Hydroxyapatite porous scaffold engineered with biological polymer hybrid coating for antibiotic Vancomycin release

The purpose of this study is to improve hydroxyapatite (HA) porous scaffolds via coating with biological polymer-HA hybrids for use as wound healing and tissue regeneration. Highly porous HA scaffolds, fabricated by a polyurethane foam reticulate method, were coated with hybrid coating solution, consisting of poly(-caprolactone) (PCL), HA powders, and the antibiotic Vancomycin. The PCL to HA ratio was fixed at 1.5 and the drug amounts were varied [drug/(PCL + HA) = 0.02 and 0.04]. For the purpose of comparison, bare HA scaffold without the hybrid coating layer was also loaded with Vancomycin via an immersion-adsorption method. The hybrid coating structure and morphology were observed with Fourier transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The effects of the hybrid coating on the compressive mechanical properties and the in vitro drug release of the scaffolds were investigated in comparison with bare HA scaffold. The PCL-HA hybrid coating altered the scaffold pore structure slightly, resulting in thicker stems and reduced porosity. With the hybrid coating, the HA scaffold responded to an applied compressive stress more effectively without showing a brittle failure. This was attributed to the shielding and covering of the framework surface by the coating layer. The encapsulated drugs within the coated scaffold was released in a highly sustained manner as compared to the rapid release of drugs directly adsorbed on the pure HA scaffold. These findings suggest that the coated HA scaffolds expand their applicability in hard tissue regeneration and wound healing substitutes delivering bioactive molecules.     

Hydroxyapatite coating of titanium by biomimetic method

The biomimetic method was used in order to deposit, on titanium substrates, an hydroxyapatite (HA) coating. The bioactive HA layer was obtained by using, in the first stage of the process, a glass having the composition 2.5CaO2SiO₂ different from the one proposed for the application of the biomimetic method. This glass can be obtained via sol–gel, a method that allows one to obtain, easily, very pure products. The growth of HA crystals was confirmed by Fourier transform infrared, SEM, EDS and X-ray photoelectron spectroscopy (XPS) results. The experimental results suggest that, as reported in the literature for other supports, the silicate ions released from the glass in the first stage bind themselves to the titanium support. In particular, from XPS analysis it is evident that the titanium substrate is well covered by a calcium phosphate layer of the type of HA.     

天然多孔材料水热合成羟基磷灰石

研究发现牡蛎白垩层是一种天然方解石质多孔微结构材料,并以其为原料,采用水热法在90℃水浴、常压条件下与磷酸氢二铵溶液反应生成羟基磷灰石.产物通过傅立叶红外光谱(FTIR)、X射线粉末衍射(XRD)、扫描电子显微镜(SEM)进行分析.结果表明,常压下反应15min就出现了羟基磷灰石.48h后白垩层几乎完全转化为羟基磷灰石,并且生成的羟基磷灰石仍完好的保留原多孔微结构.这种转化是通过两种历程完成的,即方解石表面的溶解-重结晶及其内部的固态局域规整离子交换反应.     

Boiling crisis on surfaces with porous coating

Experimental values on nucleate and film boiling of carbon dioxide on polished and porous cylindrical surfaces under conditions of saturation at reduced pressures, P/P_crit=0.93 and 0.97 are discussed. A considerable increase of the maximal, minimal specific heat fluxes and maximal heat transfer coefficient was observed on a horizontal tube with thin porous coating.     

Hydroxyapatite coating by biomimetic method on titanium alloy using concentrated SBF

This article reports a biomimetic approach for coating hydroxyapatite on titanium alloy at ambient temperature. In the present study, coating was obtained by soaking the substrate in a 5 times concentrated simulated body fluid (5XSBF) solution for different periods of time with and without the use of CaO-SiO₂ based glass as a possible source of nucleating agent of apatite formation. Optical microscopic and SEM observations revealed the deposition of Ca-P layer on the titanium alloy by both the methods. Thickness of coating was found to increase with the increase in immersion time. The use of glass did not help the formation of apatite nuclei on the substrate and the coating obtained by this method was also not uniform. EDX analysis indicated that the coating consisted of Ca-P based apatite globules, mostly in agglomerated form, and its crystallinity was poor as revealed by XRD.     

Hydrothermal-electrochemical codeposited hydoxyapatite/yttria-stabilized zirconia composite coating

Hydroxyapatite(HA)/yttria-stabilized zirconia(YSZ) composite coatings were deposited on titanium substrates using a hydrothermal electrochemical method in an electrolyte containing calcium, phosphate ions and YSZ particles. HA/YSZ composite coatings were prepared in different conditions with different electrolyte temperatures(100 ∼ 200°C), current densities(0.1 ∼ 10.0 mA/cm²), and particles content in bath(0 ∼ 100 g/L). The effect of YSZ additions on the phase composition, microstructure, thermal stability, corrosion behavior and the bonding strength of HA/YSZ composite coatings were studied. The results show that crystallinity of HA in HA/YSZ composite coatings increase continuously with the electrolyte temperature and close to stoichiometric HA. The n(Ca)/n(P) ratio at 200°C is about 1.67 according with stoichiometric HA. YSZ particles are imbedded uniformly between the HA crystals. The average HA crystal size are reduced owing to the additions of YSZ particles. After annealing at 1200°C, tetragonal phase YSZ tend to react with the released CaO to form cubic phase YSZ and CaZrO₃, which cause destabilization of HA to decompose into more α-TCP phase. The bonding strength between HA/YSZ composite coatings and titanium substrates increase with increasing volume content of YSZ in the composite coatings (V %). HA/YSZ composite coatings exhibit a better electrochemical behavior than pure HA coatings and uncoated Ti metals.     

Hydroxyapatite coating on the titanium substrate modulated by a recombinant collagen-like protein

Plenty of techniques have been developed to modify the surface character of titanium (Ti) and its alloys in order to realize their biological bond to natural bone. In this work, a biomimetic process was employed to form a hydroxyapatite (HAp) coating on the alkali-heat treated Ti substrate in 1.5 times simulated body fluid (1.5 × SBF) with the addition of a recombinant collagen-like protein. The coating was characterized using SEM-EDX, FESEM, and XRD. Results showed that the recombinant collagen-like protein could accelerate the preferential nucleation and directional growth along c axis of HAp on the pretreated Ti substrates. The investigation of in vitro cell cultivation showed that the existence of recombinant collagen-like protein in coating could improve the initial cell adhesion, proliferation and differentiation of MG-63 cells, which implied the materials possessed excellent biocompatibility and had a wide potential in biomedical application.     

Thermal conductivity of dense and porous yttria-stabilized zirconia

The thermal conductivity of dense and porous yttria-stabilized zirconia (YSZ) ceramics has been measured as a function of temperature in the range 25 to 1000 °C. The dense specimens were either single crystal (8 mol% YSZ) or sintered polycrystalline (3 mol% and 8 mol% YSZ). The porous specimens (3 mol% YSZ) were prepared using the fugitive polymer method, where different amounts of polymer spheres (of two different average sizes) were included in the starting powders before sintering. This method yielded materials with uniformly distributed porosities with a tight pore-size distributions. A theory has been developed to describe the thermal conductivity of dense YSZ as a function of temperature. This theory considers the reduction in the intrinsic thermal conductivity due scattering of phonons by point defects (oxygen vacancies and solute) and by the hopping of oxygen vacancies. It also considers an increase in the effective thermal conductivity at high temperatures due to radiation. This theory captures the essential features of the observed thermal conductivity. The Maxwell theory has been used to analyze the thermal conductivity of the porous materials. An adequate agreement was found between the theory and experiment.     

Hydroxyapatite coating by dipping method,and bone bonding strength

Hydroxyapatite (HA) was coated onto titanium rods by a dip coating method using HA sol. The HA sols were prepared by dispersing HA crystals less than 100 nm length in distilled water or physiological salt solution using an ultrasonic homogenizer. The surface of the HA coating was homogeneous as determined by scanning electron microscopy (SEM). After implantation of uncoated and HA dip coated titanium rods in dog femurs, new bone formation was observed only around the coated material. The bone bonding strength to HA coated rods was 1.0, 1.5, 2.0 and 2.5 Mpa after 1,2,3 and 4 weeks implantation, respectively, as determined by pull-out testing. These values were over twice that of the uncoated titanium rods at 1–4 weeks after implantation. The dip coated titanium exhibited superior biocompatibility to the uncoated implant and may be of great value for bone repacement applications.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Granular nanocrystalline zirconia electrolyte layers deposited on porous SOFC cathode substrates

Thin granular yttria-stabilized zirconia (YSZ) electrolyte layers were prepared by chemical vapor synthesis and deposition (CVD/CVS) on a porous substoichiometric lanthanum–strontium–manganite (ULSM) solid oxide fuel cell cathode substrate. The substrate porosity was optimized with a screen printed fine porous buffer layer. Structural analysis by scanning electron microscopy showed a homogeneous, granular nanocrystalline layer with a microstructure that was controlled via reactor settings. The CVD/CVS gas-phase process enabled the deposition of crack-free granular YSZ films on porous ULSM substrates. The electrolyte layers characterized with impedance spectroscopy exhibited enhanced grain boundary conductivity.     

Preparation of yttria-stabilized zirconia nanoplatelets using vacuum roll coating

Roll-to-roll vacuum coating on moving plastic substrates and the subsequent comminuting of the film into a flake or platelet with microscale lateral and thickness dimensions is an industrially mature technology utilized to produce clean, consistent material with high throughput. In this study, we describe the novel preparation of nanoplatelets by top-down vacuum evaporation of yttria-stabilized zirconium dioxides (YSZ) on a nanoembossed, moveable substrate for the purposes of making nanoplatelets. Microscopy and particle size analysis of the resulting YSZ nanoplatelets revealed that use of the nanoembossed substrate results in significant narrowing of the particle size distribution. However, while the YSZ coatings were conformal and successfully replicated the nanopattern of the underlying substrate, the stress in the film was inadequate to fracture the film into platelets that replicated the nanometer dimensions of the underlying pattern. It was determined that this is due to the inherent fracture toughness of the nanoplatelets and the augmented adhesion forces along the increased length scale of nanoparticle contacts. The nanoplatelets were further reduced in average size and size distribution by post-processing techniques of sonication, ball milling, and centrifugation. The nanoplatelet’s stoichiometry and crystallinity were modified by manipulating the source material, deposition parameters, and post-processing steps.     

钛涂覆多孔羟基磷灰石涂层的制备及其生物活性

在纯钛基体表面通过电泳沉积的方法制得壳聚糖/羟基磷灰石(CS/HA)复合涂层, 然后将复合涂层烧结形成多孔HA涂层。采用SEM对多孔HA涂层的形貌进行观察, XRD分析涂层的物相组成, 粘结拉伸实验测定涂层与基体的结合强度, 1.5倍人体模拟体液(1.5SBF)浸泡测定涂层的生物活性。结果表明: 当悬浮液中CS与HA质量比为1∶1时, 制得的CS/HA复合涂层经过700℃烧结处理, 涂层中CS热分解致孔形成多孔HA涂层, 孔径在10~25 μm, 涂层与基体的结合强度可达19.5 MPa; 在1.5SBF中浸泡5天后, 多孔HA涂层表面完全碳磷灰石化, 呈现较好的生物活性。      

Hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition

The aim of this study was to investigate the hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition. The Ti-35Nb-xZr ternary alloys contained from 3 wt.% to 10 wt.% Zr content were manufactured by arc melting furnace. Hydroxyapatite (HA) coatings were prepared by electron-beam physical vapor deposition (EB-PVD) method, and crystallization treatment was performed in Ar atmosphere at 300 and 500 °C for 1 h. The coated surface morphology of Ti-35Nb-xZr alloy was examined by FE-SEM, EDX and XRD, respectively. In order to evaluate the corrosion behavior, the tests were performed by potentiodynamic, cyclic polarization and AC impedance test. All the electrochemical data were obtained using a potentiostat. The Ti-35Nb-xZr alloys exhibited equiaxed structure with β phase, the peak of β phase increased with Zr contents. The hardness and elastic modulus of Ti-35Nb-xZr alloys decreased as Zr content increased. The HA coated layer was approximately 150 nm and Ca/P ratio of HA coated surface after heat treatment at 500 °C was around 1.67. The HA thin film consisted of small droplets with spherical shape by crystallization. From the anodic polarization curves, HA coated and heat treated Ti-35Nb-10Zr alloy showed higher corrosion potential than other samples. HA coated film on the Ti-35Nb-10Zr alloy can be shown high polarization resistance by crystallization.     

Mechanical examinations on dental implants with porous titanium coating

Due to its good biocompatibility, porous titanium is an interesting material for biomedical applications. Bone tissue can grow inside the porous structure and maintain a long and stable connection between the implant and the human bone. To investigate its long term stability, the mechanical behavior of porous titanium was tested under static and dynamic conditions and was compared to human bone tissue. A promising application of this material is the coating of dental implants. A manufacturing technique was developed and implants were produced. These implants were fatigue tested according to modified ISO 14801 and the micro structural change was examined. The fatigue test was statically modeled using finite element analysis (FEA). The results show that the implants resist a continuous load which is comparable to the loading conditions in the human jaw. The experiments show that the porous titanium has bone-like mechanical properties. Additionally the porous titanium shows an anisotropic behavior of its mechanical properties depending on the alignment of the pores. Finally, other potential applications of porous titanium are outlined.     

Laser induced multi-scale textured zirconia coating on Ti-6Al-4V

A textured coating of zirconia on Ti-6Al-4V alloy was produced using pulsed laser based processing technique. Scanning electron microscope observations coupled with fractal analysis revealed the multi-scale nature of the textured coating. Both stylus based profilometric measurements and fractal analysis indicated non-linear nature of the relationship between laser processing speed at constant pulse frequency (10 kHz) and roughness of the textured coating. The textured coatings produced with all the three processing speeds (40, 160, 290 cm/min) were fractal over certain length scales. Processing at 40 cm/min resulted in structures that are fractal across a large number of length scales where as higher processing speeds resulted in fractality over fewer length scales. The processing speed influenced the zirconia content in the coating and the phase transformation within Ti-matrix of the coating. Within the coating, while zirconia content decreased the amount of retained β-Ti increased with increase in processing speed. Such physical and chemical transformations are desired in a titanium bio-implant for effective contact with protein, cells and tissues at various length scales and its effective chemical performance in bio-environment.