Effects of dopamine and a dopamine analog on polydopamine-laced hydroxyapatite gelatin nanocomposites

摘要

Introduction: Hydroxyapatite with low endotoxin gelatin has been developed to mimic the biochemical and biomechanical properties of natural bone (Chang et al., 2003) Recently, polydopamine-laced hydroxyapatite gelatin-calcium silicate (PDHGCS) has been developed to address the processability of the hydroxyapatite nanocomposite for the application of bone regeneration (Ko et al., 2014). Dopamine consisting of two functional groups (catechol and ethyl amine) forms interconnected polymeric network to enhance physical property by increasing long range interactions within the material (Dyke et al., 2014)PI. We hypothesize that either increasing carbon length of amine group in dopamine or using a co-polymer P(LLA-co-PC) functionalized with catechol can further improve the mechanical property of PDHGCS. Methods and Materials: Synthesis of 12C-Dopamine: Synthesis is started with 1,2-dimethoxybenzene from which catechol function group was recovered to form the 12C-dopamine (Fig. 1). Synthesis of P(LLA-co-PC)-catechol: Copolymer was synthesized according to the previously reported method (Jason's 2012 Paper). Catechol-4C-SH was covalent attached to the polymer backbone through thiol-yne" click chemistry (Fig. 2). Preparation of PDHGCS Composites: Briefly, 150 mg Hap-Gel, 100 mg of Ca(OH)2 powder, and a series of predetermined amounts of dopamine or 12C-dopamine and P(LLA-co-PC)-catechol powders were mixed with 383 μL of 62% enTMOS on a -20 °C slab, followed by addition of 40 μL of 7.5% ammonium persulfate solution in room temperature3. The central composite design was used to determine the amount of dopamine and P(LLA-co-PC)-catechol. The mixture was then injected onto a mold to create cylindrical sample for compression tests. Results: The maximum compressive strength (-100 MPa) occurred around dopamine at 5 mg and co-polymer at 12.5 mg. The preliminary outcome suggests that the polymer was not significantly associated with the compress strength, and that the strength was a quadratic function of dopamine (p-value=0.047). Similarly, 12C-dopamine did not significantly increase the mechanical strength of the composite. Discussion and Conclusion: The low endotoxin gelatin can be incorporated into PDHGCS. Dried powder form of 12C-dopamine and P(LLA-co-PC)-catechol does not increase compressive strength of PDHGCS. Whether these constitutes can improve tensile strength remains to be tested. The incorporation of solution form (12C-dopmaine and copolymer) is under investigation. (Supported in part by NIH R01DE022816).