Hydroxyapatite whiskers provide improved mechanical properties in reinforced polymer composites

Abstract

Synthetic hydroxyapatite (HA) whiskers have been utilized as a new, biocompatible reinforcement for orthopedic biomaterials. High-density polyethylene (HDPE) was reinforced with either the synthesized HA whiskers or a commercially available spherical HA powder using a novel powder processing technique that facilitated uniform dispersion of the reinforcements in the matrix prior to compression molding. Composites were processed for up to 60 vol % HA whiskers and up to 50 vol % spherical HA. The mechanical properties of the new composite biomaterials were examined by uniaxial tensile tests. As expected, increased volume fraction of either reinforcement type over 0-50 vol % resulted in increased elastic modulus, a maximum in ultimate tensile stress, and decreased work to failure. Composites reinforced with HA whiskers had higher elastic modulus, ultimate tensile strength, and work to failure relative to composites reinforced with spherical HA. Thus, HA whisker-reinforced HDPE composites possessed improved mechanical properties over those reinforced with spherical HA. HA whisker-reinforced composites were anisotropic due to alignment of the whiskers in the matrix during processing.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

“…52, 160,168,[291][292][293][294][295] 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. 296 What's more, experimental results of these biocomposites indicate favorable cell-material interactions with increased cell activities as compared with each polymer alone.…”

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…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].…”

Crystallographic texture in pulsed laser deposited hydroxyapatite bioceramic coatings

“…These textures are believed to significantly impact the biological and biomechanical performance of hard tissues [22,24]. Texturing has also been observed in synthetic HA, which is commonly coated onto metallic implants in dentistry and orthopedics to improve implant integration with adjacent bone tissue [25][26][27]. Despite the fact that crystallographic texture is one of the dominant features that determine the properties of polycrystalline ceramics and is commonly observed in naturally occurring HA, its impact on the mechanical properties and bioactivity of HA-coated implants has so far received very little attention.…”