Browsing by Author "Costa, M.M."
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- 45S5 BAG-Ti6Al4V structures: The influence of the design on some of the physical and chemical interactions that drive cellular responsePublication . Melo-Fonseca, F.; Lima, R.; Costa, M.M.; Bartolomeu, F.; Alves, Nuno; Miranda, A.; Gasik, M.; Silva, F.S.; Silva, N.A.; Miranda, G.Multi-material Ti6Al4V cellular structures impregnated with 45S5 bioactive glass were designed and produced using Selective LaserMelting (SLM), an additive manufacturing technique, combinedwith Press and Sintering focusing on load bearing components like hip implants. These structures were designed to combine Ti6Al4V mechanical properties and promote bone ingrowth into the structure as the bioactive material (45S5) is being absorbed and replaced by newly formed bone. The influence of these structures design on some of the physical and chemical aspects that drive cellular response was assessed. Roughness, wettability, bioactive glass quantity and quality on the structures after processing and the pH measured during cell culture (as a consequence of bioactive glass dissolution) were evaluated and correlated with cellular viability, cellular distribution, morphology and proliferation on the surface and inside the structures.
- Additive manufacturing of NiTi-Ti6Al4V multi-material cellular structures targeting orthopedic implantsPublication . Bartolomeu, F.; Costa, M.M.; Alves, N.; Miranda, G.; Silva, F.S.The amount of hip revision surgeries is significantly increasing due to the loss of fixation between implant and bone, that leads to implant failure. The stiffness mismatch between Ti6Al4V hip implants and bone tissue, the non-uniform implant-bone contact pressure, and the poor wear resistance of Ti6Al4V are pointed as three critical issues that contribute to these implant’s failure. In this study, a multi-material design and fabrication concept was exploited aiming to change traditional manufacturing paradigms, by allocating different biomaterials in a single component targeting a multi-functional hip implant. Selective Laser Melting technology was explored to fabricate NiTi-Ti6Al4V multi-material cellular structures with a Ti6Al4V inner region and a NiTi outer region. This work was focused on the SLM fabrication and processing parameters validation on a commercial SLM equipment. The morphological analyses allowed to assess a successful solidification and bond between NiTi and Ti6Al4V materials in the transition region. The shear tests revealed a high bond strength of the transition region with an average strength of 33 MPa. The nano-indentation results showed that the Ti6Al4V region exhibits a higher hardness and elastic modulus when compared with the NiTi region. This work is a part of a broader objective that aims to create a NiTi-Ti6Al4V multi-material and cellular structured hip implant capable to provide customized stiffness, superior wear resistance and a controlled NiTi outer region volume change.
- Corrosion behaviour of PEEK or β-TCP-impregnated Ti6Al4V SLM structures targeting biomedical applicationsPublication . Costa, M.M.; Dantas, T.A.; Bartolomeu, F.; Alves, N.; Silva, F.S.; Miranda, G.; Toptan, F.Ti6Al4V cellular structures were produced by selective laser melting (SLM) and then filled either with beta-tricalcium phosphate (β-TCP) or PEEK (poly-ether-ether-ketone) through powder metallurgy techniques, to improve osteoconductivity and wear resistance. The corrosion behavior of these structures was explored considering its importance for the long-term performance of implants. Results revealed that the incorporation of open cellular pores induced higher electrochemical kinetics when being compared with dense structures. The impregnation of β-TCP and PEEK led to the creation of voids or gaps between the metallic matrix and the impregnated material which also influenced the corrosion behavior of the cellular structures.
- Development of β-TCP-Ti6Al4V structures: Driving cellular response by modulating physical and chemical propertiesPublication . Costa, M.M.; Lima, R.; Melo-Fonseca, F.; Bartolomeu, F.; Alves, N.; Miranda, A.; Gasik, M.; Silva, F.S.; Silva, N.A.; Miranda, G.Load-bearing implants success is strongly dependent on several physical and chemical properties that are known to drive cellular response. In this work, multi-material β-TCP-Ti6Al4V cellular structures were designed to combine Ti6Al4V mechanical properties and β-Tricalcium Phosphate bioactivity, in order to promote bone ingrowth as the bioactive material is being absorbed and replaced by newly formed bone. In this sense, the produced structures were characterized regarding roughness, wettability, β-TCP quantity and quality inside the structures after fabrication and the pH measured during cell culture (as consequence of β-TCP dissolution) and those aspects were correlated with cellular viability, distribution, morphology and proliferation. These structures displayed a hydrophilic behavior and results showed that the addition of β-TCP to these cellular structures led to an alkalization of the medium, aspect that significantly influences the cellular response. Higher impregnation ratios were found more adequate for lowering the media pH and toxicity, and thus enhance cell adhesion and proliferation.
- Engineering the elastic modulus of NiTi cellular structures fabricated by selective laser meltingPublication . Bartolomeu, F.; Costa, M.M.; Alves, N.; Miranda, G.; Silva, F.S.Nickel-titanium (NiTi) cellular structures are a very promising solution to some issues related to orthopaedic implant failure. These structures can be designed and fabricated to simultaneously address a combination of mechanical and physical properties, such as elastic modulus, porosity, wear and corrosion resistance, biocompatibility and appropriate biological environment. This ability can enhance the modest interaction currently existing between metallic dense implants and surrounding bone tissue, allowing long-term successful orthopaedic implants. For that purpose, NiTi cellular structures with different levels of porosity intended to reduce the elastic modulus were designed, modelled, selective laser melting (SLM) fabricated and characterized. Significant differences were found between the CAD design and the SLM-produced NiTi structures by performing systematic image analysis. This work proposes designing guidelines to anticipate and correct the systematic differences between CAD and produced structures. Compressive tests were carried out to estimate the elastic modulus of the produced structures and finite element analyses were performed, for comparison purposes. Linear correlations were found for the dimensions, porosity, and elastic modulus when comparing the CAD design with the SLM structures. The produced NiTi structures exhibit elastic moduli that match that of bone tissue, which is a good indication of the potential of these structures in orthopaedic implants.
- Implant surface design for improved implant stability: A study on Ti6Al4V dense and cellular structures produced by Selective Laser MeltingPublication . Bartolomeu, F.; Costa, M.M.; Gomes, J.R.; Alves, N.; Silva, F.S.; Miranda, G.Focusing on implant surface design, aiming to improve implant primary stability, SLM technology was explored to produce dense and cellular structured Ti6Al4V specimens. The SLM specimens and also a commercial casted/forged Ti6Al4V group, were sandblasted and acid-etched to obtain a moderate surface roughness topography, typically used in implant manufacturing. Ti6Al4V-bone interaction and tribological performance were assessed by performing sliding tests aiming to replicate in some extension the insertion of a hip implant. The results shown a 24 and 32% higher kinetic friction coefficient values when comparing the cellular structures with the conventional casted/forged Ti6Al4V. These friction results together with a high amount of adhered bone are promising evidences of a higher efficiency of Ti6Al4V cellular structures for enhancing implant stability.
- Multi-material cellular structured orthopedic implants design: In vitro and bio-tribological performancePublication . Costa, M.M.; Lima, R.; Alves, N.; Silva, N.A.; Gasik, M.; Bartolomeu, F.; Miranda, G.In this study, Selective Laser Melting (SLM) was used to produce mono-material Ti64Al4V- and NiTi-cubic cellular structures with an open-cell size and wall thickness of 500 μm and 100 μm, respectively. Bioactive beta-tricalcium phosphate (βTCP) and polymer poly-ether-ether ketone (PEEK) were used to fill the produced structures open-cells, thus creating multi-material components. These structures were characterized in vitro in terms of cell viability, adhesion, differentiation and mineralization. Also, bio-tribological experiments were performed against bovine plate to mimic the moment of implant insertion. Results revealed that metabolic activity and mineralization were improved on SLM mono-material groups, when compared to the control group. All cell metrics were improved with the addition of PEEK, conversely to βTCP where no significant differences were found. These results suggest that the proposed solutions can be used to improve implants performance.
- Multi-material Ti6Al4V & PEEK cellular structures produced by Selective Laser Melting and Hot Pressing: A tribocorrosion study targeting orthopedic applicationsPublication . Bartolomeu, F.; Buciumeanu, M.; Costa, M.M.; Alves, N.; Gasik, M.; Silva, F.S.; Miranda, G.Ti6Al4V-alloy is commonly used in dental and orthopedic applications where tribochemical reactions occur at material/bone interface. These reactions are one of the main concerns regarding Ti6Al4V implants due to the generation of wear particles, linked to the release of metallic ions in toxic concentration which occurs when TiO2 passive film is destroyed by means of wear and corrosion simultaneously. In the present study, a multi-material Ti6Al4V-PEEK cellular structure is proposed. Selective Laser Melting technique was used to produce Ti6Al4V dense and cellular structured specimens, whilst Hot-Pressing technique was employed to obtain multi-material Ti6Al4V-PEEK structures. This study investigates the tribocorrosion behavior of these materials under reciprocating sliding, comparing them with commercial forged Ti6Al4V. Open-circuit-potential was measured before, during and after sliding while dynamic coefficient of friction was assessed during sliding. The results showed an improved wear resistance and a lower tendency to corrosion for the multi-material Ti6Al4V-PEEK specimens when compared to dense and cellular structures mono-material specimens. This multi-material solution gathering Ti6Al4V and PEEK, besides being able to withstand the loads occurring after implantation on dental and orthopedic applications, is a promising alternative to fully dense metals once it enhances the tribocorrosion performance.
- Ti6Al4V cellular structures impregnated with biomedical PEEK: New material design for improved tribological behaviorPublication . Buciumeanu, M.; Almeida, S.; Bartolomeu, F.; Costa, M.M.; Alves, N.; Silva, F.S.In the present work, a new material design of Ti6Al4V-PEEK hybrid cellular structure with improved wear resistance is proposed. Samples with different dimensions of the open-cells (350, 400, 450, 500 μm) were fabricated by Selective laser melting (SLM) technology, while Hot pressing (HP) technology was employed to produce Ti6Al4V-PEEK hybrid cellular structures. The tribological tests were performed in Phosphate Buffered Saline solution at 37 ± 2 C. Results demonstrated that the addition of the biomedical PEEK protected the Ti6Al4V cellular structures, thus improving these hybrid structures wear resistance when increasing the amount of PEEK. The obtained results indicated that the Ti6Al4V-PEEK hybrid cellular structure with the dimensions of the opencells of 500 μm is a suitable structure for orthopedic implants, with improved properties.
- Ti6Al4V-PEEK multi-material structures – design, fabrication and tribological characterization focused on orthopedic implantsPublication . Bartolomeu, F.; Abreu, C.S.; Moura, C.G.; Costa, M.M.; Alves, N.; Silva, F.S.; Miranda, G.A multi-material concept that gathers Ti6Al4V and PEEK properties in a cellular structured component was designed, fabricated and investigated targeting hip implants. SLM and pressure assisted injection techniques were used to obtain Ti6Al4V-PEEK multi-material structures. Aiming to reproduce to some extension the tribological phenomena occurring during and after hip implant insertion, five tribological tests were outlined and performed. The obtained results showed that the presence of PEEK on the Ti6Al4V-PEEK cellular structures led to a substantial improvement on the wear resistance (62% reduction in the mass loss) when compared to the material currently available on market for hip implants. The multi-material solution here investigated shows a good compromise between the primary stability after implant insertion and the wear performance.