Abstract: Stimulation of bone healing through local application of growth factors from implants
may improve the clinical outcome in fracture treatments. However, the growth factors in reconstructive application require supraphysiologic dosing and considerable expense while hampering their clinical application. Genetic modification of mesenchymal stem cells (MSCs) to both produce and respond to osteogenic factors may have potential for use in enhancing bone healing. In this study, MSCs were genetically modified by a recombinant adenoviral containing the gene for human bone morphogenetic protein 2 (hBMP-2). The gene-transduced cells were
incorporated with a porous beta-tricalcium phosphate (TCP) as a novel complex. We investigated osteogeneic potential of gene-transduced MSCs/ceramic and the ability of the complex on facilitating bone formation in a radius segmental defect of rabbits. In vitro results showed that there were apparent hBMP2 gene expression and protein synthesis in MSCs with hBMP2 stably transfection, whereas negative expression of hBMP2 in controls. Histological studies demonstrated that gene-transfected MSCs/ceramic composite appeared an ability of heterotopic osteogenesis. In the segmental bone defects, endochondrial ossification at fracture sites was found in both transfected and untransfected MSCs-ceramic composites. While the composite with hBMP2 transfection showed the earliest and the most effective healing of the segmental bone defects both radiographically and morphologically. Our results show that genetically modified MSCs/ceramics
had enhanced osteogeneic capacity relative to unmodified MSCs or only ceramic implants. This study suggests that use of cell-and gene-activated bioceramics may offer promise for molecular design of implants to induce osteogenesis and enhance bone regeneration.
Abstract: Various recombinant growth factors have been used for promoting osteoblastic differentiation cascade. To compare the growth/differentiation factor-5 (GDF-5) and bone morphogenetic protein-2 (BMP-2) in the in vivo osteogenic potential of bone marrow mesenchymal stem cells (MSCs), the bone formation was assessed by rat subcutaneous implantation of 5 kinds of hydroxyapatite (HA) implants; namely GDF/HA composites, BMP/HA composites, MSCs/HA
composites and the MSCs/HA composites supplemented with recombinant mouse GDF-5 (GDF/MSCs/HA) or recombinant human BMP-2 (BMP/MSCs/HA). Neither the GDF/HA nor the BMP/HA composites exhibited any bone formation at any time after implantation. At both 2 and 4 weeks after implantation, obvious de novo bone formation together with active osteoblasts was seen histologically in many pores of the GDF/MSCs/HA and BMP/MSCs/HA composites.
The GDF/MSCs/HA and BMP/MSCs/HA composites also showed high alkaline phosphatase (ALP) and osteocalcin expression determined at both the protein and gene levels. Compared with GDF/MSCs/HA, the BMP/MSCs/HA composites exhibited excellent osteogenesis with relatively early osteoblastic phenotype expression. These findings indicate that the two growth factors synergistically enhance de novo bone formation capability of MSCs/HA composites and the importance of ceramic surface to retain and to deliver the molecules of growth factors for the cell differentiation and maturation.
Abstract: The incorporation of magnesium ions into the hydroxyapatite structure, which is of great interest for the developing of artificial bone, was performed starting from a wet chemical synthesis using magnesium chloride as Mg source. Different doping extents were attempted, four powders were produced and characterized in term of morphology, composition, solubility, thermal resistance,etc. in comparison with stoichiometric HA. In vitro tests with mesenchimal stem cells (MSCs) and human osteoblast like cells MG-63 cells were performed with the powder characterized
with a biological-like doping of 5%Mg. The same powder was used, in form of granules, to carry out in vivo test by filling a defect in the femur on New Zealand White rabbits. All the tests showed better performance of the Mg doped apatite compared to stoichiometric HA, in agreement with the chemico-physical features of the material.
Abstract: This study aimed to investigate the effects of hydroxyapatite on bonding strength between dental luting cement and human teeth. In the previous study, bonelike forming ability by mixing hydroxyapatite with several bone cements was reported in a protein-free acellular simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. Therefore in this experiment, we assumed that if bonelike apatite layer could form between dental luting cement and human teeth, the bonding strength between the two would improve. In addition, we expected the HA
mixed dental luting cement to improve the physical properties. Fuji I glass ionomer and Relyx™ glass ionomer cement were the selected dental luting cements and the film thickness, setting time and compressive strength were measured mixing various concentrations of hydroxyapatite. Glass ionomer cement with the most superior physical properties(Fuji I ; 20% hydroxyapatite, Relyx™ ; 15% hydroxyapatite) was immersed in the simulated body fluid for three weeks and the surface was
observed under SEM after measuring the bonding strength. As the concentration of HA increased, the film thickness of hydroxyapatite-glass ionomer cement decreased, the setting time increased, and the compressive strength increased. The most noteworthy results were that bonding strength increased, and that bonelike apatite formed on the tooth surface when observed under SEM.
Abstract: The purpose of this study was to compare the bone regenerative effect of calcium
phosphate glass and glass-ceramics in the system of CaO-CaF2-P2O5-MgO-ZnO, which is already reported that promoted the bone-like tissue formation in vitro and formed new bone in Sprague-Dawley rats. We prepared calcium phosphate glass and glass-ceramics with Ca/P ratio of 0.6 using the system CaO-CaF2-P2O5-MgO-ZnO and subsequently milled to 400 µm. 4×4 mm 1-wall intrabony defects of six beagle dogs were surgically created and used in this study. 8 weeks after
transplantation of the prepared calcium phosphate glass and glass-ceramics in the experimental group 1 and 2, respectively, the animals were sacrificed. No root resorption or ankylosis were observed in all groups. It can be examined that the prepared glass-ceramics were more effective in alveolar bone regeneration with statistical signigicant difference. In cementum regeneration, both the prepared glass
and glass-ceramics showed significantly different effect. However, there were no statistical significant difference neither in glass nor glass-ceramics in the amounts of junctional epithelium migration and connective tissue adhesion. Further study is required to control the flowability as well as reduce the absorption rate in vivo.
Abstract: The purpose of this study was to estimate hard tissue formation in two types of porous columnar hydroxyapatite (HA) in order to use as a scaffold for regeneration of dentine-pulp complex. Hard tissue formation in the columnar HA scaffold with a hollow center was compared to that in the columnar HA scaffold without a hollow center. The scaffolds were immersed in hyaluronic acid sodium salt solution and were soaked in bone marrow cell suspension. They were respectively
implanted into dorsal subcutis of rats for 4 weeks. Serially sectioned paraffin specimens were made and observed histologically. The scaffolds with a hollow center showed new hard tissue formation in many pores between the superficies and the wall of hollow. On the other hand, in the scaffolds without a hollow center, hard tissue formation was observed in only a few pores in the area near the
external superficies. The results of this study suggested that the supply of nutrition and bioactive substance from the surrounding tissue were indispensable for differentiation of bone marrow cells and formation of new hard tissue in scaffold. A large contact area of a scaffold to the surrounding tissue may contribute to nutrition supply into the pores.
Abstract: The objective of this study was to assess the behaviour of nacre pinctada margaritifera (PM) in subcutaneous site in rat and to taste the influence of sterilization on nacre properties. PM discs or powder were sterilized at 120 degree celsius in one bar of pressure during 20 minutes or with gamma ray or in alcohol (70 %) .PM discs or powder were implanted for 3, 6 and twelve weeks in subcutaneous site in rat. The methods used to assess behaviour of PM were: photonic microscopy, scaning and transmission electron microscopy and gravimetry. The results have not shown any diference between the implants. PM is biodegradable, biocompatible but did not show any osteoinductive properties.
Abstract: Polyethylene wears of 22.225 mm diameter alumina and zirconia femoral heads in
cemented total hip arthroplasty (THA) were compared at mean follow-up of five years. Ninety-six primary cemented K-MAX THA in eighty-seven patients were observed, forty-six hips with alumina heads and fifty-one hips with zirconia heads. Both of the mean linear wear rate and the mean volumetric wear rate of the polyethylene against zirconia were significantly higher that those of alumina (p<0.01, p<0.01, respectively). The monoclinic phase content and roughness rose up on the surfaces of two retrieved zirconia heads from revision surgeries. This was supposed as the differences of thermal conductivity between alumina and zirconia, for which local temperature was higher in zirconia head, leading to the phase transformation and lower-temperature aging degeneration (LTAD) of zirconia head surface.
Abstract: The safety of ceramic bearings are depending not only on the design and characteristics of the ceramic components, but also on the characteristics of the metallic tapers used for their connection to the stem and to the metal back in THRs. The modularity of today’s THRs offer the advantage of selecting the implant size that better suits the patient’s anatomy, but in this selections of the coupling several pitfalls have to be avoided. This paper is aimed to reviews the characteristics of the
ceramic-metal interfaces and their influence on the behavior of the components of ceramic bearings.
Abstract: It is well known that the introduction of zirconia into the alumina matrix has a positive
effect on bending strength of the material, and especially on toughness which is the main limit of alumina ceramics. While the many attempts made in the past to develop alumina matrix composites suitable for biomedical applications containing zirconia as a toughening phase (Zirconia Toughened Alumina – ZTA) did not leave the developmental stage, recently ball heads and inlays for THR bearings made out a three phase alumina matrix composite were introduced into the market. In the
alumina matrix of this material both zirconia and exagonal aluminate platelets are distributed, and then it belongs to the class of Zirconia and Platelets Toughened Alumina – ZPTA. Besides ball heads and inlays, also several other innovative orthopedic devices made out this new ceramic biomaterial are in different development stage. This paper reviews the present status of alumina matrix composites in orthopedic application, with special attention to ZPTA.