Electrospun Poly(γ-glutamate)/Silica Hybrids for Tissue Regeneration: Influences of Silane Coupling Agents on Chemistry, Degradation and Florescent Dye Release

Background: Electrospun hybrids consisting of poly(γ-glutamate) and silica derived from (3-glycidyloxypropyl) trimethoxysilane (GPTMS) are able to encapsulate proteins with no denaturation because of the water-based synthesis and facilitate the controlled release of encapsulated molecules into buffer solutions. We prepared new types of hybrids using (8-glycidoxyoctyl) trimethoxysilane(GOTMS) in lieu of GPTMS to examine influences of silane coupling agents on chemical structure, degradation behaviour and controlled release of molecules encapsulated in the electrospun hybrids. Methods: The calcium salt form of the polymer and GOTMS or GPTMS was mixed in water and then electrospun(polymer ratio; 48 ~ 66 wt%). Fluorescent dyes with three different molecular weights were added to the hybrid solution 0.5 h before electrospinning. The electrospun hybrids were characterised with SEM, ATR-FTIR and 29Si MAS/NMR. Degradation and molecule release behaviours of the electrospun hybrids were estimated by soaking them in buffer solutions. Results: Results of 29Si MAS/NMR demonstrated that polymer/GOTMS hybrids contained highlycondensed siloxane phases than polymer/GPTMS hybrids. Polymer/GOTMS hybrids showed a burst of Si release 12 h after soaking in buffer solutions and then stopped the release, whereas the polymer/ GPTMS hybrids showed a gradual release in the overall testing time. Some of the GOTMS in the hybrids was expected not to contribute to crosslinking between polymer chains and release from the hybrids immediately. However, the total degradation rate was smaller for the polymer/GOTMS hybrids than for the polymer/GPTMS hybrids. The polymer/GOTMS and polymer/GPTMS hybrids both exhibited molecular release with a molecular-weight dependence; however, the release rate was smaller for polymer/GOTMS than for polymer/GPTMS. Conclusion: The degradation rate and molecular release behaviour were controlled by changing the cross-linker of the hybrids from GPTMS to GOTMS. This might be because siloxane phases derived from GOTMS became more condensed and GOTMS possesses a lower hydrophilicity than GPTMS.