Mechanical and morphologic investigation of the tensile strength of a bone-hydroxyapatite interface

Abstract

For load-bearing calcium-phosphate biomaterials, it is important to understand the relative contributions of direct physical-chemical bonding vs. mechanical interlocking to interfacial strength. In the limit of a perfectly smooth hydroxyapatite (HA) surface, a tensile test of the bone-HA interface affords an opportunity to isolate the bonding contribution related to HA surface chemistry alone. This study measured the bone-HA interfacial tensile strength for highly polished (approximately 0.05 micron alumina) dense HA disks (5.25 mm in diameter, 1.3 in mm thickness) in rabbit tibiae. Each of five rabbits received four HA disks, two per proximal tibia. Pull-off loads ranged from 3.14 +/- 2.38N at 55 days after implantation to 18.35 +/- 11.9N at 88 days; nominal interfacial tensile strengths were 0.15 +/- 0.11 MPa and 0.85 +/- 0.55 MPa, respectively. SEM of failed interfaces revealed failures between HA and bone, within the HA itself and within adjacent bone. Tissue remnants on HA were identified as mineralized bone with either a lamellar or trabecular structure. Oriented collagen fibers in the bone intricately interdigitated with the HA surface, which frequently showed breakdown at material grain boundaries and a rougher surface than originally implanted. Mechanical interlocking could not be eliminated as a mode of tissue attachment and contribution to bone-HA bonding, even after implanting an extremely smooth HA surface.

Comparative Study of Microstructures and Material Properties in the Vacuum and Spark Plasma Sintered Ti-Calcium Phosphate Composites

“…Several studies have demonstrated that BCP is biocompatible with hard tissues and exhibits osteo-conductive properties. [1][2][3][4][5] BCP has been shown to form a direct bond with surrounding tissue after bone implantation. However, it has very poor mechanical properties, which severely limits its use in load-bearing implant applications.…”

A novel in vivo method for quantifying the interfacial biochemical bond strength of bone implants

“…titanium (Albrektsson et al 1981), titanium alloy (Takatsuka et al 1995), surface chemistrymodified c.p. titanium (Skripitz & Aspenberg 1998) and hydroxyapatite-coated implants (Edwards et al 1997). Our recent series of investigations on anionincorporated (sulphur or phosphorus) and cationincorporated (calcium or magnesium) titanium implants indirectly verified biochemical bonds in animal models (Sul 2003;Sul et al 2004Sul et al , 2005Sul et al , 2006Sul et al , 2008.…”

Effect of Yttria on the Phase Formation and Sintering of HA-Al2O3Biocomposites

“…Bioceramics of naturally derived biological apatites are more economic. Extensive studies have indicated that HA is biocompatible with hard tissues of human beings and exhibits osteoconductive properties [4][5][6][7].…”