Ca-deficient hydroxyapatite/polylactide nanocomposites with chemically modified interfaces by high pressure consolidation at room temperature

Journal of Materials Science (Impact Factor: 2.37). 12/2010; 45(23):6339-6344. DOI: 10.1007/s10853-010-4543-z


Hydroxyapatite (HAP) is a close synthetic analog of the bone mineral and is often considered as a material for bone graft
substitutes and tissue engineering scaffolds. Despite its attractive bioactive properties low-fracture toughness limits the
use of HAP ceramics to a number of non-load-bearing applications. To obtain a more adequate mechanical behavior, HAP is often
combined with polymers based on lactic and glycolic acids or polycaprolactone using hot pressing. In such composite materials,
the compatibility and bonding strength of HAP–polymer interfaces are critical parameters that must be controlled and improved.
This may be achieved, for example, by covalent immobilization of organic moieties on the ceramic particles surface. In this
work, the surface of calcium-deficient hydroxyapatite (CDHAP) was modified by reaction with hexamethylene diisocyanate (HDI)
in a non-aqueous suspension. Composites of CDHAP–HDI with polylactide (PLA) were high pressure consolidated at room temperature
at 2.5GPa yielding up to 90% theoretical density. The effects of total organic fraction and modification extent on compression
strength were studied. Materials with high extent of modification and high organic content exhibited compressive strength
of ~295MPa, much higher than reported in other studies. These materials are suitable candidates for load bearing orthopedic

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    ABSTRACT: In orthopedic research, increasing attention is being paid to bioresorbable composite materials as an attractive alternative to permanent metal bone healing devices. Typical composites consist of a biodegradable polyester matrix loaded with bioactive calcium phosphate ceramic particles (tricalcium phosphate, TCP or hydroxyapatite, HA) added to improve the biological response and mechanical properties of the neat polymer. The mechanical behavior of such particle-reinforced composites, however, falls far short of the expected performance in high-load bearing situations. Replicating some features of nacre—a strong and tough natural nanocomposite with a very high content of brittle inorganic phase, can pave the way for a new generation of high-strength resorbable bone implants. This chapter will concentrate on the processing of such “bio-inspired” nanocomposites with high calcium phosphate content where the strong ceramic skeleton is toughened by a small amount of continuously dispersed polymer component. To further improve the mechanical properties, manipulating the adhesion at the interface between the ceramic and polymeric nanoscale components was attempted. An original high pressure consolidation method was employed to fabricate dense bulk nanocomposites without exposing them to high processing temperatures. This allows for incorporation of biomolecules that can then be released from the implanted device to enhance bone regeneration (growth factors) or prevent infection (antibacterial drugs). Finally, it is important to evaluate how polymer addition to calcium phosphate influences cell-material or cell–cell interactions because of potential consequences for bone regeneration and vascularization. Towards this goal, CaP-polymer nanocomposites were assessed in monocultures of endothelial cells and osteoblasts and in co-culture thereof as an example of a more complex test system.
    No preview · Chapter · Jan 1970
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    ABSTRACT: The main theme here is to fabricate PLA (poly lactic-acid)/CDHA (carbonated calcium deficient hydroxyapatite) bionanocomposites, where both the constituents are biocompatible and biodegradable with one dimension in nanometer scale. Such materials are important in tissue engineering applications. The bionanocomposite fibers were fabricated via electrospinning. There are two important signatures of this paper. First, CDHA, rather than HA, is added to PLA as the second phase. As opposed to HA, CDHA mimics the bone mineral composition better and is biodegradable. Therefore, PLA/CDHA fibers should have better biodegradability while maintaining a physiological pH during degradation. To the best of our knowledge, this is the first attempt of electrospinning of such a composite. Second, the CDHA nanoparticles were synthesized using the benign low temperature biomimetic technique, the only route available for the retention of carbonate ions in the HA lattice. The structural properties, degradation behavior, bioactivity, cell adhesion, and growth capability of as-fabricated PLA/CDHA bionanocomposites were investigated. The results show that the incorporation of CDHA decreased PLA fiber diameters, accelerated PLA degradation, buffered pH decrease caused by PLA degradation, improved the bioactivity and biocompatibility of the scaffold. These results prove that PLA/CDHA bionanocomposites have the potential in tissue regeneration applications.
    No preview · Article · Mar 2011 · Journal of Materials Science Materials in Medicine
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    ABSTRACT: For several decades, composites made of polylactic acid-calcium phosphates (PLA-CaP) and polylactic acid-co-glycolic acid-calcium phosphates (PLGA-CaP) have seen widespread uses in orthopedic applications. This paper reviews the fabrication aspects of these composites, following the ubiquitous materials science approach by studying "processing-structure-property" correlations. Various fabrication processes such as microencapsulation, phase separation, electrospinning, supercritical gas foaming, etc., are reviewed, with specific examples of their applications in fabricating these composites. The effect of the incorporation of CaP materials on the mechanical and biological performance of PLA/PLGA is addressed. In addition, this paper describes the state of the art on challenges and innovations concerning CaP dispersion, incorporation of biomolecules/stem cells and long-term degradation of the composites.
    No preview · Article · Feb 2012 · Acta biomaterialia
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