Chitosan has been explored as a potential component of biomaterials and scaffolds for many tissue engineering applications. Hybrid materials, where organic and inorganic networks interpenetrate at the molecular level, have been a particular focus of interest using 3-glycidoxypropyl trimethoxysilane (GPTMS) as a covalent crosslinker between the networks in a sol-gel process. GPTMS contains both an epoxide ring that can undergo a ring opening reaction with the primary amine of chitosan and a trimethoxysilane group that can co-condense with silica precursors to form a silica network. While many researchers have exploited this ring-opening reaction, it is not yet fully understood and thus the final product is still a matter of some dispute. Here, a detailed study of the reaction of GPTMS with chitosan under different pH conditions was carried out using a combination of solution state and solid state MAS NMR techniques. The reaction of GPTMS with chitosan at the primary amine to form a secondary amine was confirmed and the rate was found to increase at lower pH. However, a side-reaction was identified between GPTMS and water producing a diol species. The relative amounts of diol and chitosan-GPTMS species were 80 and 20% respectively and this ratio did not vary with pH. The functionalisation pH had an effect on the mechanical properties of 65 wt% organic monoliths where the properties of the organic component became more dominant. Scaffolds were fabricated by freeze drying and had pore diameters in excess of 140 mm, and tailorable by altering freezing temperature, which were suitable for tissue engineering applications. In both monoliths and scaffolds, increasing the organic content disrupted the inorganic network, leading to an increase in silica dissolution in SBF. However, the dissolution of silica and chitosan was congruent up to 4 weeks in SBF, illustrating the true hybrid nature resulting from covalent bonding between the networks.

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Inorganic/organic sol–gel hybrids have nanoscale co-networks of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation in tissue engineering applications.

Hybrid materials, with co-networks of organic and inorganic components, are increasing in popularity due to their tailorable degradation rates and mechanical properties. To increase mechanical stability, particularly in water, covalent bonding must occur between the components. This can be introduced using crosslinking agents such as 3-glycidoxypropyl trimethoxysilane (GPTMS). Attachment of GPTMS to polymers in aqueous conditions is hypothesized to occur by opening of the epoxide ring by nucleophiles on the polymer chain. Despite side reactions that occur between the epoxide ring of GPTMS and water, a range of NMR techniques showed that the carboxylic acid group of poly(g-glutamic acid) reacted with GPTMS. This result was used to identify the amino acids in gelatin that reacted most rapidly with the GPTMS epoxide ring, confirming that covalent bonding occurred in gelatin-silica hybrid materials. Journal Name RSCPublishing ARTICLEThis journal is

Organic–inorganic hybrid materials composed of co-networks of biodegradable polymer and silica have potential to combine the properties of an elastic organic polymer and inorganic silica. The nanoscale interaction of the co-networks and formation of covalent bonds between them are expected to provide tailored mechanical properties and congruent degradation. Alginate is a natural polymer commonly used in tissue engineering applications due to its good biocompatibility and biodegradability. In this work we present new alginate–silica hybrids prepared through nucleophilic ring opening reaction of 3-glycidoxypropyl trimethoxysilane (GPTMS) by carboxylic groups of alginate and incorporation of this functionalized alginate into the sol–gel process to make a hybrid. The role of the GPTMS is to provide organic/inorganic covalent coupling. The reaction of alginate with GPTMS was followed using NMR, FTIR and ToF-SIMS and the dissolution behaviour, bioactivity and mechanical properties of the resultant alginate–silica hybrid monoliths were evaluated. While mechanical strength was high with values of 110–242 MPa comparable to that of cortical bone, the amount of GPTMS coupling to the alginate was low, with the rest of the GPTMS forming diols or a separate network