An investigation of siloxane cross-linked hydroxyapatite–gelatin/copolymer composites for potential orthopedic applications

Abstract

Causes of bone deficiency are numerous, but biomimetic alloplastic grafts provide an alternative to repair tissue naturally. Previously, a hydroxyapatite-gelatin modified siloxane (HAp-Gemosil) composite was prepared by cross-linking (N, N′-bis[(3-trimethoxysilyl)propyl]ethylene diamine (enTMOS) around the HAp-Gel nanocomposite particles, to mimic the natural composition and properties of bone. However, the tensile strength remained too low for many orthopedic applications. It was hypothesized that incorporating a polymer chain into the composite could help improve long range interaction. Furthermore, designing this polymer to interact with the enTMOS siloxane cross-linked matrix would provide improved adhesion between the polymer and the ceramic composite, and improve mechanical properties. To this end, copolymers of L-Lactide (LLA), and a novel alkyne derivatized trimethylene carbonate, propargyl carbonate (PC), were synthesized. Incorporation of PC during copolymerization affects properties of copolymers such as molecular weight, Tg, and % PC incorporation. More importantly, PC monomers bear a synthetic handle, allowing copolymers to undergo post-polymerization functionalization with graft monomers to specifically tailor the properties of the final composite. For our investigation, P(LLA-co-PC) copolymers were functionalized by an azido-silane (AS) via copper catalyzed azide-alkyne cycloaddition (CuAAC) through terminal alkyne on PC monomers. The new functionalized polymer, P(LLA-co-PC)(AS) was blended with HAp-Gemosil, with the azido-silane linking the copolymer to the silsesquioxane matrix within the final composite. These HAp-Gemosil/P(LLA-co-PC)(AS) composites were subjected to mechanical and biological testing, and the results were compared with those from the HAp-Gemosil composites. This study revealed that incorporating a cross-linkable polymer served to increase the flexural strength of the composite by 50%, while maintaining the biocompatibility of HAp-Gemosil ceramics.

Support for the initial attachment, growth and differentiation of MG-63 cells: a comparison between nano-size hydroxyapatite and micro-size hydroxyapatite in composites

“…27 In many other studies, the addition of HA to various materials has improved the growth of bone cells. For example, admixing HA nanoparticles into the poly-(vinyl alcohol) (PVA) hydrogel increases the adhesion and proliferation of human SV40 osteoblasts compared with the pure hydrogel, and this effect is further enhanced by combining HA with Fe 2 O 3 .…”

The role of temperature in forming sol–gel biocomposites containing polydopamine

“…The testing procedure for the biaxial flexure strength was also performed according to methods established in our previous publication. 5 Briefly, disk samples (11 mm diameter by 2.7 mm thickness) of each group were prepared in Teflon molds. The upper and lower surfaces were polished in order to obtain parallel surfaces.…”

“…4 This trend was also observed in a modified HAp-Gemosilcomposite utilizing a biodegradable polymer based on L -lactide to improve the flexural strength. 5 Though the flexural strength was indeed increased, the polymer toughened HAp-Gemosil composites were plagued by poor adhesion between the hydrophilicHAp-Gel and the hydrophobicpolymer, leading to a loss in the compressive strength. Good adhesion between components of a blend is necessary in order to maintain good mechanical properties and avoid creating internal loci which are prone to mechanical failure.…”

In-situ hybridization of calcium silicate and hydroxyapatite-gelatin nanocomposites enhances physical property and in vitro osteogenesis

“…The compressive strength was determined from the maximum strength value on the stress-strain curve. The testing procedure for the biaxial flexure strength was also performed according to Dyke [21]. Briefly, disk samples of each group were prepared in Teflon molds.…”