Hydroxyapatite and fluor-hydroxyapatite layered film on titanium processed by a sol-gel route for hard-tissue implants

Changes in the morphology, mechanical strength and biocompatibility of polymer and metal/polymer fabricated hydroxyapatite for orthopaedic implants: a review

Hydroxyapatite (HAp) is a well-known bioceramic known for its high biocompatibility and good bioactivity. The structure of HAp mimics the natural bone structure and thus, it is widely used as implants for hard tissues. Despite possessing the above properties, it lacks mechanical strength, is susceptible to the growth of microbes over time and has low degradability. Polymers can be synthetic or natural. They can be a better choice to be used as additives to improve the properties of HAp due to its better mechanical strength and high biodegradability. A combination of metals and polymers together can overcome the drawbacks of HAp to a greater extent. This review article deals with different polymers and metal/polymer fabricated HAp to show the changes in the properties of HAp following the substitution. It also deals with how better they could be used as a hard tissue implant.

Enhanced model protein adsorption of nanoparticulate hydroxyapatite thin films on silk sericin and fibroin surfaces

Hydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm² on the latter surface as compared to 1.37 µg/cm² of hydroxyapatite on glass without an intermediate silk sericin layer. The BSA adsorption on glass (blank), glass/c-HAp, glass/m-HAp, glass/sericin/c-HAp, and glass/sericin/m-HAp substrates, reported as decrease in BSA concentration versus contact time.

Defect-related luminescent nanostructured hydroxyapatite promotes mineralization through both intracellular and extracellular pathways

Hydroxyapatite (HAP) is a widely used biomaterial for bone tissue substitution due to its chemical similarity with the natural bone. Defect-related luminescent HAP materials have the same chemical composition as normal HAP and excellent biocompatibility. However, only few works have focused on the defect-related luminescent HAP materials on bone regeneration. In this work, we systematically investigated the bone regeneration pathway induced by nanostructured particles using defect-related luminescent hydroxyapatite (S2) materials. We monitored the subcellular distribution and location of S2 during osteoblast differentiation with the property of defect-related luminescence. Nano-scale S2 could be internalized by osteoblasts (OBs) via caveolae-mediated endocytosis and macropinocytosis. S2 incorporated into the lysosomes dissolved and released calcium ions for the formation of mineralized nodules. Extracellular S2 also promoted bone regeneration as a nucleation site. Taken together, the physical properties of hydroxyapatite control the bone regeneration pathway in osteoblasts.

Hydroxyapatite (HAP) is a widely used biomaterial for bone tissue substitution due to its chemical similarity with the natural bone.

Bioceramic Layers with Antifungal Properties

The sol-gel method was used to synthesize the silver doped hydroxyapatite (Ag:HAp) gels in order to produce the antifungal composite layers. The pure Ti disks were used as the substrate for the composite layers. Important information about suspensions used to make Ag:HAp composite layers were obtained from an ultrasonic technique. The identification of the phase composition of the Ag:HAp composite layers was accomplished X-ray diffraction (XRD). The morphology and the thickness of the layers was evaluated using scanning electron microscopy (SEM). The uniform distribution of the constituent elements (Ag, Ca, P, and O) in both analyzed samples was observed. The antifungal activity of the samples against Candida albicans ATCC 10231 microbial strain were investigated immediately after their preparation and six months later. SEM and confocal laser scanning microscopy (CLSM) images showed that the composite layers at the two time intervals exhibited a strong antifungal activity against Candida albicans ATCC 10231 and completely inhibited the biofilm formation.

Structural Characterization and Antifungal Studies of Zinc-Doped Hydroxyapatite Coatings

The present study is focused on the synthesis, characterization and antifungal evaluation of zinc-doped hydroxyapatite (Zn:HAp) coatings. The Zn:HAp coatings were deposited on a pure Si (Zn:HAp_Si) and Ti (Zn:HAp_Ti) substrate by a sol-gel dip coating method using a zinc-doped hydroxyapatite nanogel. The nature of the crystal phase was determined by X-ray diffraction (XRD). The crystalline phase of the prepared Zn:HAp composite was assigned to hexagonal hydroxyapatite in the P63/m space group. The colloidal properties of the resulting Zn:HAp (xZn = 0.1) nanogel were analyzed by Dynamic Light Scattering (DLS) and zeta potential. Scanning Electron Microscopy (SEM) was used to investigate the morphology of the zinc-doped hydroxyapatite (Zn:HAp) nanogel composite and Zn:HAp coatings. The elements Ca, P, O and Zn were found in the Zn:HAp composite. According to the EDX results, the degree of Zn substitution in the structure of Zn:HAp composite was 1.67 wt%. Moreover, the antifungal activity of Zn:HAp_Si and Zn:HAp_Ti against Candida albicans (C. albicans) was evaluated. A decrease in the number of surviving cells was not observed under dark conditions, whereas under daylight and UV light illumination a major decrease in the number of surviving cells was observed.

Hydroxyapatite-TiO2 Hybrid Coating on Ti Implants

A hydroxyapatite (HA)-titania (TiO2) hybrid coating is developed to improve the biocompatibility of titanium (Ti) implants. The HA predeposited layer on Ti via electron beam (e-beam) evaporation is subsequently treated by micro-arc oxidation (MAO) to produce an HA-TiO2 hybrid layer on Ti. The e-beam-deposited HA layer has a thickness of ≈1 μm and was highly dense prior to MAO. By means of MAO treatment, a rough and porous TiO2 layer is formed beneath the HA layer with a simultaneous local dissolution of the HA layer. Due to the HA precoating, high concentrations of Ca and P are preserved on the coating surface. The osteoblast-like cells on the hybrid coating layer grow and spread favorably. The cell proliferation rate on the hybrid coatings is not much different from that on pure Ti or simple MAO-treated Ti. However, the alkaline phosphatase (ALP) activity of the cells is significantly higher ( p < 0.05) on the HA-TiO2 hybrid coatings than on either the pure Ti or the simple MAO-treated specimen, suggesting that the cellular activity on the hybrid coatings is improved.

Calcium orthophosphate deposits: Preparation, properties and biomedical applications

Since various interactions among cells, surrounding tissues and implanted biomaterials always occur at their interfaces, the surface properties of potential implants appear to be of paramount importance for the clinical success. In view of the fact that a limited amount of materials appear to be tolerated by living organisms, a special discipline called surface engineering was developed to initiate the desirable changes to the exterior properties of various materials but still maintaining their useful bulk performances. In 1975, this approach resulted in the introduction of a special class of artificial bone grafts, composed of various mechanically stable (consequently, suitable for load bearing applications) implantable biomaterials and/or bio-devices covered by calcium orthophosphates (CaPO4) to both improve biocompatibility and provide an adequate bonding to the adjacent bones. Over 5000 publications on this topic were published since then. Therefore, a thorough analysis of the available literature has been performed and about 50 (this number is doubled, if all possible modifications are counted) deposition techniques of CaPO4 have been revealed, systematized and described. These CaPO4 deposits (coatings, films and layers) used to improve the surface properties of various types of artificial implants are the topic of this review.

Surface characterization and osteoblast response to a functionally graded hydroxyapatite/fluoro-hydroxyapatite/titanium oxide coating on titanium surface by sol-gel method

OBJECTIVES

To improve efficacy of current titanium and its alloys, in bioactivity and speed of osseointegration, of orthopaedic implants.

MATERIALS AND METHODS

A novel triple-layered functional graded coating, consisting of a porous hydroxyapatite (HA) outermost layer, fluoro-HA (FHA) intermediate layer and titanium oxide (TiO2 ) innermost layer, was created on a titanium substrate by a multistep sol-gel method. X-ray diffraction analysis showed TiO2 anatase and apatite crystallization in the coating.

RESULTS

Morphological analysis performed by scanning electron microscopy showed excellent bonding between coating and substrate, with a thickness of ~2 μm. Scratch testing found favourable adhesion strength of the composite coating. In addition, optical microscope images suggested good biocompatibility. Considering thet in vitro cell response, osteoblasts on the coating exhibited higher cell proliferation and ALP activity compared to pure titanium and HA coating, and demonstrated excellent coating bioactivity.

CONCLUSIONS

Current results indicated that the novel TiO2 /FHA/HA coating has promising clinical applications in orthopaedic and dental implantation.

Calcium orthophosphate coatings, films and layers

In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the interfaces, the surface properties of the implants are of the paramount importance in determining both the biological response to implants and the material response to the physiological conditions. Hence, a surface engineering is aimed to modify both the biomaterials, themselves, and biological responses through introducing desirable changes to the surface properties of the implants but still maintaining their bulk mechanical properties. To fulfill these requirements, a special class of artificial bone grafts has been introduced in 1976. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide an adequate bonding to bones. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings, films and layers used to improve the surface properties of various types of artificial implants are the topic of this review.

In vitro and in vivo studies of surface-structured implants for bone formation

Background and methods

Micronanoscale topologies play an important role in implant osteointegration and determine the success of an implant. We investigated the effect of three different implant surface topologies on osteoblast response and bone regeneration. In this study, implants with nanotubes and micropores were used, and implants with flat surfaces were used as the control group.

Results

Our in vitro studies showed that the nanostructured topologies improved the proliferation, differentiation, and development of the osteoblastic phenotype. Histological analysis further revealed that the nanotopology increased cell aggregation at the implant-tissue interfaces and enhanced bone-forming ability. Pushout testing indicated that the nanostructured topology greatly increased the bone-implant interfacial strength within 4 weeks of implantation.

Conclusion

Nanotopography may improve regeneration of bone tissue and shows promise for dental implant applications.

Evaluation of biomimetic scaffold of gelatin-hydroxyapatite crosslink as a novel scaffold for tissue engineering: biocompatibility evaluation with human PDL fibroblasts, human mesenchymal stromal cells, and primary bone cells

Biomimetic gelatin (gel)-hydroxyapatite (HA) composites have been prepared for studying hard tissue engineering scaffolds. However, the biocompatibility test of this form of material using these three cell types, which are periodontal ligament (PDL) fibroblast cells, human mesenchymal stromal cells (HMSc) and primary cells from human hip bone (HBc) has never been evaluated. The objective of this article is to prepare and evaluate the biocompatibility of gel-HA crosslinked scaffold for tissue engineering. Two different scaffolds were prepared: preparation (1), 2.5% gel/2.5% HA; preparation (2), 2.5% gel/5% HA. Three cell types including PDL, HMSc, and HBc were used. Assessment of biocompatibility and osteoblastic cellular responses was evaluated using a three-dimensional cell culture method and scanning electron microscopy (SEM). From SEM, it was observed that scaffold (1) exhibits stable porous formation with well-blended and dispersed HA powder. All three cell types were able to proliferate in both scaffolds. The HMSc and HBc got attached to the scaffolds to a significantly higher degree and subsequently proliferated more than PDL. The alkaline phosphatase (ALP) activities of HMSc and HBc were stronger when cultured in scaffold (S1) than (S2). It was seen that the two scaffold preparations show good biocompatibility with all three cell types tested. The better cellular responses with scaffold (S1) than (S2) might be due to the different structural and morphological characteristics, that is, scaffold (S1) retained more small-sized apatite crystals and a better developed pore configuration than scaffold (S2). Based on these findings, the biomimetically synthesized composite scaffolds have the potential to be used in hard tissue regeneration and tissue engineering fields.

Composite nanofiber mats consisting of hydroxyapatite and titania for biomedical applications

Composite nanofiber mats (HA/TiO2) consisting of hydroxyapatite (HA) and titania (TiO2) were fabricated via an electrospinning technique and then collagen (type I) was immobilized on the surface of the HA/TiO2 composite nanofiber mat to improve tissue compatibility. The structure and morphology of the collagen-immobilized composite nanofiber mat (HA/TiO2-col) was investigated using an X-ray diffractometer, electron spectroscopy for chemical analysis, and scanning electron microscope. The potential of the HA/TiO2-col composite nanofiber mat for use as a bone scaffold was assessed by an experiment with osteoblastic cells (MC3T3-E1) in terms of cell adhesion, proliferation, and differentiation. The results showed that the HA/TiO2-col composite nanofiber mats possess better cell adhesion and significantly higher proliferation and differentiation than untreated HA/TiO2 composite nanofiber mats. This result suggests that the HA/TiO2-col composite nanofiber mat has a high-potential for use in the field of bone regeneration and tissue engineering.

A bioactive coating of a silica xerogel/chitosan hybrid on titanium by a room temperature sol-gel process

A bioactive coating consisting of a silica xerogel/chitosan hybrid was applied to Ti at room temperature as a novel surface treatment for metallic implants. A crack-free thin layer (<2 microm) was coated on Ti with a chitosan content of >30 vol.% through a sol-gel process. The coating layer became more hydrophilic with increasing silica xerogel content, as assessed by contact angle measurement. The hybrid coatings afforded excellent bone bioactivity by inducing the rapid precipitation of apatite on their surface when immersed in a simulated body fluid (SBF). Osteoblastic cells cultured on the hybrid coatings were more viable than those on a pure chitosan coating. Furthermore, the alkaline phosphate activity of the cells was significantly higher on the hybrid coatings than on a pure chitosan coating, with the highest level being achieved on the hybrid coating containing 30% chitosan. These results indicate that silica xerogel/chitosan hybrids are potentially useful as room temperature bioactive coating materials on titanium-based medical implants.

Novel sphene coatings on Ti-6Al-4V for orthopedic implants using sol-gel method

Hydroxyapatite (HAp) is commonly used to coat titanium alloys (Ti-6Al-4V) for orthopedic implants. However, their poor adhesion strength and insufficient long-term stability limit their application. Novel sphene (CaTiSiO5) ceramics possess excellent chemical stability and cytocompatibility. The aim of this study is to use the novel sphene ceramics as coatings for Ti-6Al-4V. The sol-gel method was used to produce the coatings and the thermal properties, phase composition, microstructure, thickness, surface roughness and adhesion strength of sphene coatings were analyzed by differential thermal analysis-thermal gravity (DTA-TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), atom force microscopy (AFM) and scratch test, respectively. DTA analysis confirmed that the temperature of the sphene phase formation is 875 degrees C and XRD analysis indicated pure sphene coatings were obtained. A uniform structure of the sphene coating was found across the Ti-6Al-4V surface, with a thickness and surface roughness of the coating of about 0.5-1 microm and 0.38 microm, respectively. Sphene-coated Ti-6Al-4V possessed a significantly improved adhesion strength compared to that for HAp coating and their chemical stability was evaluated by testing the profile element distribution and the dissolution kinetics of calcium (Ca) ions after soaking the sphene-coated Ti-6Al-4V in Tris-HCl solution. Sphene coatings had a significantly improved chemical stability compared to the HAp coatings. A layer of apatite formed on the sphene-coated Ti-6Al-4V after they were soaked in simulated body fluids (SBF). Our results indicate that sol-gel coating of novel sphene onto Ti-6Al-4V possessed improved adhesion strength and chemical stability, compared to HAp-coated Ti-6Al-4V prepared under the same conditions, suggesting their potential application as coatings for orthopedic implants.

Initial attachment of osteoblastic cells onto sol-gel derived fluoridated hydroxyapatite coatings

Initial cell attachment and spreading of anchorage-dependent cells onto the material surface are crucial concerns for the development of more effective implants. In this study, MG63 cells were employed to investigate the initial cell response to sol-gel derived fluoridated hydroxyapatite (FHA) coatings. Along with that, surface roughness, wettability, and protein adsorption were also characterized for those FHA coatings, respectively. It was observed that both the surface roughness and contact angle have a slight increase in response to the incorporation of more fluorine ions. All FHA coatings showed similar amount of adsorbed proteins (approximately 1.6 microg/cm(2)) upon testing in culture medium. Cell counting showed that no significant difference was observed for the amount of initially attached cells between HA and fluoridated HA coatings during the first 4 h culture. On the other hand, the well-spread cell on all prepared coating surface indicates that the incorporated fluorine ions have no adverse effect on cell spreading process. Therefore, it was suggested from this study that the prepared fluoridated hydroxyapatite coatings have comparable bioactivity to that of pure hydroxyapatite coating, and these results are meaningful for further investigation for application of FHA coatings.

Phase conversion of tricalcium phosphate into Ca-deficient apatite during sintering of hydroxyapatite–tricalcium phosphate biphasic ceramics

In this study, we report a new observation on the phase conversion that occurs during the sintering of hydroxyapatite (HA)-tricalcium phosphate (TCP) biphasic ceramics. During the sintering of the HA-TCP mixture powders, a large amount of TCP was converted into HA, as detected by X-ray diffraction. The amount of TCP transformed into HA was approximately 10-90% of that initially added. From the electron probe microscopy analysis, the HA transformed from TCP was found to be Ca-deficient with Ca/P ratios of 1.62-1.64. The dissolution behavior and osteoblastic responses in a series of HA-TCP biphasic ceramics (10-90% TCP) were assessed. The solubility of the HA-TCP biphasic ceramics was intermediate between that of the HA and TCP pure ceramics. However, in the case of the HA-90% TCP biphasic ceramic, the solubility was even higher than that of pure TCP. The cell proliferation and alkaline phosphatase activity of the cells on the biphasic ceramics were lower than those on pure HA, but higher than those on pure TCP. However, particularly in the HA-50% TCP biphasic composition, the cellular responses were significantly higher than those on pure HA. It is considered that the Ca-deficient apatite newly formed from the TCP may affect in some way the solubility and biological properties of the HA-TCP biphasic ceramics.

Selfprotective smart orthopedic implants

In this review, we discuss current advances leading to an exciting change in implant design for orthopedic surgery. The initial biomaterial approaches in implant design are being replaced by cellular-molecular interactions and nanoscale chemistry. New designs address implant complications, particularly loosening and infection. For infection, local delivery systems are an important first step in the process. Selfprotective 'smart' devices are an example of the next generation of orthopedic implants. If proven to be effective, antibiotics or other active molecules that are tethered to the implant surface through a permanent covalent bond and tethering of antibiotics or other biofactors are likely to transform the practice of orthopedic surgery and other medical specialties. This new technology has the potential to eliminate periprosthetic infection, a major and growing problem in orthopedic practice.

Nanofiber generation of hydroxyapatite and fluor-hydroxyapatite bioceramics

In this study, we produced hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) bioceramics as a novel geometrical form, the nanoscale fiber, for the biomedical applications. Based on the sol-gel precursors of the apatites, an electrospinning technique was introduced to generate nanoscale fibers. The diameter of the fibers was exploited in the range of a few micrometers to hundreds of nanometers (1.55 microm-240 nm) by means of adjusting the concentration of the sols. Through the fluoridation of apatite, the solubility of the fiber was tailored and the fluorine ions were well released from the FHA. The HA and FHA nanofibers produced in this study are considered to find potential applications in the biomaterials and tissue engineering fields.

On the feasibility of phosphate glass and hydroxyapatite engineered coating on titanium

In this report, bioactive calcium phosphate (CaP) coatings were produced on titanium (Ti) by using phosphate-based glass (P-glass) and hydroxyapatite (HA), and their feasibility for hard tissue applications was addressed in vitro. P-glass and HA composite slurries were coated on Ti under mild heat treatment conditions to form a porous thick layer, and then the micropores were filled in with an HA sol-gel precursor to produce a dense layer. The resultant coating product was composed of HA and calcium phosphate glass ceramics, such as tricalcium phosphate (TCP) and calcium pyrophosphate (CPP). The coating layer had a thickness of approximately 30-40 microm and adhered to the Ti substrate tightly. The adhesion strength of the coating layer on Ti was as high as 30-33 MPa. The human osteoblastic cells cultured on the coatings produced by the combined method attached and proliferated favorably. Moreover, the cells on the coatings expressed significantly higher alkaline phosphatase activity than those on pure Ti, suggesting the stimulation of the osteoblastic activity on the coatings. On the basis of these observations, the engineered CaP coating layer is considered to be potentially applicable as a hard tissue-coating system on Ti-based implants.

Fibrillar assembly and stability of collagen coating on titanium for improved osteoblast responses

Collagen, as a major constituent of human connective tissues, has been regarded as one of the most important biomaterials. As a coating moiety on Ti hard-tissue implants, the collagen has recently attracted a great deal of attention. This article reports the effects of fibrillar assembly and crosslinking of collagen on its chemical stability and the subsequent osteoblastic responses. The fibrillar self-assembly of collagen was carried out by incubating acid-dissolved collagen in an ionic-buffered medium at 37 degrees C. The degree of assembly was varied with the incubation time and monitored by the turbidity change. The differently assembled collagen was coated on the Ti and crosslinked with a carbodiimide derivative. The partially assembled collagen contained fibrils with varying diameters as well as nonfibrillar aggregates. On the other hand, the fully assembled collagen showed the complete formation of fibrils with uniform diameters of approximately 100-200 nm with periodic stain patterns within the fibrils, which are typical of native collagen fibers. Through this fibrillar assembly, the collagen coating had significantly improved chemical stability in both the saline and collagenase media. The subsequent crosslinking step also improved the stability of the collagen coating, particularly in the unassembled collagen. The fibrillar assembly and the crosslinking of collagen significantly influenced the osteoblastic cell responses. Without the assembly, the collagen layer on Ti adversely affected the cell attachment and proliferation. However, those cellular responses were improved significantly when the collagen was assembled to fibrils and the assembly degree was increased. After crosslinking the collagen coating, these cellular responses were significantly enhanced in the case of the unassembled collagen but were not altered much in the assembled collagen. Based on these observations, it is suggested that the fibrillar assembly and the crosslinking of collagen require careful considerations in the collagen administration as a coating moiety.

Stimulation of osteoblast responses to biomimetic nanocomposites of gelatin–hydroxyapatite for tissue engineering scaffolds

Collagen-derived gelatin/hydroxyapatite (HA) nanocomposites were biomimetically synthesized for hard tissue engineering scaffold. In vitro osteoblastic cellular responses to the nanocomposites were assessed in comparison with those conventionally mixed gelatin-HA composites. A three-dimensional culture method involving floating cells in a culture medium was introduced to assist in the initial attachment of the cells to the scaffolds, and the proliferation and differentiation behaviors of the cells were examined. The osteoblastic MG63 cells attached to the nanocomposites to a significantly higher degree and subsequently proliferated more. The alkaline phosphatase (ALP) activity and osteocalcin produced by the cells were significantly higher on the nanocomposite scaffolds than on the conventional composite scaffolds. These improved cellular responses on the nanocomposites are considered to result from the increased ionic release and serum protein adsorption on the nanocomposites, which was derived from the different structural and morphological characteristics, i.e., the nanocomposite scaffolds retained less-crystallized and smaller-sized apatite crystals and a more well-developed pore configuration than the conventional ones. Based on these findings, the biomimetically synthesized nanocomposite scaffolds are believed to be potentially useful in hard tissue regeneration and tissue engineering fields.

Effect of fluoridation of hydroxyapatite in hydroxyapatite-polycaprolactone composites on osteoblast activity

Fluorine was administered to a system of hydroxyapatite (HA)/polycaprolactone (PCL) ceramic-polymer bioactive composites for applications as hard tissue regeneratives. The HA was fluoridated at different levels (5%, 25%, 50% and 75%) in order to produce the fluor-hydroxyapatite (FHA)/PCL composites. The osteoblastic cellular responses to the composites were examined in terms of the cell attachment, proliferation and differentiation as well as the expression of bone-associated genes. The amount of fluorine released from the composites was controlled by changing the degree of fluoridation, and the cellular responses were strongly influenced by the level of fluoridation. The MG63 cells on the FHA-PCL attached and proliferated at a similar level to those on HA-PCL. However, the fluoridation of HA increased significantly the alkaline phosphatase (ALP) activity and osteocalcin (OC) production by the cells on the composites, which was measured by an enzymatic assay. Moreover, the gene expression level of ALP and OC in the cells was up regulated on the FHA-PCL, which was confirmed semi-quantitatively by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. These findings on the fluorine-administered biological composites (FHA-PCL) suggested that fluorine plays a significant role in stimulating the bone derived cellular activity, and the FHA-PCL composites have high potential for use as hard tissue regeneratives.

Mechanical performance and osteoblast-like cell responses of fluorine-substituted hydroxyapatite and zirconia dense composite

A fluorine-substituted hydroxyapatite (FHA) and zirconia (ZrO(2)) dense composite (50:50 by volume) was fabricated, and its feasibility for hard tissue applications was investigated in terms of its mechanical properties and osteoblast-like cell (MG63) responses in vitro. The incorporation of fluorine into the hydroxyapatite (HA) structure was highly effective in producing a completely dense apatite-ZrO(2) composite through a pressureless sintering route, by preventing the thermal degradation of the apatite and ZrO(2). The resultant FHA-ZrO(2) dense composite had excellent mechanical properties, such as flexural strength (310 MPa), fracture toughness (3.4 MPam(1/2)), hardness (10 GPa), and elastic modulus (160 GPa). The flexural strength and fracture toughness of the composite showed a noticeable improvement by a factor of approximately 4 with respect to the pure apatites (HA and FHA). The MG63 cellular responses to the composite were assessed in terms of the cell proliferation (cell number and [(3)H]-thymidine incorporation) and differentiation (alkaline phosphatase activity, osteocalcin, and collagen production). The cells on the FHA-ZrO(2) composite spread and grew well, and proliferated actively during the culture period. The expression of alkaline phosphatase, osteocalcin, and collagen by the cells on the composite showed a similar trend to that on the pure apatites, although slight down-regulations were observed, implying that the FHA-ZrO(2) 50:50 composite retains the osteoblastic functionality and traits of the pure HA ceramics to a high degree. This finding, in conjunction with the considerable improvements in mechanical properties, supports the extended use of this composite for hard tissue applications.