Formation and properties of a synthetic bone composite: Hydroxyapatite–collagen

Abstract

Composites composed of microcrystalline calcium-deficient hydroxyapatite (HAp) and collagen were formed at 38 degrees C via an acid-base reaction between calcium phosphate precursors in the presence of a collagen matrix. Formation of composites having HAp:collagen weight ratios of 4.5:1, 11:1, and 22:1, along with that of pure mineral were investigated. Isothermal calorimetry and X-ray diffraction indicated complete reaction within 5 h resulting in hardened monoliths. The rate of HAp formation increased with an increase in the proportion of collagen present. Electron microscopy indicated that the acceleratory effect of collagen was associated with the provision of nucleation sites for HAp crystallization. Analysis of the solution chemistry also showed that collagen affected the calcium and phosphate concentrations and the pH. While collagen was shown to effect the kinetics of HAp formation, the rate limiting step, as shown by X-ray diffraction and solution chemistry, was the dissolution of the acidic calcium phosphate precursor, CaHPO4. Preliminary mechanical data indicated that the Young's modulus, yield strength, and work to fracture were at the lower end of the range of those values reported for bone. The porosities observed in these composites suggest that they might be osteoinductive while their compositions should allow their eventual resorption. Thus, microstructure, kinetics, and mechanical data suggest that these composites might be suitable as bone substitutes which form in vivo.

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…Such syntheses were denoted as ''biologically inspired'' which means they reproduce an ordered pattern and an environment very similar to natural ones [594][595][596]. The biologically inspired biocomposites of collagen and calcium orthophosphates (mainly, apatites) for bone substitute have a long history [29,364,499,[597][598][599][600][601][602][603][604][605][606][607][608][609][610][611][612][613][614][615] and started from the pioneering study by Mittelmeier and Nizard [616], who mixed calcium orthophosphate granules with a collagen web. Such combinations were found to be bioactive, osteoconductive, osteoinductive [29,585,[617][618][619] and, in general, artificial grafts manufactured from this type of the biocomposites are likely to behave similarly to bones and be of more use in surgery than those prepared from any other materials.…”

“…CDHA crystals were found to nucleate on the collagen fibril network, giving a material with the mechanical properties weaker than those reported for bone. More to the point, these biocomposites were without the nanostructure similar to that of bone [599,623]. The oriented growth of OCP crystals on collagen was achieved by an experimental device in which Ca 2?…”

“…Besides, collagen might be incorporated into calcium orthophosphate cements [599,623,634]. Typically, the type I collagen sponge is presoaked in PO 4 3--containing a highly basic aqueous solution and then is immersed into a Ca 2?…”

Physical properties and cellular responses to crosslinkable poly(propylene fumarate)/hydroxyapatite nanocomposites

“…However, it is very brittle and cannot be applied to the load-bearing site directly [3][4][5]. To overcome these limitations, HA has been incorporated with natural biomacromolecules such as collagen [6][7][8] and gelatin [9,10], or synthetic polymers such as poly (α-hydroxyl acids) [11][12][13][14][15], poly (ε-caprolactone) (PCL) [16,17], polyamide [18], and polymethylmethacrylate (PMMA) [19] to prepare composites using a variety of methods including surface coating, grafting, direct mixing, and biomimetic precipitation [10,11,[20][21][22][23]. Particularly, polymer/HA nanocomposites have improved mechanical properties and enhanced cell attachment, spreading, and proliferation on their surfaces by adding nano-sized HA to modify the polymer's characteristics and/or strengthen the polymer matrix [24,25].…”

Effect of Geometrical Structure on the Biodegradation of a Three-Dimensionally Perforated Porous Apatite/Collagen Composite Bone Cell Scaffold

“…[1][2][3][4][5][6][7][8][9] Kikuchi et al [10][11][12][13] prepared bone-like nano-structural composites consisting of collagen and hydroxyapatite by precipitation. The composites had excellent biocompatibility and mechanical properties after being implanted in a dog, generating osteoclast-like cells within a week, and new bone was formed on the composite by osteoblast cells.…”