UV-Cured Transparent Flexible Silicone Materials with High Tensile Strength

Release Kinetics of Metronidazole from 3D Printed Silicone Scaffolds for Sustained Application to the Female Reproductive Tract

Sustained vaginal administration of antibiotics or probiotics has been proposed to improve treatment efficacy for bacterial vaginosis. 3D printing has shown promise for development of systems for local agent delivery. In contrast to oral ingestion, agent release kinetics can be fine-tuned by the 3D printing of specialized scaffold designs tailored for particular treatments while enhancing dosage effectiveness via localized sustained release. It has been challenging to establish scaffold properties as a function of fabrication parameters to obtain sustained release. In particular, the relationships between scaffold curing conditions, compressive strength, and drug release kinetics remain poorly understood. This study evaluates 3D printed scaffold formulation and feasibility to sustain the release of metronidazole, a commonly used antibiotic for BV. Cylindrical silicone scaffolds were printed and cured using three different conditions relevant to potential future incorporation of temperature-sensitive labile biologics. Compressive strength and drug release were monitored for 14d in simulated vaginal fluid to assess long-term effects of fabrication conditions on mechanical integrity and release kinetics. Scaffolds were mechanically evaluated to determine compressive and tensile strength, and elastic modulus. Release profiles were fitted to previous kinetic models to differentiate potential release mechanisms. The Higuchi, Korsmeyer-Peppas, and Peppas-Sahlin models best described the release, indicating similarity to release from insoluble or polymeric matrices. This study shows the feasibility of 3D printed silicone scaffolds to provide sustained metronidazole release over 14d, with compressive strength and drug release kinetics tuned by the fabrication parameters.

High Tensile Strength UV-Cured Castor Oil-Based Silicone-Modified Polyurethane Acrylates

High tensile strength UV-cured transparent materials are highly desired in optical devices. In this paper, high tensile strength UV-cured transparent castor oil-based polyurethane acrylates (PUAs) with a very high transmittance over 95% (400-800 nm) were prepared from UV-curable castor oil-based polyurethane acrylates (CO-PUAs) and mercapto silicone-containing hyperbranched polymers (HBPSHs) under UV irradiation. The tensile strengths of UV-cured transparent castor oil-based PUAs can reach 12.49 MPa, which is obviously higher than that of UV-cured CO-PUAs reported previously (0.7-10.20 MPa). The chemical structure of HBPSHs will play an important role in the mechanical performance of UV-cured silicone-modified materials, and it can be concluded that the more rigid the units of α,β-dihydroxyl derivatives used in the fabrication of HBPSHs are, the higher the mechanical strength and pencil hardness of the UV-cured materials will be.

Direct sound printing

Photo- and thermo-activated reactions are dominant in Additive Manufacturing (AM) processes for polymerization or melting/deposition of polymers. However, ultrasound activated sonochemical reactions present a unique way to generate hotspots in cavitation bubbles with extraordinary high temperature and pressure along with high heating and cooling rates which are out of reach for the current AM technologies. Here, we demonstrate 3D printing of structures using acoustic cavitation produced directly by focused ultrasound which creates sonochemical reactions in highly localized cavitation regions. Complex geometries with zero to varying porosities and 280 μm feature size are printed by our method, Direct Sound Printing (DSP), in a heat curing thermoset, Poly(dimethylsiloxane) that cannot be printed directly so far by any method. Sonochemiluminescnce, high speed imaging and process characterization experiments of DSP and potential applications such as remote distance printing are presented. Our method establishes an alternative route in AM using ultrasound as the energy source.

Photo- and thermo-activated polymerization and melting processes are dominant in Additive Manufacturing (AM) while ultrasound activated sonochemical reactions have not been explored for AM so far. Here, the authors demonstrate 3D printing of structures using acoustic cavitation produced directly by focused ultrasound which creates sonochemical reactions in highly localized cavitation regions.

Preparation of Bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane and Investigation of Its Cationic UV-Curing Material Properties

Precusor EHO(3-ethyl-3-hydroxymethyloxetane) was synthesized with diethyl carbonate and trihydroxypropane as the main raw materials. Intermediate AllyEHO(3-ethyl-3-allylmethoxyoxetane) was synthesized with 3-ethyl-3-hydroxymethyloxetane and allyl bromide as the main raw materials. Prepolymer bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane was synthesized with 3-ethyl-3-methoxyoxetane)propyl and diphenylsilane. Photoinitiator triarylsulfonium hexafluoroantimonate of 3% was added to the prepolymer, and a novel kind of the photosensitive resin was prepared. They were analyzed and characterized with FTIR and ¹H-NMR. Photo-DSC examination revealed that the bis[(3-ethyl-3-methoxyoxetane)propyl]diphenylsilane has great photosensitivity. The thermal properties and mechanical properties of the photosensitive resin were examined by TGA and a microcomputer-controlled universal material testing machine, with thermal stabilities of up to 446 °C. The tensile strength was 75.5 MPa and the bending strength was 49.5 MPa. The light transmittance remained above 98%.

UV-Cured Transparent Silicone Materials with High Tensile Strength Prepared from Hyperbranched Silicon-Containing Polymers and Polyurethane-Acrylates

Flexibility and mechanical performance are essential for transparent silicone materials applied in some optical and electronic devices; however, the tensile strength of transparent silicone materials is fairly low. To overcome this problem, a kind of UV-cured transparent flexible silicone material with quite a high tensile strength and elongation at break was developed through UV-initiated thiol-ene reaction by hyperbranched silicon-containing polymers (HBPs) with a thiol substitute and acrylate-terminated polyurethanes. Unexpectedly, it is found that both the tensile strength and elongation at break of the transparent silicone materials are extraordinarily high, which can reach 3.40 MPa and 270.0%, respectively. The UV-cured materials have good UV resistance ability because their transmittance is still as high as 93.4% (800 nm) even when aged for 40 min in a UV chamber of 10.6 mW cm-2. They exhibit outstanding adhesion to substrates, and the adhesion to a glass slide, wood, and a tin plate is grade 1. The promising results encourage us to further improve the mechanical performance of flexible transparent silicone materials by effective chemical modification strategies with HBPs. An attempt was made to apply the UV-cured materials in a Gel-Pak box and it could be proved that the UV-cured materials may be one of the good candidates for use as packaging or protecting materials of optical or electronics devices such as the Gel-Pak product.

Polyester-Polysiloxane Hyperbranched Block Polymers for Transparent Flexible Materials

Highly transparent flexible silicone elastomers are useful for certain stretchable electronics and various types of smart devices. Polyester-polysiloxane hyperbranched block copolymers are synthesized by ring-opening polymerization of octamethylcyclotetrasiloxane initiated by macromolecular lithium alkoxide. Treatment of these copolymers with tetraethoxysilane and dibutylin dilaurate at room temperature gives the corresponding transparent elastic materials. The transparency of the materials can reach 90% (700-800 nm), and the starting thermal decomposition temperatures of the materials are higher than 330 °C. Very interestingly, though the highest tensile strength of the material prepared is about 0.48 MPa, the elongation at break can reach 778-815%. The results will inspire us to develop highly transparent flexible silicone materials by designing copolymers of silicone materials and hyperbranched polymers.

An Easy Fabrication Method to Prepare Inexpensive UV–Cured Transparent Silicone Modified Polyacrylate Coatings with Good Adhesion and UV Resistance

UV–curable polyacrylate is widely used in free–radical type UV–cure coating systems, the disadvantages of which including poor thermal stability and UV resistance can be overcome through chemical modification by silicone. However, it is a remarkable fact that the strategies for fabrication UV–cured silicone modified polyacrylates are somewhat complicated and the price of the products may be much expensive than pure UV–cured polyacrylates. In this work, an easy fabrication method to prepare inexpensive UV–cured transparent silicone modified polyacrylate coatings with good adhesion and UV resistance performance was developed from copolymers of acylates and thiol silicone resin by UV initiated thiol–ene click reaction without UV initiator. The striking results with a high application value should be emphasized that when the amount of thiol silicone resin is only one wt.% of the copolymer of acrylates, the UV–cured coatings obtained exhibit fairly good performance. These coatings prepared exhibit transparency higher than 96% (800 nm), adhesion property to glass slides can reach grade 0, pencil hardness can reach 6H, water absorption is less than 0.16%. In particular, it is observed obviously that the silicone modified polyacrylate coatings exhibit better UV resistance performance than the coating prepared with only copolymers of acrylates initiated by UV initiator 1173. It is proved that it is actually an easy fabrication method to prepare inexpensive UV–cured transparent silicone modified polyacrylate coatings with high performance by UV initiated thiol–ene click reaction of copolymers of acylates and thiol silicone resin.

Fabrication of Transparent UV-Cured Coatings with Allyl-Terminated Hyperbranched Polycarbosilanes and Thiol Silicone Resins

To improve thermal stability and hardness of UV-cured materials, a series of UV-cured solvent-free coatings were prepared from allyl-terminated hyperbranched polycarbosilanes and thiol silicone resins. The silicone coatings prepared have pencil hardness of 4-9 H, water absorption no more than 0.04 wt %, and transmittance higher than 94%. The temperature for the coatings' starting thermal decomposition is higher than 236 °C; especially, that of the coating prepared with G1 is as high as 371.1 °C. The UV-cured coatings in this work exhibit much higher pencil hardness than and superior thermal stability to those reported previously.

UV-Cured Coatings Prepared with Sulfhydryl-Terminated Branched Polyurethane and Allyl-Terminated Hyperbranched Polycarbosilane

The conventional polyurethane (PU) coatings have poor heat resistance, which will undergo severe pyrolysis when the temperature exceeds 200 °C. To overcome the shortcoming of conventional PU coatings, an ultraviolet (UV)-cured solvent-free hyperbranched polycarbosilane modified PU coatings was prepared by sulfhydryl-terminated polyurethane and allyl-terminated hyperbranched polycarbosilane. The initial decomposition temperature (Td5%) of the UV-cured coating ranges from 258 to 268 °C, which is obviously higher than those of the conventional PU coatings reported. The coating shows fairly low water absorption in the range of 0.6–1.36 wt% and exhibits grade 1, grade 2 and grade 3 adhesion to glass, tin plate and aluminum sheet, respectively.