Surface coatings for improvement of bone cell materials and antimicrobial activities of Ti implants

Ti surface was modified to simultaneously improve bone cell materials and antimicrobial activities. Titanium surface was first anodized in sodium fluoride and sulfuric acid electrolytic solution to form titania nanotube on the surface to improve the biocompatibility of the surface. Silver was electrodeposited on the titania nanotube surface at 5 V. Silver added titania nanotube surface was tested for compatibility with bone-cell materials interactions using human osteoblast bone cells. The antibacterial effect was studied using Pseudomonas aeruginosa. Our results show that silver-treated titania nanotube surface may provide antibacterial properties to prevent implants against postoperative infections without interference to the attachment and proliferation of bone tissue on titanium, which is commonly used in dental and orthopedic surgical procedures.     

Nanoscale neuro-integrative coatings for neural implants

Silicon microelectrode arrays (Si MEAs) have great potential in enabling chronic in vivo recording of neural activity, but this potential has been hampered by scar tissue formation at the site of implantation. In this study, we report the fabrication and characterization of nanoscale coatings that have the potential of enhancing the biocompatibility of Si electrodes. We use electrostatic layer-by-layer (LbL) assembly to prepare nanoscale bioactive coatings on silicon substrates. We use the response of chick cortical neurons to these coatings to assess potential improvement in biocompatibility in vitro. The coatings are built on oxide covered silicon wafers by alternating polycations, polyethyleneimine (PEI) or chitosan (CH), with polyanions, either gelatin or laminin (LN). We use quartz crystal microbalance (QCM) to characterize the coatings. Our analysis confirms that we achieved approximately 30-110 angstroms scale coatings via LbL assembly. In contrast to bare oxide covered silicon, coated substrates had significantly enhanced chick cortical neuron adhesion and differentiation, with multilayers of PEI-LN showing the greatest improvement. The multilayers of PEI-LN were stable for at least 7 days in physiological conditions, as determined by an enzyme-linked immunosorbent assay (ELISA). In addition, impedance spectroscopy confirmed that multilayers of PEI and LN did not increase the magnitude of impedance of Si MEAs at the biologically relevant frequency of 1 kHz. Our study demonstrates that electrostatic LbL assembly enables nanoscale bioactive coatings, and that PEI-LN multilayers significantly enhance cortical neuronal attachment and differentiation in vitro with no deleterious effects on impedance of the electrodes. Such well-controlled nanoscale coatings have the potential to significantly impact the compatibility and performance of Si MEAs in vivo.     

Biomimetic organic-inorganic nanocomposite coatings for titanium implants

A new class of organic-inorganic nanocomposites, to be used as coatings for surface enhancement of metal implants for bone replacement and repair, has been prepared by a biomimetic three-step procedure: (1) embedding amorphous calcium phosphate (ACP) particles between organic polyelectrolyte multilayers (PE MLs), (2) in situ transformation of ACP to octacalcium phospate (OCP) and/or poorly crystalline apatite nanocrystals by immersion of the material into a metastable calcifying solution (MCS) and (3) deposition of a final PE ML. The organic polyelectrolytes used were poly-L-glutamic acid and poly-L-lysine. The nanocomposites obtained by each successive step were characterized by scanning electron microscopy, energy dispersive X-ray analysis (EDS), and XRD, and their suitability as coatings for metal implants was examined by mechanical and in vitro biological tests. Coatings obtained by the first deposition step are mechanically unstable and therefore not suitable. During the second step, upon immersion into MCS, ACP particles were transformed into crystalline calcium phosphate, with large platelike OCP crystals as the top layer. After phase transformation, the nanocomposite was strongly attached to the titanium, but the top layer did not promote cell proliferation. However, when the coating was topped with an additional PE ML (step 3), smoother surfaces were obtained, which facilitated cell adhesion and proliferation as shown by in vitro biological tests using primary human osteoblasts (HO) directly seeded onto the nanocomposites. In fact, cell proliferation on nanocomposites with top PE MLs was far superior than on any of the individual components and was equivalent to proliferation on the golden standard (plastic).     

Electrophoretic deposition of zirconia-Bioglass composite coatings for biomedical implants

Composite bilayer coatings on Ti6Al4V substrates were prepared by electrophoretic deposition, a simple and fast low temperature coating technique. Biocompatible yttrium-stabilized zirconia (YSZ) in the form of nanoparticles and bioactive Bioglass (45S5) in the form of microparticles were chosen as coating materials. The first layer consisted of 5 microm of YSZ, deposited with the intention to avoid any metal tissue contact. The second layer consisted of 15-microm thick 45S5-YSZ composite, supposed to react with the surrounding bone tissue and to enhance implant fixation. The adsorption of YSZ nanoparticles on 45S5 microparticles in organic suspension was found to invert the surface charge of the 45S5 particles from negative to positive. This enabled cathodic electrophoretic deposition of 45S5, avoiding uncontrolled anodization (oxidation) of the substrate. The coatings were sintered at 900 degrees C for 2 h under argon flow. The characterization was performed using SEM, EDX, and nanoindentation (cross section). Potential applications in the orthopedics field are discussed.     

Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.     

Nitric oxide-releasing sol-gels as antibacterial coatings for orthopedic implants

To assess the benefits of nitric oxide (NO)-releasing sol-gels as potential antibacterial coatings for orthopedic devices, medical-grade stainless steel is coated with a sol-gel film of 40% N-aminohexyl-N-aminopropyltrimethoxysilane and 60% isobutyltrimethoxysilane. Upon converting the diamine groups in these films to diazeniumdiolate NO donors, the NO release from the sol-gel-coated stainless steel is evaluated at both ambient and physiological temperature. Sol-gel films incubated at 25 degrees C have a lower NO flux over the first 24 h compared to those at 37 degrees C, but release more than five times longer. The bacterial adhesion resistance of NO-releasing coatings is evaluated in vitro by exposing bare steel, sol-gel, and NO-releasing sol-gel-coated steel to cell suspensions of Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis at 25 degrees C and 37 degrees C. Cell adhesion to bare and sol-gel-coated steel is similar, while NO-releasing surfaces have significantly less bacterial adhesion for all species and temperatures investigated.     

Biocompatibility of corrosion-resistant zeolite coatings for titanium alloy biomedical implants

Titanium alloy, Ti6Al4V, is widely used in dental and orthopedic implants. Despite its excellent biocompatibility, Ti6Al4V releases toxic Al and V ions into the surrounding tissue after implantation. In addition, the elastic modulus of Ti6Al4V (～110 GPa) is significantly higher than that of bone (10–40 GPa), leading to a modulus mismatch and consequently implant loosening and deosteointegration. Zeolite coatings are proposed to prevent the release of the toxic ions into human tissue and enhance osteointegration by matching the mechanical properties of bone. Zeolite MFI coatings are successfully synthesized on commercially pure titanium and Ti6Al4V for the first time. The coating shows excellent adhesion by incorporating titanium from the substrate within the zeolite framework. Higher corrosion resistance than the bare titanium alloy is observed in 0.856 M NaCl solution at pHs of 7.0 and 1.0. Zeolite coatings eliminate the release of cytotoxic Al and V ions over a 7 day period. Pluripotent mouse embryonic stem cells show higher adhesion and cell proliferation on the three-dimensional zeolite microstructure surface compared with a two-dimensional glass surface, indicating that the zeolite coatings are highly biocompatible.     

Bioactive films on metallic surfaces for osteoconduction

A fast and effective electrochemical method was developed to make a dense calcium phosphate films on titanium and stainless steel for hard tissue replacement. The surfaces of titanium and stainless steel were cathodically treated in an electrochemical cell. By controlling the treatment parameters, a film of 100-nm thickness was deposited on the metal surface in several minutes. The thin film was amorphous calcium phosphate containing octacalcium phosphate nuclei, and also dense and ductile. The treated metals were able to induce bioactive calcium phosphate deposition after immersion in simulated body fluid (SBF) for only 1 and 2 days. In vivo study was conducted by implanting the treated specimens of titanium and stainless steel in dog's femur cavity. The treated metallic surfaces showed good ability of osteoconduction. This surface treatment method can be potentially used to enhance bioactivity of any type of metallic surfaces.     

Interfaces in graded coatings on titanium-based implants

Graded bilayered glass-ceramic composite coatings on Ti6Al4V substrates were fabricated using an enameling technique. The layers consisted of a mixture of glasses in the CaO-MgO-Na(2)O-K(2)O-P(2)O(5) system with different amounts of calcium phosphates (CPs). Optimum firing conditions have been determined for the fabrication of coatings having good adhesion to the metal, while avoiding deleterious reactions between the glass and the ceramic particles. The final coatings do not crack or delaminate. The use of high-silica layers (>60 wt % SiO(2)) in contact with the alloy promotes long-term stability of the coating; glass-metal adhesion is achieved through the formation of a nanostructured Ti(5)Si(3) layer. A surface layer containing a mixture of a low-silica glass ( approximately 53 wt % SiO(2)) and synthetic hydroxyapatite particles promotes the precipitation of new apatite during tests in vitro. The in vitro behavior of the coatings in simulated body fluid depends both on the composition of the glass matrix and the CP particles, and is strongly affected by the coating design and the firing conditions.     

Development of chitosan-vancomycin antimicrobial coatings on titanium implants

Three-dimensional (3D) fibrous hydrogels were fabricated by blending two photoactive polymers, poly(ethylene glycol) diacrylate (PEGDA) and poly(vinyl alcohol) (PVA), and the resulting solution was electrospun. PEGDA is a commonly used hydrogel material for tissue engineering applications since its interaction with cells can be tuned by crosslinking in a variety of bioactive molecules including peptides and proteins. The PVA in these materials aids in fiber formation and stabilizes the fibrous network when hydrated. The average dry fiber diameter in the hydrogels was 1.02 μm and upon swelling, the fiber diameter increased approximately six-fold. Fibers were stable under cell culture conditions for up to 5 days. The adhesive ligand, RGDS, was readily incorporated into the fibrous network via the conjugation of RGDS to PEG-monoacrylate which was then crosslinked with the fibers. The bioactivity of the fibrous hydrogels was compared with peptide-modified PEGDA-based hydrogels. The two hydrogel materials had similar cell adhesion and viability. Cell morphology on the fibrous hydrogels was dendritic showing a more in vivo like representation, as compared to spread cell morphology on the PEGDA gels. The ability to generate 3D fibrous architectures in hydrogel systems opens up new areas of investigation in cell-material interactions and tissue formation.     

骨科内植物多功能涂层研究进展

无菌性松动和植入物周围感染是骨科内固定术失败的两个主要原因,随着手术数量的日益增长,如何降低此类手术失败风险变得格外重要。在这个领域中,近期大量的研究工作致力于研制各种各样的内植物涂层,而这些涂层大多只具有抗感染作用而无骨整合作用;或者只具有骨整合作用而不具备抗感染作用。但是要使内植物长期有效,理想的涂层应兼顾骨整合和抗感染这两个功能。本文将对同时具有骨整合性和抗感染性的多功能涂层近期的研究进展和未来研究方向进行综述。     

Neutron diffraction residual strain measurements in nanostructured hydroxyapatite coatings for orthopaedic implants

The failure of an orthopaedic implant can be initiated by residual strain inherent to the hydroxyapatite coating (HAC). Knowledge of the through-thickness residual strain profile in the thermally sprayed hydroxyapatite coating/substrate system is therefore important in the development of a new generation of orthopaedic implants. As the coating microstructure is complex, non-destructive characterization of residual strain, e.g. using neutron diffraction, provides a useful measure of through thickness strain profile without altering the stress field. This first detailed study using a neutron diffraction technique, non-destructively evaluates the through thickness strain measurement in nanostructured hydroxyapatite plasma sprayed coatings on a titanium alloy substrate (as-sprayed, heat treated, and heat treated then soaked in simulated body fluid (SBF)). The influence of crystallographic plane orientation on the residual strain measurement is shown to indicate texturing in the coating. This texturing is expected to influence both the biological and fracture response of HA coatings. Results are discussed in terms of the influence of heat-treatment and SBF on the residual stress profile for these biomedical coatings. The results show that the through thickness residual strain in all three coatings was different for different crystallographic planes but was on average tensile. It is also concluded that the heat-treatment and simulated body fluid exposure had a significant effect on the residual strain profile in the top layers of HAC.     

Enhanced bone bonding of hydroxyapatite-coated titanium implants by electrical polarization

Hydroxyapatite (HAp) coatings are applied to orthopedic and dental implants made of titanium (Ti) and its alloys in order to increase their bioactivities and to offset the mechanical weakness of HAp. We examined the in vivo effects of electrical polarization on the bone bonding of HAp-coated Ti. Polarized samples with a negatively or positively charged HAp-coated surface (N- or P-surface, respectively) were randomly implanted in the femora and tibiae of canines. As controls, nonpolarized HAp-coated Ti substrates with 0-surfaces were implanted. Direct bonding between the newly formed bone and HAp-coated Ti was observed with the O-, N-, and P-surfaces. The results of a pullout test were consistent with the amount of newly formed bone bonded directly to the surface of HAp-coated Ti. Electrically polarized HAp-coated Ti substrates, especially those with N-surfaces, exposed to recipient bone enhance bone bonding and could enable earlier weight-bearing loads after operations.     

Osteogenecity of octacalcium phosphate coatings applied on porous metal implants

The biomimetic route allows the homogeneous deposition of calcium phosphate (Ca-P) coatings on porous implants by immersion in simulated physiologic solution. In addition, various Ca-P phases, such as octacalcium phosphate (OCP) or bone-like carbonated apatite (BCA), which are stable only at low temperatures, can be deposited. In this pilot study, experiments were designed with a twofold-purpose: (1) to investigate the osteoinduction of OCP-coated and noncoated porous tantalum cylinders and of dense titanium alloy cylinders (5 mm in diameter and 10 mm in length) in the back muscle of goats at 12 and 24 weeks (n = 4); and (2) to compare the osteogenic potentials of BCA-coated, OCP-coated, and bare porous tantalum cylinders in a gap of 1 mm created in the femoral condyle of a goat at 12 weeks (n = 2). In the goat muscle, after 12 weeks the OCP-coated porous cylinder had induced ectopic bone as well as bone within the cavity of the OCP-coated dense titanium cylinder. In the femoral condyle, bone did not fill the gap in any of the porous implants. In contrast with the two other groups, OCP-coated porous cylinders exhibited bone formation in the center of the implant. The nature of the Ca-P coating, via its microstructure, its dissolution rate, and its specific interactions with body fluids, may influence the osteogenecity of the Ca-P biomaterial.     

3,4-dihydroxyphenylalanine-assisted hydroxyapatite nanoparticle coating on polymer scaffolds for efficient osteoconduction

For bone regeneration applications, scaffolds made from a composite of a biodegradable polymer and ceramic have advantages over scaffolds made from only one component (biodegradable polymer or ceramic alone). In this study, a simple and rapid method was developed to induce hydroxyapatite (HA) nanoparticle adsorption on polyglycolic acid (PGA) scaffold surfaces. PGA meshes were coated with HA nanoparticles by immersing the scaffolds in a buffer solution containing 3,4-dihydroxyphenylalanine (DOPA), a critical, functional element in mussel adhesive protein known to strongly bind to various materials. Substantial HA coating on PGA scaffolds was achieved within 24 hours of immersion, as determined according to selective staining of ceramic particles, scanning electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy. To evaluate the osteoconduction efficacy of the scaffolds in vivo, PGA scaffolds, DOPA-coated PGA scaffolds, PGA scaffolds immersed in HA solution, and HA- and DOPA-coated PGA (HA-DOPA-PGA) scaffolds were implanted in critical-sized defects in mouse skulls for 8 weeks. Micro-computed tomography and histological analyses showed that bone regeneration in vivo was far more extensive on HA-DOPA-PGA scaffolds than on the other scaffolds. DOPA offers an efficient and simple method of HA coating on polymer scaffolds. HA-polymer composite scaffolds fabricated using this method could be useful as bone graft.     

钛基植人物生物陶瓷涂层的研究进展

医用钛合金材料属于生物惰性材料,广泛应用于硬组织的替换与修复领域.采用表面改性技术在钛基材料表面制成生物陶瓷涂层可改善钛基材料的生物活性和生物相容性.羟基磷灰石涂层已在临床上获得应用,但使用效果仍然受其较低的结合强度和结晶度所制约.为了获得综合性能更好的植入材料,制备了多种新型生物陶瓷涂层,其具有良好的生物活性、较好的...     

Controlled release of vanadium from titanium oxide coatings for improved integration of soft tissue implants

This study evaluates the potential of titanium oxide coatings for short-term delivery of vanadium for improved wound healing around implants. Titanium and vanadium oxides are bioactive agents that elicit different bioresponses in cells, ranging from implant integration and reduction of inflammation to modulation of cell proliferation and morphology. These oxides were combined in biomaterial coatings using metal-organic precursors and rapidly screened in cell-culture microplates to establish how vanadium-loading influences cell proliferation and morphology. Twenty-eight-day elution studies indicated that there was a controlled release of vanadium from stable titanium oxide matrices. Elution profiles were mathematically modeled for vanadium loading of 20-1.25% up to a period of 28 days. Scanning electron microscopy and energy dispersive spectroscopy of the coatings indicated that the vanadium was present as a nanoscale dispersion and not segregated micron-scale islands. The study confirmed that the observed bioresponse of cells was modulated by the soluble release of vanadium into the surrounding medium. Controlled release of vanadium from titania coatings may be used to influence soft-tissue integration of implants by modulating cell proliferation, attachment, inflammation, and wound healing dynamics.     

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 °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 μm and 0.38 μm, 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.     

Improved osteoconduction of cortical bone grafts by biodegradable foam coating

Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I--cortical bone without coating (control), Type II--cortical bone coated with PLGA-foam, Type III--cortical bone coated with PPF-foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post-operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam-coated grafts was significantly higher than in the control group (uncoated; p < 0.02). Although both foam formulations were initially equally osteoconductive, PLGA-based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF-based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA-coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF-based foams suggesting that PPF-coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.