Bioactive materials: the potential for tissue regeneration

Functional atomic force microscopy investigation of osteopontin affinity for silicon stabilized tricalcium phosphate bioceramic surfaces

Resorbable silicon stabilized tricalcium phosphate (Si-TCP)-based bioceramics are characterized from a biological perspective by measuring the intermolecular interaction force between osteopontin (OPN) protein and the material surface using atomic force microscopy (AFM). OPN protein was covalently bound to silicon nitride AFM tips and adsorption and adhesion forces were measured in an electrolyte with a composition similar to that of physiological fluids. A strong relationship exists between the adhesion force of OPN on the material surface, the number of adherent osteoclasts (OC) and the resorption of the material. OPN adhesion is strongest on hydroxyapatite (HA) surfaces, or in samples that induce a HA-like surface through a precipitation reaction in electrolytic media. It is proposed that the increased biological response of the Si-TCP phase can be attributed in part to its reactivity in a physiological electrolyte, which involves a rapid conversion to a calcium deficient HA phase with a corresponding increase in the adhesion strength of OPN to the material, with a consequentially higher OC resorption response.

Fabrication andin vitro characterization of porous biodegradable composites based on phosphate glasses and oligolactide-containing polymer networks

Degradable porous composite materials for use as temporary bone replacement or tissue engineering scaffolds were produced using a methacrylate-modified oligolactide polymer network and phosphate invert glasses in the system P2O5-CaO-MgO-Na2O-(TiO2). Porous glasses with an open interconnective porosity were produced by a salt sintering process. Compressive strengths were significantly enhanced by polymer coating of the inner surface of the porous glasses or by fabrication of glass powder-reinforced porous polymer specimens. In vitro degradation in simulated body fluid showed a degradation pattern of the composites which could be modulated by the composition and resulting solubility of the incorporated glass phase. Cytocompatibility of the composites was investigated in a FDA/EtBr viability assay using an MC3T3-E1 osteoblast-like cell line and showed good biocompatibility of the materials in vitro.

Microstructural and in vitro characterization of SiO2-Na2O-CaO-MgO glass-ceramic bioactive scaffolds for bone substitutes

In the present research work, the preparation and characterization of bioactive glass-ceramic scaffolds for bone substitutes are described. The scaffolds were prepared by starch consolidation of bioactive glass powders belonging to the SiO2-Na2O-CaO-MgO system using three different organic starches (corn, potatoes and rice) as reported in a previous screening process. The scaffolds, characterized by scanning electron microscopy, showed a porous structure with highly interconnected pores. The pores sizes assessed by mercury intrusion porosimetry put in evidence the presence of pores of 50-100 microm. The structure of the scaffolds was investigated by X-ray diffraction and revealed the glass-ceramic nature of the obtained material. The mechanical properties of the scaffolds were evaluated by means of compressive tests on cubic samples and the obtained results demonstrated their good mechanical strength. The in vitro bioactivity of the scaffolds was tested by soaking them in a simulated body fluid (SBF) and by subsequently characterizing the soaked surfaces by SEM, EDS and X-ray diffraction. Good in vitro bioactivity was found for the starting glass and for the obtained scaffolds. Moreover, the scaffold bioresorption, tested by measuring the samples weight loss in SBF at different periods of time, showed a partial resorption of the scaffolds. Cell culture testing of the three different scaffolds indicated no differences in cell number and in alkaline phosphatase activity; the morphology of the osteoblasts showed good spreading, comparable to bulk material which was used as the control.

Osteoblast Differentiation with Titania and Titania–Silica-Coated Titanium Fiber Meshes

Two surface-reactive sol-gel coatings, namely titania (TiO2) and a mixture of titania and silica (TiSi), were applied to titanium fiber meshes. Differentiation of rat bone marrow stromal cells toward an osteogenic phenotype with coated and uncoated (cpTi) substrates was compared. The amount of DNA in cpTi and TiSi matrices did not increase after day 3, but with TiO2 matrices the amount increased for 7 days. The prolonged period of proliferation with TiO2 scaffolds resulted in a delay in alkaline phosphatase induction. However, osteocalcin incorporation into extracellular matrix by day 14 was greater with TiO2 scaffolds than with cpTi scaffolds. Calcium deposition was also greater with TiO2-coated substrates than with uncoated substrates. With the TiSi scaffolds osteocalcin production and mineralization were lower than with the cpTi scaffolds. The current study confirms our previous findings that titanium fiber mesh supports attachment, growth, and differentiation of rat bone marrow stromal cells. Furthermore, the osteogenic capacities of cell-scaffold constructs under cell culture conditions were increased with a sol-gel-derived titania coating, but not with a titania-silica coating.

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

Bioactive Glass Stimulates the Secretion of Angiogenic Growth Factors and Angiogenesis in Vitro

Neovascularization of tissue-engineered constructs remains a limiting factor for the engineering of larger tissue constructs. Attempts to stimulate neovascularization, using recombinant protein or gene transfer of angiogenic growth factors, have been proposed; however, these approaches have been associated with problems regarding the delivery and duration of exposure of the growth factor. This study was performed to determine the ability of biologically active glass to stimulate the secretion of angiogenic growth factors from human stromal cells and subsequent angiogenesis. CCD18Co human fibroblasts were cultured on tissue culture surfaces coated with specific quantities of 45S5 Bioglass particles. At 24-, 48-, and 72-h intervals the gene expression of vascular endothelial growth factor (VEGF) and the protein secretion of VEGF and basic fibroblast growth factor (bFGF) from fibroblasts were measured. The effect of conditioned medium collected from Bioglass-stimulated fibroblasts on human dermal microvascular endothelial cells was assessed using in vitro angiogenesis assays. Results showed that surfaces coated with Bioglass produced a significant increase in the secretion of VEGF and bFGF. Conditioned medium from stimulated fibroblasts significantly increased the proliferation of human dermal microvascular endothelial cells and induced a significant increase in the formation of anastomosed networks of human endothelial cell tubules. It is concluded that the ability of 45S5 Bioglass to stimulate the release of angiogenic growth factors and to promote angiogenesis provides a novel alternative approach for stimulating neovascularization of tissue-engineered constructs.

Bioactive glasses for in situ tissue regeneration

Historically the function of biomaterials has been to replace diseased or damaged tissues. Recent findings show that controlled release of the ionic dissolution products of bioactive glasses results in regeneration of tissues. The mechanism for in situ tissue regeneration involves upregulation of seven families of genes that control the osteoblast cell cycle, mitosis and differentiation. In the presence of critical concentrations of Si and Ca ions, within 48 h osteoblasts that are capable of differentiating into a mature osteocyte phenotype begin to proliferate and regenerate new bone. Osteoblasts that are not in the correct phase of the cell cycle and unable to proceed towards differentiation are switched into apoptosis by the ionic dissolution products. A controlled release of soluble Ca and Si from bioactive glass--resorbable polymer composites leads to vascularised soft tissue regeneration. Gene activation by controlled ion release provides the conceptual basis for molecular design of a third generation of biomaterials optimised for in situ tissue regeneration.

In vivo tissue response to resorbable silica xerogels as controlled-release materials

Biodegradable, controlled-release carrier materials with non-toxic degradation products are valuable for local delivery of biologically active molecules. Previously, it was shown that room-temperature processed silica sol-gels (or xerogels) are porous, resorbable materials that can release molecules of various sizes in a controlled, time dependent manner. Previous in vitro studies also demonstrated benefits of silica xerogels as controlled-release materials for the treatment of bone infections. Herein the tissue and cell response to xerogels is documented using a subacute implantation procedure. The tissue response was correlated to composition, surface properties, resorption rate and incorporation of the antibiotic vancomycin. Ca- and P-free and Ca- and P-containing xerogels, with and without apatite (AP) surface, were used. Xerogels were implanted either as discs in a subcutaneous site, or as granules in the iliac crest of New Zealand white rabbits. The samples with surrounding tissue were retrieved after 2 and 4 weeks of implantation. Silica xerogels implanted either as discs subcutaneously or as granules in the iliac crest showed a favorable tissue response. The granules, either with or without Ca and P content, gradually resorbed over time. The resorption was accompanied by extensive trabecular bone growth and a minimal inflammatory response. Ca- and P-containing granules with an AP-surface layer showed a slower resorption rate and more extensive new bone growth than those without AP layer. Among AP-coated granules, those with incorporated vancomycin showed the most favorable tissue response. The present in vivo data together with prior in vitro data suggest that these xerogels have potential as controlled-release materials for the treatment of bone infections and as carrier materials for a variety of other applications.

Bone healing in osteoporotic female rats following intra-alveolar grafting of bioactive glass

We have investigated the effect of ovariectomy combined with a low Ca diet on bone healing following the implantation of bioactive glass into extraction sockets, in rats. Ovariectomized rats received a low Ca diet from the day of surgery until sacrifice while sham-operated animals were fed a standard laboratory chow. Two weeks after surgery the upper incisors were extracted and the alveolar sockets in both groups were partially filled with a particulate bioglass (PerioGlas). The animals were killed 1, 2, 3 and 9 weeks after tooth extraction and the relative volume fraction of the healing components (bone trabeculae, connective tissue and coagulum remnants) was estimated in histological paraffin sections by a histometric differential point-counting method. The bioglass particles persisted inside the socket for all the experimental periods and, as bone repair proceeded, they were progressively enclosed in newly formed bone trabeculae which in some cases established a close contact with their surface. The volume fraction of neoformed bone trabeculae relative to the volume fraction of connective tissue and coagulum remnants was greater in the sockets of ovariectomized animals implanted with bioglass than in those of the overiectomized non-implanted groups.

Cellular biocompatibility and stimulatory effects of calcium metaphosphate on osteoblastic differentiation of human bone marrow-derived stromal cells

In the present study, the in vitro biocompatibility of calcium metaphosphate (CMP) with human bone marrow stromal cells (HBMSCs) and its effect on osteoblastic differentiation have been investigated. Powder and disk forms of CMP do not exert a cytotoxic effect on the HBMSCs undergoing osteoblastic differentiation. In addition, the HBMSCs adhere to the surface of the CMP disk as successfully as to the culture plate or hydroxyapatite (HA) disk. The HBMSCs adhered to either the HA or CMP disk display an undistinguishable actin arrangement and cellular phenotypes, indicating that the CMP does not disrupt normal cellular responses. An analysis of the differentiation of the HBMSCs cultured on culture plate, the HA and the CMP disk shows that three matrices are capable of supporting osteoblastic differentiation of the HBMSCs as accessed by alkaline phosphatase (ALP) staining. Further molecular analysis of osteoblastic differentiation of HBMSCs reveals that the CMP disk has a better ability than the HA disk to induce an expression of osteoblast-related genes, including ALP, osteoprotegerin (OPG), a decoy receptor for RANK ligand, and osteopontin (OPN), a non-collagenous bone matrix protein. The results demonstrate that, in addition to favorable biocompatibility, the CMP can stimulate osteoblastic differentiation of the HBMSCs in vitro.

Carbonate formation on bioactive glasses

The system termed 58S is a sol-gel-synthesized bioactive glass composed of SiO2, CaO, and P2O5, used in medicine as bone prosthetic because, when immersed in a physiological fluid, a layer of hydroxycarbonate apatite is formed on its surface. The mechanism of bioactive glass 58S carbonation was studied in the vacuum by means of in-situ FTIR spectroscopy with the use of CO2, H2O, and CD3CN as probe molecules. The study in the vacuum was necessary to identify both the molecules specifically involved in the carbonation process and the type of carbonates formed. Bioactive glass 58S was compared to a Ca-doped silica and to CaO. On CaO, ionic carbonates could form by contact with CO2 alone, whereas on 58S and on Ca-doped silica carbonation occurred only if both CO2 and an excess of H2O were present on the sample. The function of H2O was not only to block surface cationic sites, so that CO2 could not manifest its Lewis base behavior, but also to form a liquid-like (mono)layer that allowed the formation of carbonate ions. The presence of H2O is also supposed to promote Ca2+ migration from the bulk to the surface. Carbonates formed at the surface of CaO and of Ca-bearing silicas (thus including bioactive glasses) are of the same type, but are produced through two different mechanisms. The finding that a water excess is necessary to start heavy carbonation on bioactive glasses seemed to imply that the mechanism leading to in-situ carbonation simulates, in a simplified and easy-to-reproduce system, what happens both in solution, when carbonates are incorporated in the apatite layer, and during sample shelf-aging.

Osteoinduction of porous bioactive titanium metal

This is the first report of bone induction in a non-osseous site by titanium metal, which has long been recognized as a non-bioactive material. After undergoing specific chemical and thermal treatments, porous bioactive titanium induced bone formation without the need of additional osteogenic cells or osteoinductive agents. Four types of titanium implants were implanted in the dorsal muscles of mature beagle dogs, and were examined histologically after periods of 3 and 12 months. Chemically and thermally treated titanium, as well as pure titanium, was implanted either as porous blocks or as fibre mesh cylinders. Bone formation was found only in the chemically and thermally treated porous block implants removed after 12 months. The present study shows that even a non-soluble metal that contains no calcium or phosphorus can be an osteoinductive material when treated to form an appropriate macrostructure and microstructure. This finding may elucidate the nature of osteoinduction, and lead to the advent of epochal osteoinductive biomaterials for tissue regeneration.

Bioactive glass as a drug delivery system of tetracycline and tetracycline associated with β-cyclodextrin

The aim of this study was to evaluate the physical-chemical properties, in vivo biocompatibility and antimicrobial activity of bioactive glasses (BG) used as a controlled release device for tetracycline hydrochloride and an inclusion complex formed by tetracycline and beta-cyclodextrin at 1:1 molar ratio. The BG as well as their compounds loaded with tetracycline (BT) and tetracycline:beta-cyclodextrin (BTC) were characterized by FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry and by scanning electron microscopy and energy dispersive spectroscopy. The in vivo test was carried out with female mice split into three groups treated with bioactive glass either without drugs, or associated with tetracycline, or with tetracycline:beta-cyclodextrin by subcutaneous implantation. The histological examination of tissue at the site of implantation showed moderate inflammatory reactions in all groups after 72 h. The bacterial effect was tested on A. actinomycetemcomitans suspended in BHI broth, with or without bioactive particles. A considerable bacteriostatic activity was found with BT and BTC glasses, as compared to plain glass. The presence of cyclodextrin was important to slow down the release of tetracycline for a long period of time and it was verified that the presence of tetracycline or its inclusion complex, tetracycline:beta-cyclodextrin, did not affect the bioactivity of the glass.

Effects of materials parameters on mineralization and degradation of sol-gel bioactive glasses with 3D-ordered macroporous structures

Bioactive glasses (BGs) with three-dimensionally ordered macroporous (3DOM) structures were prepared by combining a sol-gel synthesis with colloidal crystal templating. 3DOM sol-gel BGs with two compositions (20 mol % CaO-80% SiO2 and 20 mol % CaO-4% P2O5-76% SiO2) and three macropore sizes (average: 345, 440, and 790 nm) were prepared. Glasses were separated into two particle sizes (212 microm< small < 355 microm and 600 microm < large < 1000 microm). The glasses were soaked in simulated body fluid at 37 degrees C for 2 or 4 days and the effects of composition, particle size, and macropore size on the formation of apatite and glass degradation were characterized. Within the parameter range of the experiments, several comparisons could be made. First, the formation of apatite and degradation of the glass were slightly enhanced for the phosphate containing composition. Second, large particles formed less apatite and degraded less completely compared with small particles. Lastly, an increase in macropore size slowed down the glass degradation and apatite formation processes, an effect related to the decreased internal surface area of the larger pore materials.

Chemically patterned, metal-oxide-based surfaces produced by photolithographic techniques for studying protein- and cell-interactions. II: Protein adsorption and early cell interactions

Protein adsorption and adhesion of primary human osteoblasts on chemically patterned, metal-oxide-based surfaces comprising combinations of titanium, aluminium, vanadium and niobium were investigated. Single metal samples with a homogeneous surface and bimetal samples with a surface pattern produced by photolithographic techniques were used. The physical and chemical properties of the samples have been extensively characterised and are presented in a companion paper. Here, we describe their properties in terms of cell responses during the initial 24h of cell culture. Regarding the cell number and activity there was no significant difference between any of the single metal surfaces. However the morphology of cells on vanadium surfaces became spindle-like. In contrast to the behaviour on single metal samples, cells exhibited a pronounced reaction on bimetallic surfaces that contained aluminium. Cells tended to stay away from aluminium, which was the least favoured metal in all two-metal combinations. An initial cell alignment relative to the pattern geometry was detectable after 2h and was fully developed after 18h of incubation. The organisation of f-actin and microtubules as well as the localisation of vinculin were all more pronounced on non-aluminium regions. We hypothesised that the differences in cell response could be associated with differences in the adsorption of serum proteins onto the various metal oxides. Protein adsorption experiments were performed using microscopy in conjunction with immunofluorescent stains. They indicated that both fibronectin and albumin adsorption were significantly greater on the non-aluminium regions, suggesting that differences in cellular response correlate with a modulation of the concentration of serum proteins on the surface.

The effect of silica-containing calcium-phosphate particles on human osteoblastsin vitro

There is an ongoing need for more effective and less costly bone substitutes. It has previously been proposed that silica-containing bioactive glass would be more effective as a bone repair material because of its physiochemical properties. Three newly synthesized silica-containing bioactive glass formulations, HA-31 (25%), HA-11 (50%), and HA-13 (75%), were tested as biocompatible substrates for the continued proliferation and phenotype expression of human bone cells in vitro. Two currently available bioactive glasses (BioGlass(R), Hydroxyapatite) served as comparisons. The biocompatibility of these bioglasses, as well as their osteoconductive properties, was assessed by employing primary cultures of human osteoblasts and human synoviocytes for 4 days. The results obtained demonstrated that the three new bioglasses enhanced the proliferative response of osteoblasts compared with osteoblasts cultured alone. Reverse Transcription Polymerase Chain Reaction (RT-PCR) analysis indicated that osteoblasts retained their phenotypic expression by continued expression of collagen type I and alkaline phosphatase. The newly synthesized preparations of silica-containing bioactive glass did not induce stimulation of proinflammatory markers iNOS and IL-1beta in synoviocytes. In conclusion, the newly synthesized silica-containing bioactive glasses are biocompatible substrate for bone-forming osteoblasts. However, the formulations tested did not show significant advantage over the currently available bioactive glasses in vitro.

Blendas de poli (ácido lático-co-ácido glicólico)/ poli (ácido lático): degradação in vitro

Placas de copolímero de poli(ácido lactico-co-glicólico) têm sido produzidas e usadas como implantes que degradam e são absorvidos pelo organismo. Implantes que podem ser absorvidos apresentam vantagens em relação aos implantes metálicos. Nesse trabalho, foram obtidas placas a partir de blendas de poli(ácido lactico-co-glicólico)/ poli(ácido lático), (PLGA/PLLA) e caracterizadas durante o processo de degradação in vitro. Verificou-se que as blendas são imiscíveis e a estabilidade térmica das mesmas aumenta com a proporção de PLLA. O grau de cristalinidade também aumenta com a proporção de PLLA na amostra e com o tempo de degradação. Além disso, verificou-se que o PLGA degrada rapidamente e sua presença e quantidade modifica nitidamente a morfologia das blendas.

Novel approach to fabricate porous gelatin-siloxane hybrids for bone tissue engineering

Porous and bioactive gelatin-siloxane hybrids were successfully synthesized by using a combined sol-gel processing, post-gelation soaking, and freeze-drying process to provide a novel kind of materials in the developments and optimization of bone tissue engineering. The pore sizes of the hybrids can be well controlled by varying the freezing temperature. The scaffolds were soaked in a simulated body fluid (SBF) up to 14 days to evaluate the in vitro bioactivity. The Ca(2+)-containing scaffolds showed in vitro bioactivity as they biomimetically deposited apatite, but the Ca(2+)-free scaffolds failed. Cytotoxicity and cytocompatibility of those scaffolds and their extracts were monitored by the MC3T3-E1 cell responses, including the cell proliferation and the alkaline phosphatase activity. It was demonstrated that appropriate incorporation of Ca(2+) ions stimulated osteoblast proliferation and differentiation in vitro.

Broad-spectrum bactericidal activity of Ag(2)O-doped bioactive glass

Bioactive glass has found extensive application as an orthopedic and dental graft material and most recently also as a tissue engineering scaffold. Here we report an initial investigation of the in vitro antibacterial properties of AgBG, a novel bioactive glass composition doped with Ag(2)O. The bacteriostatic and bactericidal properties of this new material and of two other bioactive glass compositions, 45S5 Bioglass and BG, have been studied by using Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus as test microorganisms. Concentrations of AgBG in the range of 0.05 to 0.20 mg of AgBG per ml of culture medium were found to inhibit the growth of these bacteria. Not only was AgBG bacteriostatic, but it also elicited a rapid bactericidal action. A complete bactericidal effect was elicited within the first hours of incubation at AgBG concentrations of 10 mg ml(-1). 45S5 Bioglass and BG had no effect on bacterial growth or viability. The antibacterial action of AgBG is attributed exclusively to the leaching of Ag(+) ions from the glass matrix. Analytical measurements rule out any contribution to AgBG-mediated bacterial killing by changes in pH or ionic strength or the dissolution of other ionic species from the biomaterials. Our observations of the dissolution profiles of Ag(+) from AgBG in the presence and absence of bacteria are consistent with silver accumulation by the bacteria.

Interaction of bioactive glasses with peritoneal macrophages and monocytes in vitro

Macrophage activation was analyzed following exposure to pure, crystalline alpha-quartz powders, two bioactive gel-glass powders of different compositions, and a melt-derived glass, 45S5 Bioglass. The release of reactive oxygen metabolites (chemiluminescence test), modifications of cell morphology, the amount of tumor necrosis factor alpha (TNFalpha) secreted, and the amount of TNFalpha mRNA expression were evaluated. The 45S5 Bioglass powders elicited the highest chemiluminescence response while the two solgel glasses had a lower response with less of an oxidative burst difference between them. Particulate bioactive glasses are actively ingested by mouse peritoneal macrophages, and only the 58S solgel glass had a moderate toxic effect on the macrophages. Macrophage cell morphology showed increased size and cell spreading, consistent with the high level of cytokine secretion induced by 45S5 Bioglass. The 45S5 Bioglass powders led to an increased release of TNFalpha and expression of TNFalpha mRNA relative to unstimulated and control treated monocytes. Bioactive glasses (and particularly 45S5 Bioglass) that in vivo induce rapid bone growth appear to activate an autocrine-like process in which the response evoked by the material (for example monocyte and macrophage activation with cytokine production) enhances subsequent interactions with cells in contact with the material.

Cellulose phosphates as biomaterials. In vivo biocompatibility studies

Femoral implantation of regenerated cellulose hydrogels revealed their biocompatibility, but a complete osseointegration could not be observed. Phosphorylation was therefore envisaged as the means to enhance cellulose bioactivity. In vitro studies showed that regenerated cellulose hydrogels promote bone cells attachment and proliferation but do not mineralize in acellular simulated physiological conditions. On the contrary, phosphorylated cellulose has shown an opposite behavior, by inducing the formation of a calcium phosphate layer in simulated physiological conditions, but behaving as a poor substrate for bone cells attachment and proliferation. In order to investigate the in vivo behavior of these materials, and assess the influence of mineralization induction ability vs. bone cells compatibility, unmodified and phosphorylated cellulose hydrogels were implanted in rabbits for a maximum period of 6 months and bone regeneration was investigated. Despite the difficulties arising from the retraction of cellulose hydrogels upon dehydration during the preparation of retrieved implants, histological observations showed no inflammatory response after implantation, with bone intra-spongious regeneration of cells and the integration of the unmodified as well as the phosphorylated cellulose implants. After a maximum implantation period of 6 months, histological observations, histomorphometry and the measurement of the amount of 45Ca incorporated in the surrounding tissue indicated a slightly better osseointegration of phosphorylated cellulose, although no significant differences between the two materials were found.

Sintering temperature effects on the in vitro bioactive response of tape cast and sintered bioactive glass-ceramic in Tris buffer

Tape casting procedures were used to form thin polymeric sheets (100 microm thickness) loaded with bioactive glass particulate. Blanks were punched from the sheets, stacked, laminated, and heated in air to 500 degrees C to remove the organic phase. The resulting bioactive glass discs were sintered at 800 degrees C, 900 degrees C, or 1000 degrees C. Because the material is built up in layers and can be machined in the green state, such a processing technique can be used to form complex-shaped materials. The in vitro bioactivity of the tape cast sintered (TCS) bioactive glass-ceramic discs was then assessed in Tris buffer. The sample surface area to volume buffer (SA/V) ratio was approximately 0.1 cm(2)/mL. Tape cast bioactive glass-ceramic sintered at 900 degrees C and 1000 degrees C formed crystalline hydroxyapatite layers after 24 h in Tris buffer as indicated by FTIR, SEM, and EDS analysis. Decreasing the SA/V ratio to 0.013 cm(2)/mL allowed for the formation of crystalline hydroxyapatite layers on the surface of 800C TCS bioactive glass-ceramic. Given the dependence of the bioactive response as a function of the processing schedule and SA/V ratio, it may be possible to tailor the response to that desired in vivo or in vitro for tissue engineering studies. Biaxial flexural strength of TCS bioactive glass-ceramic increased with increasing sintering temperature. Strength of samples sintered at 1000 degrees C for 3 h increased from 87 to 120 MPa after 2 weeks' immersion in Tris buffer.

Preparation and analysis of macroporous TiO2 films on Ti surfaces for bone-tissue implants

This article describes the preparation and analysis of macroporous TiO2 films on Ti surfaces, for application in bone tissue-Ti implant interfaces. These TiO2 bioceramic films have a macroporous structure consisting of monodisperse, three-dimensional, spherical, interconnected pores adjustable in the micron size range. Micron-sized polystyrene (PS) bead templates are used to precisely define the pore size, creating macroporous TiO2 films with 0.50, 16, and 50 microm diameter pores, as shown by scanning electron microscopy. X-ray photoelectron spectroscopy shows the films to be predominantly composed of TiO2, with approximately 10% carbon. X-ray diffraction reveal rutile as the main phase when fired to the optimal temperature of 950 degrees C. Preliminary experiments find that the in vitro proliferation of human bone-derived cells (HBDC) is similar on all three pore sizes. However, higher [3H]thymidine incorporation by the HBDC is observed when they are grown on 0.50- and 16-microm pores compared to the 50-microm pores, suggesting an enhanced cell proliferation for the smaller pores.

In vitro characterisation of zirconia coated by bioactive glass

An in vitro evaluation of a biomedical device, which combines the mechanical properties of zirconia substrates with the bioactivity of two different glass layers (AP40 and RKKP), was performed. In this work, data on different kinds of analysis were reported both on as-sintered zirconia samples and on RKKP- and AP40-coated zirconia substrates. Structure, composition and morphology of the apatite layer growth on the coated samples after 30 days of soaking in an acellular simulated body fluid, serum protein adsorption, fibroblasts and human osteoblast-like cells adhesion, growth, morphology and biochemical aspects were studied. Results of soaking test in SBF, revealed the growth of an apatite layer on the surface of the glass-coated samples. Proteins adsorbed to the materials were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and results evidenced that the two glass-coated materials bound a higher amount of total protein than did the zirconia substrate. Fibroblasts and osteoblast-like cells cultured on RKKP- and AP40-coated zirconia showed a higher proliferation rate, leading to confluent cultures with higher cell density and a generally better expression of osteoblast alkaline phosphatase activity in comparison with zirconia substrate. In conclusion, our results indicate that the surface chemical characteristics of the two glass coatings AP40 and RKKP, with no great differences between them, substantially enhance zirconia integration with bone cells at least in vitro. This effect may be of significance in the stability of glass-coated zirconia orthopaedic and dental implants.

Long-term in vivo bioactivity and degradability of bulk sol-gel bioactive glasses

Melt-derived bioactive glasses have been used with success in various clinical applications for over 10 years. Recently, particles of sol-gel-derived bioactive glasses with an initial high specific surface area have been shown to exhibit excellent osteoconductive properties as well as significant degradability. In this work, we explored the long-term in vivo bioactivity and degradability of bulk sol-gel-derived glasses in a rabbit model. Two sol-gel compositions (58S and 77S Bioglass) were used. Bulk 45S5 Bioglass was used as a control. Both sol-gel-derived glasses demonstrated osteoconductive properties similar to 45S5 Bioglass. In addition, absorbability was observed for both sol-gel-derived glasses starting after 12 weeks of implantation. Total absorption reached 40% after 52 weeks. No degradation could be measured in the case of bulk 45S5 melt-derived Bioglass within 1 year of implantation. The degradation process was highly time dependent, as demonstrated by regression analysis. New bone formation was found to fill in areas that had been resorbed, similar to bone remodeling. This absorbability can be assumed to be at least partially related to an osteoclastic resorption as viable osteoclasts-like cells were found to be in direct contact with the glass surfaces.

Bone bonding in sintered hydroxyapatite combined with a new synthesized agent, TAK-778

We studied the stimulatory effects of TAK-778, a new synthetic 3-benzothiepin derivative that promotes osteoblast differentiation, in bone bonding to sintered hydroxyapatite implants in rabbit tibiae. Smooth-surfaced rectangular plates (15 x 10 x 2 mm) made of sintered hydroxyapatite were implanted into the proximal metaphyses of bilateral rabbit tibiae, with TAK-778-containing sustained-release microcapsules packed into the medullary cavity in one limb and untreated microcapsules packed in the contralateral limb to serve as a paired control. At 4, 8, and 16 weeks after implantation, bone bonding at the bone-implant interfaces was evaluated by a detaching test and undecalcified histological examination. The tensile failure load increased from 4 to 16 weeks for both groups; however, the tensile failure load of the TAK-778-treated group was significantly greater than that of the control group at each interval after implantation. Histologically, the TAK-778-treated specimens showed greater active new bone formation mainly in the medullary cavity and more extensive bonding between the implant and bone than the untreated specimens. The results of this study suggest that adding osteoinductive TAK-778 to hydroxyapatite implants may significantly accelerate bone apposition to the implants and improve the bonding process at the interface. This would help to establish an earlier and stronger bonding of orthopedic ceramic implants between the surrounding bone tissue.

Effects of amelogenin on the transforming surface microstructures of Bioglass in a calcifying solution

Topographies of a bioactive glass (45S5 type Bioglass(R)) during 0-4 h of immersion in a supersaturated calcifying solution (SCS) and the SCS containing recombinant porcine amelogenin rP172 (SCS(rP172)) were observed by atomic force microscopy. Other techniques including X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and transmission electron microscopy were used for some complementary microstructural investigations. The smooth Bioglass surface changed to be very rough after 0.5 h of SCS immersion because of glass network dissolution. Spherical silica-gel particles with diameters of 150-300 nm consisting of substructures of 20-60 nm across had formed on the sample surfaces after 1 h of SCS immersion. The chemisorption of amorphous calcium phosphate and crystallization of nanophase apatite were seen to occur epitaxially on the silica-gel structures during 1-4 h of SCS immersion. During the first 0.5 h of SCS(rP172) immersion, more than 95% of rP172 protein in solution was adsorbed onto the sample surfaces and generated spherical assemblies of 10-60 nm diameters. During 0.5-4 h of SCS(rP172) immersion, the protein assemblies of rP172 remarkably induced the formation of orientated silica-gel plates (approximately 100-nm wide and 50-nm thick) and subsequently of long and thin apatite needle crystals. The recombinant amelogenin rP172-modulated apatite crystals resembled those formed in the early stage of tooth enamel biomineralization, suggesting the functional roles of amelogenins during the oriented growth of enamel crystallites and a great potential for amelogenins in applications designed to fabricate enamel-like calcium phosphate biomaterials.

Bioabsorbable scaffolds for guided bone regeneration and generation

Several different bioabsorbable scaffolds designed and manufactured for guided bone regeneration and generation have been developed. In order to enhance the bioactivity and potential osteoconductivity of the scaffolds, different bioabsorbable polymers, composites of polymer and bioactive glass, and textured surface structures of the manufactured devices and composites were investigated in in vitro studies and experimental animal models. Solid, self-reinforced polyglycolide (SR-PGA) rods and self-reinforced poly L-lactide (SR-PLLA) rods were successfully used as scaffolds for bone formation in muscle by free tibial periosteal grafts in animal experiments. In an experimental maxillary cleft model, a bioabsorbable composite membrane of epsilon-caprolactone and L-lactic acid 50/50 copolymer (PCL/LLA) film and mesh and poly 96L,4D-lactide (PLA96) mesh were found to be suitable materials for guiding bone regeneration in the cleft defect area. The idea of solid layer and porous layer combined together was also transferred to stiff composite of poly 70L,30DL-lactide (PLA70) plate and PLA96 mesh which structure is introduced. The osteoconductivity of several different biodegradable composites of polymers and bioactive glass (BG) was shown by apatite formation in vitro. Three composites studied were self-reinforced composite of PLA70 and bioactive glass (SR-(PLA70 + BG)), SR-PLA70 plate coated with BG spheres, and Polyactive with BG.

Bioactivity of sol-gel bioactive glass coated alumina implants

Alumina on alumina total hip arthroplasty has been in use for more than 25 years with encouraging results. However, an improvement of the alumina/bone interface still is required. The objective of this study was to investigate the in vitro and in vivo osteoconductive properties of sol-gel bioactive glass coated alumina implants. Two sol-gel glass compositions (58S Bioglass(R) and 77S Bioglass(R)) were used as coatings on alumina substrates and implanted in a rabbit model. The 58S sol-gel coating was employed in two configurations, single (A58S1) and double layer (A58S2). SEM analysis after one week in simulated body fluid revealed small crystals assumed to represent the initial phase of hydroxyapatite formation, whereas no clear conclusion could be drawn from Fourier transform infrared spectroscopy data. The percentage of bone in direct contact was greater for coated implants when compared to bulk alumina implants (p <0.001). In the case of A58S1 implants, bone percentage significantly increased from 45.1% after 3 weeks up to 87. 8% after 24 weeks of implantation (p = 0.0004). The presence of osteoid tissue, related to an aluminum release from the alumina substrates, was greatly diminished when compared to melt-derived glass-coated alumina implants.

Ionic products of bioactive glass dissolution increase proliferation of human osteoblasts and induce insulin-like growth factor II mRNA expression and protein synthesis

Bioglass 45S5 is an osteoproductive material, which resorbs by releasing its constitutive ions into solution. Treatment with the ionic products of Bioglass 45S5 dissolution in DMEM for 4 days increased human osteoblast proliferation to 155% of control. Two days after treatment, differential gene expression was analyzed by cDNA microarrays. Expression of a potent osteoblast mitogenic growth factor, insulin-like growth factor II (IGF-II), was increased to 290%. Additionally, there was a 168% increase in the concentration of unbound IGF-II protein in the conditioned media of treated osteoblasts. Expression levels of IGFBP-3, an IGF-II carrier protein, metalloproteinase-2 and cathepsin-D were also increased to 200, 340, and 310% of control levels, respectively. Metalloproteinase-2 and cathepsin-D are proteases that cleave IGF-II from its carrier proteins, resulting in the release of the unbound biologically active IGF-II. We suggest that the stimulatory effect of the ionic products of Bioglass 45S5 dissolution on osteoblast proliferation may be mediated by IGF-II.