Abstract
In order to improve the interfacial bonding between hydroxyapatite (HAP) and poly-l-lactic acid (PLLA), 2-Carboxyethylphosphonic acid (CEPA), a phosphonic acid coupling agent, was introduced to modify HAP nanoparticles. After this. the PLLA scaffold containing CEPA-modified HAP (C-HAP) was fabricated by selective laser sintering (frittage). The specific mechanism of interfacial bonding was that the PO32− of CEPA formed an electrovalent bond with the Ca2+ of HAP on one hand, and on the other hand, the –COOH of CEPA formed an ester bond with the –OH of PLLA via an esterification reaction. The results showed that C-HAP was homogeneously dispersed in the PLLA matrix and that it exhibited interconnected morphology pulled out from the PLLA matrix due to the enhanced interfacial bonding. As a result, the tensile strength and modulus of the scaffold with 20% C-HAP increased by 1.40 and 2.79 times compared to that of the scaffold with HAP, respectively. In addition, the scaffold could attract Ca2+ in simulated body fluid (SBF) solution by the phosphonic acid group to induce apatite layer formation and also release Ca2+ and PO43− by degradation to facilitate cell attachment, growth and proliferation.
Highlights
Biopolymers and bioceramics composite materials have been widely applied to bone tissue engineering [1], which shows some features of natural bone in the main composition
HAP was dispersed in ethanol, and Carboxyethylphosphonic acid (CEPA) was added with a high-intensity ultrasonic probe for ultrasonic oscillations, and the mixture of HAP and CEPA was of a 1:1 molar ratio
HAP was modified by a CEPA phosphonic acid coupling agent acting as a cross-linking
Summary
Biopolymers and bioceramics composite materials have been widely applied to bone tissue engineering [1], which shows some features of natural bone in the main composition. The composite materials were designed to mimic the microstructure of cancellous and provide an ideal environment for bone regeneration. Poly-l-lactic acid (PLLA)/hydroxyapatite (HAP) becomes one of the representative composite materials, as they combine the bone-binding capabilities of HAP and the biocompatibility of PLLA [2,3]. Incorporating HAP into the PLLA matrix would improve cell proliferation and viability and neutralize the acidic degradation products released from. The weak interfacial bonding between HAP and PLLA is an obvious problem, which would bring about a low-stress failure at the interface, resulting in the deterioration of mechanical properties [6,7]. Coupling agents have been widely used to improve the interfacial bonding between biopolymers and bioceramics. Khosravi et al [8] modified montmorillonite (MMT) with coupling agent 3-glycidoxypropyltrimethoxysilane for good adhesion with PLA and reported that the –OH of 3-glycidoxypropyltrimethoxysilane reacted with the –OH of the montmorillonite surface forming
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