No abstract

Purpose: Silicate ions released from bioactive glasses and ceramics have been reported to stimulate osteogenic cell functions. Here, we evaluated osteoblast-like cell reactions to silicate ions released from two different types of materials, 45S5 bioactive glass (BG) and siloxane-doped vaterite (SiV), to investigate the influence of the ionic structure of silicate ions on osteoblast-like cell properties.Methods: BG and SiV powders were prepared by using melt-quenching and carbonation methods, respectively. Aminopropyltriethoxysilane was used as a siloxane source of SiV. MC3T3-E1 and SaOS-2 cells were cultured in media containing dissolved BG or SiV ions (10-50 ppm of Si). Cell proliferation (metabolic activity), differentiation (alkaline phosphatase activity) and mineralisation (Ca deposition) were examined. Results:29 Si NMR spectra demonstrated that Q 0,1 species and T 0-3 species were released from BG and SiV, respectively. Proliferation and mineralisation of the two types of cells were influenced by silicate ions released from BG and SiV in a concentration-dependent manner. In particular, there were significant differences (P < 0.05) in the degree of proliferation and Ca deposition levels in SaOS-2 cells treated with dissolved BG and SiV ions. Furthermore, Ca deposition in SaOS-2 cells was influenced by both the presence of silicate ions and the duration of exposure of cells to them. Conclusions:The structure of silicate ions influenced the proliferation and mineralisation of SaOS-2 cells incubated for different time periods in culture media containing different Si concentrations. Understanding the effect of Si on bone cell behaviour will enable a design-led approach to further BG optimisation. KeywordsSilicate ions, 45S5-type bioactive glass, Vaterite, Osteoblast-like cells

Protein-encapsulated fibermats are an attractive platform for protein-based bioactive materials. However, the choice of methods is still limited and not applicable to a wide range of proteins. In this study, we studied new polymeric materials for constructing protein-encapsulated fibermats, in which protein molecules are encapsulated within the nanofibers of fibermats without causing deleterious changes to protein structure or function. We constructed a protein-encapsulated fibermat using the poly(γ-glutamate) (PGA)/(3-glycidyloxypropyl)-trimethoxysilane (GPTMS) hybrid as a precursor for electrospinning. Because the PGA/GPTMS hybrid is water-soluble, protein molecules can be added to the precursor in an aqueous solution, significantly enhancing protein stability. Polycondensation during electrospinning (in-flight polycondensation) makes the obtained fibermats water-insoluble, which stabilizes the fibermat structure such that it is resistant to degradation in aqueous buffer. The molecular structure of the PGA/GPTMS hybrid gives rise to unique molecular permeability, which alters the selectivity and specificity of biochemical reactions involving the encapsulated enzymes; lower molecular-weight (MW) substrates can permeate the nanofibers, promoting enzyme activity, but higher MW substrates such as inhibitor peptides cannot permeate the nanofibers, suppressing enzyme activity. We present an effective method of encapsulating bioactive molecules while maintaining their structure and function, increasing the versatility of electrospun fibermats for constructing various bioactive materials.

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 29 Si MAS/NMR. Degradation and molecule release behaviours of the electrospun hybrids were estimated by soaking them in buffer solutions.Results: Results of 29 Si 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.