Ultrastructural study of an apatite layer formed by a biomimetic process and its bonding to bone

Hydroxyapatite Particles from Simulated Body Fluids with Different pH and Their Effects on Mesenchymal Stem Cells

Bone-like hydroxyapatite (HAp) has been prepared by biomimetic synthesis using simulated body fluid (SBF), mimicking inorganic ion concentrations in human plasma, or 1.5SBF that has 1.5-times higher ion concentrations than SBF. In this study, the controllable preparations of HAp particles from 1.5SBF with different pH values were examined. The particles obtained as precipitates from 1.5SBF showed different morphologies and crystallinities depending on the pH of 1.5SBF. Micro-sized particles at pH 7.4 of 1.5SBF had a higher Ca/P ratio and crystallinity as compared with nano-sized particles at pH 8.0 and pH 8.4 of 1.5SBF. However, a mixture of micro-sized and nano-sized particles was obtained from pH 7.7 of 1.5SBF. When Ca²⁺ concentrations in 1.5SBF during mineralization were monitored, the concentration at pH 7.4 drastically decreased from 12 to 24 h. At higher pH, such as 8.0 and 8.4, the Ca²⁺ concentrations decreased during pH adjustment and slightly decreased even after 48 h. In this investigation at pH 7.7, the Ca²⁺ concentrations were higher than pH 8.0 and 8.4.Additionally, cytotoxicity of the obtained precipitates to mesenchymal stem cells was lower than that of synthetic HAp. Controllable preparation HAp particles from SBF has potential applications in the construction of building components of cell scaffolds.

In Vitro and in Vivo Assessment of Bone-Implant Interface: A Comparative Study

The present in vitro and in vivo comparison of three bioactive (HA, AP40, RKKP) and three bioinert (Ti6-Al4-V, Al2O3, ZrO2) materials was undertaken to identify which of them provide(s) the most suitable coating for prostheses implanted in patients with altered metabolic status.

The experimental design included in vitro tests with human osteoblasts and morphological observations by scanning electron microscopy. For the in vivo evaluation, the materials were implanted in the femoral condyle of ovariectomised and intact female rats, and two months after surgery an X-ray microanalytical study was performed.

The in vitro study showed good biocompatibility with all materials. Microanalysis evidenced a similar behaviour with all materials except the two biological glasses. The differences in Ca and P content observed between intact and ovariectomised rats can be explained by the intrinsic capability of biological glasses to undergo surface modifications in the presence of alterations of the bone metabolism. Thus, their use seems to be indicated in recipients with osteoporotic pathologies.

Effect of protein adsorption layers and solution treatments on hydroxyapatite deposition on polystyrene plate surfaces in simulated body fluids

We have developed a method to functionalize polystyrene (PS) cell culture plates with hydroxyapatite (HAp) via protein adsorption layers such as human serum albumin (HSA) in simulated body fluids (SBFs). In order to investigate the versatility the method, in this study the effect of protein adsorption layers on HAp deposition on PS plate surfaces in SBF was evaluated. Pretreatments with alternate soaking process (ASP) using solutions containing calcium ions and phosphate ions followed by incubation with SBF for 24 h resulted in HAp deposition on PS plates with adsorption layers of HSA, type I collagen, hen egg white lysozyme, and poly L-glutamic acid, an acidic protein analogue: the deposition behaviors were correlated with adsorption ability and charge state of proteins. We also demonstrated that commercially available tissue culture-treated PS (TCPS) were directly coated with bone-like HAp using the same ASP and SBF processes. Human mesenchymal stem cells adhered and stretched on the HAp-coated TCPS plates in a similar manner to the case of the HAp-coated PS plates prepared via HSA adsorption layers. The results indicate that the present methods are useful for preparing bone-like HAp-coated cell culture plates that can be utilized function of adsorbed proteins and that are obtainable conveniently and at low-cost.

Biomimetic approaches with smart interfaces for bone regeneration

A 'smart tissue interface' is a host tissue-biomaterial interface capable of triggering favourable biochemical events inspired by stimuli responsive mechanisms. In other words, biomaterial surface is instrumental in dictating the interface functionality. This review aims to investigate the fundamental and favourable requirements of a 'smart tissue interface' that can positively influence the degree of healing and promote bone tissue regeneration. A biomaterial surface when interacts synergistically with the dynamic extracellular matrix, the healing process become accelerated through development of a smart interface. The interface functionality relies equally on bound functional groups and conjugated molecules belonging to the biomaterial and the biological milieu it interacts with. The essential conditions for such a special biomimetic environment are discussed. We highlight the impending prospects of smart interfaces and trying to relate the design approaches as well as critical factors that determine species-specific functionality with special reference to bone tissue regeneration.

Surface functionalization of tissue culture polystyrene plates with hydroxyapatite under body fluid conditions and its effect on differentiation behaviors of mesenchymal stem cells

The surfaces of polystyrene (PS) cell culture plates were functionalized with hydroxyapatite (HAp) under body fluid conditions utilizing protein adsorption layers and a pretreatment with an alternate soaking process (ASP) using solutions containing calcium and phosphate ions. Adsorption layers of human serum albumin (HSA) formed on the surface of each well of commercial 24-well PS plates by solution processes. CaCl2 and K2HPO4 solutions were alternately added to the wells, the plates were incubated to form the precursors, and this was followed by the addition of simulated body fluid (SBF) and a further incubation for 24h. These treatments resulted in the surfaces of the PS cell culture plates being completely covered with bone-like HAp. The coating of PS plates with HAp promoted the adhesion of mesenchymal stem cells (MSCs) and maintained cell growth that was as fast as that on tissue culture-treated PS (TCPS) plates. Osteogenic differentiation was greater, whereas adipogenic and chondrogenic differentiation was less in the culture on HAp-coated PS plates than in that on TCPS plates. The present method is useful for preparing HAp-coated PS plates at clean benches without the need for any expensive apparatus. HAp coated on PS plates by this method was a bone-like apatite with high bioactivity; therefore, the present HAp-coated PS plates are promising materials for assays of bone-related cells in the bone remodeling process.

Formation of apatite coatings on an artificial ligament using a plasma- and precursor-assisted biomimetic process

A plasma- and precursor-assisted biomimetic process utilizing plasma and alternate dipping treatments was applied to a Leed-Keio artificial ligament to produce a thin coating of apatite in a supersaturated calcium phosphate solution. Following plasma surface modification, the specimen was alternately dipped in calcium and phosphate ion solutions three times (alternate dipping treatment) to create a precoating containing amorphous calcium phosphate (ACP) which is an apatite precursor. To grow an apatite layer on the ACP precoating, the ACP-precoated specimen was immersed for 24 h in a simulated body fluid with ion concentrations approximately equal to those in human blood plasma. The plasma surface modification was necessary to create an adequate apatite coating and to improve the coating adhesion depending on the plasma power density. The apatite coating prepared using the optimized conditions formed a thin-film that covered the entire surface of the artificial ligament. The resulting apatite-coated artificial ligament should exhibit improved osseointegration within the bone tunnel and possesses great potential for use in ligament reconstructions.

Mineralization of porous hydrogels based on semi-interpenetrated networks of poly[2-ethyl(2-pyrrolidone) methacrylate] and hyaluronic acid in simulated body fluid

Poly[2-ethyl(2-pyrrolidone) methacrylate] and hyaluronic acid hydrogels were synthesized via free-radical polymerization of 2-ethyl(2-pyrrolidone) methacrylate, hyaluronic acid and different crosslinkers. The ability of these hydrogels to induce apatite formation by incubating in simulated body fluid was investigated. The effect of hyaluronic acid content, crosslinkers and immersion time on mineralization behaviour and interface properties as well as the metabolic activity of different cultured cells were also determined. The bioactivity of the poly[2-ethyl(2-pyrrolidone) methacrylate] and hyaluronic acid hydrogels along with cell viability data indicated their potential application in bone tissue engineering.

Preparation of a novel anorganic bovine bone xenograft with enhanced bioactivity and osteoconductivity

A novel anorganic bovine bone xenograft with enhanced bioactivity and osteoconductivity was prepared by an ion substitution method using sodium hypochlorite. Bovine bone granules were defatted, washed, and then soaked in sodium hypochlorite solution at room temperature. Subsequently, the granules were dried and then heat-treated at 1000°C with sodium hypochlorite. As a control, bovine bone granules were prepared with the same conditions but without sodium hypochlorite treatment. Phase, functional group, and elemental analyses by XRD, FTIR, and EPMA showed that the granules heat-treated without and with sodium hypochlorite were pure hydroxyapatite and sodium-chlorine-bearing hydroxyapatite, respectively. After soaking in simulated body fluid (SBF) for 1 week, low crystalline hydroxyl carbonate apatite fully covered the surface of sodium-chlorine-bearing hydroxyapatite, whereas it formed little on the hydroxyapatite surface. After soaking in SBF and deionized water, ICP-AES and IC analyses showed that the dissolutions of calcium, sodium, chlorine, and hydroxyl ions from sodium-chlorine-bearing hydroxyapatite notably increased compared with those from hydroxyapatite. This resultantly increased the ionic activity product of apatite in SBF and induced new formation of low crystalline hydroxyl carbonate apatite. The cytotoxicity test by BCA assay showed that there were no statistically significant differences between hydroxyapatite and sodium-chlorine-bearing hydroxyapatite. In addition, sodium-chlorine-bearing hydroxyapatite showed better osteoconductivity in the calvarial defects of New Zealand white rabbits within 4 weeks compared with that of hydroxyapatite. The results suggest that this novel anorganic bovine bone xenograft possesses encouraging potential for use as a bone grafting material due to better bioactivity and osteoconductivity than hydroxyapatite.

Osteoblast compatibility of materials depends on serum protein absorbability in osteogenesis

Titanium has an osseointegrative property, while hydroxyapatite has an osteoconductive property. It remains a matter of controversy among researchers whether hydroxyapatite has higher osteoblast compatibility than titanium. Here, we compared the activities between osteoblasts cultured on titanium and those cultured on hydroxyapatite. An osteoblast-like cell line, MC3T3-E1, was cultured on machined titanium, evaporated titanium, and hydroxyapatite disks to compare the affinity of osteoblasts to each of these materials. The adhesion and proliferation of MC3T3-E1 cells were higher on hydroxyapatite disks than on the other disks. Osteoblast differentiation was not affected by the nature of disks investigated, but calcium was more easily deposited on the hydroxyapatite disks. The amount of absorbed serum proteins detected on hydroxyapatite was greater than that on titanium. In conclusion, our results indicate hydroxyapatite is a more suitable material for osteoblast growth than titanium because of its higher absorption of serum proteins.

Synergistic effect of silanol group and calcium ion in chitosan membrane on apatite forming ability in simulated body fluid

A chitosan membrane modified with silanol groups and calcium ions on its surface and in its structure, respectively, was newly developed and evaluated for the potential application as a bioactive-guided bone-regeneration membrane. The chitosan membrane, which contained calcium nitrate tetrahydrate, was prepared and further subjected to surface modification with 3-isocyanatopropyl triethoxysilane (IPTS) following hydrolysis with HCl solution. As control, chitosan membranes which contained only calcium nitrate tetrahydrate and modified with only silanol groups were prepared, respectively. Three membranes were exposed to simulated body fluid (SBF) for a period ranging from 3 h to 7 days. The SBF exposure led to the deposition of a layer of apatite crystals on the surface of the chitosan membrane modified with silanol groups and calcium ions, while those modified with only calcium ions or silanol groups did not show the apatite-forming ability. It implies that the silanol groups and calcium ion acted together in a synergistic fashion in the formation of apatite crystals; the silanol groups and calcium ions acted as the nucleation sites and accelerator for the formation of apatite crystals, respectively. Therefore, this new chitosan membrane is likely to have a potential for the application as a bioactive guided bone regeneration membrane because of its apatite-forming ability in the SBF.

Osteoconductive and degradable electrospun nonwoven poly(epsilon-caprolactone)/CaO-SiO2 gel composite fabric

A nonwoven ceramic/polymer composite fabric composed of randomly mixed bioactive and fast degradable CaO-SiO(2) gel fibers and biodegradable poly(epsilon-caprolactone) (PCL) fibers is prepared with a simultaneous electrospinning method for potential use as bone grafting materials. A 17% PCL solution is prepared using 1,1,3,3-hexafluoro-2-propanol as the solvent, whereas the CaO-SiO(2) gel solution is prepared via a condensation reaction following the hydrolysis of tetraethyl orthosilicate. PCL and CaO-SiO(2) gel solutions are spun simultaneously with two separate nozzles. As controls, pure PCL and CaO-SiO(2) gel nonwoven fabrics are also made by the same methods. The three nonwoven fabrics were exposed to simulated body fluid for 1 week and resulted in the deposition of a layer of apatite crystals on the surfaces of both the CaO-SiO(2) gel and PCL/CaO-SiO(2) gel composite fabrics, but not on the PCL fabric. A tensile strength test showed that the fracture behavior of the CaO-SiO(2) gel fabric was brittle, that of the PCL fabric was ductile-tough, and that of the PCL/CaO-SiO(2) gel composite fabric was intermediate between that of the CaO-SiO(2) gel and PCL fabrics. Our in vivo tests showed that the CaO-SiO(2) gel and PCL/CaO-SiO(2) gel composite fabrics had good osteoconductivity and fast degradation rates in calvarial defects of New Zealand white rabbits within 4 weeks, in contrast to the pure PCL fabric. Together, these results suggest that the composite fabric composed of PCL and CaO-SiO(2) gel fibers must have a great potential for use in applications such as bone grafting because of its good osteoconductivity and adequate mechanical properties.

Control of proliferation and differentiation of osteoblasts on apatite-coated poly(vinyl alcohol) hydrogel as an artificial articular cartilage material

One of the key challenges in employing biomaterials is determining how to fix them into the surrounding tissue. To enhance the interaction with surrounding bone, amorphous hydroxyapatite (HA) was coated onto the surface of the bio-inert poly(vinyl alcohol) hydrogel (PVA-H), as an artificial cartilage material, by a pulsed laser deposition technique. Next we examined the binding effects of the HA thin film (300 nm thick) to the underlying bone using osteoblast proliferation and differentiation. A mouse osteoblast cell line, MC3T3E1, was cultured on the HA-coated and noncoated PVA-H with a water content of 33% or 53% for 3 weeks. Cell proliferation, alkaline phosphatase (ALP) activity, and levels of osteocalcin were evaluated for biocompatibility and differentiation. HA coating enhanced the cell proliferation, the ALP activity, and the levels of osteocalcin on both low and high water-content PVA-Hs. The cell growth rates on the PVA-H were lower than on tissue culture dishes even after the HA coating was added; however, osteoblastic differentiation was highly promoted by the HA coating on low water content PVA-H. These results suggested that the HA coating on the PVA-H enhanced the affinity between the bone and the PVA-H as an artificial cartilage material in surface replacement arthroplasty.

Membrane of hybrid chitosan-silica xerogel for guided bone regeneration

Chitosan-silica xerogel hybrid membranes were fabricated using a sol-gel process and their potential applications in guided bone regeneration (GBR) were investigated in terms of their in vitro cellular activity and in vivo bone regeneration ability. TEM observation revealed that the silica xerogel was dispersed in the chitosan matrix on the nanoscale. The hybrid membrane showed superior mechanical properties to chitosan in the wet state and the rapid induction of calcium phosphate minerals in simulated body fluid, reflecting its excellent in vitro bone bioactivity. Osteoblastic cells were observed to adhere well and grow actively on the hybrid membrane to a level higher than that observed on the chitosan membrane. The alkaline phosphatase activity of the cells was also much higher on the hybrid than on the chitosan membrane. The in vivo study in a rat calvarial model demonstrated significantly enhanced bone regeneration using the hybrid membrane compared to that observed using the pure chitosan one. Histomorphometric analysis performed 3 weeks after implantation revealed a fully closed defect in the hybrid membrane, whereas there was only 57% defect closure in the chitosan membrane.

Preparation and properties of a novel bone repair composite: nano-hydroxyapatite/chitosan/carboxymethyl cellulose

Nano-hydroxyapatite/chitosan/carboxymethyl cellulose (n-HA/CS/CMC) composites with weight ratios of 70/10/20, 70/15/15 and 70/20/10 were prepared through a co-solution method. The properties of the composites were characterized by means of burn-out test, IR, XRD, TEM and universal material testing machine. The degradation and bioactivity were also investigated by in vitro test in a simulated body fluid (SBF) for 8 weeks. The results showed that n-HA particles were dispersed uniformly in organic phase, and strong chemical interactions formed among the three phases. Moreover, the composites were similar to natural bone in morphology and size. In addition, the compressive strength was improved compared with n-HA/CS composite. The biodegradation rate was controllable by altering weight ratio of the CS/CMC. Meanwhile, the composites could induce apatite particles to deposit in SBF. All the above results indicate that the novel composites of n-HA/CS/CMC have a promising prospect used for bone repair materials in view of the good mechanical property, adjustable biodegradation rate and bioactivity in SBF. Additionally, the study would provide a good guide to exploit clinical application of natural cellulose.

Ultrastructural analyses of nanoscale apatite biomimetically grown on organic template

The ultrastructure of nanoscale apatite biomimetically formed on an organic template from a supersaturated mineralizing solution was studied to examine the morphological and crystalline arrangement of mineral apatites. Needle-shaped apatite crystal plates with a size distribution of ~100 to ~1000 nm and the long axis parallel to the c axis ([002]) were randomly distributed in the mineral films. Between these randomly distributed needle-shaped apatite crystals, amorphous phases and apatite crystals (~20-40 nm) with the normal of the grains quasi-perpendicular to the c axis were observed. These observations suggest that the apatite film is an interwoven structure of amorphous phases and apatite crystals with various orientations. The mechanisms underlying the shape of the crystalline apatite plate and aggregated apatite nodules are discussed from an energy-barrier point of view. The plate or needle-shaped apatite is favored in single-crystalline form, whereas the granular nodules are favored in the polycrystalline apatite aggregate. The similarity in shape in both single-crystalline needle-shaped apatite and polycrystalline granular apatite over a wide range of sizes is explained by the principle of similitude, in which the growth and shape are determined by the forces acting upon the surface area and the volume.

Coating of bone-like apatite for development of bioactive materials for bone reconstruction

Materials with bioactivity, i.e. bone-bonding ability, form a bone-like apatite layer on their surfaces in the body and bond to living bone through this bone-like apatite layer. Bone-like apatite is carbonated hydroxyapatite with small crystallites and low crystallinity. The coating of the bone-like apatite layer on the substrates is expected to be a useful technique to induce bioactivity on the substrates. The bone-like apatite layer can be formed on the surface of substrates in a solution mimicking body fluid when some functional groups are introduced to the substrates. This process is called a biomimetic process. Coating of bone-like apatite layers through this biomimetic process has received much attention in the fabrication of novel composites with bioactivity. An overview of the coating of bone-like apatite is described.

Preparation of Bioactive Poly(Lactic-Co-Glycolic)Acid and Silica Gel Fibers Mixed Non-Woven Fabric

Poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. Poly(lactic-co-glycolic)acid solution was prepared by dissolving it in the hexafluoroisopropanol. Then, they were transferred to two separate syringes which were connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica gel containing calcium and poly(lactic-co-glycolic)acid solution were spun together under the electric field of 2 ㎸/㎝. The FE-SEM observations showed that the silica gel and poly(lactic-co-glycolic)acid fibers were mixed together completely and its handling property was much improved compared to that of the non-woven silica gel fabric. After soaking in the SBF for 1 week, low crystalline apatite crystals were also observed to occur on the silica fiber surfaces first and then they were also observed to occur on the poly(lactic-co-glycolic)acid fiber surfaces. From the results, it can be concluded that the poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric made by electro-spinning method has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Ion implantation modified stainless steel as a substrate for hydroxyapatite deposition. Part I. Surface modification and characterization

Material surfaces play critical role in biology and medicine since most biological reactions occur on surfaces and interfaces. There are many examples showing that the surface properties of the materials control and are directly involved in biological reactions and processes in-vitro like blood compatibility, protein absorption, cell development, etc. The rules that govern the diversity of biological surface phenomenon are fundamental physical laws. Stainless steel doped with Cr, Ni and Mo is widely used material in medicine and dentistry due to its excellent corrosion resistance and mechanical properties. The interest in this material has stimulated extensive studies on improving its bone-bonding properties. This paper describes the surface modification of Cr-Ni stainless steel (AISI 316) by a whole surface sequential implantation of Ca and P ions (the basic ions of hydroxyapatite). Three groups of stainless steel samples are prepared: (i) ion-implanted, (ii) ion-implanted and thermally treated at 600( composite function)C in air for 1 h and (iii) initials. The surface chemistry and topography before and after the surface modification are characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy, magic mirror method, atomic force microscopy and contact angle measurements.

Fabrication of novel calcium phosphate/poly(lactic acid) fiber composites

Composites using high-modulus polylactic acid (PLA) fibers coated with calcium phosphate (CaP) were prepared using a cyclic precipitation technique. Scanning electron microscopy revealed that small nuclei of CaP formed after the first soaking cycle, while large quantities of CaP particles were observed after the sixth cycle. The amount of CaP deposited on the PLA yarn increased with deposition time in Ca(2+) and PO(4) (3-) solutions and number of cycles, and decreased with stirring rate during washing cycles. It was observed that around 35 wt % of CaP was deposited on the yarn surface after six cycles of cyclic-soaking. Based on the results, a heterogeneous nucleation and growth mechanism was proposed for the CaP deposition on the surface of hydrolyzed polyester. Composites comprising the coated fibers in a poly(caprolactone) matrix exhibited flexural moduli within the range of that of the cortical bone.

Characterisation of a duplex TiO2/CaP coating on Ti6Al4V for hard tissue replacement

An initial TiO(2) coating was applied on Ti6Al4V by electrochemical anodisation in two dissimilar electrolytes. The secondary calcium phosphate (CaP) coating was subsequently applied by immersing the substrates in a simulated body fluid (SBF) with three times concentration (SBFx3), mimicking biomineralisation of biological bone. Electrochemical impedance spectroscopy and potentiodynamic polarisation assessments in SBF revealed that the anodic TiO(2) layer is compact, exhibiting up to four-folds improvement in in vitro corrosion resistance over unanodised Ti6Al4V. X-ray photoelectron spectroscopy analysis indicates that the anodic Ti oxide is thicker than air-formed ones with a mixture of TiO(2-x) compound between the TiO(2)/Ti interfaces. The morphology of the dense CaP film formed, when observed using scanning electron microscopy, is made up of linked globules 0.1-0.5microm in diameter without observable delamination. Fourier transform infrared spectrometry with an attenuated total internal reflection analysis revealed that this film is an amorphous/poorly crystallised calcium-deficient-carbonated CaP system. The calculated Ca:P ratios of all samples (1.14-1.28) are lower than stoichiometric hydroxyapatite (1.67). These results show that a duplex coating consisting of (1) a compact TiO(2) with enhanced in vitro corrosion resistance and (2) bone-like apatite coating can be applied on Ti6Al4V by anodisation and subsequent immersion in SBF.

Simple surface modification of poly(ε-caprolactone) to induce its apatite-forming ability

A biodegradable polymer coated with a bone-like apatite layer on its surface is useful as a scaffold for bone tissue regeneration. In this work, a poly(epsilon-caprolactone) (PCL) surface was modified by an O2 plasma surface treatment to form oxygen-containing functional groups. The plasma-treated samples were subsequently dipped alternately in an alcoholic solution containing calcium ions and one containing phosphate ions to deposit apatite precursors on the surface. The surface-modified PCL samples formed a dense and uniform surface bone-like apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. This surface-modification process is applicable to two-dimensional PCL plates and three-dimensional PCL meshes. In the resulting apatite-PCL composite, the apatite layer strongly adhered to the PCL surface and remained intact after a tape-detachment test. Therefore, this type of composite material will be a useful scaffold for bone tissue engineering.

Coating of an apatite layer on polyamide films containing sulfonic groups by a biomimetic process

Coating organic polymers with hydroxyapatite is an attractive method for the development of materials for medical applications, as it allows hydroxyapatite to show its unique biological properties such as its ability for bone bonding and protein adsorption. The biomimetic process focuses attention on fabricating such hydroxyapatite-polymer hybrids, where bone-like apatite is deposited on an organic polymer surface in solutions mimicking physiological conditions. In this process, a bone-like apatite layer can be coated onto organic substrates either by using a simulated body fluid (SBF), which has ion concentrations nearly equal to those of human extracellular fluid, or by using fluids that are supersaturated with respect to apatite at ambient conditions. We previously reported that apatite was deposited on polyamide films containing carboxyl groups in a solution mimicking body fluid, when they were incorporated with calcium salts. In the present study, to find an alternative functional group effective in apatite formation, we examined the apatite-forming ability of polyamide films containing sulfonic groups in the same solution. It was found that the polyamide film containing sulfonic groups could deposit apatite on its surface in the solution when the film was incorporated with calcium salts. These results show that the sulfonic group also acts as a functional group, and is as effective for apatite deposition in the body environment as the carboxyl group.

Characterization of CO3Ap-collagen sponges using X-ray high-resolution microtomography

For reconstruction and regeneration of hard tissues, scaffold biomaterials with large size pores and high porosity are important, in addition to their roles as supporting frames. To develop a new biodegradable scaffold biomaterial, CO3Ap, which has crystallinity and a chemical composition similar to bone, was synthesized at pH 7.4 and 60 degrees C. Then, the CO3Ap was mixed with a neutralized collagen gel and the CO3Ap-collagen mixtures with different kinds of CO3Ap contents and porosity were lyophilized into sponges. Scanning electron micrography (SEM) observation of CO3Ap-collagen sponges showed favorable pores for cell invasion. Approximately 50-300 microm size pores appeared to continue through the bulk. Higher magnification of the sponge showed a better adhesion between CO3Ap crystals and collagen. X-ray high-resolution microtomography revealed a clear image of the 3D structure of the sponges. The porosity of 0, 70 and 90%(w/w) CO3Ap-collagen sponges was 79.2 +/- 2.8%, 72.6 +/- 2.4% and 48.9 +/- 6.1%, respectively. The 70%(w/w) CO3Ap-collagen sponge appeared to be the most favorable biomaterial from the viewpoint of natural bone properties. Mouse osteoblast MC3T3-E1 cells were cultured in alphaMEM with 10% FCS for 2 weeks. Hematoxylin-eosin staining confirmed osteoblast cells invaded well into the CO3Ap-collagen sponge. These sponges are expected to be used as hard tissue scaffold biomaterials for therapeutic uses.

Cell-compatible properties of calcium carbonates and hydroxyapatite deposited on ultrathin poly(vinyl alcohol)-coated polyethylene films

Poly(vinyl alcohol) (PVA) was coated onto polyethylene (PE) films by a repetitive adsorption and drying process, and then the PVA-coated PE films were alternately immersed into aqueous solutions of Ca2+ and CO3(2-) ions (alternate soaking cycles), to deposit calcium carbonate (CaCO3) onto the films. The PVA coating was essential for the CaCO3 deposition. The amount of CaCO3 deposited increased with an increasing number of cycles. Scanning electron microscopic observations and attenuated total reflection spectra revealed the presence of both calcite and aragonite as the crystal structures of CaCO3 on the film. L929 fibroblast cells adhered and proliferated on these CaCO3-deposited PE films, as well as the hydroxyapatite-coated PE films previously prepared. It was found that the PVA coating and the subsequent deposition of calcium salts on certain films facilitated cell compatibility.

A novel covalently crosslinked gel of alginate and silane with the ability to form bone-like apatite

Hybrids consisting of bone-like apatite and biodegradable polymers are attractive materials for bone repair. We have shown that an alginate gel crosslinked covalently with ethylenediamine (EDA) enhances the repair of skin and nerves. In this study, we report a novel method for fabrication of an apatite-alginate nanohybrid using a simulated body fluid (SBF). Alginate was reacted with 3-aminopropyltriethoxysilane (APES), which gives silanol groups after hydrolysis, and/or EDA, by dehydration condensation using water-soluble carbodiimide to form gels. Modification of alginate with APES alone also gave a gel, because the alginate could be crosslinked by dehydration of silanol groups derived from APES. The gels obtained were soaked in a 1 mol/L CaCl2 solution and subsequently soaked in SBF. Apatite was formed on and inside the alginate gels modified with APES, whereas it was not formed on the gels without APES. Modification of alginate with silanol groups induced not only gel formation but also the apatite-forming ability on and inside the alginate gel in SBF. Consequently, a hydroxyapatite-alginate hybrid can be produced by modification of alginate with silanol groups and subsequent soaking in CaCl2 solution and SBF. Such a material is expected to be useful in bone repair.

Action of FGMgCO3Ap-collagen composite in promoting bone formation

To improve the biological properties of materials as bone substitutes, functionally graded CO3 apatite crystals containing magnesium, FGMgCO3Ap, were synthesized to be mixed with atelocollagen and made into a composite pellet. A radio-labeled cell adhesion experiment showed that the degree of adherence of mouse MC3T3E1 osteoblast-like cells to the FGMgCO3Ap-collagen composite was better than to CO3Ap-collagen and much better than to the Ti plate. When the composites were implanted beneath the periosteum cranii of rats, the FGMgCO3Ap-collagen composite was metabolized faster than the CO3Ap-collagen composite and better formation of new bone and osteoblast arrangement at the interface between the composite and the periosteum cranii was observed. When the composites were implanted into the femur of rabbits, clear bone formation with a higher degree of bone density was observed for the FGMgCO3Ap-collagen composite. These results suggest that the Mg2+ ions taken into the apatite crystals may contribute to the acceleration of osteoblast adhesion to apatites and promote bone formation, cross-talking with osteoblasts at the molecular level.

Bioinspired organic‐inorganic composite materials prepared by an alternate soaking process as a tissue reconstitution matrix

Poly(acrylic acid) (PAAc) grafted poly(ethylene) (PE) (PAAc-g-PE) film-apatite or calcium carbonate (CaCO3) composite materials were prepared by an alternate soaking process, which simply forms apatite or CaCO3 on the polymer materials by alternate soaking in Ca(2+)- and PO(3-)4- or CO(3)2- -containing solutions. X-ray diffraction analysis of the composite films indicated the presence of hydroxyapatite or CaCO3 on the film. Scanning electron microscopic observation revealed that the whole surface of the film was covered by the apatite or CaCO3. Cell compatibility tests of the apatite- or CaCO3-coated film suggested that the greater number of cells adhered on the films and that the cell proliferation properties were extremely greater on the films.

Hydroxyapatite deposition by alternating soaking technique on poly(vinyl alcohol)-coated polyethylene films

A poly(vinyl alcohol) (PVA)-coating on polyethylene films, prepared by repetitive adsorption/drying in an aqueous PVA solution, accelerated hydroxyapatite (HAp) deposition by an altemate soaking in aqueous solutions containing Ca2+ and PO4(3-) ions. X-ray photoelectron spectra of the surface of the HAp-deposited film showed the presence of calcium and phosphorus of a suitable peak ratio for HAp formation. X-ray diffraction analyses also revealed peaks corresponding to HAp. Scanning electron microscopic observation showed the surface of the HAp layer to be smooth, with nano-ordered dotted threads in networks. A simple PVA coating on a surface will serve as a novel system for accelerated HAp formation via alternating soaking.

Deposition of bone-like apatite on silk fiber in a solution that mimics extracellular fluid

The fabrication of apatite-organic polymer hybrids is one of several attractive methods for the development of biomaterials as a substitute for bone. Such materials have both bone-bonding ability and mechanical properties analogous to natural bone. The biomimetic process has focused attention on fabricating such hybrids, where bone-like apatite is deposited on an organic polymer surface in solutions that mimic physiological conditions. In this process, a bone-like apatite layer can be coated onto organic substrates either by using a simulated body fluid (SBF) with ion concentrations nearly equal to those of human extracellular fluid, or by using fluids that are supersaturated with respect to apatite at ambient conditions. In this study, we investigated the ability of natural silk and its related materials to facilitate apatite deposition under biomimetic conditions. Cloths made of raw silk or normal silk fibers were soaked in 1.5SBF, which has 1.5 times the ion concentration of SBF. Sericin film, which is made from an extract of degummed raw silk, was soaked in 1.5SBF. The cloth and the film soaked in 1.5SBF then were characterized by scanning electron microscopic (SEM) observation, energy dispersive X-ray microanalysis (EDX), and thin-film X-ray diffraction (TF-XRD). Apatite deposition was observed on the surface of cloth made from raw silk fiber after it was soaked in 1.5SBF, but it was not observed on cloth made from normal silk fibers. The apatite deposition on the raw silk fiber cloth was accelerated when the fibers were subjected to treatment with CaCl(2) solution at a concentration of at least 1 kmol/m(3) before immersion in 1.5SBF. Apatite deposition also was observed on the sericin film after the film was soaked in 1.5SBF for 7 days. These results indicate that apatite deposition on raw silk cloth is attributable to the catalytic effect of sericin because the surface of raw silk consists of sericin whereas that of normal silk contains fibroin. The deposition of the apatite and its crystal growth are accelerated by the presence of calcium ions on the sericin after treatment with CaCl(2) solution. Thus, sericin on natural silk fiber has the potential to facilitate apatite deposition and can be useful as a polymer material in the fabrication of hybrid materials analogous to bone through biomimetic processes.

Bonelike apatite formation on ethylene-vinyl alcohol copolymer modified with silane coupling agent and calcium silicate solutions

An ethylene-vinyl alcohol copolymer (EVOH) was treated with a silane coupling agent and calcium silicate solutions, and then soaked in a simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma. A smooth and uniform bonelike apatite layer was successfully formed on both the EVOH plate and the EVOH-knitted fibers in SBF within 2 days. Part of the structure of the resulting apatite-EVOH fiber composite was similar to that of natural bone. If this kind of composite can be fabricated into a three-dimensional structure similar to natural bone, the resultant composite is expected to exhibit both mechanical properties analogous to those of natural bone and bone-bonding ability. Hence, it has great potential as a bone substitute.

Collagen-hydroxyapatite composite prepared by biomimetic process

A novel bone graft substitute comprising a porous, collagenous scaffold was biomimetically coated with hydroxyapatite using a simulated body fluid solution chemistry method. The scaffold had a porosity of approximately 85%, with pore sizes between 30 microm and 100 microm. Glutaraldehyde vapor was used to stabilize the collagenous scaffold, giving a significantly increased thermal stability over an unstabilized scaffold, as shown by differential scanning calorimetry. A thin layer (<10 microm) of crystalline hydroxyapatite was deposited onto the stabilized collagenous scaffold by soaking the collagenous construct in simulated body fluid in the presence of calcium silicate glass. The presence of crystalline hydroxyapatite was confirmed by X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. In vitro cytotoxicity testing of the composite construct using L-929 fibroblasts (ISO 10993-5) and rabbit periosteal cells revealed a cytocompatible material that supported cellular attachment and proliferation.

Apatite nucleation on silica surface: a zeta potential approach

Zeta potential measurements on pure silica, prepared by the sol-gel method from tetraethoxysilane under acidic conditions, are reported in different suspensions. Water suspensions and suspensions containing calcium or phosphate ions with and without NaCl were tested. zeta potential measurements were carried out as a function of the pH and ion concentration. Also, calcium and phosphate adsorption on silica was determined experimentally. The results of zeta potential and adsorption measurements suggest that both calcium and phosphate ions can be adsorbed on the silica surface; however, calcium adsorption is stronger than phosphate adsorption. When calcium and sodium ions are present in the suspension, calcium adsorption decreases. It seems that certain sites on the silica surface are specific for calcium adsorption.

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.

Osteoinductivity and biomechanics of a porous ceramic with autogenic periosteum

Twenty-one dogs were used to study the osteoinductivity and biomechanical properties of a biphasic porous ceramic with autogenic periosteum implanted in muscle. The ceramic implants were swathed in fresh periosteum derived from the same animals and implanted in the femur muscles. The other two groups of animals served as controls using the same material implanted in the femur bones and muscles without periosteum. Biomechanical measurements showed that, in the muscles, the experimental group had a higher bending strength than the unswathed group by the time the samples were harvested. Six months postoperatively, the strength of the samples in the experimental group had almost reached that of normal bones. The results of X-ray diffraction and infrared spectrometric analysis suggested that the degradation rate and speed of tricalcium phosphate (TCP) of the ceramic in the experimental group were faster than in the unswathed samples, but slower than in samples implanted in bones. The bone replacement and bone-inducing activity were excellent in the periosteum-swathed samples. Histologically, satisfactory bone repair was seen in the experimental samples. All results indicate that autogenic periosteum could increase bioactivity of ceramics in heterosites and improve bone formation in the surroundings of porous calcium phosphate ceramics. The data also infer that the complicated procedure of culturing bone growth factors with biomaterials in vitro to obtain bioactive grafts could be replaced by this relatively simple method.

Apatite growth on calcium adsorbed surface of wet flocculated silica particles immersed in a modified simulated body fluid

An alternative method for the calcium phosphate apatite formation onto the surface of flocculated pure silica particles is reported, in an attempt to understand the possible mechanism for the apatite formation. A stable silica sol was flocculated by adding calcium ions in aqueous solution. The wet flocks were resuspended in a basic aqueous solution containing a calcium salt, trying to allow the absorption of calcium ions onto the silica surface through a hydrogen ion exchange. The as-prepared materials were immersed in a modified simulated body fluid at different temperatures (37 and 90 degrees C) and silica concentrations. It was found that these factors have a strong influence on the apatite formation. The apatite formation was confirmed by (31)P MAS-NMR, FT-Raman, XRD, and TEM.

Behavior in simulated body fluid of calcium phosphate coatings obtained by laser ablation

Three types of calcium phosphate coatings onto titanium alloy substrates, deposited by the laser ablation technique, were immersed in a simulated body fluid in order to determine their behavior in conditions similar to the human blood plasma. Neither the hydroxyapatite coating nor the amorphous calcium phosphate coating do dissolve and the alpha-tricalcium phosphate phase of the coating of beta-tricalcium phosphate with minor alpha phase slightly dissolves. Precipitation of an apatitic phase is favored onto the hydroxyapatite coating and onto the coating of beta-tricalcium phosphate with minor alpha phase. Onto the titanium alloy substrate reference there is also precipitation but at larger induction times. However, onto the amorphous calcium phosphate coating no precipitate is formed.

Electrophoretic coating of multilayered apatite composite on alumina ceramics

By means of an electrophoretic deposition technique followed by sintering, alumina and zirconia ceramics were coated with apatitic composites composed of porous surface and intermediate layers of hydroxyapatite and an adhesive calcium phosphate layer. The electrophoretic deposition of these layers was attained by the use of a mixed solvent of acetylacetone and alcohol as well as the mixed powders of the calcium phosphates and alumina. The adhesive layer was formed by the codeposition of calcium phosphate glass powders (Ca/P = 1/2) with hydroxyapatite, while the open porosity of the surface layer was increased with the addition of alumina to the hydroxyapatite layers. The resultant phases of sintered composite layers were tricalcium phosphate and alumina with a small amount of hydroxyapatite.

Ca-adsorption and apatite deposition on silk fabrics modified with phosphate polymer chains

Silk fabric was modified with polymethacryloyloxyethylphosphate (pMOEP) by graft copolymerization. Ca-adsorption onto pMOEP-grafted silk fabric was significantly enhanced compared to that onto original silk fabric. SEM observation indicated that some crystallites were deposited on the pMOEP-grafted silk fabric after 1 week of immersion in simulated body fluid, whereas no change occurred on the surface of the original silk fabric. X-ray diffraction showed that this crystallite contained hydroxyapatite. These results indicate that pMOEP-grafted silk fabric induce hydroxyapatite formation more effectively than the original silk fabric.

A study on hydroxyapatite formation on/in the hydroxyl groups-bearing nonionic hydrogels

Using the biomimetic method, we formed a hydroxyapatite (HAp) layer on/in certain types of nonionic hydrogels that contain hydroxyl groups. The hydrogels used were poly(vinyl alcohol) (PVA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(glucosyloxyethyl methacrylate) (PGEMA), and agarose. Under an optical microscope, we observed a thin, continuous HAp layer on the top surface of the PVA, PHEMA, and PGEMA gels. On the other hand, we only observed an intermittent HAp layer on the surface of the agarose gel. The swelling ratio and the bound water content of these hydrogels were measured as an essential character in HAp formation. There was some relation among the HAp formation, the swelling ratios, and the bound water content.