ACRYLATED PVAc-g-PLLA POLYMER, A PROCESS FOR THE PREPARATION AND COMPOSITON FOR 3D PRINTING THEREOF

Abstract

The present disclosure generally relates to polymer or crosslinkers useful in effective 3D printing. The invention relates to an acrylated polyvinyl-grafted-poly(l-lactide) (acr. PVAc-g- PLLA) polymer of formula I to act as a crosslinker in a composition for printing 3D products and process for the preparation and application in 3D printing composition thereof.

Description

[0001] ACRYLATED PVAc-g-PLLA CROSSLINKER POLYMER, A PROCESS FOR THE PREPARATION AND COMPOSITON FOR 3D PRINTING THEREOF

[0002] FIELD OF THE INVENTION

[0003] Present invention relates to an acrylated polyvinyl acetate-grafted-poly (1-lactide) (PVAc-g- PLLA) polymer of formula I to act as a crosslinker in a composition for printing 3D products. Particularly, present invention also relates to a process for the preparation of PVAc-g-PLLA polymer of formula I. More particularly, present invention relates to a composition for 3D printing comprising said acrylated polyvinyl acetate-grafted-poly (1-lactide) (acr. PVAc-g- PLLA) based polymer of formula I as a crosslinker and a process of preparation thereof.

[0004] BACKGROUND OF THE INVENTION

[0005] In recent years 3-D printing technology also known as additive manufacturing, which has become powerful and emerging technique for on-demand production of complex 3-D structures in fields as diverse as tissue engineering, drug delivery, medical device fabrication, optical engineering, soft robotics, dentistry, and many others. American Society for Testing and Materials (ASTM) categorizes 3D printers into seven major categories based on their materials processing, among them fused deposition modelling (FDM), direct metal sintering (DMS), light-based stereo lithography (SLA), and digital light processing (DLP) are mostly used techniques worldwide. Among these 3D printing methods, photo curable 3D printing is highly attractive in terms of creating well-defined structure by photo crosslinking of liquid photo- curable resin formulations in presence of photo initiator which has benefits of better resolution, low waste generation, large production and economical. Although advancements in AM technology machines have been done very fast, research into developing acceptable materials is still needed to increase availability of materials for liquid-based 3D printing.

[0006] The vast majority of photo curable resins that are readily available on the market are either traditional epoxy- or small-molecule acrylate-based resins. Their usage in creating biological implants is constrained since they are often neither biocompatible nor biodegradable. In order to create biodegradable and biocompatible materials, AM technology makes considerable use of bio based polymers such as polylactic acid (PLA), polycaprolactone (PCL), polyglycolide (PGL), and Polypropylene fumarate) (PPF). Adding a photo curable group to these polymers makes them suitable for use in liquid 3D printing. The viscosity of the liquid resin compositions used in 3D printing is an important aspect that impacts the final product's quality. A viscosity level of less than 10 Pa.s is required for smooth and adhesive-free printing. The way to achieve this is by adding organic solvents or reactive diluents, to the modified the viscosity of polymeric resin. Synthesized photo curable polymers or macromers used for liquid 3D printing, such as acrylate or methacrylate of PLA, PCL, and PPF, have a higher viscosity, so ethyl lactide, DMSO, water, and dioxane are used to reduce the viscosity. The use of non-reactive solvents may result in a reduction in the size of the printed item after printing as a result of the evaporation of the solvent, which can change the mechanical characteristics of the materials. The resin's viscosity may also be reduced using heat-assisted liquid 3D printing, which involves heating the polymers to temperature above its melting point. This method can achieve higher printing speeds and better surface quality, but it requires specialized equipment and careful temperature control to prevent damage to the final product.

[0007] Another method is the use of reactive diluents that can polymerize and become part of the final polymer network. Reactive diluents are an essential component of room temperature DLP 3D printing, providing greater process control, faster printing times, and improved mechanical properties of the produced materials. In order to synthesize bio based and degradable resin formulation, PLA is the first choice due to its excellent mechanical properties and suitable degradability. Additionally, by introducing grafting PLA to others polymer backbone its mechanical properties enhanced which can be used wide range of applications.

[0008] Several reports are available on the grafting of PLA polymer i.e., i) Nan D. et al. Ind. Eng. Chem. Res. Vol. 52, pages 12897-12905, 2013 reports graft copolymers of poly(vinyl acetate)- graft-poly(l-lactide) (PVAc-g-PLLA) using partially hydrolyzed PVAcs, that is, poly(vinyl acetate-co-alcohol) [P(VAc-co-VA)], having degrees of hydrolysis of 5.2 and 9.6% were used as the macromolecular multifunctional initiator; and ii) Jing Ding et al., Ind. Eng. Chem. Res. 2009, 48, 2, 788-793, reports poly(vinyl alcohol)-graft-lactic acid (PVA-g-LA) was synthesized by melt polycondensation of PVA and lactic acid using stannous chloride as a catalyst. However, modification of poly (vinyl alcohol) -graft-poly (1-lactide) further has not been explored. By introducing a photo curable group in the terminal position of grafted poly (1-lactide) the whole polymer could be used as a crosslinker which will be further used for DLP 3D printing. Another article Pal, Shibam et al., Macromolecular Chemistry and Physics, 223.22 (2022), reports an acrylate end-functionalized linear and star poly 1-lactide (PLLA) based aliphatic, photo curable oligomeric crosslinkers, which are formulated with HEM A as a biodegradable diluent to demonstrate successful application for solvent-less 3D printing using digital light processing (DLP) technique. In contrast, the inventors of present case prepared an acrylated polyvinyl-grafted-poly (1-lactide) (acr. PVAc-g-PLLA) based crosslinker to obtain 3D printed product with more effective mechanical properties, biodegradability and resolution. Therefore, there is an unmet need to provide an effective polymer or crosslinker based on PLLA having better resolution, higher biodegradability and biocompatibility, no brittleness in printed product, thermally stable, no cytotoxicity and an enhanced stress / strain properties without breaking the 3D printed product. Addressing all these, inventors of present application provides low molecular weight photo-cross linkable graft polymer of partially hydrolyzed polyvinyl acetate and poly (lactide).

[0009] OBJECTIVES OF THE INVENTION

[0010] Main object of the present invention is to provide an acrylated polyvinyl acetate-grafted-poly (1-lactide) (PVAc-g-PLLA) polymer of formula I.

[0011] Another objective of the present invention is to provide a process for preparation of said acrylated polyvinyl acetate-grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I. Yet another objective of the present invention is to provide acrylated polyvinyl acetate-grafted- poly (1-lactide) (PVAc-g-PLLA) polymer of formula I to act as a crosslinker in a composition for printing 3D products.

[0012] Yet another object of the present invention is to provide a composition for 3D printing comprising said acrylated polyvinyl acetate-grafted-poly (1-lactide) (PVAc-g-PLLA) polymer of formula I as a crosslinker.

[0013] Yet another objective of the present invention is to provide a process of preparation of composition for 3D printing comprising said acrylated polyvinyl acetate-grafted-poly (1- lactide) (acr. PVAc-g-PLLA) polymer of formula I as a crosslinker.

[0014] Still another objective of the present invention is to provide a 3D printed product(s) with better resolution, higher mechanical properties, higher biodegradability and biocompatibility, lesser or complete absence of brittleness, and thermally stable using said acrylated polyvinyl acetate- grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I as a crosslinker.

[0015] SUMMARY OF THE INVENTION

[0016] Accordingly, present invention provides an acrylated polyvinyl acetate-grafted-poly (1-lactide) polymer (PVAc-g-PLLA) of formula I

[0017] Formula I wherein z is 40-50; x is 5-10; and y is 3-5.

[0018] In an embodiment of the present invention, molecular weight of the compound is in the range of 3500-6000 g / mol.

[0019] In another embodiment, present invention provides a process for the preparation of the polymer comprising the steps of: a) mixing vinyl acetate, an initiator, and chain transfer agent in a container to obtain a 1streaction mixture; b) reacting and deoxygenating the 1streaction mixture as obtained in step a) by one or more consecutive freeze-pump-thaw cycle(s) followed by heating at a temperature in the range of 50 to 90 °C for a time period in the range of 4 to 6 hrs to obtain polyvinyl acetate compound of Formula A;

[0020] Formula A wherein z is same as defined in claim 1; wherein the freeze-pump-thaw cycle(s) is done using a liquid nitrogen at temperature in the range of -80 to -100 °C with a high vacuum of pressure in the range of 0.001 to 0.0001 mbar and for the time period in the range of 15- 20 min for each said cycle; c) partially hydrolyzing the compound of Formula A as obtained in step b) by dissolving the compound of formula A in a 1stbase and a 1stsolvent or 1stmixture of solvents at temperature in the range of 55-65 °C for time period in the range of 5 to 8 hrs to form a 1stcrude solution; d) precipitating 1stcrude solution as obtained in step c) with water followed by drying at temperature in the range of 70 to 100 °C for time period in the range of 12-15 hrs to obtain partially hydrolyzed compound of formula B;

[0021] Formula B wherein z and x are same as defined in claim 1 ; e) mixing partially hydrolyzed compound of formula B as obtained in step d), L- lactide and a catalyst in a container to obtain 2ndreaction mixture; wherein a ratio of L-lactide and catalyst is in range of 0.15: 10 to 0.2:10; f) optionally removing moisture from the 2ndreaction mixture of step e) by applying high vacuum to the 2ndreaction mixture for time period in the range of 0.5 to 1.5 hrs; g) reacting the 2ndreaction mixture as obtained in step e) or f) by mixing in a 2ndsolvent followed by heating at a temperature in the range of 90 to 130 C for a time period in the range of 10 to 14 hrs to obtain a 2ndcrude solution; h) precipitating the 2ndcrude solution as obtained in step g) with petroleum ether followed by drying at temperature in the range of 50 to 90 C for time period of 12-15 hrs to obtain graft PVA-poly-l-lactide compound of formula C;

[0022] Formula C wherein z, x and y are same as defined in claim 1 ; i) acrylating terminal hydroxyl group of grafted PVAc-g-PLLA compound of formula C by reacting it with acryloyl halide and a 3rdsolvent in presence of 2ndbase at a temperature of 0 °C to obtain 3rdreaction mixture; j) reacting the 3rdreaction mixture as obtained in step i) at temperature in the range of 25 to 30 °C for time period in the range of 22 to 26 hrs to obtain the polymer of formula I; and k) optionally purifying the polymer of formula I as obtained in step j) to obtain pure polymer of formula I.

[0023] In yet another embodiment of the present invention, said initiator is selected from the group consisting of 2,2'-azobisisobutyronitrile (AIBN), 4,4'-azobis(4-cyanovaleric acid) (ACVA) and said chain transfer agent is selected from the group consisting of methyl(ethoxy carbonothioyl) sulfanyl acetate (MESA), ethyl 2-((ethoxycarbonothioyl)thio)acetate or S- benzyl O-ethyl carbonodithioate. In yet another embodiment of the present invention, the 1stbase is selected from the group consisting of potassium hydroxide, sodium hydroxide and potassium carbonate or mixture thereof and said 2ndbase is selected from the group consisting of triethyl amine (TEA), diethyl amine or diisopropyl amine.

[0024] In yet another embodiment of the present invention, 1stsolvent is selected from the group consisting of alcohol, water, ethanol / water mixture; wherein the 1stmixture of solvents are selected from water and alcohol; wherein 2ndsolvent is selected from the group consisting of toluene, xylene or dimethylacetamide (DMA); wherein the 3rdsolvent is selected from the group consisting of tetrahydrofuran (THF), DCM or CHCh; and wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, butanol or pentanol.

[0025] In yet another embodiment of the present invention, the catalyst used in step e) is selected from the group consisting of stannous octoate [Sn(Oct)2], diazabicyclo[5.4.0]undec-7-ene (DBU), 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), and l,5,7-triazabicyclo[4.4.0]dec-5- ene (TBD); wherein the ratio of L-lactide and catalyst used in step e) is in range of 0.15: 10 to 0.2: 10; and wherein the acryloyl halide used in step i) is selected from the group consisting of acryloyl chloride, acryloyl bromide, acryloyl fluoride or acryloyl iodide.

[0026] In yet another embodiment, present invention provides a composition for 3D printing comprising the polymer, one or more of additive(s) and a photo initiator, wherein the composition exhibits a thermal stability with 10 % weight loss in the range of 260 to 300°C.

[0027] In yet another embodiment, present invention provides a process for the preparation of a composition for 3D printing, wherein said process comprising the steps of: a) mixing the polymer of Formula I with one or more of additive(s) and photo initiator in a vial or container followed by sonicating for time period in the range of 0.5 to 1.5 hrs at temperature in the range of 25 to 30 °C to obtain a sonicated mixture; and b) covering the sonicated mixture as obtained in step a) with an aluminum foil followed by storing in a fridge for cooling at temperature in the range of -10 to 0 °C to obtain the fridge stored material; and c) keeping the fridge stored material as obtained in step b) at temperature in the range of 25-35 °C followed by shaking in a vortex for time period in the range of 3 to 8 minutes to obtain the composition.

[0028] In yet another embodiment of the present invention, the additive(s) is selected from the group consisting of hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), 1,6-hexane dioldiacrylate (HDDA), polyethylene gycol diacrylate (PEGDA), and trimethylolpropane trimethacrylate (TMPTA), or two or more mixture thereof; and the photoinitiator is selected from the group consisting of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO), 2- hydroxy 2-methylpropiophenone, bisacylphosphine oxide (BAPO).

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 shows ’ H NMR spectras of PVAc, PVAc after partially hydrolyzed PVAc, graft PVAc-g-PLLA, and acrylate PVAc-g-PLLA

[0031] Figure 2 shows specific heat flow comparison of HEMA, HEA, and acr. PVAc-g-PLLA measured from photo-DSC at 30 °C with 1 wt. % of PI.

[0032] Figure 3 shows viscosity of resins formulated with a) HEMA b) HEA.

[0033] Figure 4 shows a) 3D printed objects made using resin 6; c) merk rook using resin 2; and d) printing without and with dye under visible light and UV-light.

[0034] Figure 5 shows soft nature image of resin 6 3D printed part.

[0035] Figure 6 shows thermo gravimetric analysis of a) (R1-R3) & b) (R4-R6) 3D printed parts of resin formulations.

[0036] Figure 7 shows DSC heating curves of a) (R1-R3) & b) (R4-R6) of 3D printed parts of resin formulations.

[0037] Figure 8 shows representative stress-strain curves of the 3D printed resins, a) prepared with HEMA (R1-R3), and b) prepared with HEA (R4 to R6).

[0038] Figure 9 illustrates a) degradation study of 6 different 3D printed resins (R1-R6) in PBS solution at pH 7.4 at 40°C, and b) water uptake study of 3D printed resins (R1-R6) over two months’ time period.

[0039] Figure 10 shows WT-MEF cell viability test at 3 different times i.e., 24h, 48h, and 72h incubation (at 37 °C) with all 3D printed film determined by MTT assay relative to the positive control (cell culture medium).

[0040] Figure 11 represents a synthetic scheme for preparation of formula I, wherein x, y and z are same as defined above.

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] The terms “composition” or “photo curable resin formulations” are used herein with the same meaning which essentially comprises of said acrylate polyvinyl acetate -grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I as a crosslinker / polymer. The terms “crosslinker” or “polymer” are used herein with the same meaning which essentially comprises of said acrylated polyvinyl acetate-grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I.

[0043] The compounds described herein can be asymmetric (e.g., having one or more stereo centers). All stereoisomers, such as enantiomers and diastereomers, are intended unless otherwise indicated. Compounds of the present invention that contain asymmetrically substituted carbon atoms can be isolated in optically active or racemic forms. Methods on how to prepare optically active forms from optically inactive starting materials are known in the art, such as by resolution of racemic mixtures or by stereoselective synthesis. Many geometric isomers of olefins, C=N double bonds, and the like can also be present in the compounds described herein, and all such stable isomers are contemplated in the present invention. Cis and trans geometric isomers of the compounds of the present invention are described and may be isolated as a mixture of isomers or as separated isomeric forms. In some embodiments, the compound has the (R)-configuration. In some embodiment, compound has (S)-configuration. Resolution of racemic mixtures of compounds can be carried out by any of numerous methods known in art. Example method includes fractional recrystallization using chiral resolving acid which is optically active, salt-forming organic acid. Suitable resolving agents for fractional recrystallization methods are, for example, optically active acids, such as D and L forms of tartaric acid, diacetyltartaric acid, dibenzoyltartaric acid, mandelic acid, malic acid, lactic acid or various optically active camphorsulfonic acids like P-camphorsulfonic acid. Other resolving agents for fractional crystallization methods include stereoisomerically pure forms of a- methylbenzylamine (e.g. S & R forms or diastereomerically pure forms), 2-phenylglycinol, norephedrine, ephedrine, N-methylephedrine, cyclohexylethylamine, 1,2-diaminocyclohexane and so on.

[0044] Compounds of the invention also include tautomeric forms. Tautomeric forms result from the swapping of a single bond with an adjacent double bond together with the concomitant migration of a proton. Tautomeric forms include prototropic tautomers which are isomeric protonation states having the same empirical formula and total charge. Tautomeric forms can be in equilibrium or sterically locked into one form by appropriate substitution.

[0045] Compounds of invention can also include all isotopes of atoms occurring in intermediates or final compounds. Isotopes include those atoms having the same atomic number but different mass numbers. For example, isotopes of hydrogen include tritium and deuterium. The term, “compound,” used herein is meant to include all stereoisomers, geometric iosomers, tautomers, and isotopes of structures depicted. Compounds herein identified by name or structure as one particular tautomeric form are intended to include other tautomeric forms unless otherwise specified.

[0046] All compounds, and pharmaceutically acceptable salts thereof, can be found together with other substances such as water and solvents (e.g. hydrates and solvates) or can be isolated.

[0047] In some embodiments, the compounds of the invention, or salts thereof, are substantially isolated. By “substantially isolated” is meant that the compound is at least partially or substantially separated from the environment in which it was formed or detected. Partial separation can include, for example, a composition enriched in the compounds of the invention. Substantial separation can include compositions containing at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 97%, or at least about 99% by weight of the compounds of the invention, or salt thereof. Methods for isolating compounds and their salts are routine in the art.

[0048] The phrase “pharmaceutically acceptable” is employed herein refers to those compounds, materials, compositions, and / or dosage forms which are, within scope of sound medical judgment, suitable for use in contact with tissues of human beings and animals without excessive toxicity, irritation, allergic response, / other problem or complication, commensurate with a reasonable benefit / risk ratio.

[0049] Expressions, “ambient temperature” and “room temperature” or “rt” as used herein, are understood in art, and refer generally to temperature, e.g. reaction temperature, that is about temperature of room in which reaction is carried out, e.g. temperature from 20 to 30°C or 25- 35°C.

[0050] The present invention provides acrylated polyvinyl acetate-grafted-poly (1-lactide) (acr. PVAc- g-PLLA) polymer of formula I to act as a crosslinker / polymer in a composition for printing 3D products. The polymer of formula I is represented as:

[0051] Wherein z is 40-50; x is 5- The present invention relates to a process of preparation of an acrylated polyvinyl acetate - grafted-poly (1-lactide) (PVAc-g-PLLA) polymer of formula I to act as a crosslinker / polymer in a composition for printing 3D products, the process comprising steps of: a) preparing a 1streaction mixture comprising of vinyl acetate, an initiator, and chain transfer agent in a container; b) reacting and deoxygenating the 1streaction mixture of step a) by one or more consecutive freeze-pump-thaw cycle(s) followed by heating at a temperature in the range of 50 to 90 °C for a time period in the range of 4 to 6 hrs to obtain polyvinyl acetate compound of formula A;

[0052] Formula A, wherein z is same as defined above; wherein the freeze-pump-thaw cycle(s) is done using a liquid nitrogen at -80 to -100 °C with a high vacuum of pressure in the range of 0.001 to 0.0001 mbar and for the time period in the range of 15- 20 min for each said cycle; c) partially hydrolyzing the compound of formula, A of step b) by dissolving the compound of formula A in a 1stbase and a 1stsolvent or 1stmixture of solvents at temperature in the range of 55-65 °C for time period of 5 to 8 hrs to form a 1stcrude solution; d) precipitating 1stcrude solution of step c) with water followed by drying at temperature in the range of 70 to 100 °C for time period in the range of 12-15 hrs to obtain partially hydrolyzed compound of formula B;

[0053] Formula B, wherein z and x are same as defined above; e) preparing a 2ndreaction mixture comprises of partially hydrolyzed compound of formula B of step d), L-lactide and a catalyst in a container; wherein a ratio of L-lactide and catalyst is in range of 0.15: 10 to 0.2: 10; f) optionally removing moisture from the 2ndreaction mixture of step e); wherein the removal of moisture is done by applying high vacuum to the 2ndreaction mixture for time period in the range of 0.5 to 1.5 hrs; g) reacting the 2ndreaction mixture of step e) or f) by mixing in a 2ndsolvent followed by heating at a temperature in the range of 90 to 130 C for a time period in the range of 10 to 14 hrs to obtain a 2ndcrude solution; precipitating the 2ndcrude solution of step g) with petroleum ether followed by drying at temperature in the range of 50 to 90 C for time period of 12-15 hrs to obtain graft PVA-poly-l-lactide compound of formula C;

[0054] Formula C, wherein z, x and y are same as defined above; i) acrylate terminal hydroxyl group of grafted PVAc-g-PLLA compound of formula C by reacting it with acryloyl halide and a 3rdsolvent in presence of 2ndbase at a temperature of 0 °C to obtain 3rdreaction mixture; wherein said acryloyl halide is added over the time period of 10 to 20 minutes at 0 C; j) reacting the 3rdreaction mixture at temperature in the range of 25 to 30 °C for time period of 22 to 26 hrs to obtain the polymer / crosslinker of formula I; and k) optionally purifying the polymer / crosslinker of formula I as obtained in step j) to obtain pure polymer / crosslinker of formula I.

[0055] The initiator is selected from 2, 2'-azobisisobutyronitrile (AIBN), 4, 4’-azobis (4-cyanovaleric acid) (ACVA) and so on.

[0056] The chain transfer agent is selected from methyl (ethoxy carbonothioyl) sulfanyl acetate (MESA), ethyl 2-((ethoxycarbonothioyl) thio) acetate, S-benzyl O-ethyl carbonodithioate, and so on.

[0057] The 1stbase is selected from potassium hydroxide, sodium hydroxide and potassium carbonate, or mixture thereof.

[0058] The freeze-pump-thaw cycle(s) is done using a liquid nitrogen at -80 to -100 °C with a high vacuum of pressure in the range of 0.001 to 0.0001 mbar and for the time period in the range of 15- 20 min for each said cycle.

[0059] In order to prepare low molecular weight PVAc-g-PLLA of formula I to effectively further use in DLP 3D printing, and this can be effectively done by presence of step i) because of which a high yield of 90-95 % with highly pure polymer of formula I is obtained.

[0060] The 1stsolvent is selected from alcohol, water, ethanol / water mixture.

[0061] The alcohol is selected from methanol, ethanol, propanol, butanol, pentanol and so on.

[0062] The 1stmixture of solvents are selected from water and alcohol. The 1stmixture of solvents are selected from water and ethanol, water and methanol, water and propanol, water and butanol, water and pentanol, and so on.

[0063] The ratio of said 1stmixture of solvents is in range of 0.5:9.5 to 1.5:8.5.

[0064] Precipitation of step d) is done by treating the 1stcrude solution with water or deionized water for at least two times at temperature of 25-30°C to remove unreacted monomers.

[0065] The catalyst used in step e) is selected from stannous octoate [Sn(Oct)2], diazabicyclo[5.4.0]undec-7-ene (DBU), 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), l,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and so on.

[0066] The ratio of L-lactide and catalyst used in step e) is in range of 0.15: 10 to 0.2: 10.

[0067] The removal of moisture of step f) is done by applying high vacuum to the 2ndreaction mixture for time period in the range of 0.5 to 1.5 hrs.

[0068] The 2ndsolvent is selected from toluene, xylene, Dimethylacetamide (DMA) and so on.

[0069] The precipitation of step h) is done by treating the 2ndcrude solution with petroleum ether as solvent for at least 2 time at temperature of 25-30 °C to remove unreacted monomers.

[0070] The acryloyl halide is selected from acryloyl chloride, acryloyl bromide, acryloyl fluoride or acryloyl iodide.

[0071] 3rdsolvent is selected from tetrahydrofuran (THF), DCM, CHCI3, and so on.

[0072] The 2ndbase is selected from triethyl amine (TEA), diethyl amine, diisopropyl amine and so on.

[0073] Acryloyl halide used in step i) is added over the time period of 10 to 20 minutes at temperature of O °C.

[0074] The compound of formula A, B, C or I as synthesized herein is optionally purified by literature methods known to a person skilled in the art e.g. drying, evaporation, concentration methods, chromatographic techniques (conventional or advanced) and so on.

[0075] Specifically, the compound of formula I of step k is purified by first evaporating the solvent followed by addition of chloroform to dissolve the polymer. Then, the dissolved polymer is washed with brine water three times and dried over sodium sulfate, and finally, chloroform was evaporated and acrylate polymer was dried in a vacuum oven overnight (8 to 12 hrs) at temperature of 40 °C.

[0076] The compounds / polymers / intermediates obtained by the process provides single isomeric compound (ee) or mixture of isomeric forms / compounds from single reaction.

[0077] The process for synthesis of compound of formula I may be done in batch mode.

[0078] The yield of compound of formula I is in range of 83 to 95%; and the conversion rate is of about 95%. A synthetic scheme for preparation of formula I is provided in Fig. 11 where Poly (vinyl acetate) (PVAc) of pre-defined molecular weight was synthesized starting from vinyl acetate using Reversible Addition Fragmentation chain Transfer (RAFT) polymerization in the bulk where 2, 2'-azobisisobutyronitrile (AIBN) was used as the initiator and Methyl (ethoxy carbonothioyl) sulfanyl acetate (MESA) was used as the chain transfer agent.

[0079] The present invention relates to a composition for 3D printing comprising said acrylate polyvinyl acetate-grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I as a cros slinker / polymer.

[0080] The present invention is to provide a process of preparation of composition for 3D printing comprising said acrylated polyvinyl acetate -grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I as a crosslinker / polymer.

[0081] The present invention relates to a composition for 3D printing comprising:

[0082] 1. said acrylated polyvinyl acetate -grafted-poly (1-lactide) (acr. PVAc-g-PLLA) polymer of formula I as a crosslinker / polymer,

[0083] 2. one or more of additive(s), and

[0084] 3. photoinitiator.

[0085] The amount of said acrylated polyvinyl-grafted-poly (1-lactide) (PVAc-g-PLLA) polymer of formula I as a crosslinker / polymer is in range of 30 to 50 wt% of total weight of the composition.

[0086] The amount of said one or more of additive(s) is in range of 49.5 to 69.5 wt. % or 48.5 to 68.5 wt. % of total weight of the composition.

[0087] The amount of said photoinitiator is in range of 0.5 to 1.5 wt. % of total weight of the composition.

[0088] The additive is selected from hydroxyethyl acrylate (HEA) and hydroxyethyl methacrylate (HEMA), 1,6-hexane dioldiacrylate (HDDA), polyethylene glycol diacrylate (PEGDA), and trimethylolpropane trimethacrylate (TMPTA), or two or more mixture thereof.

[0089] Photoinitiator is selected from diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO), 2- hydroxy 2-methylpropiophenone, bisacylphosphine oxide (BAPO) and so on.

[0090] The present invention relates to a process of preparation of said composition for 3D printing, the process comprising steps of: a) mixing the acrylate PVAc-g-PLLA crosslinker with one or more of additive(s) and photoinitiator in a vial or container followed by sonication of the mixture for 0.5 to 1.5 hrs at temperature of 25 to 30 °C; and b) covering said sonicated mixture of step a) with an aluminium foil followed by storing in a fridge for cooling at temperature of -10 to 0 °C to protect it from undergoing premature curing; and c) before using for printing, the fridge stored material of step b) is kept at 25-35 °C followed by shaking in a vortex for time period of 3 to 8 minutes.

[0091] The sonication in step a) is done by using a commercial sonicator with 42 kHz sonication frequency, wherein the sample vial was dipped into sonicator water bath and sonicated for 10 to 20 min. at sonicator frequency of around 15 to 25 kHz and temperature in range of 25 to 35°C.

[0092] In a nutshell, 3D printing provides immense amenities to fabricate customized scaffold designs using solid or liquid-based biomaterials for tissue engineering and medical device applications. Though for the fabrication of scaffold from liquid-based resin 3D printing, different types of organic solvents are used to compromise the viscosity in case of polymerization. Here, inventors have developed a new resin formulation mixing with synthesized post-modified graft polymer of acrylate poly(vinyl alcohol)-g-poly(lactic acid) (acr. PVAc-g-PLLA). 2- hydroxyethyl acrylate (HEA), and 2-hydroxyethyl methacrylate (HEMA) were used as reactive diluents for different resin formulations. Poly(vinyl alcohol) (PVA) was hydrolyzed from poly(vinyl acetate) (PVAc) which is synthesized by the Reversible addition-fragmentation chain-transfer (RAFT) polymerization process of vinyl acetate. Partially hydrolyzed PVAc was used as a macroinitiator of Ring-Opening Polymerization (ROP) of L-lactide. Inventors observed depending on reactive diluent and mixing of their weight percentage the mechanical properties of the 3D printed part can be tuned from hard to soft materials. This resin formulation can be employed for the preparation of a bio-cellular matrix, tissue engineering, soft robotics, elastomeric actuators, etc. applications.

[0093] In general, the synthesis of polymer / crosslinker is started from PVAc (polyvinyl acetate) polymer targeting 50 repeat units which is further partially hydrolyzed to polyvinyl alcohol and then grafted with l-lactide by the ring-opening polymerization process. Further, the crosslinker polymer is used to formulate resins with different weight ratios with HEMA and HEA avoiding the use of non-reactive organic solvent. The resins show optimum viscosity and printability in room-temperature DLP 3D printer with very high resolution. The printed structure shows a variation in mechanical properties depending on the use of reactive diluent. The new PVAc-g- PLLA composition will probably expand the selection of photocurable DLP printing materials which showed better-printed parts with degradable.

[0094] EXAMPLES Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0095] Materials

[0096] Vinyl acetate, (3S, 6S)-3, 6-dimethyl-l, 4-dioxane-2, 5-dione, 2-hydroxy ethyl acrylate (HEA), stannous 2-ethyl hexanoate (Sn(Oct)2), 2-Hydroxy ethyl methacrylate(HEMA), were purchased from Sigma Aldrich (India) and used as such without further purification. Acrylic acid and triethyl amine were purchased from Sigma Aldrich (India) and purified by distillation. Phenylbis(2,4,6-trimethyl benzoyl) phosphine oxide (TPO) was purchased from TCI chemical (India) Pvt. Ltd and used as such. Carbon disulfide (CS2), Ethanol, Potassium hydroxide (KOH), Methyl bromoacetate, Azobisisobutyronitrile (AIBN), Toluene, Thionyl chloride (SOCI2), Tetrahydrofuran (THF), Chloroform (CHCI3), Methanol (MeOH), isopropyl alcohol (IPA), Dichloromethane (DCM), Hexane and Sodium sulfate (Na2SO4) were purchased locally. For gel permeation chromatography HPLC grade chloroform was purchased from Merck Chemicals (India).

[0097] Example 1: General synthesis of polymer / crosslinker of formula I (acrylate of graft copolymer PVAc-g-PLLA)

[0098] A. Synthesis of acryloyl chloride

[0099] Acrylic acid (20 g, 278 mmol) was taken in a two-neck round-bottomed (RB) flask, and 40 ml of dry DCM was added to it under a nitrogen atmosphere. Then 20.2 ml of SOCI2 (33.07 g, 278 mmol) was added drop-wise at cold conditions. The reaction was run for refluxed for 4 hrs at 50 °C. DCM was removed by distillation at 50 °C then the temperature was increased to 75°C to get the pure acryloyl chloride. Yield: 88 %.1H NMR spectrum (400 MHz, CDCI3) 8 in ppm: 6.65 (dd, 1H), 6.32-6.38 (dd, 1H), 6.20 (dd, 1H).13C NMR spectrum (100 MHz, CDCI3) 6 in ppm: 166.06, 136.29, 132.72

[0100] B. Synthesis methyl (ethoxy carbonothioyl) sulfanylacetate (MESA)

[0101] Methyl (ethoxy carbonothioyl) sulfanyl acetate (MESA) was prepared by adding potassium hydroxide (0.05 mol) in ethyl alcohol 20 ml and stirring until the formation of a clear solution in a 100 ml round bottom flask. Carbon disulfide (10 ml, 0.17 mol) was added into the reaction mixture dropwise with constant stirring and left the reaction for 5 hrs. Methyl bromide (7.65 g, 0.05 mol) was added slowly and the reaction was further run for 12 hrs. The formed precipitate was filtered out using Whatman filter paper and the filtrate solution was evaporated in a rota- evaporator. Diethyl ether was added and run through the basic alumina. At last diethyl ether was evaporated and the light-yellow color product was obtained. Yield: 96%. ’ H NMR spectrum (400 MHz, CDCI3) 8 in ppm: 4.13 (t, 4H), 4.35 (q, 2H), 5.15 (m, 16H), 1.57 (m, 64H).13C NMR spectrum (100 MHz, CDCI3) 6 in ppm: 169.60, 69.00, 66.69, 28.32, 25.32, 20.52, 16.63.

[0102] C. Synthesis of poly(vinyl acetate) (PVAc)

[0103] Poly(vinyl acetate) was synthesized from vinyl acetate monomer using the bulk Reversible Addition Fragmentation chain Transfer (RAFT) polymerization method. 16ml (174 mmol) of vinyl acetate was taken in a 50 ml RB flask, 2,2'-azobisisobutyronitrile (AIBN) (15 mg, 0.09 mmol) was used as initiator and Methyl (ethoxy carbonothioyl) sulfanyl acetate (MESA) (676 mg, 3.84 mmol) used as chain transfer agent. The reaction mixture was thoroughly deoxygenated by three consecutive freeze-pump-thaw cycles. The RB flask was immersed into the preheated oil bath at 70°C for 5 hrs. After that, the RB was taken out from the oil bath and cooled to room temperature to stop the reaction. Yield: 80%.

[0104] 'HNMR spectrum (400 MHz, CDC13) 6 in ppm: 4.86 (t, 44H), 4.62 (q, 2H), 3.66 (s, 3H), 2.32 (t, 3H), 2.02 (m, 139H), 1.77 (m, 88H), 1.42 (t, 3H).13C NMR spectrum (100 MHz, CDC13) 6 in ppm: 170.63, 62.20, 66.63, 51.91, 39.43, 21.28, 13.09.

[0105] D. Partially hydrolysis of PVAc

[0106] Poly(vinyl acetate) was partially hydrolyzed with KOH. Poly(vinyl acetate) (10g, 116.2 mmol) was taken in a 250 ml RB flask and dissolved in the methanol-water mixture in a 9: 1 ratio.

[0107] Potassium hydroxide (140 mg, 2.5 mmol) was dissolved in methanol and added to the reaction. The RB was immersed in the preheated oil bath for 6 hrs. The solvent was evaporated and again dissolved in a minimum quantity of methanol. The hydrolyzed polymer was precipitated in deionized water two or three times to remove the trace amount of potassium hydroxide. The polymer was dried in an oven under a vacuum at 80 °C. Yield: 94%.

[0108] ’ H NMR spectrum (400 MHz, CDCI3) 6 in ppm: 4.88 (m, 37), 4.65 (q, 2H), 3.66 (s, 3H), 2.35 (s, 11H), 2.04 (m, 113H), 1.78 (m, 80H), 1.41 (t, 3H).13C NMR spectrum (100 MHz, CDCI3) 6 in ppm: 170.36, 67.85, 66.52, 66.25, 51.71, 38.65, 21.00, 13.73. E. Synthesis of graft copolymer of poly(vinyl alcohol)-graft- poly(L-lactide) (PVAc-g-

[0109] PLLA)

[0110] The partially hydrolyzed PVAc was used as a macroinitiator for the ring-opening polymerization of L-lactide. The synthetic procedure was designed for the 50 wt. % content of

[0111] PLLA in PVAc-g-PLLA. 10 g of partially hydrolyzed PVAc, 10 g of L-lactide, and 0.1 g of

[0112] Sn(Oct)2 (Iwt. % with respect to the amount of L-lactide monomer) were taken into a 250 ml RB flask. A high vacuum was applied to the reaction mixture to remove a trace quantity of moisture for 1 h. 40 ml of dry toluene was added to the reaction RB and immersed into preheated oil bath mixture and proceeded at 110°C for 12 hr. after that, the reaction was cooled to room temperature and the polymer was precipitate in pet ether 3-4 times to remove unreacted monomers. The graft polymer was dried under a vacuum oven overnight at 70 °C. Yield: 94%.1H NMR spectrum (400 MHz, CDCh) 8 in ppm:1H NMR spectrum (400 MHz, CDCI3) 6 in ppm: 5.18 (m, 6H), 5.05 (m, 147H), 4.87 (m, 40H), 4.64 (q, 2H), 4.35 (q, 1H), 3.67 (s, 3H), 1.99-2.02 (m,123H), 1.77-1.85 (m,75H), 1.69 (m, 156H), 1.50-1.57 (m, 16H), 1.43 (m, 6H).13C NMR spectrum (100 MHz, CDCh) 6 in ppm: 170.02, 166.99, 72.12, 67.62, 60.02, 38.76, 20.67, 15.47.

[0113] F. Synthesis of acrylate of graft copolymer PVAc-g-PLLA

[0114] Acrylaiton of terminal hydroxyl group of grafted polylactide in PVAc-g-PLLA polymer was done with acryloyl chloride. Firstly, the 5g of PVAc-g-PLLA polymer was taken into a twonecked 100 ml RB flask, and followed by 50 ml of dry THF was added by a syringe under a nitrogen atmosphere. RB was covered with ice to maintain the temperature at 0°C and 1.5 ml of Triethyl amine was added and stirred for 30 min. Acryloyl chloride was added slowly for a period of 15 min at 0°C. The reaction was further run for 24 h at room temperature. After completion of reaction, THF was evaporated and chloroform was added to dissolve polymer. The polymer was washed with brine water three times and dried over sodium sulfate. Finally, chloroform was evaporated and acrylate polymer was dried in vacuum oven overnight at 40°C. Yield: 94%.

[0115] 1HNMR spectrum (400 MHz, CDC13) 8 in ppm: %.1H NMR spectrum (400 MHz, CDCI3) 6 in ppm: 6.55-6.59 (m, 9H), 6.16-6.23 (m, 16H), 6.10 (m, 2H), 5.19 (m, 5H), 5.03 (m, 27H), 4.87 (m, 35H), 4.66 (q, 1H), 4.36 (q, 2H), 3.67 (s, 3H), 2.00-2.03 (m, 112H), 1.76-1.84 (m, 74H), 1.57-1.69 (m,102H), 1.43 (m, 6H).13C NMR spectrum (100 MHz, CDCI3) 6 in ppm: 169.28, 167.05, 134.41, 127.09, 72.12, 68.66, 25.24, 20.67, 16.29, 15.45.

[0116] Poly (vinyl acetate) (PVAc) of pre-defined molecular weight was synthesized starting from vinyl acetate using Reversible Addition Fragmentation chain Transfer (RAFT) polymerization in the bulk where 2,2'-azobisisobutyronitrile (AIBN) was used as the initiator and Methyl (ethoxy carbonothioyl) sulfanyl acetate (MESA) was used as the chain transfer agent. MESA was synthesized according to the literature procedure. Figure 1 shows the proton NMR spectrum of PVAc (bottom most plot). PVAc was obtained in 95% yield and the integration of proton signals of the terminal -CO(O)CH3 unit (labelled ‘d’ in Figure 1) versus the proton labelled ‘a’ on the backbone or -OC(O)CH3 of the repeat unit (labelled ‘c’) revealed a number average molecular weight (Mn) of 43 which was close to the targeted Mn of 50 units. The PVAc polymer was partially hydrolyzed at 60°C in KOH / MeOH basic medium resulting in 94 % yield. The appearance of a sharp peak at 2.34 ppm in the NMR value of partially hydrolyzed PVAc corresponding to the hydroxyl group (which overlaid with terminal -CH2 protons) and slight changes in the properties like reduced solubility in chloroform compared to the starting PVAc polymer indicated partial hydrolysis. However, it was difficult to extract the information regarding the extent of hydrolysis from the proton NMR spectra as the peaks corresponding to protons of -OC(O)CH3 of the repeat unit (labelled ‘c’) were merged with the protons of the backbone. The partially hydrolyzed PVAc was used as a macroinitiator for the ring opening polymerization (ROP) of 1-lactide using Sn(Oct)2 as a catalyst following the literature report. The formation of PLLA graft on the PVAc backbone was confirmed by the appearance of new peaks corresponding to the PLLA backbone (protons labelled ‘e’) around 5.05 ppm and also at 1.50-1.69 ppm corresponding to the methyl group on the graft backbone (labelled ‘f and f ) as seen in Figure 1 (middle spectrum). A peak at 5.18 ppm corresponding to the terminal - C(O)CH(CH3)OH (protons labelled ‘e1’) accounted for an average of about 7 protons. Since the terminal group of the PLLA graft on the PVAc backbone gives a direct indication of the number of graft chains (in turn the number of hydrolysed units), it could be hypothesized that on an average 7 hydrolysed units were present per repeat chain (average degree of hydrolysis nearly 15%). The terminal hydroxyl group of PVAc-g-PLLA was converted to acryloyl groups by reaction of the graft polymer with acryloyl chloride as detailed in Figure 1. The final product acrylate PVAc-g-PLLA crosslinker was obtained as a viscous liquid in 94% yield after the workup followed by drying. Figure 1 (top) compares the proton NMR spectra of the starting PVAc polymer and the graft polymer with the final acrylate PVAc-g-PLLA crosslinker. The characteristic peaks of acrylate double bonds could be observed in the region 6.10 to 6.59 ppm. The integration indicated about 8 acrylate units, which was in agreement with the previous assignment of an average of about 7 graft chains per PVAc backbone chain. The number of PLLA repeat units per graft chain was estimated from the integration of the protons labelled ‘e’ at 5.05 ppm. The integration value was obtained as 30 which upon division over 7 (average number of grafts per chain) indicated about 5 PLLA repeat units per graft.

[0117] The molecular weight of all four polymers was determined using gel permission chromatography (GPC). Chloroform was used as eluent and standard was polystyrene. The GPC molecular weights are tabulated in Table 1.

[0118] Table 1. The molecular weight of all four synthesized PLLA polymers apolystyrene standard

[0119] Example 2

[0120] A) Resin Formulation

[0121] Photocurable resin formulations were developed using a synthesized acrylate PVAc-g-PLLA crosslinker and varying proportions of reactive diluents, HEMA and HEA. Photoinitiator TPO percentage was determined via photo DSC. Resins were prepared with crosslinker, diluent, and initiator, sonicated, and mixed before printing. Curing kinetics and photoinitiator percentages were studied using photo-DSC. Curing enthalpy was measured at 30 °C under nitrogen. Theoretical polymerization heat and curing percentages were calculated based on literature data. Experimental heat of polymerization (Figure 2) for HEMA, HEA, and acrylate PVAc-g- PLLA crosslinker was measured at 1 wt. % PI, yielding values of 403.6 j g-1, 590.2 j g-1, and 91.24 j g-1. Curing percentages were determined relative to 100% double bond conversion: HEMA achieved nearly 96%, HEA about 80%, and acrylate PVAc-g-PLLA crosslinker approximately 92% curing. Table 2 lists the composition of six photocurable resin formulations prepared by varying the weight percentages of the components. The first three formulations (Rl, R2 and R3) were prepared by mixing 50, 40, & 30 wt. % the acrylated PVAc-g-PLLA with HEMA while the remaining three resins (R4, R5 and R6) were prepared by mixing same weight percentage of acrylated PVAc-g-PLLA with HE A.

[0122] Table 2. Weight percentages of HEMA, HEA, and acr. PVAc-g-PLLA crosslinker to prepare resins B) Photo-Differential Scanning Calorimetry (Photo-DSC)

[0123] The Photo-Differential scanning calorimetry (Photo-DSC) studies were carried out in a TA Discover 250 second-generation differential scanning calorimeter equipped with a photo calorimetric unit (Onmi cure series 2000). A 200 W high-pressure mercury lamp which transmits the light of wavelength 320-500 nm, provides the irradiation to the sample chamber via a dual-quartz light guide with neutral density. The sample preparation was similar to that described in the resin formulation. A minimum of 5 mg of samples were weighed out exactly into the sample pan and the pan was kept in a DSC cell. Measurement was carried out under a constant nitrogen flow rate of 50 ml / min. Before exposing the sample pan to the UV light irradiation, the sample was initially held in an isothermal condition for 2 minutes under a nitrogen atmosphere and equilibrated at 30 °C, following which the electronic UV light shutter was opened and the sample was exposed to UV light for 5 minutes of irradiation. The shutter was closed automatically at the end of irradiation time. The peaks were integrated to get the curing enthalpy from the plot of normalized heat flow as a function of irradiation time. The optimum weight percentage of TPO required for these formulations were arrived at by following photo DSC experiments where the TPO weight percentage was varied from 0.5 to 3 wt. %.

[0124] The curing enthalpy of all six-resin formulations increase with increasing PI concentration. The HEMA series of resin formulations (Rl, R2, R3) have the optimum curing enthalpy at 1.5 wt. % of photoinitiator, while for the HEA series of resins (R4, R5, R6), the optimum curing enthalpy was observed at 1 wt. % of PI. The values are listed in Table 3.

[0125] Table 3. Curing enthalpy of six resin formulations

[0126] C) Viscosity measurement: Viscosity of resin formulations was measured using Rotational parallel plate measurements without added photoinitiator. The experiment was performed using the Anton Paar Physica Modular Compact Rheometer (MCR) 301. The test was performed in cup and bob with the diameter 18.08 mm and 16.66 mm respectively. The prepared resin formulation without adding photoinitiator was poured into the cup (almost 5 gm sample) and bob insert inside into the resin to applying shear by rotation. The shear rate was increased from 1 to 1000 per second to measure the viscosity in Pa. s. The temperature of resin was constant during experiment at 30°C.

[0127] The ideal viscosity for DLP 3D printing resin formulation will depend on the specific type of materials used and the desired outcome after the 3D printing. To get a well 3D printed part the viscosity should be in a specific range of less than 10 Pa.s. The viscosity of DLP resin depends on the factors, including the resin formulation, the temperature, and the printing speed. To get reasonable viscosity some customized 3D printers are available in which electrical heat can be transferred to the resin bed. But during printing and post printing time extra precaution need to be taken care. Some resins are specifically designed to have a low viscosity, which helps to reduce the formation of air bubbles or imperfections during 3D printing. The viscosity of all resin formulations is shown in Figure 3 and the values are listed in Table 4 in Pa.s.

[0128] Table 4. Viscosity of all resin formulations with HEMA and HEA.

[0129] The viscosities of the resin formulation were measured at 30 °C without adding photoinitiator. The Newtonian fluid-like nature of the resin formulation was confirmed by measuring the viscosity of each resin which was constant with increasing shear rate. Resins prepared with HEMA showed the viscosity from 0.016 Pa.s to 0.042 Pa.s whereas resins prepared with HEA showed little higher viscosity ranging from 0.019 Pa.s to 0.065 Pa.s. All prepared resin formulations were appropriate for the DLP 3D printing at room temperature with smooth and warpage free 3D printed par.

[0130] D) 3D Printing: The solvent free resin formulations were used for the DLP 3D printing in a resin 3D printer. The commercial 3D printer was purchased from Utpal3DSystem, Gujarat, India. The DLP 3D printer comprising with the 405 nm LED light source and the resin bed size 120X68X200 mm and the printing was performed at room temperature. The intensity of the LED light source was 10 mW cm-2measured using UNO Genetic laser power meter. Firstly, the resin was poured into the resin bed up to a certain level and then the printing parameter was fixed. The thickness of each layer was 100 microns and the bottom layer exposure time was 50 s for first 10 layers and then each layer exposure was 45 s. A Elegoo mars test rook standard stl. file was print to performed the quality of the resin formulation. After finishing the printing, the printed part was washed with isopropyl alcohol in a resin washer with rotation for 3 minutes and kept in UV chamber for post-curing for 1 h.

[0131] After optimizing the viscosity of all resin formulation DLP 3D printing was performed using commercial DLP 3D printer at room temperature. To get the lower viscous liquid resin formulation mostly organic solvents (dioxane, DMSO, toluene etc.) were use as diluent. After printing with organic solvent resin formulation, the printed part could shrink or wrapped due to evaporation of non-reactive organic solvent. Heat assisted customized DLP 3D printers were used to avoid the use of organic solvent. The formulated highly viscous photopolymer resins will be liquid using heat in resin bed and the printing will be performed. HEMA and HEA as reactive diluent avoiding organic solvent and the DLP printing was performed at room temperature. All the formulated resins are printable at room temperature. ASTM D638 type V samples were successfully printed which were further used for the mechanical test measurement. The visual resolution of the 3D printed parts were good in quality and very sharp edges. Figure 4 shows the printed objects the first printed part was printed using resin 6 where 70 wt. % HEA used as diluent and second printed part printed using resin 2 which prepared using 60 wt. % of HEMA. The holes in the first printed part sharp enough. The printing of the merk rook with high resolution justify the quality of the formulated resin. The small written Elegoo mars rook on the printed part is also visible. Most interestingly the resin 1, resin 2, and resin 3 printed parts are hard enough whereas the resin 4, resin 5, and resin 6 printed parts are soft and elastomeric in nature (Figure 5). The resin prepared with HEMA showed higher mechanical strength whereas resin prepared with HEA were showed higher elongation properties.

[0132] E) Mechanical Test: The tensile strength of the 3D printed part was measured using Universal Testing Machine (Instron, series 33R4204) with a 1 KN capacity load cell at room temperature. The tensile test was performed with the ASTM D638 type V sample with the average of five specimen samples. The gauge length of each sample was 10 mm and the experiment was performed at room temperature with the stretching rate of 5 mm min1. The tensile strength, young’s modulus, elongation, and toughness was measured at the point of break.

[0133] Mechanical and Thermal Properties of 3D Printed Parts

[0134] The tensile tests conducted on 3D printed materials highlighted the significant impact of reactive diluents in resin formulations on mechanical properties. Using ASTM D638 type V dumbbell- shaped samples, five samples per resin formulation were examined. Findings from Figures 8a and 8b and Table 5 revealed that 3D printed parts with HEMA as a diluent exhibited higher tensile strengths (12.27 ±1.02 Mpa, 13.33+1.88 Mpa, and 20.60+2.39 Mpa for resin 1, resin 2, and resin 3 respectively) and Young's moduli (256.54+35.4 Mpa, 918.19+21.46 Mpa, and 1972.06+46.42 Mpa for resin 1, resin 2, and resin 3 respectively) compared to tensile strengths (0.37+0.14 Mpa, 0.87+0.05 Mpa, and 1.12+0.22 Mpa for resin 4, resin 5, and resin 6 respectively) and Young's moduli (1.82+0.59 Mpa, 2.04+0.10 Mpa, and 2.22+0.36 Mpa respectively) those printed parts with HEA. The study found that 3D printed materials with HEMA as the reactive diluent had higher tensile strength and Young's modulus compared to those with HEA, but lower elongation. Increasing the weight percentage of HEMA or HEA in the resin formulations led to higher tensile strength and Young's modulus. The material's mechanical and thermal properties were influenced by the acrylate PVAc-g-PLLA crosslinker polymer and the choice of reactive diluents (HEMA and HEA). The presence of PLLA grafting chains disrupted molecular structure regularity, affecting crystallinity and potentially reducing tensile strength. The increased stiffness in HEMA-based prints might be due to a higher effective molecular weight between crosslinking sites and the steric structure of the methyl group in HEMA. The thermal properties of the 3D printed materials were further investigated by TGA and DSC experiments (Figure 6a, 6b and figure 7a, 7b). The 3D printed parts showed good thermal stability with 10 % weight loss observed in the range of 260 to 300°C for all the six resin formulations. The DSC analysis revealed the glass transition temperature (Tg) of the HEMA formulations (R 1, R2, and R3) to be 50°C, 76°C, and 82°C respectively, while that for the HEA formulations (R4, R5, and R6) were 20°C, 14°C, and 13°C respectively. It could be observed that increasing the wt. % of HEMA in the resin formulation resulted in higher Tgvalues making the printed materials stiffer. On the other hand, increasing the HEA content resulted in enhancing the elasticity of the 3D printed objects using the formulations R4 to R6. The values of Tgand 10 % weight loss temperatures of the 3D printed parts are tabulated in Table 5.

[0135] Table 5. Tensile strength, Young’s modulus, Elongation, Glass transition and 10 weight % degradation temperature of 3D printed resin products.

[0136] F) In vitro degradation study: Three rectangular specimens of each resin formulation 3D printed part were immersed in 200 ml Phosphate Buffer Solution (PBS) maintaining the pH 7 at 37°C temperature. The buffer solution was prepared by mixing NaCl, KC1, NaiHPCh. and KH2PO4 in ratio of 137 mM, 2.7 mM, 10 mM, and 1.8 mM respectively in 1000 ml deionized water. The rectangular specimens were kept inside a dialysis tube and each side was closed with thread and immersed into the PBS solution with constant stirring over the 2 months of time period. The water uptake and the degradation were measured after one week by taking out the sample, wiped with tissue paper, and kept in vacuum for dry at 50°C. The water uptake was calculated using equation 1 water uptake eq. 1 where the wtwet is the weight of the specimens in wet state after wiping with the tissue paper and the wetdry is the weight after drying in vacuum oven. The PBS solution was replaced in every week without hampering the pH of the PBS solution.

[0137] In Vitro Degradation and swelling analysis

[0138] The study delved into the degradation and water uptake dynamics of 3D printed parts over two months, tracking weight loss and water absorption weekly in a pH 7.4 phosphate buffer solution at 40°C to simulate biological conditions. Notably, the water uptake exhibited an initial increase, followed by a reduction in the third week, maintaining relative stability thereafter, attributed to unreacted hydrolyzed PVAc polymer and reactive diluent hydroxyl groups. HEA- based materials displayed higher water uptake than HEMA-based counterparts due to crosslinked polymeric networks formed by HEA. Enhanced degradability of HEA -based prints was tied to their greater water permeability, correlated with higher water uptake. The materials printed HEA showed water uptake of almost 240 % within 2ndweek of the experiment and then from 3rdweek onwards their water uptake reduced by 150 % and remain constant may be due to the increasing degradation of the printed materials in the PBS solution. Whereas, the HEMA- used printed materials exhibit lower water uptake of almost 100 % and with incubation time remained the same. The degradation of the HEA-used printed parts showed higher degradability compare to HEMA-used printed materials due to more water permeability inside the printed materials as a result of water uptake value. The degradation mechanism centered on hydrolytic ester bond cleavage within PLLA polymers, with pronounced initial weight loss tapering beyond the fourth week. Periodic solution replacement was necessitated to maintain consistent pH and track the production of 1-lactic acid, a degradation byproduct.

[0139] Due to this, PBS solution of replaced periodically to maintain pH until over experiment, weight loss percentage of 3D-printed square samples was in Figure 9, and the values are tabulated in Table 6.

[0140] Table 6. Weight loss percentage in PBS, and cell viability of six resin printed materials.

[0141] G) In Vitro Cell Viability Test

[0142] The biocompatibility and cytotoxicity of the polymers were evaluated using a 3-(4,5- Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in 96 well plates. Initially, complete media were prepared by combining 1% penicillin-streptomycin, 10% fetal bovine serum, and Dulbecco's Modified Eagle Medium (DMEM) media. Subsequently, 1000 cells were seeded into each well and incubated for 16 hours in a 5% CO2 environment at physiological temperature. After the incubation period, the media were removed, and / or 2 mg of the polymer (3D printed film) was added to each well in 300 pL of fresh media. The cells were then further incubated for different time points, namely 24 hours, 48 hours, and 72 hours, respectively, under physiological conditions. Each experiment was conducted in triplicate. For the control row, only media was added without any polymer sample. Following the incubation, the media were aspirated, and any remaining films were removed from the wells. Next, MTT molecules were dissolved in complete media, and 100 pL of a 0.5 mg / mL concentration was added to each well. The cells were then incubated for an additional 4 hours at physiological temperature. During this incubation, the MTT molecule is reduced by the mitochondrial reductase NADPH cellular oxidoreductase enzyme, leading to the formation of purple formazan crystals. These crystals are insoluble in the media. After the 4-hour incubation, 100 pL of HPLC-grade DMSO was added to each well and placed on a shaker for 15 minutes to completely dissolve the MTT crystals in the DMSO. The absorbance of the 96 well plates was then measured at 570 nm using a Varioscan reader. The obtained data were plotted to show the percentage cell viability against the concentrations of the tested polymers. To assess biocompatibility and cytotoxicity of polymers, MTT assay was examined. 3D-printed films from R1 to R6 were incubated with wild-type mouse embryonic (WT-MEF) cells inside 96 well plates and cell viability was determined by MTT assay for 3 different times of incubation (24 h, 48 h, and 72 h). As shown in Figure 10, 3D printed films did not exhibit any in-vitro cytotoxicity under tested conditions. 3D printed films showed more than 90 % cell viability even after 72 h of incubation which gave clear indication of feasibility of PVAc-g-PLLA polymer for 3D printing in biomedical applications.

[0143] ADVANTGAES OF THE INVENTION

[0144] • Provides acrylated polyvinyl acetate-grafted -poly (1-lactide) (acr. PVAc-g-PLLA) based crosslinker to obtain 3D printed product with more effective mechanical properties, biodegradability and resolution.

[0145] • Effectively provides a liquid / semisolid phase crosslinker / polymer of formula I with lower molecular weight compared to conventional / commercial polymers / crosslinkers (around 1.6 kD),

[0146] • No organic solvent and heat required for 3D printing in case of use of said cros slinker / polymer.

[0147] • Lactide with acr. PVA causes higher biodegradability and biocompatibility.

[0148] • Enhanced stress / strain properties with elongation upto 100% without breaking the 3D product.

[0149] • No brittleness in printed product.

[0150] • Thermally stable (at 260-300 °C with only upto 10% degradation).

[0151] • No cytotoxicity (making it biocompatible).

Claims

We Claim1. An acrylated polyvinyl acetate-grafted-poly (1-lactide) polymer (PVAc-g-PLLA) of formula IFormula I wherein z is 40-50; x is 5-10; and y is 3-5.

2. The polymer as claimed in claim 1, wherein molecular weight of the compound is in the range of 3500-6000 g / mol.

3. A process for the preparation of the polymer as claimed in claim 1, comprising the steps of: a) mixing vinyl acetate, an initiator, and chain transfer agent in a container to obtain a 1streaction mixture; b) reacting and deoxygenating the 1streaction mixture as obtained in step a) by one or more consecutive freeze-pump-thaw cycle(s) followed by heating at a temperature in the range of 50 to 90 °C for a time period in the range of 4 to 6 hrs to obtain polyvinyl acetate compound of Formula A;Formula A wherein z is same as defined in claim 1; wherein the freeze-pump-thaw cycle(s) is done using a liquid nitrogen at a temperature in the range of -80 to -100 °C with a high vacuum of pressure in the range of 0.001 to 0.0001 mbar and for the time period in the range of 15- 20 min for each said cycle; c) partially hydrolyzing the compound of Formula A as obtained in step b) by dissolving the compound of formula A in a 1stbase and a 1stsolvent or 1stmixture of solvents at a temperature in the range of 55-65 °C for a time period in the range of 5 to 8 hrs to form a 1stcrude solution;d) precipitating 1stcrude solution as obtained in step c) with water followed by drying at a temperature in the range of 70 to 100 °C for a time period in the range of 12-15 hrs to obtain partially hydrolyzed compound of formula B ;Formula B wherein z and x are same as defined in claim 1 ; e) mixing partially hydrolyzed compound of formula B as obtained in step d), L- lactide and a catalyst in a container to obtain 2ndreaction mixture; wherein a ratio of L-lactide and catalyst is in range of 0.15: 10 to 0.2:10; f) optionally removing moisture from the 2ndreaction mixture of step e) by applying high vacuum to the 2ndreaction mixture for a time period in the range of 0.5 to 1.5 hrs; g) reacting the 2ndreaction mixture as obtained in step e) or f) by mixing in a 2ndsolvent followed by heating at a temperature in the range of 90 to 130 °C for a time period in the range of 10 to 14 hrs to obtain a 2ndcrude solution; h) precipitating the 2ndcrude solution as obtained in step g) with petroleum ether followed by drying at a temperature in the range of 50 to 90 °C for a time period of 12-15 hrs to obtain graft PVA-poly-l-lactide compound of formula C;Formula C wherein z, x and y are same as defined in claim 1 ; i) acrylating terminal hydroxyl group of grafted PVAc-g-PLLA compound of formula C by reacting it with acryloyl halide and a 3rdsolvent in presence of 2ndbase at a temperature of 0 °C to obtain 3rdreaction mixture; j) reacting the 3rdreaction mixture as obtained in step i) at a temperature in the range of 25 to 30 °C for a time period in the range of 22 to 26 hrs to obtain the polymer of formula I; andk) optionally purifying the polymer of Formula I as obtained in step j) to obtain pure polymer of formula I.

4. The process as claimed in claim 3, wherein said initiator is selected from the group consisting of 2,2'-azobisisobutyronitrile (AIBN), 4,4'-azobis(4-cyanovaleric acid) (ACVA) and said chain transfer agent is selected from the group consisting of methyl(ethoxy carbonothioyl) sulfanyl acetate (MESA), ethyl 2-((ethoxycarbonothioyl)thio)acetate or S- benzyl O-ethyl carbonodithioate.

5. The process as claimed in claim 3, wherein the 1stbase is selected from the group consisting of potassium hydroxide, sodium hydroxide and potassium carbonate or mixture thereof and said 2ndbase is selected from the group consisting of triethyl amine (TEA), diethyl amine or diisopropyl amine.

6. The process as claimed in claim 3, wherein the 1stsolvent is selected from the group consisting of alcohol, water, ethanol / water mixture; wherein the 1stmixture of solvents are selected from water and alcohol; wherein the 2ndsolvent is selected from the group consisting of toluene, xylene or dimethylacetamide (DMA); wherein the 3rdsolvent is selected from the group consisting of tetrahydrofuran (THF), DCM or CHCE; and wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, butanol or pentanol.

7. The process as claimed in claim 3, wherein the catalyst used in step e) is selected from the group consisting of stannous octoate [Sn(Oct)2], diazabicyclo[5.4.0]undec-7-ene (DBU), 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), and 1,5,7- triazabicyclo[4.4.0]dec-5-ene (TBD); wherein the ratio of L-lactide and catalyst used in step e) is in range of 0.15: 10 to 0.2: 10; and wherein the acryloyl halide used in step i) is selected from the group consisting of acryloyl chloride, acryloyl bromide, acryloyl fluoride or acryloyl iodide.

8. A composition for 3D printing comprising the polymer as claimed in claim 1, one or more of additive(s) and a photo initiator, wherein the composition exhibits a thermal stability with 10 % weight loss in the range of 260 to 300°C.

9. A process for the preparation of a composition for 3D printing as claimed in claim 8, wherein said process comprising the steps of: a) mixing the polymer of Formula I as claimed in claim 1 with one or more of additive(s) and photo initiator in a vial or container followed by sonicating for a time period in the range of 0.5 to 1.5 hrs at a temperature in the range of 25 to 30 °C to obtain a sonicated mixture; andb) covering the sonicated mixture as obtained in step a) with an aluminum foil followed by storing in a fridge for cooling at a temperature in the range of -10 to 0 °C to obtain the fridge stored material; and c) keeping the fridge stored material as obtained in step b) at a temperature in the range of 25-35 °C followed by shaking in a vortex for a time period in the range of 3 to 8 minutes to obtain the composition.

10. The composition as claimed in claim 8 and 9, wherein the additive(s) is selected from the group consisting of hydroxy ethyl acrylate (HE A), hydroxyethyl methacrylate (HEMA), 1,6-hexane dioldiacrylate (HDD A), polyethylene gycol diacrylate (PEGDA), and trimethylolpropane trimethacrylate (TMPTA), or two or more mixture thereof; and the photoinitiator is selected from the group consisting of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO), 2-hydroxy 2-methylpropiophenone, bisacylphosphine oxide (BAPO).

Images