This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

https://mech.pg.edu.pl/documents/14057592/14057638/1611.pdf

Fabrication methods of porous metals for use in orthopaedic applications

https://www.tpbin.com/Uploads/Subjects/643149a0-8194-4c67-bf05-73fae6f0d14f.pdf

Development of new metallic alloys for biomedical applications

Bone marrow has been shown to contain a population of rare mesenchymal stem cells that are capable of forming bone, cartilage, and other connective tissues. We examined the effect of cultured autologous mesenchymal stem cells on the healing of critical-sized (twenty-one-millimeter-long) segmental defects in the femora of adult female dogs. Autologous mesenchymal stem cells were isolated from bone marrow, grown in culture, and loaded onto porous ceramic cylinders consisting of hydroxyapatite (65 per cent) and beta-tricalcium phosphate ceramic (35 per cent). The animals were randomly assigned to one of three groups. In Group A (six dogs), a porous ceramic cylinder that had been loaded with autologous mesenchymal stem cells was implanted in the defect. In Group B (six dogs), a ceramic cylinder that had not been loaded with cells was placed in the defect. In Group C (three dogs), the defect was left untreated (no ceramic cylinder was implanted). Radiographs were made immediately after the operation and at four-week intervals. At sixteen weeks, the animals were killed, the involved femora were removed, and undecalcified histological sections from the defects and adjacent bone were prepared. Histological and histomorphometric studies were carried out to examine the healing of the defects and the formation of bone in and around the ceramic implants. Atrophic non-union occurred in all of the femora that had untreated defects, and only a small amount of trabecular bone formed at the cut ends of the cortex of the host bone in this group. In contrast, radiographic union was established rapidly at the interface between the host bone and the implants that had been loaded with mesenchymal stem cells. Numerous fractures, which became more pronounced with time, developed in the implants that had not been loaded with cells. Histological and morphometric analyses demonstrated that both woven and lamellar bone had filled the pores of the implants that had been loaded with mesenchymal stem cells; the amount of bone was significantly greater (p < 0.05) than that found in the pores of the implants that had not been loaded with cells. In addition, a large collar of bone (mean maximum thickness, 3.14 millimeters) formed around the implants that had been loaded with cells; this collar became integrated and contiguous with callus that formed in the region of the periosteum of the host bone. The collar of bone remodeled during the sixteen-week period of study, resulting in a size and shape that were comparable with those of the segment of bone that had been resected. Callus did not develop around the cortex of the host bone or around the defect in any of the specimens in the other two groups.

The effect of implants loaded with autologous mesenchymal stem cells on the healing of canine segmental bone defects

Biomechanics of cellular solids.

This study evaluated a porous tantalum biomaterial (Hedrocel) designed to function as a scaffold for osseous ingrowth. Samples were characterized for structure, Vickers microhardness, compressive cantilever bending, and tensile properties, as well as compressive and cantilever bending fatigue. The structure consisted of regularly arranged cells having struts with a vitreous carbon core with layers of CVI deposited crystalline tantalum. Microhardness values ranged from 240-393, compressive strength was 60 +/- 18 MPa, tensile strength was 63 +/- 6 MPa, and bending strength was 110 +/- 14 MPa. The compressive fatigue endurance limit was 23 MPa at 5 x 10(6) cycles with samples exhibiting significant plastic deformation. SEM examination showed cracking at strut junctions 45 degrees to the axis of the applied load. The cantilever bending fatigue endurance limit was 35 MPa at 5 x 10(6) cycles, and SEM examination showed failure due to cracking of the struts on the tension side of the sample. While properties were variable due to morphology, results indicate that the material provides structural support while bone ingrowth is occurring. These findings, coupled with the superior biocompatibility of tantalum, makes the material a candidate for a number of clinical applications and warrants further and continued laboratory and clinical investigation.

Structure, metallurgy, and mechanical properties of a porous tantalum foam.

The need for alternatives to autogenous bone grafts is widely recognized. This study compared the torsional strength of canine femora 1 year after grafting with one of three forms of a collagen/hydroxyapatite/tricalcium phosphate bone grafting material (COLLAGRAFT15), autogenous bone, or no graft. The groups were compared to each other and to the unoperated contralateral femora. Results of torsional testing were evaluated for torsional strength, torsional displacement, total energy to fracture and White fracture mode. Data analysis showed lower torsional strength of the operated vs. unoperated femora with the exception of morsellized COLLAGRAFT15 material, which had higher strength. However, the only difference in the operated groups was that the morsellized COLLAGRAFT15 had greater strength than several groups including the autogenous bone group. There was no difference found in angular displacement between any of the groups. However, there was a difference in the energy to fracture in both strip forms of the COLLAGRAFT15. The final conclusion is that in this model, grafting with COLLAGRAFT15 provided torsional properties at one year postoperatively at least equivalent to autogenous bone. © 1994 John Wiley & Sons, Inc.

Torsional properties of healed canine diaphyseal defects grafted with a fibrillar collagen and hydroxyapatite/tricalcium phosphate composite.

This study was designed to evaluate the biomechanical pull-out strength and mechanism of pull-out in cantilever bending of the Synthes cervical spine locking plate (CSLP) using a porcine spine model of four different length 4.35 mm diameter expansion screws and the 3.5 mm bicortical cancellous screw with and without end plates removed. Ten constructs using each screw length were tested in single cycle cantilever bending by loading the free end of the plate in both flexion and extension, with vertebral end plates both intact and violated. No discernable yield during loading in extension was observed while a yield was observed in flexion. Loads at specific displacements were greater once the end plates had been violated. The load experienced by unicortical screws of long constructs using cantilever bending was greater with the end plate violated. This was not expected, but is explained by the viscoelastic behavior of bone. This deformation mechanism accounts for the higher loads necessary for failure when the end plates are removed. In light of these results, the addition of a 16 mm or longer 4.35 mm expansion screw seems warranted, keeping in mind that the 18 mm and longer screws have some threat of penetrating the posterior cortex of the vertebral body.

Lance D. Dillon

Papers

Structure, metallurgy, and mechanical properties of a porous tantalum foam.

Torsional properties of healed canine diaphyseal defects grafted with a fibrillar collagen and hydroxyapatite/tricalcium phosphate composite.

Biomechanical pull-out strength of the cervical spine locking plate (CSLP) expansion screws