Effect of aging time of sol on structure and in vitro calcium phosphate formation of sol-gel-derived titania films

Titania-based sol-gel coatings with Ag, Ca-P applied on titanium substrate developed for implantation

This research work is focused on the investigation of newly developed titania sol-gel coatings containing silver, calcium and phosphate with appropriate abilities to be implanted into the human body. These abilities include adhesion, bioactivity, antibacterial property and cytocompatibility of prepared coatings. Four types of coatings were applied on a titanium substrate by dip-coating technique under different conditions (TCP1, TCP2, TCPA1 and TCPA2). Surfaces of coatings after the firing without silver featured different distribution of circular areas containing Ca. The coatings TCPA1 and TCPA2 were made up of unhomogeneously situated silver. Adhesion of the coatings to the substrates was measured by a tape test. All types of the coatings demonstrated very good adhesion. Isolated cracks that appeared during the firing did not have a negative influence on the adhesion properties. Bioactivity of the coatings was tested in vitro using a simulated body fluid. Three of the four types demonstrated bioactive properties (TCP1, TCP2 and TCPA2), that is, precipitation of crystalline hydroxyapatite as was confirmed by X-ray diffraction. The antibacterial effect (against Escherichia coli and Staphylococcus epidermidis) and cytotoxicity (toward L929 and U-2 OS cell lines, direct and indirect test) were then tested. All the coatings demonstrated very good antibacterial effect against both bacteria after 4- and 24-hr interaction. All the coating types were evaluated as cytocompatible in the indirect test. Cells were able to grow even directly on the coatings.

Effects of Pre-Treatments on Bioactivity of High-Purity Titanium

Titanium and its alloys are frequently employed in medical and dental clinics due to their good tissue compatibility, including commercially available pure Ti, Ti6A4V, or Ti-15Zr-4Ta-4Nb. Yet, they may behave very differently when in contact with our plasma because of their own chemical composition. The present study was designed to compare the in vitro behavior of highly pure Ti (>99.99%; hpTi) with those of the above titanium specimens when they were subjected to heating in air (HT), H₂O₂ and heating (CHT), and heating in air after forming grooves on the surface (GT). Since one of the measures of material-tissue compatibility has been in vitro apatite formation in artificial plasma, like simulated body fluid (SBF) of the Kokubo recipe, the apatite deposition in SBF on their surface and in their grooves were examined in terms of the X-ray diffraction, scanning electron microscopy, and energy dispersion X-ray analysis. The results showed that hpTi was as active in in vitro apatite deposition as the other reference titanium samples mentioned above. Moreover, GT specimens of hpTi induced apatite deposition on the platform of the grooves as well as in the grooves. Therefore, hpTi was concluded to have better activity, and to be clinically applicable.

Solid state microwave synthesis of highly crystalline ordered mesoporous hausmannite Mn3O4films

Microwave calcination of ordered micelle templated manganese carbonate films leads to highly crystalline, ordered mesoporous manganese oxide, while similar temperatures in a furnace lead to disordered, amorphous manganese oxide.

Influence of the Al content on the in vitro bioactivity and biocompatibility of PVD Ti1−xAlxN coatings for orthopaedic applications

The biomedical applications of titanium aluminium nitride (Ti_1−xAlxN) coatings strongly depend on roughness, wettability and aluminium content.

Promoting bone-like apatite formation on titanium alloys through nanocrystalline tantalum nitride coatings

The study aims to advance the applicability of titanium alloys as bone implant materials by tackling some important aspects of surface robustness and bioactivity.

How Can Nanotechnology Help to Repair the Body? Advances in Cardiac, Skin, Bone, Cartilage and Nerve Tissue Regeneration

Nanotechnologists have become involved in regenerative medicine via creation of biomaterials and nanostructures with potential clinical implications. Their aim is to develop systems that can mimic, reinforce or even create in vivo tissue repair strategies. In fact, in the last decade, important advances in the field of tissue engineering, cell therapy and cell delivery have already been achieved. In this review, we will delve into the latest research advances and discuss whether cell and/or tissue repair devices are a possibility. Focusing on the application of nanotechnology in tissue engineering research, this review highlights recent advances in the application of nano-engineered scaffolds designed to replace or restore the followed tissues: (i) skin; (ii) cartilage; (iii) bone; (iv) nerve; and (v) cardiac.

Biocompatibility of sol-gel-derived titania-silica coated intramedullary NiTi nails

We investigated bone response to sol-gel-derived titania-silica coated functional intramedullary NiTi nails that applied a continuous bending force. Nails 26 mm in length, either straight or with a radius of curvature of 28 or 15 mm, were implanted in the cooled martensite form from a proximal to distal direction into the medullary cavity of the right femur in 40 Sprague-Dawley rats. Body temperature restored the austenite form, causing the curved implants to generate a bending force on the bone. The femurs were examined after 24 weeks. Bone length measurements did not reveal any bowing or shortening of the bone in the experimental groups. The results from histomorphometry demonstrated that the stronger bending force, together with sol-gel surface treatment, resulted in more bone deposition around the implant and the formation of significantly less fibrous tissue. Straight intramedullary nails, even those with a titania-silica coating, were poorly attached when compared to the implants with a curved austenite structure.

Effect of hydroxyapatite and titania nanostructures on early in vivo bone response

PURPOSE

Hydroxyapatite (HA) or titania nanostructures were applied on smooth titanium implant cylinders. The aim was to investigate whether nano-HA may result in enhanced osseointegration compared to nano-titania structures.

MATERIALS AND METHODS

Surface topography evaluation included detailed characterization of nano-size structures present at the implant surface combined with surface roughness parameters at the micro- and nanometer level of resolution. Microstructures were removed from the surface to ensure that bone response observed was dependent only on the nanotopography and/or chemistry of the surface. Early in vivo histological analyses of the bone response (4 weeks) were investigated in a rabbit model.

RESULTS

In the present study, nano-titania-coated implants showed an increased coverage area and feature density, forming a homogenous layer compared to nano-HA implants. Bone contact values of the nano-titania implants showed a tendency to have a higher percentage as compared to the nano-HA implants (p = .1).

CONCLUSION

Thus, no evidence of enhanced bone formation to nano-HA-modified implants was observed compared to nano-titania-modified implants. The presence of specific nanostructures dependent on the surface modification exhibiting different size and distribution did modulate in vivo bone response.

Soft tissue attachment on sol-gel-treated titanium implants in vivo

This study was designed to examine the attachment and reactions of soft tissues to sol-gel-derived TiO2 coatings. In the first experiment, TiO2 coated and uncoated titanium cylinders were placed subcutaneously into the backs of rats for 3, 11 and 90 days. Tissue response and implant surfaces were characterized with routine light microscopy and scanning electron microscopic (SEM) analysis. In the second experiment, TiO2-coated and uncoated discs were implanted subcutaneously into the backs of rats for 14 and 21 days. The discs were pulled out from the implantation sites with a mechanical testing device using a constant speed of 5 mm/min. Rupture force was registered, after which the discs were assigned for SEM and transmission electron microscopic (TEM) analysis. All the coated implants showed immediate contact with the surrounding soft tissues without a clear connective tissue capsule. Significantly better soft tissue response was measured for all the coated compared to the uncoated cylinders (p<0.01). Higher rupture forces were measured for all coated discs, although the differences were not statistically significant. An immediate and tight connection between connective tissue fibroblasts and coatings was noticed in TEM analysis. Our study indicates that TiO2 coatings improve soft tissue attachment on a titanium surface.

Peri-implant tissue response to TiO2 surface modified implants

OBJECTIVES

The objective of this study was to evaluate peri-implant soft tissue attachment and alveolar bone height on nanoporous TiO(2) thin film on commercial titanium dental implants compared with unmodified standard implants.

MATERIAL AND METHODS

In six adult beagle dogs, the mandibular premolars P2-P4 were extracted bilaterally. Sol-gel-derived nanoporous TiO(2) thin film was produced on smooth coronal part of standard ITI Straumann implants (4.1 mm x 8.0 mm) by dip coating method. After 3 months healing period of the extraction sockets modified (n=24) and unmodified (n=11) control implants were placed bilaterally. The animals were killed after 8 weeks and the samples were retrieved and processed for histologic/histomorfometric and TEM/SEM evaluations.

RESULTS

Histological examination showed mild or absent inflammatory reaction in peri-implant connective tissues around the surface modified implants. Further, junctional epithelium (JE)/connective tissue (CT) appeared to be in immediate contact with the experimental implants. Of the experimental implants, 22% were judged to be detached from the implant surface while 45% of the untreated control implants were detached. Dense plaques of hemidesmosomes were found in TEM evaluation of the JE cell membrane facing the surface-treated implants. In the histomorfometric analysis, the distance between the implant margin and alveolar bone crest was significantly shorter in surface-treated implants than in the control implants (P<0.02).

CONCLUSION

Nanoporous sol-gel-derived TiO(2) thin film on ITI Straumann dental implants improved soft tissue attachment in vivo.

Reconstruction of critical size calvarial bone defects in rabbits with glass–fiber-reinforced composite with bioactive glass granule coating

The aim of this study was to evaluate glass-fiber-reinforced composite as a bone reconstruction material in the critical size defects in rabbit calvarial bones. The bone defect healing process and inflammatory reactions were evaluated histologically at 4 and 12 weeks postoperatively. Possible neuropathological effects on brain tissue were evaluated. The release of residual monomers from the fiber-reinforced composite (FRC) was analyzed by high performance liquid chromatograph (HPLC).

RESULTS

At 4 weeks postoperatively, fibrous connective tissue ingrowth to implant structures was seen. Healing had started as new bone formation from defect margins, as well as woven bone islets in the middle of the defect. Woven bone was also seen inside the implant. Inflammation reaction was slight. At 12 weeks, part of the new bone had matured to lamellar-type, and inflammation reaction was slight to moderate. Control defects had healed by fibrous connective tissue. Histological examinations of the brain revealed no obvious damage to brain morphology. In HPLC analysis, the release of residual 1,4-butanedioldimethacrylate and methylmethacrylate from polymerized FRC was low.

CONCLUSIONS

This FRC-implant was shown to promote the healing process of critical size calvarial bone defect in rabbits. After some modifications to the material properties, this type of implant has the potential to become an alternative for the reconstruction of bone defects in the head and neck area in the future.

Comparison between sol-gel-derived anatase- and rutile-structured TiO2 coatings in soft-tissue environment

The bioactivity of the surface reactive TiO(2) coatings for medical implants can be locally modified by CO(2) laser processing to match with the properties of surrounding tissues. The TiO(2) coatings heat-treated at 500 degrees C exhibit in vitro bioactivity. With further CO(2) laser treatment they exhibit enhanced in vitro bioactivity. The aim of this in vivo study was to compare the performance of heat-treated anatase-structured TiO(2) coatings with preheat-treated and CO(2) laser-treated rutile-structured coatings in terms of their ability to attach soft connective tissues. The coatings were characterized with TF-XRD and AFM. TiO(2)-coated discs were implanted in rats. The samples were analyzed with routine histology, SEM-EDS, and TEM. In both groups, already at 3 days, soft connective tissues were in immediate contact with the surface. No thick crystalline CaP layer was detected by SEM-EDS, but a thin amorphous CaP layer was detected by XPS. No gap between the cell membrane and the coating could be observed in TEM pictures. No differences were observed between the anatase- and rutile-structured coatings in terms of tissue responses. Further studies are needed to verify if the tissues are adherent to the surface of the implant.

Sol-gel-derived TiO(2)-SiO (2) implant coatings for direct tissue attachment. Part I: design, preparation and characterization

A series of sol-gel derived TiO(2)-SiO(2) mixed oxide coatings were prepared by carefully controlling the process parameters to obtain silica-releasing coatings consisting of nanoparticles. These features are of paramount importance for enhanced cell adhesion and activation. To achieve both these goals the Ti-alkoxide and Si-alkoxide were first separately hydrolysed and the titania-silica mixed sol was further reacted before the dipping process to obtain the desired particle sizes resulting to the biologically favourable topographical features. Silica release was observed from all the prepared coatings and it was dependent on SiO(2) amount added to the sols, i.e., the higher the added amount the higher the release. In addition, calcium phosphate was able to nucleate on the coatings. From the obtained SiO(2) dissolution data, together with the detailed XPS peak analysis, the mixed oxide coatings are concluded to be chemically heterogeneous, consisting of TiO(2) and SiO(2) species most likely linked together by Ti-O-Si bonds. TiO(2) is chemically stable making long-term implant coating possible and the desired nanoscale dimensions were well preserved although the composition was changed as a consequence of SiO(2) dissolution under in vitro conditions.

Titania and Titania-Silica Coatings for Titanium: Comparison of Ectopic Bone Formation within Cell-Seeded Scaffolds

The aim of this study was to compare titania (TiO(2))-coated, titania-silica (TiSi)-coated, and uncoated (cpTi) titanium fiber meshes as scaffolds for bone engineering. The scaffolds were loaded with bone marrow stromal cells and implanted subcutaneously in rats. Ectopic bone formation after 1, 4, and 12 weeks of implantation was evaluated using histology and histomorphometry. After 1 week of implantation, multiple patches of unorganized mineralizing tissue were seen in all implants. The amount of this bone-like tissue clearly increased from 1 to 4 weeks. Bone apposition occurred in direct contact with coated meshes, while a thin layer of unmineralized fibrous tissue was often observed surrounding cpTi mesh fibers. After 12 weeks, the structure of bone, with bone marrow-like tissue, was further matured and mesh fibers were embedded in lamellar bone. No statistical differences in the amount of mineralized bone were observed between scaffold types at any point of time. Only TiSi scaffolds showed further increase in bone area from 4 to 12 weeks (p < 0.01). A notable difference was that the sol-gel coatings resulted in enhanced initial bone contact and distribution of bone tissue, whereas uncoated implants showed bone formation mainly in the center of the scaffolds. In conclusion, TiO(2)-based sol-gel coatings may be used in tissue engineering to gain more uniform distribution of bone throughout titanium fiber mesh scaffolds.

Plasma-controlled nanocrystallinity and phase composition of TiO2: A smart way to enhance biomimetic response

This contribution sheds light on the role of crystal size and phase composition in inducing biomimetic apatite growth on the surface of nanostructured titania films synthesized by reactive magnetron sputtering of Ti targets in Ar+O(2) plasmas. Unlike most existing techniques, this method enables one to deposit highly crystalline titania films with a wide range of phase composition and nanocrystal size, without any substrate heating or postannealing. Moreover, by using this dry plasma-based method one can avoid surface hydroxylation at the deposition stage, almost inevitable in wet chemical processes. Results of this work show that high phase purity and optimum crystal size appear to be the essential requirement for efficient apatite formation on magnetron plasma-fabricated bioactive titania coatings.

Topography and surface energy dependent calcium phosphate formation on Sol-Gel derived TiO2 coatings

Heterogeneous nucleation and growth of calcium phosphate (CaP) on sol-gel derived TiO(2) coatings was investigated in terms of surface topography and surface energy. The topography of the coatings was derived from AFM measurements, while the surface energy was determined with contact angle measurements. The degree of precipitation was examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The precipitation of CaP was found to be dependent on both topography and surface energy. A high roughness value when combining the RMS roughness parameter S(q) with the number of local maxima per unit area parameter S(ds) enhances CaP formation. The hydrophilicity of the coating was also found to be of importance for CaP formation. We suggest that the water contact angle, which is a direct measure of the hydrophilicity of the surface, may be used to evaluate the surface energy dependent precipitation kinetics rather than using the often applied Lewis base parameter.

Effect of Ceramic Coating by Aerosol Deposition on Abrasion Resistance of a Resin Composite Material

Aerosol deposition (AD coating) is a novel technique to coat solid substances with a ceramic film. The purpose of the present study was to investigate the effect of AD coating on abrasion resistance of a resin composite material. A 5-microm-thick aluminum oxide layer was created on the polymerized resin composite. The specimen was cyclically abraded using a toothbrush abrasion simulator for 100,000 cycles. Abraded surface was then measured with a profilometer to determine the average roughness (Ra) and maximum roughness (Rmax). It was found that abrasion cycling increased the Ra value of the No-AD-coating group, but decreased the Ra and Rmax values of the AD coating group. Moreover, the AD coating group showed significantly smaller Ra and Rmax values after 100,000 abrasion cycles as compared to the No-coating control group. Microscopic observation supported these findings. In conclusion, the resistance of the resin composite against toothbrush abrasion was improved by AD coating.

Plasma-treated nanostructured TiO2 surface supporting biomimetic growth of apatite

Although some types of TiO(2) powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO(2) coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO(2) surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO(2) coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO(2) surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO(2) with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO(2) coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.

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.

TF-XRD examination of surface-reactive TiO2 coatings produced by heat treatment and CO2 laser treatment

When surface-reactive (bioactive) coatings are applied to medical implants by means of CO2 laser processing, the bioactivity of the surface of the implant can be locally modified to match the properties of the surrounding tissues to provide a firm fixation of the implant. The aim of this study was to compare the heat treated TiO2 coatings with the laser-treated TiO2 coatings in terms of amorphous-crystalline-phase development. The coatings were characterized with thin-film X-ray diffraction (TF-XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The TiO2 coatings heat treated at 500 degrees C known to be bioactive in SBF (simulated body fluid) consisted mainly of anatase with some rutile-phase, suggesting a predominant effect of anatase on reactivity of coatings. However, the coatings preheat-treated at 500 degrees C with further laser treatment exhibited enhanced bioactivity while consisting mainly of rutile. These findings indicated a key role of both rutile and anatase for the reactivity of the coatings. Without preheat treatment, by laser treatment alone, the amorphous titania coatings developed into mixed anatase/rutile containing coatings. This structural organization and the increase in crystal size are thus considered to be the reasons for their bioactivity. The SBF results indicate the possibility to control bioactivity by altering laser power used through the anatase/rutile crystallinity enhancement.

Evaluation of calcium titanate as apatite growth promoter

Calcium titanate (CaTiO(3), perovskite) has been used to determine its apatite nucleation ability and propose a possible nucleation initial step. Measurements of calcium leaching from the calcium titanate surface and phosphate adsorption experiments were carried out separately by using commercial calcium titanate suspensions at room temperature. Adsorption behaviour determined by zeta potential measurements shows that phosphate is strongly adsorbed on the calcium titanate surface. It was found that the higher the pH, the higher the Ca present on the calcium titanate surface, but phosphate adsorption followed this trend only up to pH 7.4. Results suggest that phosphate ions are not adsorbed only on Ca sites but also on TiO(2) groups sites of the surface, formed after calcium leaching from the surface. When both ions are simultaneously added in a modified simulated body fluid containing calcium titanate, at 37 degrees C, apatite growth occurs on its surface after 1 week of immersion.

Acid-induced bioactive titania surface

Nano- and conventional-TiO(2) powders were deposited onto titanium alloy using atmospheric plasma spraying technology. As-sprayed titania coatings were treated by H(2)SO(4) and HCl solutions at room temperature for 24 h, and the bioactivity was evaluated by simulated body fluid tests. Measured X-ray diffraction patterns indicated that as-sprayed titania coatings obtained from both nano and conventional powders were composed of primary rutile as well as a small quantity of anatase and Ti(3)O(5). The surface of as-sprayed coatings prepared from the conventional powder was rougher than that from nanopowder. After immersion in simulated body fluid for 2 weeks, both acid-treated nano- and titania coatings have induced carbonate-containing hydroxyapatite to form on the surfaces. However, this phenomenon did not appear on the surface of as-sprayed nano- and conventional-titania coatings. The results obtained indicated that the bioactivity of plasma sprayed titania coatings was improved by the acid treatment and had nothing to do with phase composition and particle size of the original TiO(2) powders.

Use of sol-gel-derived titania coating for direct soft tissue attachment

A firm bond between an implant and the surrounding soft tissue is important for the performance of many medical devices (e.g., stents, canyls, and dental implants). In this study, the performance of nonresorbable and reactive sol-gel-derived nano-porous titania (TiO(2)) coatings in a soft tissue environment was investigated. A direct attachment between the soft tissue and the sol-gel-derived titania coatings was found in vivo after 2 days of implantation, whereas the titanium control implants showed no evidence of soft tissue attachment. The coated implants were in immediate contact with the connective tissue, whereas the titanium controls formed a gap and a fibrous capsule on the implant-tissue interface. The good soft tissue attachment of titania coatings may result from their ability to initiate calcium phosphate nucleation and growth on their surfaces (although the formation of poorly crystalline bonelike apatite does not occur). Thus, the formation of a bonelike CaP layer is not crucial for their integration in soft tissue. The formation of bonelike apatite was hindered by the adsorption of proteins onto the initially formed amorphous calcium phosphate growth centers, thus preventing the dissolution/reprecipitation processes required for the formation of poorly crystalline bonelike apatite. These findings might open novel application areas for sol-gel-derived titania-based coatings.

Local induction of calcium phosphate formation on TiO2 coatings on titanium via surface treatment with a CO2 laser

Sol-gel-derived TiO(2) coatings are known to promote bonelike hydroxyapatite formation on their surfaces in vitro and in vivo. Hydroxyapatite integrates into bone tissue. In some clinical applications, the surface of an implant is simultaneously interfaced with soft and hard tissues, so it should match the properties of both. A new method is introduced for treating the coatings locally in a controlled manner. The local densification of sol-gel-derived titania coatings on titanium substrates with a CO(2) laser was studied in terms of the in vitro calcium phosphate-inducting properties. CO(2)-laser-treated multilayer coatings were compared with furnace-fired coatings prepared with the same recipe and previously shown to be bioactive. Additionally, local areas of furnace-fired multilayer coatings (previously shown to be bioactive in vitro) were further laser-treated to achieve various properties in the same implant. Topological surface properties were examined with atomic force microscopy. The formation of hydroxyapatite was studied with Fourier transform infrared and scanning electron microscopy energy-dispersive X-ray analysis. The results show that calcium phosphate formation can be adjusted locally by laser treatment. Calcium phosphate is a bonelike hydroxyapatite. The local treatment of sol-gel-derived coatings with a CO(2) laser is a promising technique for creating implants with various properties to interface different tissues and a possible way of coating implants that do not tolerate furnace firing.

Structural dependence of apatite formation on titania gels in a simulated body fluid

The apatite-forming ability of titania gels with different structures has been investigated in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Titania gels with an amorphous structure or with an anatase or rutile structure were prepared by the sol-gel process with a subsequent heat treatment at various temperatures. The titania gels with an amorphous structure did not induce apatite formation on their surfaces in the simulated body fluid, whereas gels with an anatase or rutile structure induced apatite formation on their surfaces. The deposition of apatite was more pronounced on the anatase gels than on the rutile gels. This indicates that a specific structure of titania is effective in inducing apatite formation in a body environment. Such a specific structure was assumed in this study to be the crystalline planar arrangement in the anatase structure, which facilitates epitaxy of the apatite crystal.

Surface properties of in vitro bioactive and non-bioactive sol-gel derived materials

The acid-base properties of several in vitro bioactive (able to form bone mineral-like calcium phosphate on their surfaces) and non-bioactive sol-gel processed oxides are studied. The amount of Lewis acid sites was calculated from the pyridine adsorption using the Langmuir adsorption model. The Henry adsorption model was used in cases where no specific affinity between the adsorbent and the probe molecule was observed. The results were used to calculate the specific amounts of acidic and basic sites on SiO2- and TiO2-based materials. The zeta potential was measured for dip-coated TiO2 films, calcium- and phosphate-doped TiO2 films and for a non-bioactive Al2O3 film. Also, the calcium phosphate formation in simulated body fluid on in vitro bioactive TiO2 film was studied with zeta potential measurements. The results showed dependence on the negative surface charge and the important role of calcium adsorption in the beginning of the calcium phosphate formation. Surface topography of the films was investigated with atomic force microscopy, including a detailed analysis of the peak heights and distribution over cross sections. It was observed that in vitro bioactivity was strongly dependent on the nanoscale dimensions. Consequently, the in vitro calcium phosphate formation seems to be due to both the chemical interactions and the surface structure.

Osteoblast differentiation of bone marrow stromal cells cultured on silica gel and sol-gel-derived titania

Primary cultures of osteogenic precursor cells derived from rat bone marrow stroma were performed on commercially available pure titanium discs (Ti c.p.) and surface modified Ti c.p.using a sol-gel technique (Ti sol). In separate repeated experimental runs, cell behavior and in vitro mineralization were compared with cultures on silica gel bioactive glass discs (S53P4). All substrates were incubated in simulated body fluid prior to the experiment. Overall, variable effects between experimental runs were seen. Apparently, this was due to the heterogeneous nature of the used cell population. Therefore, only careful conclusions can be made. Initial cell adhesion and growth rates between 3 and 5 days of culture--analyzed by cell numbers--were in general comparable for the two titanium substrates, while initial growth up to day 3 is suggested to be higher in Ti c.p. compared to Ti sol. Although initial cell adhesion on the S53P4 glass discs was lower than the titanium substrates, cell growth rates appeared to be higher on the silica gel compared to the two titanium substrates. Further, there were some indications that the early and late osteoblast differentiation markers, alkaline phosphatase and osteocalcin, monitored up to day 24, were elevated in Ti c.p cultures compared to Ti sol cultures. There were no differences observed in in vitro mineralization between the titanium groups. S53P4 seemed to display a substantially higher differentiating capacity for both osteogenic cell markers as well as in vitro mineralization compared to the two titanium substrates.

In vitro bioactivity and structural features of mildly heat-treated sol-gel-derived silica fibers

The ability of sol-gel-derived silica fibers heat treated at a low temperature to induce formation of bone-like calcium phosphate (HCA) on their surfaces provides alternatives for the design of novel biomaterials, for example as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers, which were heat-treated at 175 degrees and 250 degrees C. In addition, the differences in the surface topography (in a nanometer scale) of different fibers with respect to their in vitro bioactivity were studied. The structure of the fibers was varied using three different factors: (1) spinnable sols having varying structures and sizes of silica polymers to establish varying viscosity levels; (2) aging of green-state fibers; and (3) heat treatment of fibers. The in vitro bioactivity and solubility tests were done in simulated body fluid (SBF). To monitor surface topography and roughness of the heat-treated silica fibers, a scanning probe microscopy (SPM) with tapping mode AFM was used. Different fibers obtained clearly different properties. The fibers spun at about eta > 3.0 Pas had the best properties with respect to bioactivity, especially when they were heat-treated at 175 degrees C. It was found that surface structure in a nanometer scale was the most important factor controlling the in vitro bioactivity of heat-treated silica fibers. The correct proportions between the peaks and peak distances at the surfaces are suggested to be important with respect to in vitro bioactivity. The results indicate that peak distance distribution between 5-50 nm, especially between 5-20 nm, together with a peak height > or = 1 nm is most favorable for calcium phosphate formation.

Influence of sol and stage of spinnability on in vitro bioactivity and dissolution of sol-gel-derived SiO2 fibers

The ability of the sol-gel-derived green state silica fibers to induce the formation of bone-like calcium phosphate (HCA) on their surfaces has not been studied earlier. Bioactive silica fibers provide alternatives for the design of novel products, e.g., as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers. Different fibers with different bulk structures were prepared by changing the composition and controlling the stage of spinnability. Additionally, the influence of the aging time of the fibers on the bulk structure of the samples was investigated. Furthermore, the ability to form calcium phosphate was investigated in vitro in the simulated body fluid (SBF). Transmission electron microscopy was used to illustrate the bulk structure of the green state fibers and scanning electron microscopy to illustrate the formed calcium phosphate layer on the fibers. The fibers were additionally characterized by measuring the dissolution of the silica in the SBF. In vitro bioactive silica fibers were successfully prepared. The calcium phosphate layer was formed within 1-5 days in the best case. The structural stability and the in vitro bioactivity varied with the aging time expect in one case where practically stable fibers could be prepared. The concentration of silica released in the SBF had no direct connection with the HCA formation. The silica-rich gel layer was not observed on the fibers, but the structure of the fibers was suggested to have an important role in the HCA formation.