Porous Ti Samples Research Articles

Development of porous silver nanoparticle/polycaprolactone/polyvinyl alcohol coatings for prophylaxis in titanium interconnected samples for dental implants

Stress shielding phenomenon, poor osseointegration, or bacterial infections of titanium dental implants are widely recognized as key problems that deeply affect their survival rate. In this work, a joint solution to solve these three limitations is proposed. The first two issues were minimized applying porous Ti samples. This substrate exhibits an appropriated biomechanical equilibrium (stiffness and mechanical resistance) and good biofunctionality (ability to promote bone ingrowth). On the other hand, the porous Ti disc was coated with biocompatible and non-toxic polymeric composites matrices using poly-ε-caprolactone and partially acetylated polyvinyl alcohol, combined with silver nanoparticles as a therapeutic antimicrobial agent. The optimization of the best blend composition and optimal nanoparticles concentration were investigated. Finally, the two composites with the best antimicrobial activity were infiltrated into porous Ti discs. The deposited coatings presented good adhesion and a honeycomb-like surface structure that could promote vascularization of the implant and enhance osseointegration.

Influences of sintering temperature on pore morphology, porosity, and mechanical behavior of porous Ti

The purpose of this study was to determine the influences of the sintering temperature on the pore morphology, porosity, and mechanical behavior of titanium foams. Porous Ti samples were successfully manufactured using the metal powder metallurgy method in conjunction with sintering at the four temperatures (900, 1000, 1100, and 1200 °C). The sintering temperature significantly influenced the pore morphology, porosity, and mechanical behavior of the titanium foams. The titanium foams were characterized using an optical microscope in conjunction with scanning electron microscopy. A fracture showed the appearance and growth of a sintering neck between adjacent particles. As the sintering temperature increased, the sintering necks gradually became clearer. The porosity decreased from 56.48% to 46.83% as the sintering temperature increased from 900 °C to 1200 °C, while the initial yield strength of the porous titanium increased from 101.81 to 208.01 MPa. The porous titanium foams produced by the metal powder metallurgy method have a significant utilization potential in hard-tissue engineering.

Effects of pore size and porosity on cytocompatibility and osteogenic differentiation of porous titanium

To find out the optimal porosity and pore size of porous titanium (Ti) regarding the cytocompatibility and osteogenic differentiation. Six groups of porous Ti samples with different porosities and pore sizes were fabricated by the powder metallurgy process. The microstructure and compressive mechanical properties were characterized. The cytocompatibility was examined by a series of biological tests as protein absorption with BCA assay kit, cell attachment with laser scanning confocal microscopy and vinculin expression, cell proliferation with CCK-8 assay. Cell differentiation and calcification were detected by qPCR and Alizarin Red S dying respectively. Pores distributed homogeneously throughout the porous Ti samples. The compressive test results showed that Young’s modulus ranged from 2.80 ± 0.03 GPa to 5.43 ± 0.34 GPa and the compressive strength increased from 112.4 ± 3.6 MPa to 231.1 ± 9.4 MPa. Porous Ti with high porosity (53.3 ± 1.2%) and small pore size (191.6 ± 3.7 μm) adsorbed more proteins. More MC3T3-E1 cells adhered onto dense Ti samples than onto any other porous ones already after culture and no difference was identified within the porous groups. The porous structure of porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 μm facilitated cell differentiation and calcification. Small pores were not beneficial to the osteo-initiation at the very beginning. Porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 μm fabricated by powder metallurgy process showed the expected mechanical property and improved osseointegration as implants in dental treatment.

Mechanical, Electrochemical and Biological Behavior of 3D Printed-Porous Titanium for Biomedical Applications

Porosity is a feature that can be designed into 3D printed parts, notably surgical implants, and porosity is associated with improved biocompatibility and osseointegration. It is imperative to evaluate the electrochemical behavior of 3D printed-porous Ti to identify the optimum porosity with low corrosion kinetics for biomedical applications. The objective of this study was to evaluate the corrosion kinetics, mechanical properties, and biocompatibility of 3D printed porous Titanium alloy metal. 3D printed porous Ti samples of 11 mm diameter and 7 mm thick with five porosity levels (0%, 20%, 40%, 60%, and 80%) were manufactured, mechanically tested, studied for characterization and Electrochemical behavior. The cell proliferations was also conducted on different groups for the examination of their biocompatibility, which might indicate the influence of porosity to the cellular activities. The results showed that increasing porosity corresponds with decreasing mechanical strength and increasing corrosion characteristics. Corrosion current, Icorr values ranged from 10−7 to 10−4 A, and Ecorr values ranged from + 100 to − 600 mV for all five porosity-level samples. Analysis of EIS data indicated that capacitance values ranged from 0.00025 to 0.0015F. In addition, sample porosity showed evidence of other corrosion forms such as crevice corrosion and intergranular corrosion. The results of cell proliferations demonstrated all groups of specimens are biocompatible and the ones with 0% and 40% porosity exhibited the highest increments of cells, implying their potential in biomedical application. The study revealed that 3D printed Ti samples with larger porosity were subjected to increased electrochemical corrosion. A porosity between 40 and 60% 3D printed porous Ti study sample was found optimum for the biomedical application. The development of future biomedical devices will have to maintain a balanced approach between the osseointegration of large porosities and increased corrosion tendencies to optimize safer devices through additive manufacturing or 3D printing for better patient outcomes. Further studies will evaluate 3D-printed tribocorrosion properties and biocompatibility via osteoblast culture.

Effect of bio-functional MAO layers on the electrochemical behaviour of highly porous Ti

Ti foams are attractive for orthopaedic applications due to reduced Young's modulus and ability of bone in-growth. However, poor corrosion behaviour and lack of bioactivity are yet to be overcome. In the present work, highly porous Ti samples were processed by powder metallurgy with space holder technique and bio-functionalized by micro-arc oxidation, resulting in nano/micro structured TiO2 surfaces containing bioactive elements. The electrochemical behaviour of these bio-functionalized highly porous Ti surfaces was evaluated through potentiodynamic polarization and EIS in physiological solution at body temperature. Results showed that bio-functionalization improved the corrosion behaviour of highly porous Ti. However, increased macro-porosity led to an increased corrosion rate.

Fabrication of Ti+Mg composites by three-dimensional printing of porous Ti and subsequent pressureless infiltration of biodegradable Mg.

A semi-degradable Ti+Mg composite with superior compression and cytotoxicity properties have been successfully fabricated using ink jet 3D printing followed by capillary mediated pressureless infiltration technique targeting orthopaedic implant applications. The composite exhibited low modulus (~5.2GPa) and high ultimate compressive strength (~418MPa) properties matching that of the human cortical bone. Ti+Mg composites with stronger 3D interconnected open-porous Ti networks are possible to be fabricated via 3D printing. Corrosion rate of samples measured through immersion testing using 0.9%NaCl solution at 37°C indicate almost negligible corrosion rate for porous Ti (~1.14μm/year) and <1mm/year for Ti+Mg composites for 5days of immersion, respectively. The composite significantly increased the SAOS-2 osteoblastic bone cell proliferation rate when compared to the 3D printed porous Ti samples and the increase is attributed to the exogenous Mg2+ ions originating from the Ti+Mg samples. The cell viability results indicated absent to mild cytotoxicity. An attempt is made to discuss the key considerations for net-shape fabrication of Ti+Mg implants using ink jet 3D printing followed by infiltration approach.

Effects of acid-alkali treatment on bioactivity and osteoinduction of porous titanium: An in vitro study

BackgroundTo elucidate the bioactivity and bone regeneration of porous titanium surfaces treated using acid-alkali combination, and to define the optimal alkali reaction time. MethodsTen groups of porous Ti with at least 3 per group undergoing different acid-alkali treated time were prepared. The surface was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), bicinchoninic acid method (BCA), optical contact angle measurement and Raman spectrometry. Compression testing was performed with a universal testing machine. The bioactivity and osteoinduction were evaluated by a series of biological tests using a simulated body fluid (SBF) test, cell proliferation test, vinculin, ALP and OCN expression, and cell mineralization. ResultsThe acid-alkali treatment formed micro- and nano-scale structures on the sample surfaces. The alkali treatment for 12 h achieved the sharpest nano-scale surface relief and the most protein absorption. The treated porous surface was coated with a NaHTiO3 layer. The acid-alkali etching did not compromise the elastic modulus and compressive strength of the porous Ti samples. In addition to hydroxyapatite, a perovskite phase was also formed on the treated porous samples in SBF. Non-treated dense Ti showed more cell adhesion and proliferation (P < 0.05), while osteoinduction and mineralization were more pronounced on the treated porous sample (P < 0.05). ConclusionAcid-alkali treatment is an effective means of generating nano-scale relief on porous Ti surface, and is beneficial for bioactivity and bone regeneration. The 15 min acid and 12 h alkali etching is the optimal combination. The osteoinductive efficacy may be attributable to the surface physical chemistry and the formation of hydroxyapatite and perovskite layers, rather than direct cell adhesion and proliferation.

A Simple and Economical Device to Process Ti Cylinders with Elongated Porosity by Freeze-Casting Techniques: Design and Manufacturing

Nowadays, the development of materials with gradient porosity is an important aim for many applications, especially in the field of bone tissue replacement. This research work shows the design and manufacture of a simple and economical device to process Ti cylinders with elongated and high interconnected porosity by freeze-casting techniques. The influence of the vessel material on the internal lamellar structure of the porous Ti samples is also studied. The device has been validated with: (i) a thermal gradient from-10 °C at the cold surface to 20 °C at the hot surface; and (ii) a cylindrical vessel with 12 mm diameter of alumina or Teflon. These working conditions have allowed maintaining the freezing conditions during the full process (alumina vessel: 30 minutes; Teflon vessel: 3 hours). After the solidification of the Ti aqueous suspension, the ice is sublimated (24 hours at-50 °C and 0.070 mbar). Then, the resulting powder is sintered (1150 °C for 5 h at high vacuum ~ 10-5 mbar), obtaining the porous Ti sample with the final structural strength. Finally, a detailed study of the most relevant porosity features is performed: porosity ratio and interconnectivity degree by Archimedes’ method, and size and shape of the pores by image analysis at three different zones along the longitudinal cross section. The results indicate the viability of the device to enhance the directional freezing and thus, the elongated porosity. Teflon vessel present the best results, with an average porosity ratio and porosity size of 39.5 % and 123.3 μm, respectively. This suggests an optimal biomechanical and bifunctional balance of this porous material.

Influence of macroporosity on NIH/3T3 adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 over bio-functionalized highly porous titanium implant material.

Highly porous Ti implant materials are being used in order to overcome the stress shielding effect on orthopedic implants. However, the lack of bioactivity on Ti surfaces is still a major concern regarding the osseointegration process. It is known that the rapid recruitment of osteoblasts in bone defects is an essential prerequisite for efficient bone repair. Conventionally, osteoblast recruitment to bone defects and subsequent bone repair has been achieved using growth factors. Thus, in this study highly porous Ti samples were processed by powder metallurgy using space holder technique followed by the bio-functionalization through microarc oxidation using a Ca- and P-rich electrolyte. The biological response in terms of early cell response, namely, adhesion, spreading, viability, and proliferation of the novel biofunctionalized highly porous Ti was carried out with NIH/3T3 fibroblasts and MC3T3-E1 preosteoblasts in terms of viability, adhesion, proliferation, and alkaline phosphatase activity. Results showed that bio-functionalization did not affect the cell viability. However, bio-functionalized highly porous Ti (22% porosity) enhanced the cell proliferation and activity. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 73-85, 2019.

Tribocorrosion behavior of bio-functionalized highly porous titanium

Titanium and its alloys are widely used in orthopedic and dental implants, however, some major clinical concerns such as poor wear resistance, lack of bioactivity, and bone resorption due to stress shielding are yet to be overcome. In order to improve these drawbacks, highly porous Ti samples having functionalized surfaces were developed by powder metallurgy with space holder technique followed by anodic treatment. Tribocorrosion tests were performed in 9g/L NaCl solution using a unidirectional pin-on-disc tribometer under 3N normal load, 1Hz frequency and 4mm track diameter. Open circuit potential (OCP) was measured before, during and after sliding. Worn surfaces investigated by field emission gun scanning electron microscope (FEG-SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Results suggested bio-functionalized highly porous samples presented lower tendency to corrosion under sliding against zirconia pin, mainly due to the load carrying effect given by the hard protruded oxide surfaces formed by the anodic treatment.

Independent tuning of stiffness and toughness of additively manufactured titanium-polymer composites: Simulation, fabrication, and experimental studies

Titanium (Ti) alloys are one of the most appropriate metals for bio-medical applications, specifically in making implants. However, the high difference between the stiffness of the Ti alloys and compact bone results in stress shielding of the bone and stress concentration at the implant, both of which are undesirable and could result in implant failure. One method to reduce the stiffness of a dense implants and avoid the stress shielding is adding porosity to the structure. This however results in considerable reduction in the toughness of the structure, which is also undesirable for the long-term success of implants. In this work, we study a new method for independently tuning the stiffness and toughness of the material by adding various polymers to the additively manufactured porous Ti structures. Porous Ti samples with two levels of porosity are fabricated through additive manufacturing. Three different types of thermoplastic polymers are utilized to fill the pores and make the titanium-polymer composite parts. Compression simulations and tests are performed on both porous and composite specimens to compare the mechanical behavior of these structures. Various finite element simulations are conducted on different structures and the results are verified with experiments. Simulation results and experimental findings indicate that filling porous Ti with thermoplastic polymers leads to an increase in the toughness of the structure. The percentage increase of the toughness is assessed as a function of the polymer toughness and the level of porosity in various samples. Our results pave the way for designing polymer-composite structures with independently tunable stiffness and toughness for being employed in a broad range of applications.

Mesenchymal Stem Cell Response to Surface Altered Porous Ti

This work aims to investigate the influence of surface conditioning of porous Ti for enhancing its biological activity, as assessed by in vitro stem cell testing. Porous Ti samples with an average porosity of 32% were processed by Powder Metallurgy with dextrin as a space holder. The samples were subjected to H2O2 treatment to form an enhanced TiO2 film, followed by a heat treatment at 400°C and 600°C aiming to the crystallization of the as-formed amorphous titanium oxide. Samples characterization was performed by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD). The treated surfaces revealed to be made of both anatase and rutile TiO2, with groove–shaped structure and cracks on the surface of the TiO2 film. The intrinsic biocompatibility of the chemically modified porous Ti surfaces was assessed in vitro. In our cell culture tests, stem cells were found to attach and proliferate better on the chemically treated Ti surfaces compared to the control untreated Ti surfaces.

Influence of Ti Powder Characteristics on the Mechanical Properties of Porous Ti Using Space Holder Technique

Porous Ti samples were fabricated by powder metallurgy technique using three kinds of Ti powder and the space holder of polymethyl methacrylate. The final morphological features and mechanical properties were described. Results show that there is only α-Ti phase in porous Ti samples. After sintering, the oxygen content of three porous Ti is increased from the range of 0.34–0.63 wt% to 0.95–1.3 wt%. The porous Ti prepared from the uneven powders with an average particle size of (22.75 ± 11.09) μm presents the largest micro-pore size, grain size, and oxygen content, which lead to the lowest strength and Young’s modulus.

The influence of pore size on osteoblast phenotype expression in cultures grown on porous titanium

This study investigated the effect of pore size on osteoblastic phenotype development in cultures grown on porous titanium (Ti). Porous Ti discs with three different pore sizes, 312μm (Ti 312), 130μm (Ti 130) and 62μm (Ti 62) were fabricated using a powder metallurgy process. Osteoblastic cells obtained from human alveolar bone were cultured on porous Ti samples for periods of up to 14 days. Cell proliferation was affected by pore size at day 3 (p=0.0010), day 7 (p=0.0005) and day 10 (p=0.0090) in the following way: Ti 62<Ti 130<Ti 312. Gene expression of bone markers evaluated at 14 days was affected, RUNX2 (p=0.0153), ALP (p=0.0153), BSP (p=0.0156), COL (p=0.0156), and OPN (p=0.0156) by pore size as follows: Ti 312<Ti 130<Ti 62. Based on these results, the authors suggest that porous Ti surfaces with pore sizes near 62μm, compared with those of 312μm and 130μm, yield the highest expression of osteoblast phenotype as indicated by the lower cell proliferation rate and higher gene expression of bone markers.

Microstructures and mechanical properties of titanium/biodegradable-polymer FGM for bone tissue fabricated by spark plasma sintering method

Ti and Ti alloys are widely used as metallic implants, because of their good mechanical properties and nontoxic behavior. However, they have problems as the implant-materials, namely, high Young's modulus comparing that of bone and low bonding ability with bone. There is a need to develop the Ti and Ti alloys with lower Young's modulus and good bonding ability. In previous study, Ti composite containing biodegradable poly- l-lactic-acid (PLLA) fiber has been fabricated to improve these problems. However, this composite has low strength because of the imperfect sintering of Ti matrix. To improve its strength, sintering of Ti matrix should be completed. In this study, Ti–NaCl composite material was fabricated by spark plasma sintering (SPS) method using powder mixture of Ti and NaCl to complete the sintering of Ti matrix. To obtain porous Ti samples, Ti–NaCl composite were put into hot water of 317 K. The porous Ti was dipped into PLLA melt in order to introduce PLLA into the pores of porous Ti. Finally, Ti/PLLA composite was obtained, and PLLA plays a role as reinforcement of Ti matrix. It was found that the Ti/PLLA composite has gradient structure and mechanical properties.

Fabrication of Titanium / Biodegradable-Polymer FGM for Medical Application

Ti and Ti alloys are widely used as metallic implants, because of their good mechanical properties and nontoxic behavior. However, they have problems as the implant-materials, namely, high Young’s modulus comparing that of bone and low bonding ability with bone. There is a need to develop the Ti and Ti alloys with lower Young’s modulus and good bonding ability. In previous study, Ti composite containing biodegradable poly-L-lactic-acid (PLLA) fiber has been fabricated to improve these problems. However, this composite has low strength because of the imperfect sintering of Ti matrix. To improve its strength, sintering of Ti matrix should be completed. In this study, Ti-NaCl composite material was fabricated by spark plasma sintering (SPS) method using powder mixture of Ti and NaCl to complete the sintering of Ti matrix. To obtain porous Ti samples, Ti-NaCl composite were put into hot water of 100 oC. The porous Ti was dipped into PLLA melt in order to introduce PLLA into the pores of porous Ti. Finally, Ti-PLLA composite was obtained, and PLLA plays a role as reinforcement of Ti matrix. It was found that the Ti-PLLA composite has gradient structure and mechanical properties.

Influence of calcium ion deposition on apatite-inducing ability of porous titanium for biomedical applications

In the present study, the influence of calcium ion deposition on the apatite-inducing ability of porous titanium(Ti) was investigated in a modified simulated body fluid (m-SBF). Calcium hydroxide (Ca(OH) 2) solutions with five degrees of saturation were used to hydrothermally deposit Ca ions on porous Ti with a porosity of 80%. Apatite-inducing ability of the Ca-ion-deposited porous Ti was evaluated by soaking them in m-SBF for up to 14 days. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) confirmed that a thin layer of calcium titanate (CaTiO 3)/calcium oxide (CaO) mixture with a nanostructured porous network was produced on porous Ti substrates after hydrothermal treatment at 200 °C for 8 h. X-ray photoelectron spectroscopy results demonstrated that the content of the Ca ions deposited on Ti and the thickness of the CaTiO 3/CaO layer increased with increasing saturation degree of the Ca(OH) 2 solution. The thickest (over 10 nm) CaTiO 3/CaO layer with the highest Ca content was achieved on the Ti treated in an oversaturated Ca(OH) 2 solution (0.2 M). SEM, XRD, transmission electron microscopy and Fourier transformed infrared spectroscopy analysis indicated that the porous Ti samples deposited with the highest content of Ca ions exhibited the best apatite-inducing ability, producing a dense and complete carbonated apatite coating after a 14 day soaking in m-SBF. The present study illustrated the validity of using Ca ion deposition as a pre-treatment to endow desirable apatite-inducing ability of porous Ti for bone tissue engineering applications.

Corrosion Resistance Evaluation of Porous Titanium with Biomimetic Coatings

In this work, porous titanium samples processed by powder metallurgy and coated with biomimetic coatings, obtained during different periods of immersion in a simulated body fluid (SBF), were tested for corrosion resistance in a phosphate buffer solution (PBS). Uncoated samples were also tested for comparison. The corrosion resistance of both types of titanium samples was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarisation curves. The electrochemical results indicated the formation of a surface film on the porous Ti samples with immersion in the SBF solution and this biomimetic film increased their corrosion resistance. This film helps osteointegration besides increasing corrosion resistance.

Surface modification of laser-processed porous titanium for load-bearing implants

We report the surface modification of laser-processed porous Ti with a bioactive TiO2 layer via an anodization process to enhance its osteoconductive properties. The 300 nm thick TiO2 layer had a nanoporous structure with pore diameters of 50 nm, which enhanced the ability to form apatite precipitations in simulated body fluids in vitro. The resulting new nano surface morphology of a bioactive TiO2 layer on these porous Ti samples promises to have a significant impact in reducing an implant’s in vivo healing time due to faster tissue integration.

Processing and biocompatibility evaluation of laser processed porous titanium

The Laser Engineered Net Shaping (LENS™) method was used to fabricate porous Ti implants. Porous Ti structures with controlled porosity in the range of 17–58 vol.% and pore size up to 800 μm were produced by controlling LENS™ parameters, which showed a broad range of mechanical strength of 24–463 MPa and a low Young’s modulus of 2.6–44 GPa. The effects of porous structure on bone cell responses were evaluated in vitro with human osteoblast cells (OPC1). The results showed that cells spread well on the surface of porous Ti and formed strong local adhesion. MTT assay indicated LENS™ processed porous Ti provides a preferential surface for bone cell proliferation. Porous Ti samples also stimulated faster OPC1 cell differentiation compared with polished Ti sheet, which could be due to the change in cell morphology within the pores of Ti samples. More extracellular matrix and a higher level of alkaline phosphatase expression were found on the porous samples than on the Ti sheet. This can be beneficial for faster integration of porous implant with host bone tissue. The results obtained also indicated that a critical pore size of 200 μm or higher is needed for cell ingrowth into the pores, below which OPC1 cells bridged the pore surface without any growth in the pores.