Quasi-biological apatite film induced by titanium in a simulated body fluid

Three-dimensional cell-laden collagen scaffolds: From biochemistry to bone bioengineering

The bones can be viewed as both an organ and a material. As an organ, the bones give structure to the body, facilitate skeletal movement, and provide protection to internal organs. As a material, the bones consist of a hybrid organic/inorganic three-dimensional (3D) matrix, composed mainly of collagen, noncollagenous proteins, and a calcium phosphate mineral phase, which is formed and regulated by the orchestrated action of a complex array of cells including chondrocytes, osteoblasts, osteocytes, and osteoclasts. The interactions between cells, proteins, and minerals are essential for the bone functions under physiological loading conditions, trauma, and fractures. The organization of the bone's organic and inorganic phases stands out for its mechanical and biological properties and has inspired materials research. The objective of this review is to fill the gaps between the physical and biological characteristics that must be achieved to fabricate scaffolds for bone tissue engineering with enhanced performance. We describe the organization of bone tissue highlighting the characteristics that have inspired the development of 3D cell-laden collagenous scaffolds aimed at replicating the mechanical and biological properties of bone after implantation. The role of noncollagenous macromolecules in the organization of the collagenous matrix and mineralization ability of entrapped cells has also been reviewed. Understanding the modulation of cell activity by the extracellular matrix will ultimately help to improve the biological performance of 3D cell-laden collagenous scaffolds used for bone regeneration and repair as well as for in vitro studies aimed at unravelling physiological and pathological processes occurring in the bone.

Reactivity of Titanium Dental Implant Surfaces in Simulated Body Fluid

Osseointegration of titanium (Ti) implants in bone is crucial for dental implant treatment. Bacterial challenge possibly leading to peri-implantitis threatens long-term success. For the improvement of osseointegration, an understanding of materials and tissue intervention is needed. This in vitro study analyzed changes of different implant surfaces exposed to simulated body fluid (SBF). Implants were analyzed by scanning electron microscopy/X-ray photoelectron spectroscopy. Supernatants (SNs) were assessed using inductively coupled plasma-mass spectrometry (ICP-MS). Additional calcium (Ca) and phosphate (P) crystals developed (Hank's buffered salt solution (HBSS)) on implants with layered surfaces. ICP of SN demonstrated a decreased Ca/P ratio. After incubation with human serum (HS), layers appeared flattened containing <1% Ca/P. The etched/machined implants showed the formation of a surface transformation layer or coating consisting of crystalline Ca/P precipitations and a decrease in the Ca/P ratio in the supernatant. Incubation in HS induced noncrystalline coverage, and increased Ti/Ca/P was detected in supernatants. HBSS induced crystals on surfaces of modified implants and crystalline covers on nonmodified implants containing Ca/P. The serum did not show the development of HA-like structures but showed dissolving effects. Titanium surfaces show completely altered behavior when incubated in serum-containing SBF.

Different Cell and Tissue Behavior of Micro-/Nano-Tubes and Micro-/Nano-Nets Topographies on Selective Laser Melting Titanium to Enhance Osseointegration

Background and Purpose

Micro-/nano-tubes (TNTs) and micro-/nano-nets (TNNs) are the common and sensible choice in the first step of combined modifications of titanium surface for further functionalization in the purpose of extended indications and therapeutic effect. It is important to recognize the respective biologic reactions of these two substrates for guiding a biologically based first-step selection.

Materials and Methods

TNTs were produced by anodic oxidation and TNNs were formed by alkali-heat treatment. The original selective laser melting (SLM) titanium surface was set as control. Surface characterization was evaluated by scanning electron microscopy, surface roughness, and water contact angle measurements. Osteoclastogenesis and osteogenesis were measured. MC3T3-E1 cells and RAW 264.7 cells were used for in vitro assay in terms of adhesion, proliferation, and differentiation. In vivo assessments were taken on Beagle dogs with micro-CT and histological analysis.

Results

TNN and TNT groups performed decreased roughness and increased hydrophilicity compared with SLM group. For biological detections, the highest ALP activity and osteogenesis-related genes expression were observed in TNT group followed by TNN group (P <0.05). Interestingly, when it comes to the osteoclastogenesis, TNNs displayed lowest TRAP activity and osteoclastogenesis-related genes expression and TNTs were lower than SLM but higher than TNNs (P <0.05). BV/TV around implants was highest in TNT group after 4 weeks (P <0.05). HE, ALP and TRAP staining showed that osteogenic and osteoclastic activity around TNTs were both higher than TNNs (P <0.05).

Conclusion

TNNs and TNTs have dual advantages in promotion of osteogenesis and inhibition of osteoclastogenesis. Furthermore, TNNs showed better capability in inhibiting osteoclast activity while TNTs facilitated stronger osteogenesis. Our results implied that TNT substrates would take advantage in early application after implantation, while diseases with inappropriate osteoclast activity would prefer TNN substrates, which will guide a biologically based first-step selection on combined modification for different clinical purposes.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

BACKGROUND

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials.

PURPOSE AND SCOPE

This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems.

SUMMARY

We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO₂ -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO₂ coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated.

CONCLUSION

Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Enhanced bone healing in porous Ti implanted rabbit combining bioactive modification and mechanical stimulation

To improve the bone healing efficiency of porous titanium implants, desired biological properties of implants are mandatory, involving bioactivity, osteoconductivity, osteoinductivity and a stable environment. In this study, bare porous titanium (abbr. pTi) with the porosity of 70% was fabricated by vacuum diffusion bonding of titanium meshes. Hydroxyapatite-coated pTi (abbr. Hap-pTi) was obtained by successively subjecting pTi to alkali heat treatment, pre-calcification and simulated body fluid. Both pTi and Hap-pTi were respectively implanted into the tibia defect model (ϕ10 mm × 6 mm) in New Zealand white rabbits, then subjected to non-invasively axial compressive loads at high-magnitude low-frequency (HMLF), which were denoted as F-pTi and F-Hap-pTi, respectively. Bone repairing efficiencies were analyzed by postoperative X-ray examination, optical observation and HE staining after 14 and 30 days of implantation. ALP and OCN contents in serum were also examined at 30 days. Results showed that the sham group and sham group with mechanical stimulation (abbr. F-sham) preferably caused bone fractures. Qualitatively, Hap-pTi reduced the risk of bone fractures and enhanced bone healing slightly more effectively compared to bared pTi. However, both Hap-pTi combined with mechanical stimulation and F-pTi in the case of bioactive modification could result in a higher bone healing efficiency (F-Hap-pTi). The molecular signaling investigation of ALP and OCN contents in serum further revealed a probable synergistic effect of Hap coating coupling with HMLF compression on improving bone repairing efficiency. It provides a candidate of clinically applicable therapy for osseous defects.

Effects of Cu content on electrochemical response in Ti-based metallic glasses under simulated body fluid

Systematic characterization of the corrosion response of the Cu-free Ti45Zr40Si15 and Cu-containing Ti40Zr40Si15-Cu5 and Ti45Zr20-Cu35 metallic glasses (MGs) in the Hank's solution is conducted, in terms of the open circuit potential, potentiodynamic polarization, as well as electrochemical impedance measurements. The Cu role in the Ti-based MGs, tentatively to be applied for bio-implants, is established and modeled. The presence of nobler Cu will impose two opposite effects. The minor positive effect of minor shift of Ecorr is not a major issue, but the negative effect on local pitting and ion release would cause a major drawback. The ICP-MS indicates that the release of Cu ions increases with increasing Cu content. For more promising anti-pitting ability, the Cu content in Ti-based MGs should be kept as low as possible, better to be none or less than about 5 at.%.

A functional polyester carrying free hydroxyl groups promotes the mineralization of osteoblast and human mesenchymal stem cell extracellular matrix

Functional groups can control biointerfaces and provide a simple way to make therapeutic materials. We recently reported the design and synthesis of poly(sebacoyl diglyceride) (PSeD) carrying a free hydroxyl group in its repeating unit. This paper examines the use of this polymer to promote biomineralization for application in bone tissue engineering. PSeD promoted more mineralization of extracellular matrix secreted by human mesenchymal stem cells and rat osteoblasts than poly(lactic-co-glycolic acid) (PLGA), which is currently widely used in bone tissue engineering. PSeD showed in vitro osteocompatibility and in vivo biocompatibility that matched or surpassed that of PLGA, as well as supported the attachment, proliferation and differentiation of rat osteoblasts and human mesenchymal stem cells. This demonstrates the potential of PSeD for use in bone regeneration.

Synthesis and application of nanostructured calcium phosphate ceramics for bone regeneration

In the past two decades, nanotechnology has entered the field of regenerative medicine, resulting in the development of a novel generation of instructive, nanostructured biomaterials that are able to orchestrate cellular behavior by presenting specific morphological and biological cues. Using nanotechnology, materials containing nanosized features (e.g., pores, patterns, textures, grain sizes) can be obtained that exhibit properties that are considerably altered compared with micron-structured materials. Inspired by the hierarchical nanostructure of bone, the application of nanostructured materials for bone regeneration is gaining increasing interest in the field of biomaterials research. Because crystallographic and chemical studies have shown that synthetic hydroxyapatite closely resembles the inorganic phase found in bone and teeth, synthesis and applications of nanostructured calcium phosphate ceramics have been reviewed. Synthesis techniques for the preparation of calcium phosphate nanoparticles include precipitation, sol-gel, and hydrothermal processes, whereas four main biomedical applications of nanostructured calcium phosphate ceramics in bone regeneration have been addressed in more detail, that is, (1) polymer/calcium phosphate nanocomposites, (2) nanostructured monophasic calcium phosphate bone fillers, (3) nanostructured precursor phases for calcium phosphate cements, and (4) nanostructured calcium phosphate coatings.

Cathodic alkaline treatment of zirconium to give the ability to form calcium phosphate

The cathodic polarization technique to form an alkaline environment on a zirconium (Zr) surface, discussed in the present study, is unique, and gives the ability to form calcium phosphate in a simulated body fluid to Zr; on the other hand, many previous studies have been conducted using immersion in alkaline solutions. In this study, two discrete techniques were investigated. Zr was cathodically polarized in an electrolyte without calcium and phosphate ions, and Zr was cathodically polarized in another electrolyte containing calcium and phosphate ions, Hanks' solution, to directly form a calcium phosphate layer. The surface was characterized using X-ray photoelectron spectroscopy, and the performance of the material was evaluated by immersion in Hanks' solution. As a result, the ability to form calcium phosphate in Hanks' solution was given by cathodic polarization in the Na(2)SO(4) solution containing H(2)O(2). In addition, a cathodic potential under -1.5 V(SCE) is required to form hydroxyapatite directly in Hanks' solution. This research clearly reveals useful surface modification techniques giving the ability to form calcium phosphate in a simulated body fluid by cathodic polarization.

Rapid screening, in vitro study of metal oxide and polymer hybrids as delivery coatings for improved soft-tissue integration of implants

Metal-organic chemistry allows for molecular mixing and creation of a range of submicron phase-separated structures from normally brittle metal oxides and flexible polymers with improved bioactivity and delivery properties. In this study, we used a high throughput platform to investigate the influence of organic metal oxide doping of polydimethylsiloxane (PDMS) coatings on cellular bioactivity and controlled release of vanadium compared with titanium oxide coatings without additional PDMS. Metal-organic-derived titanium and or vanadium was doped into PDMS and used to form a coating on the bottom of cell culture microplates in the absence of added water, acids, or bases. These hybrid coatings were rapidly screened to establish how titanium and vanadium concentration influences cell proliferation, adhesion, and morphology. We demonstrate that titanium doping of PDMS can be used to improve cell proliferation and adhesion, and that vanadium doping caused a biphasic dose response in proliferation. A 28-day vanadium and titanium elution study indicated that titanium was not released, but the presence of PDMS in coatings increased delivery rates of vanadium compared with titania coatings without polymer. Hybrid coatings of titanium-doped polymers have potential for improving wound healing dynamics, soft-tissue integration of medical implants, and use as controlled delivery vehicles.

Mineralization behavior with mesenchymal stromal cells in a biomimetic hyaluronic acid-based scaffold

A biomimetic hyaluronic acid (HA)-based polymer scaffold was analysed in vitro for its characteristics and potential to support mineralization as carrier-vehicle. Biomimetic apatite crystal nucleation on the scaffold surface was obtained by a fine control of the pH level that increased ionic solubility thus controlling apatite formation kinetic. Different concentrations of human mesenchymal stromal cells (h-MSCs) were seeded on the scaffold, osteogenesis was induced in the presence or absence of fibroblast growth factor -2 and mineralization was analysed at different time points. We found that only at the highest h-MSCs concentration tested, the cells were uniformly distributed inside and outside the scaffold and proliferation started to decrease from day 7. Electron microscopy analysis evidenced that h-MSCs produced extracellular matrix but did not establish a direct contact with the scaffold. We found mineralized calcium-positive areas mainly present along the backbone of the scaffold starting from day 21 and increasing at day 35. FGF-2 treatment did not accelerate or increase mineralization. Non-biomimetic HA-based control scaffold showed immature mineralized areas only at day 35. Our data demonstrate that the biomimetic treatment of an HA-based scaffold promotes a faster mineralization process suggesting its possible use in clinics as a support for improving bone repair.

Effect of functional end groups of silane self-assembled monolayer surfaces on apatite formation, fibronectin adsorption and osteoblast cell function

Bioactive glass (BG) can directly bond to living bone without fibrous tissue encapsulation. Key mechanistic steps of BG's activity are attributed to calcium phosphate formation, surface hydroxylation and fibronectin (FN) adsorption. In the present study, self-assembled monolayers (SAMs) of alkanesilanes with different surface chemistry (OH, NH(2) and COOH) were used as a model system to mimic BG's surface activity. Calcium phosphate (Ca-P) was formed on SAMs by immersion in a solution that simulates the electrolyte content of physiological fluids. FN adsorption kinetics and monolayer coverage was determined on SAMs with or without Ca-P coating. The surface roughness was also examined on these substrates before and after FN adsorption. The effects of FN-adsorbed, Ca-P-coated SAMs on the function of MC3T3-E1 were evaluated by cell growth, expression of alkaline phosphatase activity and actin cytoskeleton formation. We demonstrate that, although the FN monolayer coverage and the root mean square (rms) roughness are similar on --OH and --COOH terminated SAMs with or without Ca-P coating, higher levels of ALP activity, more actin cytoskeleton formation and more cell growth are obtained on --OH- and --COOH-terminated SAMs with Ca-P coating. In addition, although the FN monolayer coverage is higher on Ca-P-coated --NH(2)-terminated SAMs and SiO(x) surfaces, higher levels of ALP activity and more cell growth are obtained on Ca-P-coated --OH- and --COOH-terminated SAMs. Thus, with the same Ca-P coatings, different surface functional groups have different effects on the function of osteoblastic cells. These findings represent new insights into the mechanism of bioactivity of BG and thereby may lead to designing superior constructs for bone grafting.

Incorporation of bovine serum albumin into biomimetic coatings on titanium with high loading efficacy and its release behavior

Bovine serum albumin (BSA) was employed as a model protein to study its loading efficiency into a calcium phosphate (CaP) coating on titanium substrates. It is found that the protein loading efficiency can be adjusted by varying the specific configurations of the coating system such as simulated body fluid (SBF) volume, solution height and container selection for the SBF. A BSA loading efficiency as high as 90% was achieved when the ratio of the substrate surface area to modified SBF (m-SBF) volume was as high as 0.072. The release of BSA from the biomimetic coatings was also investigated in vitro. A sustained release was achieved although a large quantity of BSA was still trapped in the coating after 15 days of immersion in a phosphate buffer solution. A much faster release rate would be expected when the coating is implanted in vivo due to the active involvement of osteoclast cells and enzymes.

PLD bioactive ceramic films: the influence of CaO-P2O5 glass additions to hydroxyapatite on the proliferation and morphology of osteblastic like-cells

This work consists on the evaluation of the in vitro performance of Ti6Al4V samples PLD (pulsed laser deposition) coated with hydroxyapatite, both pure and mixed with a CaO-P2O5 glass. Previous studies on immersion of PLD coatings in SBF, showed that the immersion apatite films did not present the usual cauliflower morphology but replicated the original columnar structure and exhibited good bioactivity. However, the influence of glass associated to hydroxyapatite concerning adhesion, proliferation and morphology of MG63 cells on the films surface was unclear. In this study, the performance of these PLD coated samples was evaluated, not only following the physical-chemical transformations resulting from the SBF immersion, but also evaluating the cytocompatibility in contact with osteoblast-like MG63 cells. SEM and AFM confirmed that the bioactive ceramic PLD films reproduce the substrate's surface topography and that the films presented good adherence and uniform surface roughness. Physical-chemical phenomena occurring during immersion in SBF did not modify the original columnar structure. In contact with MG63 cells, coated samples exhibited very good acceptance and cytocompatibility when compared to control. The glass mixed with hydroxyapatite induced higher cellular proliferation. Cells grown on these samples presented many filipodia and granular structures, typical features of osteoblasts.

Improvement of bonding strength between biomimetic apatite coating and substrate

Bone-like apatite coatings were prepared using a biomimetic method in a modified simulated body fluid (m-SBF). The effect of the m-SBF volume on the apatite coating quality was studied. Three m-SBF volumes, 50, 100, and 200 mL, were employed to immerse titanium substrates in a sealed container so as to produce apatite coatings with different properties, namely types I, type II, and type III apatite coatings, respectively. The coatings were characterized using X-ray diffraction and environmental scanning electron microscope. The bonding between the coating and the Ti substrate was evaluated using an adhesive strength test. All three apatite coatings demonstrated a poorly crystallized structure, and the coatings formed exhibited a uniformed surface morphology. Further increasing the m-SBF volume, small globules of apatite started to form on the surface of the coating. The bonding strength for the three coating systems were 8.52 +/- 2.41, 10.36 +/- 2.78, and 17.23 +/- 2.55 MPa for types I, II, and III apatite coatings, respectively. The failure analyses suggested that type III coating failed mostly at the interface between the coating and the substrate, while type I and II coatings failed mostly within the apatite coating. Our study revealed that a dense, thick, well-adhered apatite coating could be achieved by carefully controlling the volume of m-SBF.

Preparation and characteristics of nano-grained calcium phosphate coatings on titanium from ultrasonated bath at acidic pH

Electrochemically deposited nano-grained calcium phosphate coatings were produced on titanium substrates using aqueous electrolyte at acidic pH. Different coatings were produced by using cathodic current densities ranging from 10 to 50 mA/cm(2) from an ultrasonated electrolytic bath. These coatings contained dicalcium phosphate dihydrate as the predominant phase and hydroxyapatite as the minor phase. With increasing current density, hydroxyapatite content in the coatings increased. Dicalcium phosphate grains had size in the range of 55-85 nm and hydroxyapatite had grains in the size range of 20-25 nm. Scanning electron microscopy showed that the morphology of the coatings obtained at lower current densities had acicular structure. With increasing current densities, the needles became blunt and small and finally, at 50 mA/cm(2) the coating had globular deposits. Surface roughness of the coatings also increased with increasing deposition current density. Tensile bond strengths of the coatings were in the range of 3.6-6.9 MPa and decreased with increase of deposition current density. Heat-treatment of the coatings for 2 h at 500 degrees C completely eliminated the dicalcium phosphate phase and resulted in mono hydroxyapatite phase containing grains in the size range of 20-30 nm.

Metal oxide coated cell culture arrays for rapid biological screening

The biointerface of metallic alloy implants is a spontaneously formed metal oxide layer. This study presents a novel method for creating titanium oxide xerogel coated microplates for high-throughput biological screening that overcomes several limitations of using bulk metal samples to study oxides. Metal-organic precursors were used to evaluate the influence of Al, V, Ca, and P doped smooth and textured titanium oxide xerogel coatings on the bioresponse of human fibroblasts to increase understanding of the soft tissue sealing around transepithelial devices. Coatings made of titanium n-butoxide were characteristically smooth, while those of titanium isopropoxide were micro- and nanofeatured. Screening consisted of WST-1 proliferation assay, calcein AM cell number and viability assay, and a modified cell seeding efficiency and centrifugation adhesion assay. Small variations in initial attachment and centrifugation adhesion of human fibroblasts were observed among the coatings and comparable to tissue-culture treated polystyrene. Proliferation and viability at 24 and 48 h were reduced by the 10 and 20% vanadium additions. Metal oxide coated microplates are adaptable to the investigation of a wide range of metal-organic derived chemistries and the influence of oxide texture, and level of oxide crystallinity and oxide grain size on the biological responses of cells.

Formation of calcium phosphates on titanium implants with four different bioactive surface preparations. An in vitro study

The aim of the present study was to compare the nucleating and growing behaviour on four types of bioactive surfaces by using the simulated body fluid (SBF) model. Titanium discs were blasted and then prepared by alkali and heat treatment, anodic oxidation, fluoridation, or hydroxyapatite coating. The discs were immersed in SBF for 1, 2, 4 and 6 weeks. Calcium phosphates were found on all specimens, as analysed with scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX). After 1 and 2 weeks of SBF immersion more titanium was accessible with SEM/EDX on the blasted surfaces than the four bioactive surface types, indicating a difference in coverage by calcium phosphates. The Ca/P mean ratio of the surfaces was approximately 1.5 after 1 week, in contrast to the fluoridated specimens which displayed a Ca/P mean ratio of approximately 2. Powder X-ray diffraction (P-XRD) analyses showed the presence of hydroxyapatite on all types of surfaces after 4 and 6 weeks of immersion. The samples immersed for 6 weeks showed a higher degree of crystallinity than the samples immersed for 4 weeks. In conclusion, differences appeared at the early SBF immersion times of 1 and 2 weeks between controls and bioactive surface types, as well as between different bioactive surface types.

Electronic states spectroscopy of hydroxyapatite ceramics

Photoluminescence, surface photovoltage spectroscopy and high-resolution characterization methods (Atomic Force Microscopy, Scanning Electron Microscopy, X-ray spectroscopy and DC conductivity) are applied to nanostructured Hydroxyapatite (HAp) bioceramics and allowed to study electron (hole) energy states spectra of the HAp and distinguish bulk and surface localized levels. The measured trap spectra show strong sensitivity to preliminary heat treatment of the ceramics. It is assumed that found deep electron (hole) charged states are responsible for high bioactivity of the HAp nanoceramics.

The Effect of Initial pH on Morphology of Biomimetic Apatite Coating

Bone-like apatite coatings were prepared using a biomimetic method in a simulated body fluid (SBF). The effect of initial pH values on the surface morphology of biomimetic apatite coating was studied. The coatings were characterized using X-ray diffraction and environmental scanning electron microscope. It was revealed that the morphology of the biomimetic apatite coating could be tailored by manipulating the initial pH of the SBF solution.

Strontium-substituted apatite coating grown on Ti6Al4V substrate through biomimetic synthesis

During the last few years Strontium has been shown to have beneficial effects when incorporated at certain doses in bone by stimulating bone formation. It is believed that its presence locally at the interface between an implant and bone will enhance osteointegration and therefore, ensure the longevity of a joint prosthesis. In this study we explore the possibility of incorporating Sr into nano-apatite coatings prepared by a solution-derived process according to an established biomimetic methodology for coating titanium based implants. The way this element is incorporated in the apatite structure and its effects on the stereochemistry and morphology of the resulting apatite layers was investigated, as well as its effect in the mineralization kinetics. By using the present methodology it was possible to incorporate increasing amounts of Sr in the apatite layers. Sr was found to incorporate in the apatite layer through a substitution mechanism by replacing Ca in the apatite lattice. The presence of Sr in solution induced an inhibitory effect on mineralization, leading to a decrease in the thickness of the mineral layers. The obtained Sr-substituted biomimetic coatings presented a bone-like structure similar to the one found in the human bone and therefore, are expected to enhance bone formation and osteointegration.

Osteoblast response to zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate

Calcium phosphate bioceramics, such as hydroxyapatite, have long been used as bone substitutes because of their proven biocompatibility and bone binding properties in vivo. Recently, a zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate (Zr-ACP) has been synthesized, which is more soluble than hydroxyapatite and allows for controlled release of calcium and phosphate ions. These ions have been postulated to increase osteoblast differentiation and mineralization in vitro. The focus of this work is to elucidate the physicochemical properties of Zr-ACP and to measure cell response to Zr-ACP in vitro using a MC3T3-E1 mouse calvarial-derived osteoprogenitor cell line. Cells were cultured in osteogenic medium and mineral was added to culture at different stages in cell maturation. Culture in the presence of Zr-ACP showed significant increases in cell proliferation, alkaline phosphatase activity (ALP), and osteopontin (OPN) synthesis, whereas collagen synthesis was unaffected. In addition, calcium and phosphate ion concentrations and medium pH were found to transiently increase with the addition of Zr-ACP, and are hypothesized to be responsible for the osteogenic effect of Zr-ACP.

Corrosion test, cell behavior test, andin vivo study of gradient TiO2 layers produced by compound electrochemical oxidation

This paper describes efforts to improve implant biocompatibility and durability by applying a hybrid technique using composite oxidation. Pure titanium was used as the substrate material. A porous oxide film as the outer layer was produced by micro-arc oxidation and a dense oxide film as the inner layer was produced by pre-anodic oxidation. In this study, physicochemical characteristics, corrosion test, cell attachment behavior, and in vivo studies were used to compare this gradient layer with untreated titanium. The results revealed that the gradient layer was composed of two layers of oxide films which were made up of rutile and anatase and the surface was porous with calcium and phosphor. The corrosion resistance of the gradient layer was improved remarkably, which was about three times the values for titanium and two times the value for the dense layer. The cell-material interaction study indicated that L929 cells seeded and cultured on the gradient layer appeared to attach well and the rate of proliferation was the greatest. The study in vivo showed that the gradient layer had good biocompatibility. This gradient layer provides a material with high corrosion resistance, bioactivity, and biological properties suitable for tissue engineering applications.

Hydroxyapatite growth on anodic TiO2 nanotubes

In the present work, we study the growth of hydroxyapatite formation on different TiO(2) nanotube layers. The nanotube layers were fabricated by electrochemical anodization of titanium in fluoride-containing electrolytes. To study various nanotube lengths, layers with an individual tube diameter of 100 nm were grown to a thickness of approximately 2 mum or 500 nm. The ability to form apatite on the nanotube layers was examined by immersion tests combined with SEM, XRD and FT-IR investigations. For reference, experiments were also carried out on compact anodic TiO(2) layers. The results clearly show that the presence of the nanotubes on a titanium surface enhances the apatite formation and that the 2-mum thick nanotube layer triggers deposition faster than the thinner layers. Tubes annealed to anatase, or a mixture of anatase and rutile are clearly more efficient in promoting apatite formation than the tubes in their "as-formed" amorphous state.

Biological fabrication of nacreous coating on titanium dental implant

Titanium screws with 3.5mm diameter and 8mm length, as well as titanium flat sheets with size 4 mm x 8 mm x 0.3mm, were implanted into the epithelial mantle pearl sacs of a fresh water bivalve (Hyriopsis cumingii Lea) by replacing the pearls. After 45 days of cultivation, the implant surfaces were deposited with a nacre coating with iridescent luster. The coating could conform to some extent the thread topography of the screw implant and was about 200-600 microm in thickness. The coating was composed of a laminated nacreous layer and a transitional non-laminated layer that consisted mainly of vaterite and calcite polymorphs of calcium carbonate. The transitional layer was around 2-10 microm thick in the convex and flat region of the implant surface and could form close contact with titanium surface; while the transitional layer was much thicker in the steep concave regions and could not form close contact with the titanium surface. The reasons for inhomogeneity in thickness and the variation in interface character were discussed and the improvement to the design of the dental implant with respect to this coating method was suggested in the paper. The results suggest that it is possible to fabricate a biologically active and degradable, and mechanically tough and strong nacre coating on titanium dental implant by this novel coating technology.