Effects of geometry of hydroxyapatite as a cell substratum in BMP-induced ectopic bone formation

Abstract

Three different types of porous hydroxyapatite with pore sizes of 100-200 micrometer in diameter-porous particles of hydroxyapatite (PPHAP), porous blocks of hydroxyapatite (PBHAP), and honeycomb-shaped hydroxyapatite (HCHAP)-were compared in terms of their abilities to induce osteogenesis when implanted subcutaneously with recombinant human BMP-2 into rats and extracted at 1, 2, 3, and 4 weeks. Histologically, direct bone formation occurred in PPHAP and PBHAP while only endochondral ossification took place in HCHAP. Interestingly, cartilage in the central zones and bone in the orifice zones of the tunnels of the HCHAP were observed at 2 weeks. After 3 weeks, the cartilage disappeared and bone formation occurred throughout the inner surface of the tunnels of the HCHAP, always leaving space for capillaries within the tunnels. Alkaline phosphatase activity and osteocalcin content were the highest in HCHAP among the three hydroxyapatite implants. These results clearly indicate that BMP-induced bone formation is highly dependent on the geometry of the carrier, which provides feasible structural factors for vascularization.

Periodontal repair following implantation of beta-tricalcium phosphate with different pore structures in class III furcation defects in dogs

“…Biomaterial characteristics, such as porosity, density, and crystallinity, affect the outcome of periodontal regeneration [6][7][8][9][10][11] . Several studies have reported that porous structures enhance bone formation in bone defects [12][13][14][15][16] . Furthermore, it has been shown that pore size has an effect on vascularization 17,18) .…”

Advancements in three-dimensional titanium alloy mesh scaffolds fabricated by electron beam melting for biomedical devices: mechanical and biological aspects

“…In the case of bio-inert materials, porosity and pore size generally do not affect osteogenesis, but with regard to bioactive materials, porosity and pore size significantly influence osteogenesis [47][48][49]. It is pertinent to keep in mind that porosity is not the cause for hypoxia, which is considered responsible for encouraging osteochondral ossification [1,50]. During design, degree of porosity and pore size are important considerations from the per-spective of long term structural support.…”

Bone Engineering: A Matter of Cells, Growth Factors and Biomaterials

“…At the cell level, substrates of this kind must have specific biochemical (molecular) properties, physicochemical characteristics (surface free energy, charge, hydrophobicity, and so on), and a specific geometric conformation (they must be three dimensional and show interconnected porosity) (Jin, 2000). From the biomaterial point of view, the scaffolds used for bone engineering purposes have to meet a number of criteria, including (1) biocompatibility (nonimmunogenicity and nontoxicity); (2) resorbability (showing resorption rates commensurate with the bone formation rates); (3) preferably radiolucency (to allow the new bone to be distinguished radiographycally from the implant); (4) osteoconductivity; (5) mechanical properties to match those of the tissues at the site of implantation; (6) easy to manufacture and sterilize; and they must be (7) easy to handle in the operating theater, preferably without requiring any preparatory procedures (in order to limit the risk of infection).…”