Fabrication of porous titanium implants with biomechanical compatibility

By using H₂O₂ as foaming reagent, porous titanium with open and interconnected pore morphology was obtained. The morphology, pore structure and elemental composition were observed by SEM–EDX. The mechanical property was determined by compressive test. The results show that the compressive strength and Young's modulus of porous titanium with 64% porosity were 102 ± 10 MPa and 3.3 ± 0.8 GPa, respectively, and for 76% porosity porous titanium, the values were 23 ± 10 MPa and 2.1 ± 0.5 GPa. These results suggest that the former has sufficient mechanical properties for clinical use under load-bearing conditions and the latter has the potential application for tissue engineering scaffolds.     

凝胶注模成型制备医用多孔钛植入材料及其性能

应用一种新的近净成型技术——凝胶注模成型技术，成功制备大尺寸、复杂形状医用多孔钛人造骨替代材料，并研究了凝胶注模成型工艺参数对浆料流动特性、坯体强度及烧结体孔隙、力学性能的影响。研究结果表明：预混液中有机单体的浓度、单体／交联剂比例以及固相含量是决定钛粉浆料表观粘度、Gelcasting坯体强度的重要参数；对于医用多孔钛植入材料的凝胶注模成型工艺，适合的顸混液单体浓度为30％（质量分数），单体，交联剂比例为120：1，浆料固相含量为34％（体积分数）；1100℃保温1．5h是凝胶注模成型多孔钛较为适合的烧结工艺路线；所制得孔隙度46．5％、开孔隙度40．7％多孔钛的抗压强度158．6MPa、弹性模量8．5GPa，与自然骨基本匹配，适合作为人造骨替代材料。     

Synthesis of porous titanium implants by environmental-electro-discharge-sintering process

Porous Ti implants with various porosities were first fabricated by environmental-electro-discharging-sintering (EEDS) of atomized spherical Ti powders. Powders in two size range (50–100 and 200–250 μm) were settled by vibration into a quarts tube and subjected to a high voltage and high density current pulse. A single pulse of 0.75–2.0 kJ/0.7 g-powder, using 150, 300 and 450 μF capacitors, was applied to produce fully porous and porous-surfaced Ti implant compacts. The solid core was automatically formed in the center of the compact after discharge and porous layer consisted of particles connected in three dimensions by necks. The solid core and neck sizes increased with an increase in input energy and capacitance. On the other hand, pore volume decreased with increased capacitance and input energy due to the formation of a solid core. Capacitance and input energy are the only controllable discharge parameters even though the heat generated during a discharge is the unique parameter that determines the porosity of compact. It was shown that EEDS of spherical Ti powders can efficiently produce fully porous and porous-surfaced Ti implants with various porosities in short times (<400 μs) by manipulating the discharging conditions such as input energy and capacitance including powder size.     

Osseointegration evaluation of laser-deposited titanium dioxide nanoparticles on commercially pure titanium dental implants

The nanotechnology field plays an important role in the improvement of dental implant surfaces. However, the different techniques used to coat these implants with nanostructured materials can differently affect cells, biomolecules and even ions at the nano scale level. The aim of this study is to evaluate and compare the structural, biomechanical and histological characterization of nano titania films produced by either modified laser or dip coating techniques on commercially pure titanium implant fixtures. Grade II commercially pure titanium rectangular samples measuring 35?×?12?×?0.25?mm length, width and thickness, respectively were coated with titania films using a modified laser deposition technique as the experimental group, while the control group was dip-coated with titania film. The crystallinity, surface roughness, histological feature, microstructures and removal torque values were investigated and compared between the groups. Compared with dip coating technique, the modified laser technique provided a higher quality thin coating film, with improved surface roughness values. For in vivo examinations, forty coated screw-designed dental implants were inserted into the tibia of 20 white New Zealand rabbits’ bone. Biomechanical and histological evaluations were performed after 2 and 4 weeks of implantation. The histological findings showed a variation in the bone response around coated implants done with different coating techniques and different healing intervals. Modified laser-coated samples revealed a significant improvement in structure, surface roughness values, bone integration and bond strength at the bone-implant interface than dip-coated samples. Thus, this technique can be an alternative for coating titanium dental implants.     

Bone response to a titanium aluminium nitride coating on metallic implants

The design, surface characteristics and strength of metallic implants are dependant on their intended use and clinical application. Surface modifications of materials may enable reduction of the time taken for osseointegration and improve the biological response of bio-mechanically favourable metals and alloys. The influence of a titanium aluminium nitride (TAN) coating on the response of bone to commercially pure titanium and austenitic 18/8 stainless steel wire is reported. TAN coated and plain rods of stainless steel and commercially pure titanium were implanted into the mid-shaft of the femur of Wistar rats. The femurs were harvested at four weeks and processed for scanning electron and light microscopy. All implants exhibited a favourable response in bone with no evidence of fibrous encapsulation. There was no significant difference in the amount of new bone formed around the different rods (osseoconduction), however, there was a greater degree of shrinkage separation of bone from the coated rods than from the plain rods (p = 0.017 stainless steel and p = 0.0085 titanium). TAN coating may result in reduced osseointegration between bone and implant.     

In vivo osseointegration of dental implants with an antimicrobial peptide coating

This study aimed to evaluate the in vivo osseointegration of implants with hydrophobic antimicrobial GL13K-peptide coating in rabbit femoral condyles by micro-CT and histological analysis. Six male Japanese Rabbits (4 months old and weighing 2.5?kg each) were included in this study. Twelve implants (3.75?mm wide, 7?mm long) were randomly distributed in two groups, with six implants in the experimental group coated with GL13K peptide and six implants in the control group without surface coating. Each implant in the test and the control group was randomly implanted in the left or right side of femoral condyles. On one side randomly-selected of the femur, each rabbit received a drill that was left without implant as control for the natural healing of bone. After 3?weeks of healing radiographic evaluation of the implant sites was taken. After 6?weeks of healing, rabbits were sacrificed for evaluation of the short-term osseointegration of the dental implants using digital radiography, micro-CT and histology analysis. To perform evaluation of osseointegration, implant location and group was double blinded for surgeon and histology/radiology researcher. Two rabbits died of wound infection in sites with non-coated implants 2?weeks after surgery. Thus, at least four rabbits per group survived after 6?weeks of healing. The wounds healed without suppuration and inflammation. No implant was loose after 6?weeks of healing. Radiography observations showed good osseointegration after 3 and 6?weeks postoperatively, which proved that the tissues followed a natural healing process. Micro-CT reconstruction and analysis showed that there was no statistically significant difference (P?>?0.05) in volume of bone around the implant between implants coated with GL13K peptide and implants without coating. Histomorphometric analysis also showed that the mineralized bone area was no statistically different (P?>?0.05) between implants coated with GL13K peptide and implants without coating. This study demonstrates that titanium dental implants with an antimicrobial GL13K coating enables in vivo implant osseointegration at similar bone growth rates than gold-standard non-coated dental implants up to 6?weeks of implantation in rabbit femurs.     

Effect of different surface treatments on bioactivity of porous titanium implants

The work aims to characterize the structure and to evaluate in vitro the effect of different surface treatments on the bioactivity of medical grade Ti6Al7Nb alloy implants manufactured by selective laser melting. In order to improve the bioactivity of these samples, they were subjected to heat treatment, chemical treatment, and impregnation with bioactive materials. To evaluate the apatite forming ability, the samples were immersed in simulated body fluid solution) and characterized before and after immersion by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The composition and the texture of the surfaces after the applied treatments have a selective effect on apatite layer development on the surface of samples.     

Histomorphometric study of bone reactions with different hydroxyapatite coating thickness on dental implants in dogs

The purpose of this study was to evaluate the effects of different hydroxyapatite (HA) coating thicknesses on osseointegration after dental implantation in dogs. Six dogs, weighing 10-15 kg, were used in this study. The fixtures, with HA coatings of different thicknesses and made by Dentis, were implanted for 12 weeks in right iliac crestal bone sites and for 6 weeks in left iliac crestal bone sites. Implants in the control group were coated with resorbable blast medium, whereas those in the experimental group were coated with HA of different thicknesses (1, 5, and 15 μm). All dogs were sacrificed at 12 weeks after implant placement, and histological and histomorphometric analyses were performed. The implants were all successful, and a significant difference between the control and experiment groups was observed at 6 weeks, although no significant difference between the control and experimental groups was seen at 12 weeks. These results suggested that HA implant coating may positively affect early osseointegration, but coating thickness had no significant effect on ultimate osseointegration.     

Galvanic corrosion behavior of titanium implants coupled to dental alloys

The corrosion of five materials for implant suprastructures (cast-titanium, machined-titanium, gold alloy, silver-palladium alloy and chromium-nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium implant. Various electrochemical parameters E_CORR, i_CORR Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. Besides, the metallic ions released in the saliva environment were quantified during the corrosion process by means of inductively coupled plasma-mass spectrometry technique (ICP-MS). The cast and machined titanium had the most passive current density at a given potential and chromium-nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper-rich phases was observed through energy dispersive X-ray analysis. ©2000 Kluwer Academic Publishers     

Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO₂) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO₂ coating can be made by performing the PEO in an ammonium acetate (CH₃COONH₄) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO₂ led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity.     

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.     

Formation and bioactivity of porous and nanostructured TiO2/beta-TCP coating on titanium

Titanium and its alloys have been widely used as hard tissue implants due to their excellent mechanical properties and biocompatibility. However, their near bio-inertness and metallic ion release are still the problems with clinical uses. In this paper, porous and nanostructured TiO2/beta-tricalcium phosphate (beta-TCP) composite coatings were prepared on titanium substrates by plasma electrolytic oxidation (PEO) in a Ca and P-containing electrolyte. The influence of PEO electric current density on phase composition and bioactivity of the coatings were studied. X-ray diffraction, scanning electron microscopy and Fourier transfer infrared spectroscopy were utilized to characterize the phase composition and microstructure of the coatings. Simulated body fluid immersion tests were employed on the coatings to evaluate their bioactivity. The results reveal that TiO2/beta-TCP composite coating with pores size less than 10 microm and grains of 50-100 nm in size was prepared. The electric current density of PEO is an important factor in the formation of the composite coating. The TiO2/beta-TCP composite coating shows good bioactivity, which are attributed to the incorporation of beta-TCP.     

Variation of roughness and adhesion strength of deposited apatite layers on titanium dental implants

It is known that surface roughness and chemical composition of the titanium surface influence the osseointegration of titanium implants. Most commercial dental implants offer a shot-blasted rough surface. It is also known that apatite layers coating the surface of titanium implants improve bone response, but the adhesion of the layer to the substrate poses some problems.In this study the roughness and adhesion strength to a titanium dental implant surface of an apatite layer deposited via wet chemistry after a thermochemical treatment were compared with those of plasma-sprayed apatite layers and machined titanium surfaces. Different surface conditions have been studied: (a) as-received machined dental implant surface; (b) grit-blasted titanium surface; (c) grit-blasted and thermochemically-treated titanium surface; (d) titanium surfaces coated with plasma-sprayed apatite. The morphology and roughness of the samples were measured and compared. The adhesion of the apatite layers to the titanium was compared by means of a scratch test.Measured roughness showed that the deposition of an apatite layer did not affect roughness but plasma-sprayed apatite produced a decrease on roughness values when compared to control samples. Both roughness and adhesion strength of the deposited apatite layer to the titanium substrate were higher than those of the plasma-sprayed apatite.     

Biological characterization of a new silicon based coating developed for dental implants

Taking into account the influence of Si in osteoblast cell proliferation, a series of sol–gel derived silicon based coating was prepared by controlling the process parameters and varying the different Si-alkoxide precursors molar rate in order to obtain materials able to release Si compounds. For this purpose, methyltrimethoxysilane (MTMOS) and tetraethyl orthosilicate (TEOS) were hydrolysed together and the sol obtained was used to dip-coat the different substrates. The silicon release ability of the coatings was tested finding that it was dependent on the TEOS precursor content, reaching a Si amount value around ninefolds higher for coatings with TEOS than for the pure MTMOS material. To test the effect of this released Si, the in vitro performance of developed coatings was tested with human adipose mesenchymal stem cells finding a significantly higher proliferation and mineralization on the coating with the higher TEOS content. For in vivo evaluation of the biocompatibility, coated implants were placed in the tibia of the rabbit and a histological analysis was performed. The evaluation of parameters such as the bone marrow state, the presence of giant cells and the fibrous capsule proved the biocompatibility of the developed coatings. Furthermore, coated implants seemed to produce a qualitatively higher osteoblastic activity and a higher number of bone spicules than the control (uncoated commercial SLA titanium dental implant).     

Fabrication of biomimetic apatite coating on porous titanium and their osteointegration in femurs of dogs

In the present study, porous titanium with three-dimensionally interconnected pores and a porosity of 74.3 ± 3.8% was made by a slurry foaming method. After being pretreated with acid–alkali or alkali–heat method and then immersed into a supersaturated calcium phosphate solution to form a biomimetic apatite coating on the surface, the porous titanium samples were hemi-transcortically implanted into the femurs of dogs for two months. The experimental results showed that the surface apatite coatings deposited on acid–alkali and alkali–heat treated porous titanium had different morphology and thickness. However, histological and histomorphometric analysis confirmed that both types of apatite-coated implants had excellent osteointegration with host bone, and their osteoconduction had also no significant difference. This study proved that both acid–alkali and alkali–heat treatments might have the same efficiency in activating porous titanium, and the apatite-coated porous titanium could be potential to be used in clinic.     

Hydroxyapatite coating on porous zirconia

Since hydroxyapatite has excellent biocompatibility and bone bonding ability, porous hydroxyapatite ceramics have been intensively studied. However, porous hydroxyapatite bodies are mechanically weak and brittle, which makes shaping and implantation difficult. One way to solve this problem is to introduce a strong porous network onto which hydroxyapatite coating is applied. In this study, porous zirconia and alumina-added zirconia ceramics were prepared by ceramic slurry infiltration of expanded polystyrene bead compacts, followed by firing at 1500 °C. Then a slurry of hydroxyapatite–borosilicate glass mixed powder was used to coat the porous ceramics, followed by firing at 1200 °C. The porous structures without the coating had high porosities of 51% to 69%, a high pore interconnectivity, and sufficiently large pore window sizes (300 μm–500 μm). The porous ceramics had compressive strengths of 5.3˜36.8 MPa and Young's moduli of 0.30˜2.25 GPa, favorably comparable to the mechanical properties of cancellous bones. In addition, porous hydroxyapatite surface was formed on the top of the composite coating, whereas a borosilicate glass layer was found on the interface. Thus, porous zirconia-based ceramics were modified with a bioactive composite coating for biomedical applications.     

Gradient surface porosity in titanium dental implants: relation between processing parameters and microstructure

To be successful, an implant should be biocompatible, strong and contain surface pores to promote osseointegration. A one-step microwave sintering procedure of titanium powders was attempted in this work. The idea was to take advantage of the peculiar way microwave couple with metallic powders, i.e. generating heat in the interior of the sample and dissipating it away through the surface. This non-conventional heating of titanium powder produced a dense core with surface porosity. The dense core provides the strength while the surface pores promote bone growth. The experiments were carried out in a semi-industrial grade microwave cavity using a alpha-SiC susceptor. Power levels of 1-1.5 kW, and soaking periods of approximately 30 min were used. Microstructural characterization was carried out by a scanning electron microscope. The sintered titanium had gradient porosity on the surface with a thickness of about 100-200 microm depending on the microwave power. The pores were interconnected with size ranging from 30 to 100 microm. This kind of microstructure is favorable for cell growth. Tensile strength values as high as 400 MPa were obtained for these samples.