Porous Hydroxyapatite Ceramics Research Articles

Effects of interconnecting porous structure of hydroxyapatite ceramics on interface between grafted tendon and ceramics

The purpose of this study was to evaluate histologically and biomechanically the interface between porous hydroxyapatite ceramics and a tendon grafted into ceramics, and to compare the interface in two ceramics with different porous structures: interconnected porous calcium hydroxyapatite ceramics (IP-CHA) with an effective porosity index (interpore diameter > 20 microm) of 63.6%, and porous calcium hydroxyapatite ceramics with less interconnection (HA-L) with an effective porosity index of 5.5%. The tendon-IP-CHA complex and the tendon-HA-L complex were implanted into the bone defects made in both knees of rabbits. With IP-CHA, abundant fibrous tissue, including vessels and collagen fiber continuity, was observed inside interface-region pores. The amount of osseous tissue in interface-region pores increased over time, and at 24 weeks after operation, the tendon was in direct contact with the osseous tissue in IP-CHA. With HA-L, the amount of fibrous tissue in interface-region pores was low and did not increase. The results of biomechanical analysis revealed that the maximum tendon pull-out load from IP-CHA was significantly higher than that from HA-L. With the porous hydroxyapatite ceramics having highly interconnecting porous structure, a bioactive interface was achieved between ceramics and grafted tendon. On the basis of these results, we conclude that bone defects, including tendon insertion, can be reconstructed using IP-CHA.

Hydroxyapatite coating on porous zirconia

Since hydroxyapatite has excellent biocompatibility and bone bonding ability, porous hydroxyapatite ceramics have been intensively studied. However, porous hydroxyapatite bodies are mechanically weak and brittle, which makes shaping and implantation difficult. One way to solve this problem is to introduce a strong porous network onto which hydroxyapatite coating is applied. In this study, porous zirconia and alumina-added zirconia ceramics were prepared by ceramic slurry infiltration of expanded polystyrene bead compacts, followed by firing at 1500 °C. Then a slurry of hydroxyapatite–borosilicate glass mixed powder was used to coat the porous ceramics, followed by firing at 1200 °C. The porous structures without the coating had high porosities of 51% to 69%, a high pore interconnectivity, and sufficiently large pore window sizes (300 μm–500 μm). The porous ceramics had compressive strengths of 5.3˜36.8 MPa and Young's moduli of 0.30˜2.25 GPa, favorably comparable to the mechanical properties of cancellous bones. In addition, porous hydroxyapatite surface was formed on the top of the composite coating, whereas a borosilicate glass layer was found on the interface. Thus, porous zirconia-based ceramics were modified with a bioactive composite coating for biomedical applications.

Electrovector Effect of Polarized Porous Hydroxyapatite Ceramics

Porous HA ceramics has been developed for the scaffold materials because the porous structure has been recognized to be necessary to invasion of body fluid and ingrowth of bone. The synthesized porous HA ceramics with several porosities were electrically polarized, and then the TSDC spectra were measured. The maximum electric current density and the stored polarization charges decreased with increasing the porosity. Therefore it was thought that the decreasing the amount of proton of porous HA ceramics was one of the reasons of decreasing of the maximum electric current densities and the stored charges. The simulated body fluid (SBF) test implied that electrovector effects enhanced the apatite formabilities.

Chemical Functionalization of a Hydroxyapatite Based Bone Replacement Material for the Immobilization of Proteins

Hydroxyapatite (HAP) has a great potential as a bone replacement material because of its similarity to the crystal structure of inorganic matrix of bone. Several years ago we showed that porous hydroxyapatite ceramics (Endobon, Merck) can be covalently modified for the immobilization of proteins [Jennissen, H.P. (1999) PCT Patent WO9926674A2] opening the possibility for the immobilization of growth factors and morphogens. Application of this technique to the immobilization of recombinant human bone morphogenetic protein 2 (rhBMP-2) on hydroxyapatite would be of high medical interest, because of the decisive role of bone morphogenetic proteins in bone development and osteogenesis. In this paper it will be shown that the model protein ubiquitin and rhBMP-2 can be immobilized non-covalently and covalently after chemical modification of a hydroxyapatite ceramic surface (Bio-Oss J Cancellous Block, Geistlich, = HAP-wafers). It could be shown that only small amounts of protein are adsorbed to non-functionalized HAP surfaces (control). In contrast ubiquitin and rhBMP-2 can be very efficiently immobilized non-covalently (up to 2.4mg protein/g HAP) and covalently (up to 9.7mg protein/g HAP) on porous HAPwafers. In desorption experiments it is shown that the bound rhBMP-2 is slowly released making such surfaces applicable as long term drug delivery devices for enhancing bone growth and osteointegration of implant materials.

Bone tissue engineering with porous hydroxyapatite ceramics

The main principle of bone tissue engineering strategy is to use an osteoconductive porous scaffold in combination with osteoinductive molecules or osteogenic cells. The requirements for a scaffold in bone regeneration are: (1) biocompatibility, (2) osteoconductivity, (3) interconnected porous structure, (4) appropriate mechanical strength, and (5) biodegradability. We recently developed a fully interconnected porous hydroxyapatite (IP-CHA) by adopting the "form-gel" technique. IP-CHA has a three-dimensional structure with spherical pores of uniform size that are interconnected by window-like holes; the material also demonstrated adequate compression strength. In animal experiments, IP-CHA showed superior osteoconduction, with the majority of pores filled with newly formed bone. The interconnected porous structure facilitates bone tissue engineering by allowing the introduction of bone cells, osteotropic agents, or vasculature into the pores. In this article, we review the accumulated data on bone tissue engineering using the novel scaffold, focusing especially on new techniques in combination with bone morphogenetic protein (BMP) or mesenchymal stem cells.

Improving the properties of porous hydroxyapatite ceramics by fabricating methods

Hydroxyapatite (HA) ceramic is a widely used ma-terial for bone graft substitutes primarily because ofits close composition to human bone and its high bio-compatibility with surrounding living tissues [1–5]. Inrecent years, attention has been particularly focused onthe fabrication of porous bioceramics, for the porousnetwork allows the tissue to infiltrate, which furtherenhances the implant-tissue attachment [6–10]. Up tonow, porous HA bioceramics have been applied in fill-ing bone defects, eye ball prosthesis, dental implants,and so on [11–13], which has developed into an im-portant division of the biomedical field. However, asindicated by Hulbert

Fabrication of Porous Hydroxyapatite Ceramics by Microwave Sintering Method

Microwave processing of porous hydroxyapatite ceramics was investigated in a dual frequency microwave-sintering furnace. The results revealed that microwave-sintering process could get sintered ceramics at much shorter sintering time and at lower sintering temperature than that of the conventionally heat-sintering process. Further, the microwave-sintered samples showed much smaller grain size and more uniform microstructure and reached a comparable compressive strength. The mechanism of rapid heating behavior of hydroxyapatite ceramics in microwave was also discussed. The results revealed that microwave processing was a promising method for sintering porous hydroxyapatite ceramics.

Influence of Powder Particle Size of Slurries on Mechanical Properties of Porous Hydroxyapatite Ceramics

The effect of different particle sizes on the flexural strength and microstructure of three different types of hydroxyapatite (HAp) powders was studied. The powder characteristics of laboratory synthesized HAp powder (Lab1 and Lab2) were obtained through a wet milling method, and the median particle size and the specific surface area of powders are different with the dryness period. The median particle sizes of Lab1 and Lab2 are 0.34 µm and 0.74 µm, and the specific surface areas of Lab1 and Lab2 are 38.01 m2/g and 19.77 m2/g. The commercial HAp had median particle size of 1.13 µm and specific surface area of 11.62m2/g. The different powder characteristics affected the slip characteristics, and the flexural strength and microstructure of the sintered porous HAp bodies are also different. The optimum value for the minimum viscosity in these present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were investigated. The flexural strengths of the porous HAp ceramics prepared by heating at 1200°C for 3 hrs in air were 17.59 MPa for Lab1 with a porosity of 60.48％, 10.51 MPa for Lab2 with a porosity of 57.75％, and 3.92 MPa for commercial HAp with a porosity of 79.37％.

Fabrication of hydroxyapatite ceramics with controlled pore characteristics by slip casting

Porous hydroxyapatite (HAp) ceramics with controlled pore characteristics were fabricated using slip casting method by mixing PMMA with HAp powder. The optimum conditions of HAp slip for slip casting was achieved by employing various experimental techniques, zeta potential and sedimentation, as a function of pH of the slips in the pH range of 4-12. HAp suspensions displayed an absolute maximum in zeta potential values and a minimum in sedimentation height at pH 11.5. The optimal amount of dispersant for the HAp suspensions was found at 1.0 wt% according to the viscosity of 25 vol% HAp slurry. The rheological behaviour of HAp slurry displays a shear-thinning behavior without thixotropy, which is needed in slip casting processing. The pore characteristics of sintered porous hydroxyapatite bioceramics can be controlled by added PMMA particle size and volume. The obtained ceramics exhibit higher strength than those obtained by dry pressing.

A clinical study of using the interconnected porous hydroxyapatite ceramics for distal radius fractures

A clinical study of using the interconnected porous hydroxyapatite ceramics for distal radius fractures

Development of porous ceramics with well-controlled porosities and pore sizes from apatite fibers and their evaluations.

Porous hydroxyapatite (HAp) ceramics possessing well-controlled porosities and pore sizes were developed by firing apatite-fiber compacts mixed with carbon beads and agar. The total porosities could be controlled in the range from 40 to 85% by varying compaction pressure (20-40 MPa), firing temperature (1000-1300 degrees C) and carbon/HAp ratio (0/10-10/10 (w/w)). Most of the pores were regarded as open pores. The pore sizes were mainly affected by the carbon-bead diameter (5, 20 or 150 microm) and partly by the compaction pressure and the firing temperature. The pore sizes of the porous HAp ceramics derived from the carbon beads of 150 microm in diameter were distributed in the two separate ranges of several micrometers and more than 100 microm.

The influence of dispersant concentration on the pore morphology of hydroxyapatite ceramics for bone tissue engineering

There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting windows whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated varying slip deflocculation in order to control the resulting porosity, pore size and interconnecting window size whilst maintaining mechanical strength. Hydroxyapatite (HA) porous ceramics were prepared using a modified slip casting process. Rheological measurements of the HA slips were used to identify deflocculation conditions which resulted in changes in the cell and window sizes of the resulting ceramics. Sintered ceramics were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pore and window size distribution was determined by SEM. XRD analysis confirmed that the crystal structure remained HA after the sintering process. SEM showed that HA porous ceramics presented a highly interconnected porous network with average pore sizes ranging from 391±39 to 495±25 μm. The average window size varied from 73±5 to 135±7 μm. Pore diameters obtained were controllable in the range 200–500 μm. Window sizes were in the range 30–250 μm. The use of dispersant concentration allows pore and window size to be modified whilst maintaining control over porosity demonstrated by a porosity of 85% for seven different dispersant concentrations. The advantage of this approach allows the correlation between the rheological conditions of the slip and the resultant sintered ceramic properties. In particular, optimising the ceramic strength by controlling the agglomeration during the casting process.

Bone tissue engineering using novel interconnected porous hydroxyapatite ceramics combined with marrow mesenchymal cells: quantitative and three-dimensional image analysis.

We developed fully opened interconnected porous calcium hydroxyapatite ceramics having two different pore sizes. One has pores with an average size of 150 microm in diameter, an average 40-microm interconnecting pore diameter, and 75% porosity (HA150). The other has pores with an average size of 300 microm in diameter, an average 60-100-microm interconnecting pore diameter, and 75% porosity (HA300). Because of its smaller pore diameter, HA150 has greater mechanical strength than that of HA300. These ceramics were combined with rat marrow mesenchymal cells and cultured for 2 weeks in the presence of dexamethasone. The cultured ceramics were then implanted into subcutaneous sites in syngeneic rats and harvested 2-8 weeks after implantation. All the implants showed bone formation inside the pore areas as evidenced by decalcified histological sections and microcomputed tomography images, which enabled three-dimensional analysis of the newly formed bone and calculation of the bone volume in the implants. The bone volume increased over time. At 8 weeks after implantation, extensive bone volume was detected not only in the surface pore areas but also in the center pore areas of the implants. A high degree of alkaline phosphatase activity with a peak at 2 weeks and a high level of osteocalcin with a gradual increase over time were detected in the implants. The levels of these biochemical parameters were higher in HA150 than in HA300. The results indicate that a combination of HA150 and mesenchymal cells could be used as an excellent bone graft substitute because of its mechanical properties and capability of inducing bone formation.

Controllable porosity hydroxyapatite ceramics as spine cage: fabrication and properties evaluation.

A procedure was designed to prepare porosity-graded hydroxyapatite (HA) ceramics simulating the bimodal structure of natural bone, which could be used to build a cage that would promote the reconstruction of the anterior column after vertebrectomy or corpectomy in tumor and trauma surgery. HA ceramics with controllable pore size distribution and porosity were developed by using chitosan and Poly(vinyl alcohol) (PVA) as the pore-forming agents. HA ceramics with worthwhile properties such as a wide range of volume porosity (10-50%) and pore size (nanometer to 400 microm) can be obtained from this method, which allows the fabrication of HA ceramics with desirable porous characteristics simulating the bimodal natural bone architecture expected to provide advantages for bony fusion in the intervertebral foramina. When coated with chitosan-gelatin network, the bending strength of the porous HA ceramics significantly improved. The polymer network coated porous HA have potential application in the construction of cages for spinal operations.

Functionally graded materials for biomedical applications

Functional gradation is one characteristic feature of living tissue. Bio-inspired materials open new approaches for manufacturing implants for bone replacement. Different routes for new implant materials are presented using the principle of functional gradation. An artificial biomaterial for knee joint replacement has been developed by building a graded structure consisting of ultra-high molecular weight polyethylene (UHMWPE) fibre reinforced high-density polyethylene combined with a surface of UHMWPE. The ingrowth behaviour of titanium implants into hard tissue can be improved by depositing a graded biopolymer coating of fibronectin, collagen types I and III with a gradation, derived from the mechanisms occurring during healing in vivo. Functionally graded porous hydroxyapatite (HAP) ceramics can be produced using alternative routes, e.g. sintering of laminated structures of HAP tapes filled with polymer spheres or combining biodegradable polyesters such as polylactide, polylactide- co-glycolide and polyglycolide, with carbonated nanocrystalline hydroxyapatite. HAP–collagen I scaffolds are an appropriate material for in vitro growth of bone. The scaffold has to be functionally graded in order to create an optimised mechanical behaviour as well as the intended improvement of the cell ingrowth.

Preparation of Porous Hydroxyapatite Ceramics from Hollow Spherical Agglomerates Using a Foaming Agent of Hydrogen Peroxide

Preparation of Porous Hydroxyapatite Ceramics from Hollow Spherical Agglomerates Using a Foaming Agent of Hydrogen Peroxide

Strength enhancement of porous hydroxyapatite ceramics by polymer impregnation

Strength enhancement of porous hydroxyapatite ceramics by polymer impregnation

一方向貫通気孔を持つ多孔質アパタイトの製造と組織制御

By using molten wax colloidal process with graphite powders as combustible pore-forming agents, a method for controlling the porosity and pore size of porous hydroxapatite ceramics has been developed. Porous hydroxyapatite with unidirectionally aligned continuous pores were fabricated by multistage extrusion of green billets. Starting billet of this multistage extrusion was made from stacking hydoxyapatite green disks of outer diameter 50mm and inner diameter 25mm filled with 100% graphite green disks of 25mm. In order to make the porous matrix, the mixture of hyroxyapatite and graphite was used instead of hydroxyapatite. By the primary extrusion, hexagonal rods with the graphite in the central part were extruded. These extruded hexagonal rods were bundled to make composite billets for the next stage extrusion. This process was repeated for several stages. Finally, the extruded rods of proper stage were sintered. Size of the continuous pore can be controlled by total extrusion ratio. The pore diameter obtained in the present work was from 350μm to 8μm. The porosity can be controlled by the billet structure. The mean flexural strength of the porous hydroxyapatite ceramics obtained in this work was from 32MPa to 56MPa.

Thermal Stability of Hydroxyapatite Whiskers Prepared by Homogenous Precipitation

Hydroxyapatite (HA) whiskers prepared by homogenous precipitation method were heat treated in air. The phase composition of HA whiskers and their microstructure were investigated before and after the heat treatment using XRD, FT‐IR, SEM, and TG‐DSC techniques. It was revealed that the HA whiskers obtained were morphologically stable at elevated temperatures below 1200°C. A phase transition of the HA whiskers took place obviously at about 1200°C. The thermal stability of HA whiskers was related to the chemical composition and crystallinity. They could be used as reinforcement materials in dense HA ceramics and porous HA ceramics.

Hydroxyapatite ceramics as a carrier of gene-transduced bone marrow cells

AbstractThe aim of this study was to develop an efficient exogenous gene delivery system using cultured marrow cells and porous hydroxyapatite ceramics. Bone marrow cells were obtained from the femoral shaft of a Fischer 344 rat and cultured in a medium containing 15% fetal bovine serum until confluent. After trypsinization, cells were subcultured at a cell density of 1 ×104 cells/cm2 in the presence of fetal bovine serum. The subcultured bone marrow cells were infected with recombinant retroviruses carrying the lacZ gene. The retrovirus infection was performed seven times from day 1 to day 7 during the culturing procedure. Cells expressing the lacZ gene were stained blue with the X-gal staining and represented approximately 80%. Composites of virus-infected bone marrow cells and hydroxyapatite ceramics were implanted at the subcutaneous site of recipient Fischer 344 rats. Four weeks after the implantation the ceramics were harvested. The histological sections of the ceramics showed abundant bone formation in the pores of the ceramics and obviously blue-stained osteoblasts and osteocytes. Other cell types that were stained blue were some fibroblastic cells and endothelial cells in the newly formed capillaries. These findings indicate that osteoblasts and osteocytes in the newly formed bone were derived from the cultured bone marrow cells, and therefore gene transfection by retroviruses did not disturb the bone formation process. Because of the durability of the newly formed bone tissue, creating composites of cultured bone marrow cells and hydroxyapatite ceramics might be an ideal method for exogenous gene transfection.