Biocompatibility of bioresorbable poly(L-lactic acid) composite scaffolds obtained by supercritical gas foaming with human fetal bone cells

The aim of this investigation was to test the biocompatibility of three-dimensional bioresorbable foams made of poly(L-lactic acid) (PLA), alone or filled with hydroxyapatite (HA) or beta-tricalcium phosphate (beta-TCP), with human primary osteoblasts, using a direct contact method. Porous constructs were processed by supercritical gas foaming, after a melt-extrusion of ceramic/polymer mixture. Three neat polymer foams, with pore sizes of 170, 310, and 600 microm, and two composite foams, PLA/5 wt% HA and PLA/5 wt% beta-TCP, were examined over a 4-week culture period. The targeted application is the bone tissue-engineering field. For this purpose, human fetal and adult bone cells were chosen because of their highly osteogenic potential. The association of fetal bone cells and composite scaffold should lead to in vitro bone formation. The polymer and composite foams supported adhesion and intense proliferation of seeded cells, as revealed by scanning electron microscopy. Cell differentiation toward osteoblasts was demonstrated by alkaline phosphatase (ALP) enzymatic activity, gamma-carboxylated Gla-osteocalcin production, and the onset of mineralization. The addition of HA or beta-TCP resulted in higher ALP enzymatic activity for fetal bone cells and a stronger production of Gla-osteocalcin for adult bone cells.     

In vivo evaluation of a novel porous hydroxyapatite to sustain osteogenesis of transplanted bone marrow-derived osteoblastic cells

Biosynthetic bone grafts are considered to contain one or more of three critical components: osteoprogenitor cells, an osteoconductive matrix, and osteoinductive growth factors. The basic requirements of the scaffold material are biocompatibility, mechanical integrity, and osteoconductivity. A major design problem is satisfying these requirements with a single composite. In this study, we hypothesize that one composite that combines bone marrow-derived osteoblasts and a novel mechanical reinforced porous hydroxyapatite with good biocompatibility and osteoconductivity (HA/BMO) can reach these requirements. A novel sintered porous hydroxyapatite (HA) was prepared by the following procedures. The HA slurry was foamed by adding polyoxyethylenelaurylether (PEI) and mixing. The pores were fixed by crosslinking PEI with diepoxy compounds and the HA porous body was sintered at 1200 degrees C for 3 h. The HA sintered porous body had a high porosity (77%), and was completely interconnected. Average pore diameter was 500 microm and the interconnecting path 200 microm in diameter. The compressive (17 MPa) and three-point bending (7 MPa) strengths were high. For in vivo testing, the 2-week subcultured HA/BMO (+) composites were implanted into subcutaneous sites of syngeneic rats until 8 weeks after implantation. These implants were harvested at different time points and prepared for the biochemical analysis of alkaline phosphatase activity (ALP) and bone osteocalcin content (OCN), and histological analysis. ALP and OCN in the HA/BMO group were much higher than those in the HA without BMOs control group 1 week after implantation (p < 0.001). Light microscopy revealed mature bone formation in the HA/BMO composite 4 weeks after implantation. In the SEM study, mineralized collagenous extracellular matrix was noted in HA/BMO composite 2 weeks after implantation with numbers of active osteoblasts. We conclude that the composite of the novel HA and cultured BMOs has osteogenic ability in vivo. These results provide a basis for further studies on the use of this composite as an implant in orthopaedic surgery.     

An osteoconductive collagen/hyaluronate matrix for bone regeneration.

A new type of collagen-hyaluronate (COL/HA) matrix was synthesized by cross-linking collagen fibers with modified hyaluronate polymers bearing active formyl groups. The resulting matrix is a three-dimensional scaffold consisting of interconnected pores with an average size of 40 microm and a high pore volume/surface area ratio. The covalent nature of the bond between the collagen fibers and the modified hyaluronate was demonstrated by extended elution with phosphate buffered saline and by extraction in increasing ionic gradients. The fraction of covalently bound hyaluronate in the matrix ranged from 5 to 25 w%. The total hyaluronate content of the COL/HA matrix affected both the in vitro non-enzymatic and enzymatic degradation as well as the in vivo turnover. When implanted in cranial defects in rats, the COL/HA matrix demonstrated good biocompatibility and exhibited greater osteoconductive potential than matrices composed of either cross-linked collagen or cross-linked hyaluronate alone.     

Effect of osteoblastic culture conditions on the structure of poly(DL-lactic-co-glycolic acid) foam scaffolds

Poly(DL-lactic-co-glycolic acid) (PLGA) foams are an osteoconductive support that holds promise for the development of bone tissue in vitro and implantation into orthopedic defects. Because it is desirable that foams maintain their shape and size, we examined a variety of foams cultured in vitro with osteoblastic cells. Foams were prepared with different porosities and pore sizes by the method of solvent casting/porogen leaching using 80, 85, and 90 wt% NaCl sieved with particle sizes of 150-300 and 300-500 microm and characterized by mercury intrusion porosimetry. Foams seeded with cells were found to have volumes after 7 days in static culture that decreased with increasing porosity: the least porous exhibited no change in volume while the most porous foams decreased by 39 +/- 10%. In addition, a correlation was observed between decreasing foam volume after 7 days in culture and decreasing internal surface area of the foams prior to seeding. Furthermore, foams prepared with the 300-500 microm porogen had lower porosities, greater mean wall thicknesses between adjacent pores, and larger volumes after 7 days in culture than those prepared with the smaller porogen. Two culture conditions for maintaining cells, static and agitated (in a rotary vessel), were found to have similar influences on foam size, cell density, and osteoblastic function for 7 and 14 days in culture. Finally, we examined unseeded foams in aqueous solutions of pH 3.0, 5.0, and 7.4 and found no significant decrease in foam size with degradation. This study demonstrates that adherent osteoblastic cells may collapse very porous PLGA foams prepared by solvent casting/particulate leaching: a potentially undesirable property for repair of orthopedic defects.     

A preliminary study on the enhancement of the osteointegration of a novel synthetic hydroxyapatite scaffold in vivo

Synthetic hydroxyapatite, a bioactive calcium phosphate, is clinically used as a bone replacement bioceramic because of its similarity in composition to bone mineral, biocompatibility, and osteoconductive nature. The aim of this study was to evaluate the bioactivity of a novel synthetic porous hydroxyapatite (PHA) in vivo in rabbit and to investigate the enhancement of its bioactivity and osteointegration. In the investigation reported here, insulin-like growth factor-I (IGF-I) has been used to enhance the bioactivity of PHA. Cylindrical PHA implants with or without IGF-I were implanted bilaterally in rabbit femurs. Fluorochrome bone markers were administered at 7-day intervals. The implants with the attached bone were retrieved at postmortem, 1 and 3 weeks after implantation, for histological and histomorphometric analysis. Undecalcified sections stained with toluidine blue showed new bone formation. Mineralization of the new bone formed in the interface, surrounding trabecular bone, and within the pores of the implants was studied. Lamellar bone mineral apposition rate (MAR) was assessed and compared among treatment groups, sham, PHA alone, and PHA with IGF-I (500 ng/implant), by fluorochrome label incorporation using UVL microscopy. We report for the first time, that the supplementation of PHA implants with IGF-I significantly increased new bone formation and MAR (6.58 +/- 0.08 microm/day) compared with implantation of PHA alone (4.08 +/- 0.05 microm/day) or sham operation (3.11 +/- 0.12 microm/day). These results suggest that synthetic PHA might provide a delivery system for bioactive agents to accelerate bone healing in orthopedic procedures.     

Bioactive sol-gel foams for tissue repair.

Bioactive glasses are known to have the ability to regenerate bone, but their use has been restricted mainly to powder, granules, or small monoliths. This work reports on the development of sol-gel foams with potential applications as bone graft implants or as templates for the in vitro synthesis of bone tissue for transplantation. These bioactive foams exhibit a hierarchical structure with interconnected macropores (10-500 microm) and a mesoporous framework typical of gel-glasses (pores of 2-50 nm). The macroporous matrixes were produced through a novel route that comprises foaming of sol-gel systems. Three glass systems were tested to verify the applicability of this manufacturing route, namely SiO(2), SiO(2)-CaO, and SiO(2)-CaO-P(2)O(5). This new class of material combines large pores to support vascularization and 3-D tissue growth with the ability that bioactive materials have to provide bone-bonding and controlled release of ionic biologic stimuli to promote bone cell proliferation by gene activation.     

In vivo evaluation of a porous hydroxyapatite/poly-DL-lactide composite for use as a bone substitute

We investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles and compared it with porous HA. Six weeks after implantation, the HA/PDLLA was covered with bone and contacted the bone directly. The amount of newly formed bone in the pores was similar in both materials during the examined period. The newly formed bone in the HA/PDLLA tended to increase over 26 weeks, but that in the HA did not show a significant increase after 12 weeks. By 26 weeks, remodeling of the newly formed bone in the pores was seen and bone marrow tissue was found in the pores of the HA/PDLLA. The porous HA/PDLLA was resorbed much faster than the porous HA. Porous HA/PDLLA was resorbed continuously through bone formation and remodeling. Conversely, porous HA was scarcely resorbed throughout the period. HA/PDLLA is thought to be degraded almost completely after about 1 year, and in this study, porous HA/PDLLA showed excellent osteoconductivity and faster resorption than HA. Therefore, HA/PDLLA might be a desirable material for bone substitutes.     

Enhancement of the in vivo osteogenic potential of marrow/hydroxyapatite composites by bovine bone morphogenetic protein

A composite of marrow mesenchymal stem cells and porous hydroxyapatite (HA) has in vivo osteogenic potential. To investigate factors enhancing the osteogenic potential of marrow/HA composites, we prepared a bone morphogenetic protein (BMP) fraction from the 4M guanidine extract of bovine bone by heparin-sepharose affinity chromatography. Marrow/HA composites or composites containing marrow mesenchymal stem cells, BMP, and HA (marrow/BMP/HA composites) were implanted subcutaneously in 7-week-old male Fischer rats. BMP/HA composites and HA alone were also implanted. The implants were harvested after 2, 4, or 8 weeks and were prepared for histological and biochemical studies. Histological examination showed obvious de novo bone formation together with active osteoblasts at 2 weeks, as well as more extensive bone formation at 4 and 8 weeks in many pores of the marrow/BMP/HA composites. The marrow/HA composites did not induce bone formation at 2 weeks, but there was moderate bone formation at 4 weeks. At 2 weeks, only marrow/BMP/HA composites resulted in intensive osteogenic activity, judging from alkaline phosphatase and osteocalcin expression at both the protein and gene levels. These results indicate that the combination of marrow mesenchymal stem cells, porous HA, and BMP synergistically enhances osteogenic potential, and may provide a rational basis for their clinical application, although further in vivo experiment is needed.     

HA/TCP compounding of a porous CaP biomaterial improves bone formation and scaffold degradation--a long-term histological study

In the present study, two biphasic calcium phosphate biomaterials (BCP) with HA/TCP ratios of 50/50 and 30/70 were obtained from a pure HA biomaterial. The biomaterials which showed the same three-dimensional geometry were implanted into corticocancellous costal defects of sheep. In the specimens of all three biomaterials, abundant bone formation, mineral dissolution from the biomaterial scaffolds, and active cellular resorption of the scaffolds was present after 6 and 12 months. Backscattered electron microscopy showed bone invasion into the pores of the scaffolds and micromechanical interlocking at the bone/biomaterial interface without intervening soft tissue. The pattern of bone formation and scaffold resorption was different for cortical and cancellous bone. No time-based effect, however, was observed. Overall, the BCP biomaterials had formed significantly more bone than the HA biomaterial. Also, scaffold resorption, which was followed by a replacement with newly formed bone, was significantly higher in the BCP biomaterials. Although no significant differences were observed between both BCP biomaterials, the present study had confirmed the assumption that HA/TCP compounding was suitable to improve bone formation and scaffold resorption in the investigated biomaterials and at the same time maintain the osteoconductive properties of the scaffolds.     

Quantitative comparison of osteoconduction of porous, dense A-W glass-ceramic and hydroxyapatite granules (effects of granule and pore sizes).

The osteoconductive potentials of dense, small porous and large porous apatite- and wollastonite-containing glass-ceramic (A-W GC) granules of various sizes implanted in rat tibiae were evaluated quantitatively, by determining their affinity indices. The average affinity indices of all types of A-W GC were high. The dense A-W GC granules had the highest values (97.0+/-5.5%), followed by the large porous (87.1+/-8.4%) and then the small porous granules (79.0+/-8.4%). There were no significant differences among the osteoconductive potentials of the different sizes of each form of A-W GC granule. The osteoconductive potentials of four types of commercially available porous hydroxyapatite (HA) granules were compared with those of the small porous A-W GC granules, using the affinity index and the proportion of newly formed bone relative to that of the granules in the bone defect. The values of the former parameter for three types of HA and those of the latter for four were significantly inferior to those of A-W GC. The difference between the osteoconductive potentials of A-W GC and HA was considered to be related to the rate of surface apatite layer formation.     

Freeze casting of porous hydroxyapatite scaffolds. I. Processing and general microstructure

Freeze casting of aqueous suspensions on a cold substrate was investigated as a method for preparing hydroxyapatite (HA) scaffolds with unidirectional porosity. In the present paper, we report on the ability to manipulate the microstructure of freeze-cast constructs by controlling the processing parameters. Constructs prepared from aqueous suspensions (5-20 volume percent particles) on a steel substrate at -20 degrees C had a lamellar-type microstructure, consisting of plate-like HA and unidirectional pores oriented in the direction of freezing. Sintering for 3 h at 1350 degrees C produced constructs with dense HA lamellas, porosity of approximately 50%, and inter-lamellar pore widths of 5-30 microm. The thickness of the HA lamellas decreased but the width of the pores increased with decreasing particle concentration. Decreasing the substrate temperature from -20 degrees C to -196 degrees C produced a finer lamellar microstructure. The use of water-glycerol mixtures (20 wt % glycerol) as the solvent in the suspension resulted in the production of finer pores (1-10 microm) and a larger number of dendritic growth connecting the HA lamellas. On the other hand, the use of water-dioxane mixtures (60 wt % dioxane) produced a cellular-type microstructure with larger pores (90-110 microm). The ability to produce a uniaxial microstructure and its manipulation by controlling the processing parameters indicate the potential of the present freeze casting route for the production of scaffolds for bone tissue engineering applications.     

Osteoconduction at porous hydroxyapatite with various pore configurations

To assess the histological response and the reinforcing effects of bone ingrowth within porous hydroxyapatite (HA) implants depending on pore geometry, four kinds of cylindrical-type with parallel linear pores phi50, 100, 300, 500 microm), one kind of sponge-type with irregular interconnecting pores (phi250 microm) and one cross-type with crossing linear pores (phi100 x 120 microm) of porous HA were prepared. Eighty-four rabbits were divided into six groups, and a 5 x 5 x 7 mm sized porous HA block was inserted through the medial cortical window of the proximal tibia. Histomorphological changes were examined using light and scanning electron microscopy. A biomechanical compression test was performed using material test machines. After implantation, the implants showed different histological changes depending on pore geometry. Active osteoconduction was also found in the phi50 microm sized cylindrical-type porous HA. Evidence of remodeling of new bone and bone marrow formation within porous HA was found in the larger cylindrical-types (phi300, 500 microm), and the sponge- and cross-types. The biomechanical test showed that the ultimate compressive strength increased significantly in the phi300 microm sized cylindrical-type, and in the sponge- and cross-types eight weeks after implantation. Porous HA with cylindrical pores could be a useful graft material due to its strength, osteoconductivity and the ease with which its pore geometry can be controlled.     

Fibrin glue as an osteoinductive protein in a mouse model

Fibrin sealant or fibrin glue (FG) has been found to be effective as a wound-healing substance in surgery. However, its role in bone fracture healing and osseous tissue response is not fully understood. This ambiguity questions the potential of FG as an inductive protein. The present study was undertaken to evaluate the osteoinductive property of FG when coated with calcium phosphate and glass ceramics and implanted in the extraskeletal site of male Swiss albino mice. Implant materials used for this study were hydroxyapatite (HA) porous granules (300-350 microm), bioactive glass system (BGS)-AW type and calcium phosphate calcium silicate system (HABGS) non-porous granules (300-350 microm). Uncoated granules (control) and coated granules with 2.5 mg FG and 5 mg FG were implanted in the quadriceps muscle of mice and sacrificed after 28 days. Histologically, HA, BGS and HABGS implanted animal groups showed good healing response. However, neo-osteogenesis was observed only in the BGS and HABGS granules impregnated with FG. Furthermore, bone formation was observed to be more conspicuous in 5 mg FG coated BGS and HABGS granules when compared with 2.5 mg FG coated BGS and HABGS granules. Fluorochrome labeling proved that mineralization had already started by day 15 with FG preadsorbed BGS and HABGS granules. On the contrary, the uncoated granules did not show any de novo bone formation. This experimental study provides an evidence of the positive role of FG as a potential osteoinductive biologic tissue adhesive.     

Hydroxyapatite and gelatin composite foams processed via novel freeze-drying and crosslinking for use as temporary hard tissue scaffolds

Hydroxyapatite (HA) and gelatin composites were fabricated in a foam type via a novel freeze-drying and crosslinking technique. The morphological and mechanical properties of and in vitro cellular responses to the foams were investigated. The HA powder was added at up to 30 wt % into the gelatin solution, and the mixtures were freeze-dried and further crosslinked. The pure gelatin foam had a well-developed pore configuration with porosity and pore size of approximately 90% and 400-500 microm, respectively. With HA addition, the porosity decreased and pore shape became more irregular. The HA particulates, in sizes of about 2-5 microm, were distributed within the gelatin network homogeneously and made the framework surface rougher. All the foams had high water absorption capacities, showing typical hydrogel characteristics, even though the HA addition decreased the degree of water absorption. The HA addition made the foam much stronger and stiffer (i.e., with increasing HA amount the foams sustained higher compressive stress and had higher elastic modulus in both dry and wet states). The osteoblast-like human osteosarcoma cells spread and grew actively on all the foams. The cell proliferation rate, quantified indirectly on the cells cultured on Ti discs coated with gelatin and gelatin-HA composites using MTT assay, exhibited an up-regulation with gelatin coating compared with bare Ti substrate, but a slight decrease on the composite coatings. However, the alkaline phosphatase activities expressed by the cells cultured on composites foams as well as their coatings on Ti discs were significantly enhanced compared with those on pure gelatin foam and coating. These findings suggest that the gelatin-HA composite foams have great potential for use as hard tissue regeneration scaffolds.     

Viable osteogenic cells are obligatory for tissue-engineered ectopic bone formation in goats

In this study we investigated the bone-forming capacity of tissue-engineered (TE) constructs implanted ectopically in goats. As cell survival is questionable in large animal models, we investigated the significance of vitality, and thus whether living cells instead of only the potentially osteoinductive extracellular matrix are required to achieve bone formation. Vital TE constructs of porous hydroxyapatite (HA) covered with differentiated bone marrow stromal cells (BMSCs) within an extracellular matrix (ECM) were compared with identical constructs that were devitalized before implantation. The devitalized implants did contain the potentially osteoinductive ECM. Furthermore, we evaluated HA impregnated with fresh bone marrow and HA only. Two different types of HA granules with a volume of approximately 40 microm were investigated: HA70/800, a microporous HA with 70% interconnected macroporosity and an average pore size of 800 microm, and HA60/400, a smooth HA with 60% interconnected macropores and an average size of 400 microm. Two granules of each type were combined and then treated as a single unit for cell seeding, implantation, and histology. The tissue-engineered samples were obtained by seeding culture-expanded goat BMSCs on the HA and subsequently culturing these constructs for 6 days to allow cell differentiation and ECM formation. To devitalize, TE constructs were frozen in liquid nitrogen according to a validated protocol. Fresh bone marrow impregnation was performed perioperatively (4 mL per implant unit). All study groups were implanted in bilateral paraspinal muscles. Fluorochromes were administered at three time points to monitor bone mineralization. After 12 weeks the units were explanted and analyzed by histology of nondecalcified sections. Bone formation was present in all vital tissue-engineered implants. None of the other groups showed any bone formation. Histomorphometry indicated that microporous HA70/800 yielded more bone than did HA60/400. Within the newly formed bone, the fluorescent labels showed that mineralization had occurred before 5 weeks of implantation and was directed from the HA surface toward the center of the pores. In conclusion, tissue-engineered bone formation in goats can be achieved only with viable constructs of an appropriate scaffold and sufficient BMSCs.     

Marrow cell induced osteogenesis in porous hydroxyapatite and tricalcium phosphate: a comparative histomorphometric study of ectopic bone formation

To investigate the bone formation ability of porous hydroxyapatite (HA) and tricalcium phosphate (TCP), ceramic discs were implanted with or without rat marrow cells into subcutaneous sites in syngeneic rats. The discs of HA and TCP had identical microstructures: pore size was 190-230 microns, porosity was 50-60%, and they were fully interconnected. Implants without marrow cells (discs themselves) did not show bone formation, whereas implants with marrow cells showed bone formation in the pores of the ceramics. The bone formation of both HA and TCP occurred initially on the surface of the ceramic and progressed towards the center of the pore. The de novo bone was quantitated from decalcified serial sections of the implants. One month after implantation with marrow cells, the percentage fractions of the pore area filled with bone for implanted HA and TCP were 16.9 and 15.1, respectively. At 2 months after implantation with marrow cells, the fractions of bone were 34.3 and 30.9, respectively. These results indicate that both HA and TCP ceramics can show comparable osteogenic ability in the presence of marrow cells.     

注射型纳米羟基磷灰石/聚酰胺生物活性骨修复材料的研究

利用羟基磷灰石纳米晶体与聚酰胺66复合，构成新型生物活性骨修复材料，探讨用于不规则骨缺损修复的注射型纳米复合人工骨的生物学特性及骨组织修复能力。对该材料进行X射线衍射分析、凝结时间、凝结强度等研究及动物实验研究，评价该材料的组织相容性和缺损骨组织的修复能力。结果表明该材料的X射线衍射谱与羟基磷灰石／聚酰胺复合材料的X射线衍射谱相同；液固比为0．5时复合材料易于注射；在生理盐水或血液中的凝固时间为25～30min；在生理盐水中固化48h后，抗压强度为37MPa。植入后牙槽嵴表面软组织愈合良好，实验侧牙槽嵴修复高度明显大于对照侧；组织形态学观察，4周时材料周围未见有成骨迹象，16周时材料被包裹并在与其相连的区域出现成骨早期的片状结缔组织。研究证实，以一定的复合比例构成的纳米羟基磷灰石／聚酰胺66复合材料组织相容性良好，可以注射方式实现对不规则骨缺损的修复。     

In vivo evaluation of a porous hydroxyapatite/poly-DL-lactide composite for bone tissue engineering

As reported previously, a porous composite of uncalcined hydroxyapatite (u-HA) and poly-DL-lactide (PDLLA) showed excellent osteoconductivity and biodegradability as a bone substitute in rabbit model. In this study, to investigate the usefulness of this composite as a scaffold loaded with cells, we estimated whether this material showed osteogenesis on implantation to extraosseous site. On loading with syngeneic bone marrow cells and implantation into rat dorsal subcutaneous tissue, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. The osteogenesis in the u-HA/PDLLA had progressed, and newly formed bone tissue was found in the material by 6 weeks. To investigate the osteoinductive properties of the material, we implanted this porous composite material into extraosseous canine dorsal muscle. At 8 weeks, osteogenesis was seen in the pores of the material. Newly formed bone could be observed adjacent to the material. In addition, cuboidal osteoblasts adjacent to the newly formed bone were evident. Neither cartilage nor chondrocytes were found. These results might indicate that the material induced osteogenesis by intramembranous ossification. Conversely, similar porous PDLLA did not induce osteogenesis during the observation period. Therefore, porous HA/PDLLA, which has osteoconductive and osteoinductive properties, might be a useful material for use as a bone substitute and cellular scaffold.     

Characterization of a bovine collagen-hydroxyapatite composite scaffold for bone tissue engineering

Different biomaterials have been used as scaffolds for bone tissue engineering. Here we characterize a biomaterial composed of sintered (1100 degrees C) and powdered hydroxyapatite (HA) and type I collagen (Coll), both of bovine origin, designed for osteoconductive and osteoinductive scaffolds. Coll/HA proportions were 1/2.6 and 1/1 (wet weight), and particles sizes varied from 200 to 400 microm. Vv (volume density) and Sv (surface to volume density) for the HA particles in the composite ranged from 0.48 +/- 0.06 to 0.55 +/- 0.02 and 5.090 +/- 0.545 to 6.366 +/- 0.289 microm(-1), respectively. Due to the relatively small changes in Vv and Sv, a macroporosity could be characterized for the biocomposite. X-ray diffraction and infrared spectroscopy showed that the sintered bone was composed essentially of HA with minimum additional groups such as surface calcium hydroxide, surface and crystal water, free carbon dioxide and possibly brushite. Mass spectrometry detected carbonates at A and B sites of HA, and weakly bound to the structure. Human osteoblasts adhered and spread on both the HA particle surface and the collagen fibers, which seemed to guide cells between adjacent particles. The biocomposite studied has several characteristics considered as ideal for its use as a scaffold for osteoconduction and osteoinduction.     

Characterization of the structure and permeability of titanium foams for spinal fusion devices

Titanium foams produced via the space-holder method are used for spinal fusion devices since their combination of an open-cell structure and bone-like mechanical properties promises potentially excellent bone ingrowth. Earlier studies have indicated that the size of the pores and interconnects must be greater than 100microm for effective bone ingrowth and vascularization. Hence, the quantification of the pore and interconnect size is required for efficient scaffold design. In this study, microcomputed tomography (microCT) was used to obtain the three-dimensional (3D) structure of Ti foams with three levels of porosity (51%, 65% and 78%). Novel algorithms were then applied to quantify both the pore and interconnect size of Ti foams as a function of porosity. All foams possessed a modal pore and interconnect size in excess of 300microm, satisfying the requirement of being greater than 100microm. The pore and interconnect size also dominates the flow properties or permeability of open-cell structures. Therefore, the microCT data was also used to generate a mesh for computational fluid dynamics analysis to predict the permeability. The calculated permeability (117-163x10(-12)m(2) depending on direction) for the Ti foams with 65% porosity was first validated against experimental measurements (98-163x10(-12)m(2)) and then compared to prior authors' measurements in healthy cancellous bovine bone (233-465x10(-12)m(2)). The close match among all the permeability values proves the suitability of the material for biomedical skeletal-implant applications.