Low temperature formation of calcium-deficient hydroxyapatite-PLA/PLGA composites

Abstract

Hydroxyapatite-biodegradable polymer composites have been formed by a low temperature chemical route. Precomposite structures were prepared by combining alpha-Ca(3)(PO(4))(2) (alpha-tricalcium phosphate or alpha-TCP) with poly(L-lactic) acid and poly(DL-lactide-co-glycolide) copolymers. The final composite structure was achieved by in situ hydrolysis of alpha-TCP to Ca(9)(HPO(4))(PO(4))(5)OH (calcium deficient hydroxyapatite or CDHAp) either in solvent cast or pressed precomposites. Hydrolysis was performed at 56 degrees C-a temperature slightly above the glass transition of the polymers. The effects of polymer chemistry, composite formation technique, and porosity on hydrolysis kinetics and degree of transformation were examined with isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and scanning electron microscopy. Calorimetric data and XRD analyses revealed that hydrolysis reactions were inhibited in the presence of the polymers. Isothermal calorimetry indicated the extent of the alpha-TCP to CDHAp transformation in 24 h to be 85% in the solvent cast composites containing PLGA (85:15) copolymer; however, XRD analyses suggested almost complete reaction. The CDHAp formation extent was 26% for the pressed composites containing the same polymer. In the presence of NaCl as a pore generator, 81% transformation was observed for the pressed composites. This transformation occurred without any chemical reaction between the polymer-inorganic components, as determined by Fourier transform infrared spectroscopy. Minimal transformation to CDHAp occurred in composites containing poly(L-lactic) acid.

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…More complex carbonated-FA/PLA porous biocomposite scaffolds are also known [323]. An interesting list of references, assigned to the different ways of preparing HA/poly(a-hydroxyesters) biodegradable composites, might be found in publications by Durucan and Brown [49,324,325]. The authors prepared CDHA/PLA and CDHA/PLGA composites by solvent casting technique with a subsequent hydrolysis of a-TCP to CDHA in aqueous solutions.…”

“…The authors prepared CDHA/PLA and CDHA/PLGA composites by solvent casting technique with a subsequent hydrolysis of a-TCP to CDHA in aqueous solutions. The presence of both polymers was found to inhibit a-TCP hydrolysis, if compared with that of single-phase a-TCP; what is more, the inhibiting effect of PLA exceeded that of PLGA [49,324,325]. The physical interactions between calcium orthophosphates and poly(ahydroxyesters) might be easily seen in Fig.…”

“…In another study, CDHA/poly(a-hydroxyester) composites were prepared by a low-temperature chemical route [324]. In that study, pre-composite structures were prepared by combining a-TCP with PLA, PLGA and copolymers thereof.…”

“…The final biocomposite structure was achieved by in situ hydrolysis of a-TCP to CDHA performed at 56°C either in solvent cast or pressed precomposites. That transformation occurred without any chemical reaction between the polymer and calcium orthophosphates, as it was determined by FTIR spectroscopy [324].…”

Biodegradable Poly(Lactic Acid)/Multiwalled Carbon Nanotube Nanocomposite Fabrication Using Casting And Hot Press Techniques

“…Poly(lactic acid) (PLA) is extensively used in the production of surgical thread, implant materials, controlled drug delivery systems, and minimally invasive surgery due to its unique properties such as biodegradability, biocompatibility, and shape-memory qualities [1][2][3][4][5][6]. Poly-L(lactic acid) (PLLA), on the other hand, lacks sufficient mechanical properties for medical applications.…”