the actions of b) a determined number of times.

36. A three-dimensional article, which is transparent, formed by the method of claim 35.

37. The three-dimensional article of claim 36 wherein the three-dimensional article has a Young’s modulus below 10 MPa and an elongation at break of least 50%.

38. The three-dimensional article of claim 37 wherein the three-dimensional article has an elongation at break of least 100%.

39. The three dimensional article of claim 36 which has a transmittance of at least 90 %, optionally at least 95%, and further optionally at least 99%, in the range of 420 to 680 nm and has less than 5% haze, optionally less than 2% haze, and further optionally less than 1% haze.

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