Multicomponent Alloys for Biomedical Applications

Titanium alloys are considered to be the most advanced materials for orthopedic implants due to the favorable combination of mechanical properties, low density, tissue tolerance, high strength-to-weight ratio, good resistance to corrosion by body fluids, biocompatibility, low density, nonmagnetic properties, and the ability to join with the bone. This is the reason why we decided to assess the resistance of two titanium alloys currently used for orthopedic implants, namely, Ti6Al7Nb and Ti6Al4V, as reference, to cyclic fatigue by dynamic tests with crevice corrosion stimulation. According to the results obtained, the examined electrochemical quantities, the visual and SEM observations, and EDX analysis reveal better corrosion behavior of the prostheses made of Ti6Al4V—anodized series compared to prostheses made of Ti6Al7Nb. The further comparison of two explanted proximal modules, made of Ti6Al7Nb and Ti6Al4V, to the same type of prostheses evaluated by cyclic fatigue dynamic tests with crevice corrosion stimulation reveals that there are significant similarities, in particular with regard to the electrolyte diffusion, deposition of products and corrosion. Cation extraction tests which were carried out for Ti6Al7Nb prostheses that have undergone particular surface treatments show significant differences depending on the surface treatment and demonstrate that orthopedic implant materials are not “inert.

Tribology of Medical Devices

Importance of tribology in a number of medical devices and surgical instruments is reviewed, including artificial joints, artificial teeth, dental implants and orthodontic appliances, cardiovascular devices, contact lenses, artificial limbs and surgical instruments. The current focus and future developments of these medical devices are highlighted from a tribological point of view, together with the underlying mechanisms

Current standards and ethical landscape of engineered tissues—3D bioprinting perspective

Tissue engineering is an evolving multi-disciplinary field with cutting-edge technologies and innovative scientific perceptions that promise functional regeneration of damaged tissues/organs. Tissue engineered medical products (TEMPs) are biomaterial-cell products or a cell-drug combination which is injected, implanted or topically applied in the course of a therapeutic or diagnostic procedure. Current tissue engineering strategies aim at 3D printing/bioprinting that uses cells and polymers to construct living tissues/organs in a layer-by-layer fashion with high 3D precision. However, unlike conventional drugs or therapeutics, TEMPs and 3D bioprinted tissues are novel therapeutics and need different regulatory protocols for clinical trials and commercialization processes. Therefore, it is essential to understand the complexity of raw materials, cellular components, and manufacturing procedures to establish standards that can help to translate these products from bench to bedside. These complexities are reflected in the regulations and standards that are globally in practice to prevent any compromise or undue risks to patients. This review comprehensively describes the current legislations, standards for TEMPs with a special emphasis on 3D bioprinted tissues. Based on these overviews, challenges in the clinical translation of TEMPs & 3D bioprinted tissues/organs along with their ethical concerns and future perspectives are discussed

Current standards and ethical landscape of engineered tissues—3D bioprinting perspective

Tissue engineering is an evolving multi-disciplinary field with cutting-edge technologies and innovative scientific perceptions that promise functional regeneration of damaged tissues/organs. Tissue engineered medical products (TEMPs) are biomaterial-cell products or a cell-drug combination which is injected, implanted or topically applied in the course of a therapeutic or diagnostic procedure. Current tissue engineering strategies aim at 3D printing/bioprinting that uses cells and polymers to construct living tissues/organs in a layer-by-layer fashion with high 3D precision. However, unlike conventional drugs or therapeutics, TEMPs and 3D bioprinted tissues are novel therapeutics and need different regulatory protocols for clinical trials and commercialization processes. Therefore, it is essential to understand the complexity of raw materials, cellular components, and manufacturing procedures to establish standards that can help to translate these products from bench to bedside. These complexities are reflected in the regulations and standards that are globally in practice to prevent any compromise or undue risks to patients. This review comprehensively describes the current legislations, standards for TEMPs with a special emphasis on 3D bioprinted tissues. Based on these overviews, challenges in the clinical translation of TEMPs & 3D bioprinted tissues/organs along with their ethical concerns and future perspectives are discussed

Mechanical Properties of Biomaterials Used in Total Hip and Knee Arthroplasty

Total hip and knee arthroplasty (THA and TKA) represent two of the most successful operations in orthopedics. For a total hip or knee prosthesis to function successfully, it must transfer mechanical loads up to seven times the individual’s body weight from the axial skeleton to the lower extremities with minimal friction and wear. This is achieved by constructing prostheses from integrated components of different mechanical properties: a shock-absorbing and low-friction interface between the native joint and implant; a harder and stronger piece supporting the deformable interface, and an anchor securing the implant and transferring loads to the native bone. As early as the 1960s, polymers such as ultra-high molecular weight polyethylene (UHMWPE) were known to perform successfully at the joint-implant interface. Both ceramics and metals have historically been used for the main support of the implant, although metals and especially titanium alloys have taken preference in recent years. Recently, a flood of innovations has allowed material scientists to maximize the mechanical properties of these materials to increase mechanical strength, adjust elasticity, and improve biocompatibility. These innovations include the development of metal alloys and ceramic composites, reinforcement with carbon nanotubes and hydroxyapatite, antioxidant doping, gamma radiation-induced crosslinking, and bioactive coatings. Today, not only the mechanical properties but also the wear resistance and osseointegration of total hip and knee implants are far improved. This has led to better mechanical and physiological integration of the implants with the body and the necessary durability for younger patients’ more active lifestyles. In this paper, these innovations will be explored within the framework of implant mechanics to provide a comparative assessment of current materials’ mechanical capabilities, advantages, and disadvantages.undergraduat

Thermal spray of a drug delivery system onto femoral orthopaedic implant

Hydroxyapatite bioceramics are proven to be good materials for bone replacement and repair applications, due to their similarity in chemical composition to bone. Plasma spraying has been commonly used to apply hydroxyapatite coatings onto metallic implants for use in orthopaedic surgeries. The addition of HA coatings was successful in improving the performance of titanium implants. However, this type of implant has shown some limitations with regards to mechanical (implant loosening) and biological (infections) behaviour. It is thought that local drug delivery would be useful to prevent implant failures that could be treated with therapeutic agents (drug/growth factor). It is hypothesised in this work that polymers proven in drug delivery for other applications could be successfully applied to implants using existing technology in the sector. This research aims to introduce biodegradable materials (polymers) to the existing HA-titanium combination and to bare titanium implants in order to act as a drug-delivery vehicle. The proposed materials (PCL, PMMA and PHBV) consisted of biodegradable and non-biodegradable polymers (used separately or as a composite) that are widely used as drug delivery systems. The method used to apply these drug delivery systems in this project was flame spraying, due to its superior mechanical advantages over other techniques. Taking into account the thermal sensitivity of the chosen polymers and the high process temperature generated by the process, the mains challenges of this study were to obtain viable coatings with regards to all coating properties (chemical, physical, biological) and to control the mechanical characteristics of such coatings by varying the process parameters. Screening tests were conducted to determine the spraying parameters suitable for each polymer, followed by a more thorough Design of Experiments analysis to understand the relationship between three process factors: traverse speed, number of passes and spraying distance, and four coatings properties: thickness, roughness, adhesion and wettability. Chemical, physical, physiological and biological tests were also performed in order to study the suitability of the proposed polymers for such an application. The optimal process parameters to spray the PCL and PHBV matrices were: traverse speed of 0.152 m/s and 0.33 m/s, spraying distance of50 cm and 42.5 cm number of passes of 6 and 14, respectively. Viable polymer composites were obtained with the optimised spraying parameters on bare titanium and on HA coatings. These polymer coatings were not chemically damaged following flame spraying and all physiological and biological indicators suggested that the deposition technique used in this project is well suited for applying polymeric materials on orthopaedic implants for use as bioactive and drug delivery systems

Mode III cleavage of a coin-shaped titanium implant in bone: effect of friction and crack propagation

International audienceEndosseous cementless implants are widely used in orthopaedic, maxillofacial and oral surgery. However, failures are still observed and remain difficult to anticipate as remodelling phenomena at the bone-implant interface are poorly understood. The assessment of the biomechanical strength of the bone-implant interface may improve the understanding of the osseointegration process. An experimental approach based on a mode III cleavage mechanical device aims at understanding the behavior of a planar bone-implant interface submitted to torsional loading. To do so, coin-shaped titanium implants were inserted on the tibiae of a New Zealand White rabbit for seven weeks. After sacrifice, mode III cleavage experiments were performed on bone samples. An analytical model was developed to understand the debonding process of the bone-implant interface. The model allowed to assess the values of different parameters related to bone tissue at the vicinity of the implant with the additional assumption that bone adhesion occurs over around 70% of the implant surface, which is confirmed by microscopy images. The approach allows to estimate different quantities related to the bone-implant interface such as: torsional stiffness (around 20.5 N.m.rad-1), shear modulus (around 240 MPa), maximal torsional loading (around 0.056 N.m), mode III fracture energy (around 77.5 N.m-1) and stress intensity factor (0.27 MPa.m1/2). This study paves the way for the use of mode III cleavage testing for the investigation of torsional loading strength of the bone-implant interface, which might help for the development and optimization of implant biomaterial, surface treatment and medical treatment investigations

Surface Modification Strategies for Antimicrobial Titanium Implant Materials with Enhanced Osseointegration

The use of exogenous materials to replace or repair dysfunctional tissues and organs has seen dramatic improvements since the time of the ‘physician-hero’. The past three decades have heralded the advancement of various materials and technologies for medical implant devices to repair, replace or regenerate irreversibly damaged tissues. Improvement in health outcomes, evident in life expectancy increase, has brought in its wake the increased need to replace or repair tissues, particularly weight-bearing bone tissues. Titanium (Ti), a non-magnetic, corrosion resistant, osseo-integrating metal, with a higher strength-to-weight ratio than the traditional stainless steel, has emerged as the material of choice for replacing bone and other support tissues. However, the quest for improved performance (osseointegration) and reduction in implant related infection resulting in the need for resection surgeries, has necessitated the need to improve the titanium-tissue interface mediated osseointegration process, and confer antimicrobial properties to the implant material surface. In this work, a simple cost effective physical and chemical modification strategies have been developed, to alter the surface chemistry, increase the surface water wettability and confer a nano topographic characteristic to the Ti surface. These surface parameters have been demonstrated to enhance the osseointegration process. The chemical treatments resulted in oxides containing the following ions: Calcium (Ca), for improvement of osteogenic cell adhesion to Ti surface, Silver (Ag), and Zinc (Zn) for conferring antimicrobial properties to the novel surface, and their composites (CaAg, CaZn and CaZnAg), Scanning electron microscope (SEM) profiles of the modified surface suggest that, ions are chemically bound and not physically deposited onto the Ti surface. Further evidence of this is provided by the release profile of these elements from the modified surface over a 28-day period. We have also demonstrated that, the physically modified Ti surface is better at incorporating our elements of interest than the commercially pure titanium (cpTi) surface. xi The results from a Staphylococcus aureus biofilm formation assay, and U2OS bone cell adhesion and proliferation studies, suggest that, the physical modifications enhanced both the antimicrobial performance and the osteoblast-like cell adhesion and proliferation. The suggestion also is that, the incorporated Ca further enhances the adhesion and proliferation of bone-like cells, whereas Zn and markedly Ag improve the modified Ti surface’s antimicrobial properties. However, Ag alone has been shown to have a toxic effect on the bone cells; a promising combination treatment involving Ca, Zn and Ag appears to have beneficial response in all tests