SYNTHESIS OF HIGH THERMOSTABLE SILICONE GELS CONSTRUCTED WITH LADDERLIKE POLYSILSESQUIOXANES

Heat-resistant silicone gels were synthesized by replacing the single main chain polymethylhydrosiloxane with reactive ladderlike polyhydrosilsesquioxane copolymers. Because of the interaction between polydimethylsiloxane chains and the ladderlike polysilsesquioxanes chains, the cyclization of the polydimethylsiloxane chains is hindered. The high thermal stability of the ladderlike polymers can improve the thermal stability of the silicone gels without sacrificing their good comprehensive properties.

Trap Characteristics and Their Temperature-dependence of Silicone Gel for Encapsulation in IGBT Power Modules

Silicone gel is a prevailing material for encapsulation in insulated gate bipolar transistor(IGBT)power modules.The space charge transport behavior in silicone gel is significant to evaluate the electrical insulation characteristics.This paper focuses on the trap characteristics and electrical properties of the silicone gel,which were rarely studied before.The experiments are performed on the surface potential decay of silicone gel after the charge injection.Then,the energy distributions of electron or hole traps are determined by a double-trap energy level model,which can be fitted by the Gaussian distribution.In addition,the mobilities of positive and negative charges are determined,which are 1.38×10^(-12) m^(2)·V^(-1)·s^(-1) and 1.74×10^(12) m^(2)·V^(-1)·s^(-1),respectively.Furthermore,considering the heat as a byproduct resulting in thermal issues,the temperature-dependence of surface potential decay characteristics are also studied in this paper.When temperature rises,the decay rate of surface potential increases,especially when the temperature is higher than 80℃.Finally,the contrastive analysis illustrates that the trap characteristics of silicone gel are between the trap characteristics in liquid-state material and solid-state material,which supports the phenomenon that silicone gel is more resistive to the sharp edges in power modules.This work can provide a useful reference for the design of encapsulation in high-voltage IGBT power modules.

In vivo biological stability of chemically pretreated silicone gel inserts intended for use in keratoprostheses

Background Pretreatment with chemical agents could alter the surface chemistry of the silicone gel, which makes it suitable for epithelial migration onto its surface and thus enhances the cytobiocompatibility. This study aimed to evaluate the biological response of the corneal stroma to porous silicone gel pretreated with different chemical agents in vivo. Methods The porous silicone gels were treated with a mixed acid solution containing 23.2% H2SO4 and 0.8% K2Cr207 for 10 or 15 minutes or with 30% H202 for 15 minutes. Discs （4 mm in diameter） were inserted into interlamellar stromal pockets of New Zealand white rabbits and followed up for a period of 3 months. Clinical evaluations such as corneal infiltration, edema and neovascularization were performed daily. At 3 months, the fibroplasias and collagen deposition were examined under light and scanning electron microscopy （SEM） and by immunohistochemical analysis. Results Pretreatment of the discs obviously decreased conjunctival congestion, discharge, cornea edema, and the extent of neovascularization. More fibroblasts migrated into the pretreated discs than into the control, and collagen was deposited, indicating that the biocompatibility of the corneal replacements was enhanced by the chemical pretreatments. From immunohistochemical analysis, Type I collagen deposition in the pretreated silicone discs was greater than in the control. Conclusions Chemical treatment of silicone gel is effective in decreasing rabbit corneal inflammation, encouraging fibroblast in-growth, and enhancing tissue compatibility. Pretreated gels show good biological stability when used as a skirt material in Keratoprosthesis （Kpros）.

Mechanical characterization of soft silicone gels via spherical nanoindentation for applications in mechanobiology

As a biocompatible material,soft silicone gels like CY52-276 have been applied to many engineering fields associated with interactions between mammalian cells and extracellular matrices/substrates,due to its nontoxicity,ease of preparation,optical transparency and tunable mechanical properties.Precise quantification of mechanical properties of silicone gels is crucial for quantitatively investigating mechanical responses of cells to microenvironments.Addressing the material with high surface energy,we design a new strategy for the nanoindentation technique to reduce or even eliminate the effect of interfacial adhesions with the aid of some specified buffers.Next,we dissect the dependence of its Young’s modulus on the ratios of monomers and crosslinkers and curing conditions,and therefore identify a dose-response relationship between its moduli and the corresponding prepolymer compositions.With the non-linear large deformation nanoindentation tests,we further showed that the two-parameter Mooney-Rivlin model may well characterize the hyperelastic deformations of the materials with different composition ratios.These pave the way for more precise exploration of the interaction between cells and extracellular matrix and the underlying mechanotransduction pathways in mechanobiology.

STUDY OF PROPERTIES AND TOXICOLOGY OF MEDICAL ORGANIC SILICON GEL CRYSTALS

The authors perpared artifical crystals from silicon elastomer, which ensured medical purity, studied how to improve the light transmittance and the characteristics of moulding (sulfurization). This material has been applied to many clinical cases.

Effect of chemical treatment of silicon gel on tissue compatibility

Background Silicon gel is unfavourable for cell attachment and growth. This study was to study if pretreating the surface of silicon gel with chemical agents affects the proliferation of epithelial cells Methods Silicon gel was made and treated with either mixed acid solution (containing 232 g/dm 3 of H 2SO 4 and 8 g/dm 3 of K 2Cr 2O 7) or 300 cm 3/dm 3 peroxide for 5, 10, and 15 minutes or 10, 15, and 20 minutes, respectively The cultured corneal epithelial cells were seeded onto those silicon gels and kept for 13 days Immunohistochemical investigations were then carried out for integrin (alpha 6 or beta 4) and actin KH*2/5DResults Growth of the epithelial cells in silicon gels treated with mixed acid solution for 10 minutes and 15 minutes was much significant than that in the untreated gels After a 12-hour culture, a small number of corneal epithelial cells were proliferated on the surface of the silicon gels that had been treated with peroxide for 15 minutes After a 3-day culture, those cells were further proliferated and fused together The corneal epithelial cells did not grow well in the silicon gels treated with peroxide for 10 or 20 minutes Immunostaining revealed the expression of actin and integrin alpha 6 or beta 4 on the silicon gels that were treated with mixed acid solution for 10 minutes or peroxide for 15 minutes Conclusion Silicon gels treated either with mixed acid solution for 10 or 15 minutes or with peroxide for 15 minutes improves cell proliferation

Grafting β-CD Copolymer Metal Complex from Silicon Gel by SI-ATRP

Polymers grafted from solid surface are being extensively studied with a range of objectives.The most popular living/controlled polymerization used in polymers grafted from solid surfaces is the surface-initiated atom transfer radical polymerization（SI-ATRP）[1,2].An attractive feature of atom transfer radical polymerization（ATRP） is to simultaneously grow chains from multifunctional surface.Thus the grafted polymer with well-defined structures could be designed and controlled.ATRP has proven to be a powerful tool to synthesize homopolymers and copolymers,under easily accessible experimental conditions[3-7].Furthermore it is useful for the functionalization of material surfaces by grafting certain polymers.