Ti Foam Research Articles

Initial evaluation of bone ingrowth into a novel porous titanium coating

Porous metals (sintered beads and meshes) have been used for many years for different orthopedic applications. Metal foams have been recently developed. These foams have the advantage of being more porous than the traditional coatings. Their high porosity provides more space for bone ingrowth and mechanical interlocking and presents more surface for implant-bone contact. The objective of this study was to evaluate in vivo bone ingrowth into Ti implants covered with a novel Ti foam coating. This foam contains 50% in volume of interconnected pores and a higher surface area compared to dense Ti. Both coated implants and dense Ti controls were placed transcortically in the rat tibia. The animals were sacrificed at 2 weeks after implantation, and the amount of bone in the implants was determined using backscattered electron imaging and X-ray microtomography. Already at this time interval, the pores within the Ti foam showed 97.7% bone filling, and the bone-implant contact area was significantly increased compared to dense Ti controls. These initial results indicate that this novel Ti foam is biocompatible, has the capacity to sustain bone formation, and can potentially improve osseointegration.

Bone Formation Following Implantation of Titanium Sponge Rods into Humeral Osteotomies in Dogs: A Histological and Histometrical Study

Titanium (Ti) is widely proven to enhance bone contact and growth on its surface. It is expected that bone defects could benefit from Ti to promote healing and to increase strength of the implanted area. The present study aimed at comparing the potential of porous Ti sponge rods with synthetic hydroxyapatite (HA) for the healing of bone defects in a canine model. Six mongrel dogs were submitted to three trephined osteotomies of 6.0 x 4.0 mm in one humerus and after 2 months another three osteotomies were performed in the contralateral humerus. A total of 36 defects were randomly filled either with Ti foam, particulate HA, or coagulum (control). The six animals were killed 4 months after the first surgery for histological and histometrical analysis. The Ti-foam surface was frequently found in intimate contact with new bone especially at the defect walls. Control sites showed higher amounts of newly formed bone at 2 months - Ti (p = 0.000) and HA (p = 0.009) - and 4 months when compared with Ti (p = 0.001). Differently from HA, the Ti foam was densely distributed across the defect area which rendered less space for bone growth in the latter's sites. The use of Ti foams or HA resulted in similar amounts of bone formation in both time intervals. Nevertheless, the presence of a Ti-foam rod preserved defect's marginal bone height as compared with control groups. Also, the Ti-foam group showed a more mature bone pattern at 4 months than HA sites. The Ti foam exhibited good biocompatibility, and its application resulted in improved maintenance of bone height compared with control sites. The Ti foam in a rod design exhibited bone ingrowth properties suitable for further exploration in other experimental situations.

Effect of pore size on the tensile behavior of open-cell Ti foams: Experimental results

Open-cell Ti foams having an average pore size of 50 and 150 µm, respectively have been subjected to room temperature tensile tests to explore their tensile properties. Since extensometry is difficult in foams due to problems such as localized surface deformation and attachment of clip gauges, the foams' mechanical properties have been measured in this work accurately by the help of a camera which records the resulting dimensional changes during the loading. The camera acts as a non-contact extensometer and thus it helps in avoiding any small amounts of pre-deformation that might be caused by the attachment of conventional extensometer to the sample's surface prior to testing. Ti foam samples of smaller pores were found to experience higher strength and elongation than those with larger ones. The cell walls in both foam samples failed suddenly in the 45° maximum shear plane direction.

Effects of Hydroxyapatite on Titanium Foam as a Bone Ingrowth Surface in Acetabular Shells: A Canine Study

This study investigated a highly porous titanium foam with and without a PeriApetite coating as an alternative surface for implant fixation. Twelve mongrel canines received staged total hip replacements under International Animal Care and Use Committee (IACUC) approval from our institution. Animals were randomly placed in three- or six-month groups for sacrifice. Seventeen total hips were available for evaluation. The area and depth of ingrowth was measured by SEM. At three months, PeriApetite Ti foam had 37% more depth and almost 10% more bone ingrowth. Both groups were found not to be different at the six-month mark with over 36% of ingrowth calculated on SEM. The results prove not only that titanium foam is a viable ingrowth surface but also that PA coating can enhance the time to bony incorporation.

Characterization of the deformation behavior of intermediate porosity interconnected Ti foams using micro-computed tomography and direct finite element modeling

Under load-bearing conditions metal-based foam scaffolds are currently the preferred choice as bone/cartilage implants. In this study X-ray micro-computed tomography was used to discretize the three-dimensional structure of a commercial titanium foam used in spinal fusion devices. Direct finite element modeling, continuum micromechanics and analytical models of the foam were employed to characterize the elasto-plastic deformation behavior. These results were validated against experimental measurements, including ultrasound and monotonic and interrupted compression testing. Interrupted compression tests demonstrated localized collapse of pores unfavorably oriented with respect to the loading direction at many isolated locations, unlike the Ashby model, in which pores collapse row by row. A principal component analysis technique was developed to quantify the pore anisotropy which was then related to the yield stress anisotropy, indicating which isolated pores will collapse first. The Gibson–Ashby model was extended to incorporate this anisotropy by considering an orthorhombic, rather than a tetragonal, unit cell. It is worth noting that the natural bone is highly anisotropic and there is a need to develop and characterize anisotropic implants that mimic bone characteristics.

Porous NiTi by creep expansion of argon-filled pores

NiTi powders are densified in the presence of argon gas, whose initial pressure is varied between 1 and 33 atm, to create NiTi billets containing isolated Ar-filled pores. Upon vacuum annealing, the pressurized pores expand by creep of the surrounding NiTi matrix at rates which are in agreement with a simple analytical model up to 16% porosity. Beyond this porosity, foaming becomes very slow, as pores connect with each other and with the specimen surface where the gas escapes. This is due to failure of previous NiTi powder boundaries weakened by oxides insoluble in NiTi; this mechanism does not occur in Ti foams which dissolve their oxides at high temperature, allowing higher levels of pore expansion and foam porosity. NiTi with 10–16% porosity exhibits Young's moduli of 48–57 GPa, and may be useful for high-strength, low stiffness biomedical implants with superelastic or shape-memory properties.

A Preliminary Study on Cell Wall Architecture of Titanium Foams

AbstractBio-inspired architectures, especially metallic foams, have been receiving an increasing interest for the last 10 years due to their unusual mechanical properties. Among commonly dealt foamed metals, like aluminum and steel, titanium possesses a distinctive place because of its high strength-to-weight ratio, excellent corrosion resistance and biocompatibility. In this study, Ti foams were produced by a very simple and common method, sintering under inert atmosphere with fugitive space holder. Removal of the space holder was conducted by dissolution in hot deionized water which makes it possible to minimize contamination of Ti. Sintering of remaining Ti skeleton at 1300 °C offered a wide range of properties and cost savings. The effects of the processing parameters such as sintering temperature and powder characteristics on the 3D foam architecture were investigated by using X-ray microtomography (μ-CT). Use of bimodal Ti powders caused a decrease in final theoretical density when compared to the ones prepared with the same amount of space holder but with monomodal Ti powders. It was also observed that the use of bimodal Ti powders decreased compressive strength, by introducing pores into the cell walls, when compared to the ones having the same theoretical density.

MECHANICAL PROPERTIES OF TITANIUM FOAM FOR BIOMEDICAL APPLICATIONS

Understanding the mechanical behaviour of pure titanium ( Ti ) foam is crucial for the design and development of Ti foam-based load-bearing implants. In this work, pure titanium foam is fabricated by a powder metallurgical process using the space-holder technique with a spacer size of 500 to 800 µm. Experimental data from static compression testing on the Ti foam are presented. The application of theoretical formulae to predict Young's modulus and yield strength of titanium foams is also discussed. A foam with 63% porosity, 87 ± 5 MPa yield strength, and 6.5 ± 1.3 GPa Young's modulus is found to be appropriate for a number of dental and orthopaedic applications.

Fabrication of porous titanium scaffold materials by a fugitive filler method

A clean powder metallurgy route was developed here to produce Ti foams, using a fugitive polymeric filler, polypropylene carbonate (PPC), to create porosities in a metal-polymer compact at the pre-processing stage. The as-produced foams were studied by scanning electron microscopy (SEM), LECO combustion analyses and X-ray diffraction (XRD). Compression tests were performed to assess their mechanical properties. The results show that titanium foams with open pores can be successfully produced by the method. The compressive strength and modulus of the foams decrease with an increasing level of porosity and can be tailored to those of the human bones. After alkali treatment and soaking in a simulated body fluid (SBF) for 3 days, a thin apatite layer was formed along the Ti foam surfaces, which provides favourable bioactive conditions for bone bonding and growth.

Characterization of the structure and permeability of titanium foams for spinal fusion devices

Titanium foams produced via the space-holder method are used for spinal fusion devices since their combination of an open-cell structure and bone-like mechanical properties promises potentially excellent bone ingrowth. Earlier studies have indicated that the size of the pores and interconnects must be greater than 100 μm for effective bone ingrowth and vascularization. Hence, the quantification of the pore and interconnect size is required for efficient scaffold design. In this study, microcomputed tomography (μCT) was used to obtain the three-dimensional (3D) structure of Ti foams with three levels of porosity (51%, 65% and 78%). Novel algorithms were then applied to quantify both the pore and interconnect size of Ti foams as a function of porosity. All foams possessed a modal pore and interconnect size in excess of 300 μm, satisfying the requirement of being greater than 100 μm. The pore and interconnect size also dominates the flow properties or permeability of open-cell structures. Therefore, the μCT data was also used to generate a mesh for computational fluid dynamics analysis to predict the permeability. The calculated permeability (117–163 × 10 −12 m 2 depending on direction) for the Ti foams with 65% porosity was first validated against experimental measurements (98–163 × 10 −12 m 2) and then compared to prior authors’ measurements in healthy cancellous bovine bone (233–465 × 10 −12 m 2). The close match among all the permeability values proves the suitability of the material for biomedical skeletal-implant applications.

Simulation of Three-Point Bending Test of Titanium Foam for Biomedical Applications

Using Titanium (Ti) foam as an implant material is a new approach for biomedical applications and it is important to understand the mechanical behaviors of this new foam material. In the present study, the bending of the Ti foam has been simulated and compared against recently published data [1]. FE Analysis has been performed by Abaqus software. Stiffness and Yield strength of foams between 50% (cortical bone) to 80% (cancellous bone) porosity range were considered. This study showed that crushable foam material model in Abaqus, which has developed primarily for Aluminum (Al) foam alloys, is also valid for Ti Foam before any crack or damage occurs in the sample.

112 Sintering of Multi-Component Mixtures during Manufacturing of Ti Foams

112 Sintering of Multi-Component Mixtures during Manufacturing of Ti Foams

Investigations on the Machining of Sintered Titanium Foams Utilizing Face Milling and Peripheral Grinding

Titanium foams are regarded as potent materials for biomedical applications such as bone implants, and are, if possible, manufactured close to their final shape by sintering processes. There are cases, however, in which it is necessary to generate the final shape by machining, and problems resulting from the porous structure and the material characteristics become critical. In this article, two important methods of machining, i.e. face milling and peripheral grinding, are investigated for their applicability to Ti foams, and their scope and limitations are discussed.

Energy Absorption in Closed-Cell Al-Zn-Mg-Ca-Ti Foam

Cellular metallic foams have interesting potential for impact energy absorption. In this study, modification of solid in a closed-cell Al‐ Ca‐Ti foam was carried out, adding the strengthening elements of Zn and Mg for enhancement of energy absorption. Samples with dimensions of 100 × 100 × 100 mm 3 were examined at a dynamic strain rate corresponding to the crashing speed of automobiles. The compression deformation behavior of the Al‐7Zn‐0.5Mg‐1.5Ca‐1.5Ti (by mass%) foam was found to be different from that of the original Al‐1.5Ca‐1.5Ti (by mass%) foam. Plateau stress could be effectively enhanced with the combined effect of strengthening solid alloy and increasing the aspect ratio of cell wall thickness against cell edge length. Plateau stress of the modified foam was independent of strain rate, while the stress in Al‐Ca‐Ti foam exhibited a certain strain rate sensitivity. Plateau strain, designated as the strain where the compressive stress reached 1.5 times higher value than the yield stress, was also enhanced by the present modification. As a result, absorption energy was also effectively enhanced but was independent of strain rate as a result of the present modification.

Processing of biocompatible porous Ti and Mg

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Young's modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Reinforcing the tips of engine blades with cubic boron nitride

Powder methods are highly applicable for the processing of more challenging metals and forms. Examples of materials that encompass both of these are metallic foams, which are advanced materials that consist of a network of interconnected or randomly spaced macropores separated by dense or microporous cell walls. These macropores can be either open or closed, or mix of those two, depending on the manufacturing process. One popular metal foam that has received a huge amount of interest in the last decade is Ti foam, due to it offering a unique combination of properties, such as high strength to weight ratio and high permeability combined with excellent biocompatibility. In this study the use of metal injection molding of titanium powder in combination with a space holder (to create large pore spaces) is examined for the production of open pore Ti foams for biomedical applications. Potassium chloride with two different particle shapes (spherical and cubic) was used as a space holder. It was found that feedstocks prepared with spherical KCl particles had a lower viscosity and better flowability compared to those made using cubic particles. Ti foams with a total porosity of 61.25% ± 0.29 were successfully produced. The structure of the foams produced was characterized using SEM and X-ray micro-computed tomography.