Bioactive macroporous titanium implants highly interconnected

Intervertebral implants should be designed with low load requirements, high friction coefficient and low elastic modulus in order to avoid the stress shielding effect on bone. Furthermore, the presence of a highly interconnected porous structure allows stimulating bone in-growth and enhancing implant-bone fixation. The aim of this study was to obtain bioactive porous titanium implants with highly interconnected pores with a total porosity of approximately 57?%. Porous Titanium implants were produced by powder sintering route using the space holder technique with a binder phase and were then evaluated in an in vivo study. The size of the interconnection diameter between the macropores was about 210?μm in order to guarantee bone in-growth through osteblastic cell penetration. Surface roughness and mechanical properties were analyzed. Stiffness was reduced as a result of the powder sintering technique which allowed the formation of a porous network. Compression and fatigue tests exhibited suitable properties in order to guarantee a proper compromise between mechanical properties and pore interconnectivity. Bioactivity treatment effect in novel sintered porous titanium materials was studied by thermo-chemical treatments and were compared with the same material that had undergone different bioactive treatments. Bioactive thermo-chemical treatment was confirmed by the presence of sodium titanates on the surface of the implants as well as inside the porous network. Raman spectroscopy results suggested that the identified titanate structures would enhance in vivo apatite formation by promoting ion exchange for the apatite formation process. In vivo results demonstrated that the bioactive titanium achieved over 75?% tissue colonization compared to the 40?% value for the untreated titanium.     

Novel production method of porous surface Ti samples for biomedical application

A porous implant material with adequate pore structure and the appropriate mechanical properties for bone ingrowth has long been sought. This article presents details of the development, characterization and in vivo evaluations of powder metallurgy-processed titanium samples exhibiting a dense core with an integrated porous surface for biomedical applications. A space-holder method was applied to investigate the effects of different percentages and particle sizes of the urea on bone neoformation in 30 rabbits. The samples were previously characterized using scanning electron microscopy and mechanical testing. After 8 and 12 weeks of implantation, bone ingrowth was histologically and histometrically analyzed and push-out testing was performed. This study demonstrated that the association of a dense core integrated with the greatest number of interconnected pores of the smallest size is a promising biomaterial for bone tissue engineering. This sample exhibits appropriate mechanical properties combined with increased bone ingrowth, providing enhanced resistance to displacement.     

Ti–6Al–4V–0.5B—A Modified Alloy for Implants Produced by Metal Injection Molding

Permanent implants have to fulfill a great variety of requirements related to both material and geometry. In addition, manufacturing costs play a role, which is getting steadily more and more important. Metal Injection Molding (MIM) of titanium alloy powders may contribute to the development of implants with higher functionality without increasing the price. High degree of freedom with regard to geometry, high material efficiency, and the possibility to create even porous structures are main benefits from applying this technique. Today, even long‐term implants made from Ti–6Al–4V by MIM are commercially available. However, in order to improve fatigue behavior it is beneficial to perform a minor variation of Ti–6Al–4V by adding a low amount of boron. In this paper the mechanical, biological, and corrosion properties of specimens manufactured from Ti–6Al–4V–0.5B alloy by MIM are presented. In order to exclude unknown reactions in the body environment due to the boron content, corrosion, and biological tests are performed. Tensile and fatigue tests characterize the mechanical properties. Potentiodynamic polarization and electrochemical impedance spectroscopy are done in comparison to wrought and to MIM processed Ti–6Al–4V material. For cell experiments cancellous bone cells are cultured to perform adhesion, proliferation, and viability experiments. The results presented here show that the alloy Ti–6Al–4V–0.5B satisfies all basic needs of a material for highly loaded permanent implants manufactured by MIM.     

医用多孔金属的制备及其生物活化研究进展

医用多孔金属材料,特别是多孔钛及钛合金能够提供与人体骨组织相匹配的力学性能,并促进骨组织长入以提高其与骨的固定度,在人体硬组织修复与替换方面具有广泛的应用前景。重点围绕多孔钛及钛合金的制备方法及适用于其复杂孔隙结构的表面生物活化方法,综述了各种方法在多孔钛及钛合金上的应用现状。目前适用于多孔钛及钛合金制备的技术主要有粉末冶金法、钛纤维烧结法、自蔓延高温合成法、选区电子束熔化技术和选区激光熔化技术,适用于多孔钛及钛合金表面生物活化的技术主要有溶胶凝胶法、仿生矿化法、电化学沉积法和微弧氧化法。多孔钛及钛合金的力学相容性和表面生物活性需要同时满足临床要求,才能进一步扩大其在医学领域的应用范围。     

Australian Coral as a Biomaterial: Characteristics

In order to produce effective implants, the materials used must be biocompatible. Hydroxyapatite (HAp) is a bioactive material similar to the mineral component of teeth and bone which is often used for orbital implants and bone graft applications. HAp can be manufactured from corals via hydrothermal conversion. Coral is particularly useful as a starting material for hydroxyapatite production because of its porous nature. When a porous structure is used tissue ingrowth can occur readily and hence an excellent mechanical bond can be achieved. A large pore size and a high degree of pore interconnections are desirable implant properties. In the present paper a comparison of the properties of four different species of Australian coral has been made to determine the most favourable species to use as a starting material for hydrothermal conversion.     

Fatigue behavior of porous biomaterials manufactured using selective laser melting

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S–N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S–N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S–N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S–N curves. It is shown that the measured data points conform to the fitted power law very well, R² = 0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (< 0.2) is lower than that of corresponding solid material (c.a. 0.4).     

Tailor‐Made Composites Based on Titanium for Medical Devices

For special advanced applications in medicine biomaterials can be tailor‐made as composites if a single material is not able to fulfill the various requirements. In most cases a functional surface layer, which may have the required physical, mechanical, or biological properties, covers a structural material: titanium and its alloys for preference. Three classes of composites based on titanium materials offer special properties: Ti/porous Ti composites have special mechanical properties for isoelastic implants; Ti/ceramic composites show special biological properties used for improved osseointegration of the implants; and the special physical properties of Ti/ceramic composites makes them suitable for heart pacemaker leads.     

Evaluating mechanical properties and degradation of YTZP dental implants

Lately new biomedical grade yttria stabilized zirconia (YTZP) dental implants have appeared in the implantology market. This material has better aesthetical properties than conventional titanium used for implants but long term behaviour of these new implants is not yet well known. The aim of this paper is to quantify the mechanical response of YTZP dental implants previously degraded under different time conditions and compare the toughness and fatigue strength with titanium implants. Mechanical response has been studied by means of mechanical testing following the ISO 14801 for Standards for dental implants and by finite element analysis. Accelerated hydrothermal degradation has been achieved by means of water vapour and studied by X-ray diffraction and nanoindentation tests. The results show that the degradation suffered by YTZP dental implants will not have a significant effect on the mechanical behaviour. Otherwise the fracture toughness of YTZP ceramics is still insufficient in certain implantation conditions.     

Dynamics of bone tissue mineralization in porous titanium and the mechanical properties of a titanium-bone tissue composite

We studied the dynamics of bone tissue mineralization in the pores of a titanium matrix and the mechanical properties of the resulting titanium-bone tissue composite. It is shown that the mineralization process is virtually accomplished within six months after implantation of a porous titanium article into the organism. As the pores and channels in the titanium matrix are filled with bone tissue, the material becomes a composite with mechanical properties higher as compared to those of the porous implant or bone tissue.     

Processing and mechanical properties of autogenous titanium implant materials

Pure titanium and some of its alloys are currently considered as the most attractive metallic materials for biomedical applications due to their excellent mechanical properties, corrosion resistance, and biocompatibility. It has been demonstrated that titanium and titanium alloys are well accepted by human tissues as compared to other metals such as SUS316L stainless steel and Co–Cr–Mo type alloy. In the present study, highly porous titanium foams with porosities 80% are produced by using a novel powder metallurgical process, which includes the adding of the selected spacers into the starting powders. The optimal process parameters are investigated. The porous titanium foams are characterized by using optical microscopy and scanning electron microscopy. The distribution of the pore size is measured by quantitative image analyses. The mechanical properties are investigated by compressive tests. This open-cellular titanium foams, with the pore size of 200–500 m are expected to be a very promising biomaterial candidates for bone implants because its porous structure permits the ingrowths of new-bone tissues and the transport of body fluids.     

In vivo assessment of the osteointegrative potential of phosphatidylserine-based coatings

The successful implantation of titanium-based implants for orthopaedic and dental applications is often hindered because of their mobility, which arises because of a lack of direct binding of the metal surface to the mineral phase of the surrounding bone. Ceramic coatings, although ensuring the integration of the implant within the tissue, are unstable and carry risks of delamination and of failure. Recently, a novel biomimetic approach has been developed where porous titanium implants are coated with calcium-binding phospholipids able to catalyse the nucleation of discrete apatite crystals after only 30 min incubation in simulated body fluids. The present work assesses the osteointegrative potential of this new class of coatings in an in vivo rabbit model and compares its performance with those of bare porous titanium and hydroxyapatite-coated titanium. The data obtained show that phosphatidylserine-based coatings, whilst resorbing, drive the growing bone into apposition with the metal surface. This is in contrast to the case of bare titanium.     

A numerical investigation of porous titanium as orthopedic implant material

Porous titanium is being developed as an alternative orthopedic implant material to alleviate the inherent problems of bulk metallic implants by reducing the stiffness to be comparable to bone stiffness and allowing complete bone ingrowth. However, a porous microstructure is susceptible to local permanent plastic strain and residual stress under cyclic loading which reduces damage tolerance and therefore limits their application as orthopedic implants. The mechanical properties of porous titanium are governed by the microstructural configurations such as pore morphology, porosity, and bone ingrowth. To understand the influence of these features on performance, the macroscopic and microscopic responses of porous Ti are studied using three-dimensional finite element models. The models are generated based on simulated microstructures of experimental materials at porosities of 15%, 32% and 50%. The results show the effect of porosity and bone ingrowth on Young’s modulus, yield stress, and microscopic stress and strain distribution. Importantly, simulations predict that the bone ingrowth reduces the stress and strain localization under cyclic loading so significantly that it counteracts the concentration condition caused by the increased porosity of the structure.     

Comparison of the tissue reaction to implants made of a beta titanium alloy and pure titanium. Experimental study on rabbits

Commercially pure titanium (Ti cp) has been used successfully as an implant material in fracture fixation devices for many years. Ti cp is comparatively soft, but the mechanical properties, such as strength and ductility, can be adjusted by different means over a wide range. Titanium changes its crystal structure from a hexagonal (alpha) phase to the cubic (beta) phase at about 882 °C. Cubic titanium has the advantage of being very malleable (ductile), but in order to stabilize it at room temperature, additions of suitable alloying elements are required. In this study the soft tissue reaction to implants made from a beta titanium alloy (Ti–Mo–Zr–Al) with four different surface treatments is evaluated. The results are compared to Ti cp implants having the same surface conditions, and to electropolished stainless steel plates as controls. A minimum of four small plates of each group were implanted in rabbit tibiae for 3 months. Histomorphometric results show that the thickness of the soft tissue reaction layer, and the number of blood vessels, connective tissue cells (fibroblasts, fibrocytes), lymphocytes, and foreign body giant cells are not significantly different between beta titanium and Ti cp plates. For stainless steel plates the soft tissue reaction layer is thicker, and the numbers of macrophages and connective tissue cells are higher. Excellent biocompatibility was observed for this beta titanium alloy. The mechanical properties of this alloy surpass those of Ti cp, and because of the good tissue tolerance, this material seems to be advantageous and should enter into clinical testing.     

多孔钛的研究进展

作为结构功能一体化材料,多孔钛在众多工业领域具有广泛的应用前景,已成为近年来十分活跃的研究方向。简要回顾了多孔钛的研究历史,重点介绍了多孔钛的制备方法与孔结构,并对多孔钛的渗透性能、力学性能和耐腐蚀性能以及主要的商业应用进行了介绍。众多研究和应用表明,多孔钛的性能与功能强烈依赖于孔结构,不同方法制备多孔钛的孔结构可以归纳为均一孔结构、双峰孔结构、梯度孔结构、蜂窝结构和闭孔结构5种类型。除孔结构外,与致密钛合金一样,多孔钛的力学性能和耐腐蚀性能还对间隙元素C,N,O敏感,制备过程中应加以控制。与基于粉末固态扩散机制的传统制备技术相比,增材制造技术由于可以获得任意形式的孔结构,在多孔钛未来的发展和应用中,将呈现出越来越重要的作用。     

Porous titanium implant materials and their potential in orthopedic surgery

In orthopedic surgery bony defects remains a challenge. In generally autologous or heterologous bony transplants can be used. Main problem is the limited amount of bone and donor site morbidity. Nowadays excellent implants and scaffolds at low costs are necessary in respect to the financial problems in our health care system and the strong financial limitations in clinical medicine. Recently a biomimetic approach, in which a porous synthetic bone substitute with properties similar to these of trabecular bone has been developed (VITOFOAM?). Aim of our study was to investigate whether cp‐Ti or Ti6Al4V or stainless steel (316L) porous metal implants achieve material properties comparable to bone. Materials and Methods Three cp‐Ti, Ti6Al4V and stainless steel (316L) porous metal specimen each with a pore size of 150 to 600 μm have been tested in respect to determine the Young’s Modulus E (GPa), Compression Strength (MPa) and Porosity (%) under axial compression. Results Young’s Modulus of the cp‐ Ti samples was in the range of 1.2 to 2.8 GPa, for Ti6Al4V 2.3 to 4.1 GPa could be achieved. Compression Strength for cp‐ Ti and Ti6Al4V ranged from 30 to 65 MPa with porosity values ranged from 71 to 80 %. Discussion The highly porous nature of VITOFOAM? combined with the good biocompatibility of cp‐ Ti or Ti6Al4V and the mechanical properties make these materials ideal bone scaffolds. Trabecular bone shows pore sizes of 300–1500 μm, Young’s Modulus of 0.2–2 GPa and Compression Strength from 5–50 MPa. Porosity of spongious bone ranges from 30 to 95 %. These values are comparable to the values achieved with VITOFOAM?. Porous titanium foam with its osteoconductive properties may therefore be an ideal and cheap alternative. Implant costs can be lowered to 50 % for implants e.g. for intercorporal interbody fusion in spinal surgery. Actually further research is done to show the possibility in spinal surgery or loading technologies with Tricalciumphosphat, Hydroxylapatit, Antibiotics or Cytostatics.     

多孔钽植入物在骨缺损中的应用进展EI北大核心CSCD

多孔金属钽具有良好的生物相容性与骨传导能力,相比于传统的金属植入物材料有较低的弹性模量与高的摩擦因数,可以避免发生应力遮挡效应且具有与人类松质骨类似的多孔结构。多孔钽的力学性能优势与优秀的生物学性能,在骨修复材料领域受到越来越多的关注,且已研发并应用于多种部位的骨缺损修复中。随着多孔钽材料制备方法的更新与多种改性方法的提出,多孔钽进一步展示了在临床应用中的广阔前景。本文从多孔钽材料的制备工艺、细胞毒性、与骨结合特性以及目前在临床的应用情况等方面,介绍多孔钽植入物在骨缺损中的应用进展,并提出了多孔钽在表面改性建立复合体系、优化制备工艺及个性化制备技术的发展方向,为多孔钽植入物在治疗骨缺损的临床应用提供参考。     

A comparative study of zirconium and titanium implants in rat: osseointegration and bone material quality

Permanent metal implants are widely used in human medical treatments and orthopedics, for example as hip joint replacements. They are commonly made of titanium alloys and beyond the optimization of this established material, it is also essential to explore alternative implant materials in view of improved osseointegration. The aim of our study was to characterize the implant performance of zirconium in comparison to titanium implants. Zirconium implants have been characterized in a previous study concerning material properties and surface characteristics in vitro, such as oxide layer thickness and surface roughness. In the present study, we compare bone material quality around zirconium and titanium implants in terms of osseointegration and therefore characterized bone material properties in a rat model using a multi-method approach. We used light and electron microscopy, micro Raman spectroscopy, micro X-ray fluorescence and X-ray scattering techniques to investigate the osseointegration in terms of compositional and structural properties of the newly formed bone. Regarding the mineralization level, the mineral composition, and the alignment and order of the mineral particles, our results show that the maturity of the newly formed bone after 8 weeks of implantation is already very high. In conclusion, the bone material quality obtained for zirconium implants is at least as good as for titanium. It seems that the zirconium implants can be a good candidate for using as permanent metal prosthesis for orthopedic treatments.     

Low cycle fatigue behavior of Ti6Al4V thermochemically nitrided for its use in hip prostheses

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Besides, titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes difficult the use of titanium and Ti6Al4V in some biomedical applications, like articulating components of prostheses. Some surface treatments are available in order to correct these problems, like thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Low cycle fatigue behavior in air of Ti6Al4V alloy has been studied. Results show a reduction of low cycle fatigue life up to 10% compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.     

Evaluation of channel-like porous-structured titanium in mechanical properties and osseointegration

The porous titanium with a channel-like pore structure fabricated by infiltration casting followed by selectively dissolving the precursor woven three dimensional(3 D) structure technique was comprehensively investigated by means of mechanical tests, in vitro and in vivo evaluation. Such porous structure exhibited superiority in compressive, tensile strength and osseointegration. At 40% porosity, the average compressive and tensile strength reached about 145 MPa and 85 MPa, which was superior to that of other porous titanium, e.g., Selective Laser Melting or powder sintered ones, and was comparable to that of the human cortical bone. Without any bioactive surface treatment, this porous titanium exhibited good cell adhesion, rapid cell proliferation and excellent osseointegration. Based on the study, the 0.4 mm pore size resulted in the most rapid cell proliferation and the maximal BV/TV ratio and trabecular bone number of the new bone that ingrew into the porous titanium. To balance the excellent osseointegration and adequate mechanical properties, the optimal structural parameters were 0.4 mm pore size with40% porosity. This porous titanium is very promising for orthopedic applications where compressive and tensile load-bearing is extremely important.     

Polyetheretherketone and titanium surface treatments to modify roughness and wettability-Improvement of bioactivity and antibacterial properties

Among the materials available for implant production,titanium is the most used while polyetherether-ketone (PEEK) is emerging thanks to its stability and to the mechanical properties similar to the ones of the bone tissue.Material surface properties like roughness and wettability play a paramount role in cell adhesion,cell proliferation,osteointegration and implant stability.Moreover,the bacterial adhesion to the biomaterial and the biofilm formation depend on surface smoothness and hydrophobicity.In this work,two different treatments,sandblasting and air plasma,were used to increase respectively roughness and wettability of two materials:titanium and PEEK.Their effects were analyzed with profilometry and contact angle measurements.The biological properties of the material surfaces were also investigated in terms of cell adhesion and proliferation of NIH-3T3 cells,MG63 cells and human Dental Pulp Stem Cells.Moreover,the ability of Staphylococcus aureus to adhere and form a viable biofilm on the samples was evaluated.The biological properties of both treatments and both materials were compared with samples of Synthegra(R) titanium,which underwent laser ablation to obtain a porous micropatterning,character-ized by a smooth surface to discourage bacterial adhesion.All cell types used were able to adhere and proliferate on samples of the tested materials.Cell adhesion was higher on sandblasted PEEK samples for both MG63 and NIH-3T3 cell lines,on the contrary,the highest proliferation rate was observed on sandblasted titanium and was only slightly dependent on wettability;hDPSCs were able to proliferate similarly on sandblasted samples of both tested materials.The highest osteoblast differentiation was ob-served on laser micropatterned titanium samples,but similar effects,even if limited,were also observed on both sandblasted materials and air plasma treated titanium.The lowest bacterial adhesion and biofilm formation was observed on micropatterned titanium samples whereas,the highest biofilm formation was detected on sandblasted PEEK samples,and in particular on samples not treated with air-plasma,which displayed the highest hydrophobicity.The results of this work showed that all the tested materials were able to sustain osteoblast adhesion and promote cell proliferation;moreover,this work highlights the fea-sible PEEK treatments which allow to obtain surface properties similar to those of titanium.The results here reported,clearly show that cell behavior depends on a complex combination of surface properties like wettability and roughness and material nature,and while a rough surface is optimal for cell adhesion,a smooth and less hydrophilic surface is the best choice to limit bacterial adhesion and biofilm formation.