Preparation And Characterization Of Injectable Polyphosphazene/Gelatin Composite Hydrogel

Hydrogels are widely recognized as useful materials for a wide range of tissue engineering and biopharmaceutical applications due to their excellent properties, such as excellent biocompatibility, favorable biodegradability and low mechanical irritation of surrounding tissues when they are implanted in vivo.In this paper, a kind of injectable polyphosphazene/gelatin composite hydrogel scaffold was obtained through two paths. It was proposed to crosslink gelatin by using of functionalized polyphosphazene instead of small molecular agents, such as glutaraldehyde etc., in order to obtain biocompatible and physiologically stable polymer/natural macromolecules composite hydrogel materials.One route was that parahydroxybenzaldehyde (PHBA) was linked to the main chain of poly(dichloro)phosphazene (PDCP) to substitute part of phosphorus chlorine bonds (P-Cl), and methoxy ethanol substituted for the remaining P-Cl. Polyphosphazene of controllable aldehyde ratio was gained,and the water-solubility chould be adjusted by altering the ratio of the two substituents. Then, an injectable hydrogel was synthesized with gelatin contained amino side groups using the polyphosphazene with aldehyde groups as crosslinkerThe other was that poly(tyramine-co-methoxyethoxyl) phos-phazene (PTMEP) was synthesized; meanwhile the phenolic hydroxyl (Ph) groups were grafted onto the chain of gelatin to gain gelatin derivatives by the chemical reaction between tyramine or p-hydroxyphenylpropionic acid (HPA) and carboxyl groups or amino groups of gelatin; then PTMEP and gelatin derivatives were crosslinked via horseradish peroxidase (HRP)/H2O2-catalyzed reaction in order to obtain an injectable, composite hydrogel scaffold.Poly(4-aldehyde-benzoxyl-co-methoxyethoxyl)phosphazene (PABMEP) and PTMEP were prepared successfully. And the chemical structure and molecular weight were characterized by FT-IR,1H NMR and measurement of intrinsic viscosity. PABMEP and gelatin, which were dissolved in phosphate buffer saline (PBS) respectively, were mixed for gelation. The gelation time and water absorption rate (WAR) were tuneable by changing substituted ratio of aldehyde group, the concentration and mixing proportion. It was expected to obtain an injectable polyphosphazene/gelatin composite hydrogel through the second pathway. In theory, the control of gelation time, mechanical properties and crosslinking uniformity would be easily achieved by changing the concentration of HRP and H2O2 and the propotion. This part of experiment is still undergoing.Osteogenic biological activity of poly [(alanino ethyl ester)x (glycino ethyl ester)2-x] phosphazene (PAGP) was evaluated via biomineralization in stimulated body fluid (SBF). According to the feature that phosphorous (P) and nitrous (N) atoms in PAGP were dragged to fiber surface with solvent evaporation during the solidification of nanofibers, and the PAGP nanofibers were prepared by electrospinning after dissloving Trifluoroethanol (TFE), tetrahydrofuran (THF) and chloroform (TCM). Effects of different element composition of nanofibers' surface on mineralization were researched by measurement of water contact angle (WCA), X-ray photoelectron spectroscopy (XPS), X-ray diffreaction spectroscopy (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), fourier transform infrared spectroscopy (FTIR).Compared with the biomineralized property of poly(L-lactic acid) (PLLA), it was demonstrated that polyphosphazene materials possessed better biomimetic mineralized property. The P/N element enrichment of nanofibrous nanofibers' surface could affect the minarelization. In supersaturated SBF, the the calcium hydrogen phosphate dihydrate (DCPD) was firstly formed after the induction period, and the DCPD would be gradually transformed into hydroxyapatite.