Microstructural characteristics of calcium hydroxyapatite/poly‐ l‐lactide based composites

Abstract

Besides its high osteoinductive properties, hydroxyapatite (HAp) exhibits a relatively low mechanical strength. In order to improve the mechanical properties and reliability of HAp based composites, the addition of selected polymers is highly recommended. The main objective of this work is to study the microstructural characteristics of HAp/poly-L-lactide (PLLA) composites obtained by cold or hot processing. The composites were prepared from a mixture of a chloroform solution of poly-L-lactide with granulated HAp. After elimination of chloroform by vacuum evaporation, dense compacts were obtained by cold or hot pressing. The pressing pressure ranged from 98.10 to 294.3 MPa for both cold and hot pressing. The hot pressing was performed in the temperature region 293-457 K for a time period of 15-60 min. Depending on the PLLA amount and the pressing procedure it is possible to obtain highly porous or nearly fully dense composites. The scanning electron microscopy examination of fracture as well as of free surfaces revealed that the final porosity and wetting are affected to a great extent by the synthesis conditions and amount of polymer added. An increase in temperature to 457 K for a longer period of time results in fully dense compacts. The formation of a nearly continuous polymer network that leads to the hardening of HAp has also been observed. However, it should be pointed out that some layers of HAp may be free of polymer film since PLLA penetrates more deeply into the porous HAp.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

“…The latter was explained by increased compaction and penetration of pores at higher pressure in conjunction with a greater fluidity of the polymer at higher temperatures. The combination of high pressures and temperatures was found to decrease porosity and guarantee a close apposition of a polymer to the particles, thereby improving the compressive strength 286 and fracture energy 324 of the biocomposites. The PLLA/HA biocomposites' scaffolds were found to improve cell survival over plain PLLA scaffolds.…”

“…The desirable mechanical properties of polymers compensate for a poor mechanical behavior of calcium orthophosphate bioceramics, while, in turn, the desirable bioactive properties of calcium orthophosphates improve those of polymers, expanding the possible uses of each material within the body. [158][159][160][286][287][288][289][290] Namely, polymers have been added to calcium orthophosphates in order to improve their mechanical strength, 158,286 and calcium orthophosphate fillers have been blended with polymers to improve their ©2 0 1 1 L a n d e s B i o s c i e n c e .…”

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…The latter was explained by increased compaction and penetration of pores at higher pressure, in conjunction with a greater fluidity of the polymer at higher temperatures. The combination of high pressures and temperatures was found to decrease porosity and guarantee a close apposition of a polymer to the particles, thereby improving the compressive strength [228] and fracture energy [260] of the biocomposites. The PLLA/HA biocomposites scaffolds were found to improve cell survival over plain PLLA scaffolds [261].…”

“…The desirable mechanical properties of polymers compensate for a poor mechanical behavior of calcium orthophosphate bioceramics, while in turn the desirable bioactive properties of calcium orthophosphates improve those of polymers, expanding the possible uses of each material within the body [127][128][129][228][229][230][231]. Namely, polymers have been added to calcium orthophosphates in order to improve their mechanical strength [127,228] and calcium orthophosphate fillers have been blended with polymers to improve their compressive strength and modulus, in addition to increase their osteoconductive properties [48,129,137,[232][233][234][235][236]. Furthermore, biocompatibility of such biocomposites is enhanced because calcium orthophosphate fillers induce an increased initial flash spread of serum proteins compared with the more hydrophobic polymer surfaces [237].…”

The Formation and Characterization of Nanocrystalline Phases by Mechanical Milling of Biphasic Calcium Phosphate/Poly-L-Lactide Biocomposite

“…1) Calcium hydroxyapatite/poly-L-lactide (HAp/PLLA) composite biomaterial belongs to this group of composites that can be successfully implemented in bone tissue reparation due to their osteoconductive and biocompatible properties. [2][3][4] HAp/PLLA consists of a biononresorbable ceramic component (hydroxyapatite, HAp) and a bioresorbable polymer component (poly-L-lactide, PLLA). The structure of the HAp/polymer composite closely imitates natural bone tissues, 5) that enable the successful application of this composite as bone substitute material.…”