Biomaterials for Orthopedic Implant

ABSTRACT
In this study electrochemical behaviors of SS 316L and Co-Cr-Mo alloys were
studied using electrochemical method by potentiostat in simulated body fluid (SBF) at
pH=7.4 and 37oC in absence and presence of 7 and 12 g/dL uric acid which causes
arthritis. Corrosion parameters for two implants were calculated which include
corrosion potentials (Ecorr), corrosion current densities (icorr), cathodic and anodic Tafel
slops (bc & ba), polarization resistance (Rp) and corrosion rates (CR).
Increases uric acid in human body gives decreasing in corrosion rate for SS 316L
because of formation organometallic complexes between acid molecules and released
metal ions, but an increase in corrosion rate for Co-Cr-Mo alloy because of low affinity
of cobalt ions to formation organometallic complexes. General comparison between
two implants shows that the Co-Cr-Mo alloy has lower corrosion rate than SS 316L in
the same conditions due to Cr content. This means that using Co-Cr-Mo alloy better
than SS 316L as bioimplant.

Tissue engineering is a newly emerging biomedical technology, which aids and increases the repair and regeneration of deficient and injured tissues. It employs the principles from the fields of materials science, cell biology, transplantation, and engineering in an effort to treat or replace damaged tissues. Tissue engineering and development of complex tissues or organs, such as heart, muscle, kidney, liver, and lung, are still a distant milestone in twenty-first century. Generally, there are four main challenges in tissue engineering which need optimization. These include biomaterials, cell sources, vascularization of engineered tissues, and design of drug delivery systems. Biomaterials and cell sources should be specific for the engineering of each tissue or organ. On the other hand, angiogenesis is required not only for the treatment of a variety of ischemic conditions, but it is also a critical component of virtually all tissue-engineering strategies. Therefore, controlling the dose, location, and duration of releasing angiogenic factors via polymeric delivery systems, in order to ultimately better mimic the stem cell niche through scaffolds, will dictate the utility of a variety of biomaterials in tissue regeneration. This review focuses on the use of polymeric vehicles that are made of synthetic and/or natural biomaterials as scaffolds for three-dimensional cell cultures and for locally delivering the inductive growth factors in various formats to provide a method of controlled, localized delivery for the desired time frame and for vascularized tissue-engineering therapies.

Nanoengineering the topology of titanium (Ti) implants has the potential to enhance cytocompability and biocompatibility properties as implant surfaces play a decisive role in determining clinical success. Despite developments in various surface engineering strategies, antibacterial properties of Ti still need to be enhanced. Here a facile, cost-effective hydrothermal route was used to develop nano-patterned structures on a Ti surface. Changing hydrothermal treatment parameters such as temperature, pressure, and time, resulted in various topographies, crystal phases, and hydrophobicity. Specifically, hydrothermal treatment performed at 225°C for 5 h, presented a novel topography with nanoflower features, exhibited no mammalian cell cytotoxicity for a time period of 14 days, and increased calcium deposition from osteoblasts. Treated samples also demonstrated antibacterial properties (without resorting to the use of antibiotics) against Staphylococcus aureus and methicillin resistant Staphylococcus aureus. In conclusion, hydrothermal oxidation on an etched Ti surface can generate surface properties that have excellent prospects for the biomedical field.

Surgical prostheses and implants used in hard-tissue engineering should satisfy all the clinical, mechanical, manufacturing, and economic requirements in order to be used for load-bearing applications. Metals, and to a lesser extent, polymers are promising materials that have long been used as load-bearing biomaterials. With the rapid development of additive manufacturing (AM) technology, metallic and polymeric implants with complex structures that were once impractical to manufacture using traditional processing methods can now easily be made by AM. This technology has emerged over the past four decades as a rapid and cost-effective fabrication method for geometrically complex implants with high levels of accuracy and precision. The ability to design and fabricate patient-specific, customized structural biomaterials has made AM a subject of great interest in both research and clinical settings. Among different AM methods, laser powder bed fusion (L-PBF) is emerging as the most popular and reliable AM method for producing load-bearing biomaterials. This layer-by-layer process uses a high-energy laser beam to sinter or melt powders into a part patterned by a computer-aided design (CAD) model. The most important load-bearing applications of L-PBF-manufactured biomaterials include orthopedic, traumatological, craniofacial, maxillofacial, and dental applications. The unequalled design freedom of AM technology, and L-PBF in particular, also allows fabrication of complex and customized metallic and polymeric scaffolds by altering the topology and controlling the macro-porosity of the implant. This article gives an overview of the L-PBF method for the fabrication of load-bearing metallic and polymeric biomaterials.

Among AM
technologies, electron beam melting (EBM) processes metal powders by means of an
electron beam. Since all the manufacturing steps occur under vacuum, EBM is an ideal
manufacturing method for highly reactive metals such as Ti and its alloys that are
prone to oxidization. Moreover, EBM reaches high production rates and enables the
manufacturing of patient-specific prostheses and support-free porous structures

Stem/progenitor cell-based therapeutic approach in clinical practice has been an elusive dream in medical sciences, and improvement of stem cell homing is one of major challenges in cell therapy programs. Stem/progenitor cells have a homing response to injured tissues/organs, mediated by interactions of chemokine receptors expressed on the cells and chemokines secreted by the injured tissue. For improvement of directed homing of the cells, many techniques have been developed either to engineer stem/progenitor cells with higher amount of chemokine receptors (stem cell-based strategies) or to modulate the target tissues to release higher level of the corresponding chemokines (target tissue-based strategies). This review discusses both of these strategies involved in the improvement of stem cell homing focusing on mesenchymal stem cells as most frequent studied model in cellular therapies.

Commercially available polycrystalline alumina is implanted at different energies and various ion doses. Microstructural changes, elemental analysis, and evidence of compound formation of AlN and AlON are observed using scanning electron microscopy, electron dispersive X‐ray spectroscopy, and GXRD techniques, respectively. Nanohardness increases due to the formation of the hard phase of nitrides. It increases with the increase in ion dose but decreases at higher ion dose. A similar trend is also observed in the corrosion resistance studied in Ringer solution. Corrosion resistance also improves with the increase in ion dose and decreases with the further increasing ion dose

Nanoengineering the topology of titanium (Ti) implants has the potential to enhance cytocompability and biocompatibility properties as implant surfaces play a decisive role in determining clinical success. Despite developments in various surface engineering strategies, antibacterial properties of Ti still need to be enhanced. Here a facile, cost-effective hydrothermal route was used to develop nano-patterned structures on a Ti surface. Changing hydrothermal treatment parameters such as temperature, pressure, and time, resulted in various topographies, crystal phases, and hydrophobicity. Specifically, hydrothermal treatment performed at 225 °C for 5 h, presented a novel topography with nanoflower features, exhibited no mammalian cell cytotoxicity for a time period of 14 days, and increased calcium deposition from osteoblasts. Treated samples also demonstrated antibacterial properties (without resorting to the use of antibiotics) against Staphylococcus aureus and methicillin resistant Staphylococcus aureus. In conclusion, hydrothermal oxidation on an etched Ti surface can generate surface properties that have excellent prospects for the biomedical field.

The increasing trend of total knee replacement (TKR) revision surgery, which is associated with aseptic loosening, makes it a challenging research subject. The concern of loosening can be partially improved by selecting the optimal materials for TKR components. Therefore, this paper considers selection of the best material among the set of alternatives for femoral component of TKR through the multi-criteria decision making approach. The comprehensive VIKOR method was used to select the optimum material, and a systematic technique for sensitivity analysis of weights was introduced to find more reliable results. The obtained ranking order suggested the use of new materials over the existing ones. Porous and dense NiTi shape memory alloys were ranked first and second respectively.