Comparison of multiple linear regression and artificial neural network in developing the objective functions of the orthopaedic screws

Optimizing the orthopaedic screws can greatly improve their biomechanical performances. However, a methodical design optimization approach requires a long time to search the best design. Thus, the surrogate objective functions of the orthopaedic screws should be accurately developed. To our knowledge, there is no study to evaluate the strengths and limitations of the surrogate methods in developing the objective functions of the orthopaedic screws. Three-dimensional finite element models for both the tibial locking screws and the spinal pedicle screws were constructed and analyzed. Then, the learning data were prepared according to the arrangement of the Taguchi orthogonal array, and the verification data were selected with use of a randomized selection. Finally, the surrogate objective functions were developed by using either the multiple linear regression or the artificial neural network. The applicability and accuracy of those surrogate methods were evaluated and discussed. The multiple linear regression method could successfully construct the objective function of the tibial locking screws, but it failed to develop the objective function of the spinal pedicle screws. The artificial neural network method showed a greater capacity of prediction in developing the objective functions for the tibial locking screws and the spinal pedicle screws than the multiple linear regression method. The artificial neural network method may be a useful option for developing the objective functions of the orthopaedic screws with a greater structural complexity. The surrogate objective functions of the orthopaedic screws could effectively decrease the time and effort required for the design optimization process.     

An investigation into the flexural characteristics of functionally graded cobalt chrome femoral stems manufactured using selective laser melting

In order to reduce the stress shielding of the femur following Total Hip Arthroplasty (THA), stiffness matching strategies between the host bone and femoral stem still need to be investigated. Additive Layer Manufacturing (ALM) technologies such as Selective Laser Melting (SLM) can produce components from a single alloy with varying mechanical properties, and hence, functionally graded parts. This work considers the flexural characteristics of laser melted cobalt chrome femoral stems, by using a combination of mechanical testing and finite element analysis. A functionally graded design methodology was considered in order to reduce the weight and stiffness of the femoral stems. Three separate functionally graded designs were investigated by incorporating square pore cellular structures of varying density. The results confirmed that selective laser melting can repeatedly manufacture a functionally graded femoral stem that is 48% lighter and 60% more flexible than a traditional fully dense stem. However, there are concerns associated with the repeatability of the manufacturing process for producing stems with cellular structures that incorporate strut sizes, which are equal to or less than 0.5 mm.     

Corrosion of bio implants

Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO₂ film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.     

Bioceramic composites for orthopaedic applications: A comprehensive review of mechanical,biological, and microstructural properties

Bioceramics have been widely utilized for orthopaedic applications in which the biocompatibility and mechanical properties of the materials are vital characteristics to be considered for their clinical use. Till date, extensive studies have been devoted to developing a range of scientific ways for tailoring the microstructure of bioceramics in order to attain the trade-off of mechanical properties and biocompatibility of the final product. Owing to low reactivity, earlier stabilization and longer functional life of bioceramic, the developed implants are capable of replicating the mechanical behaviour of original bone. As the safety of the patient and its ultimate functionality are the ultimate goal of the selected implant material hence, the present literature survey investigates and brings forth the important aspects associated to the mechanical, biological and microstructural characteristics of bioceramics employed in orthopaedic applications. The review paper majorly focuses on effective utilization of various materials as an additive in bioceramics and processing techniques used for enhancement of properties, enabling the use of material in orthopaedic applications. The influence of various additives on the microstructure, mechanical properties and biological performance of developed bioceramics orthopaedic implants has been elaborately discussed. Furthermore, future prospects are proposed to promote further innovations in bioceramics research.     

Computer-aided reverse engineering of the human musculoskeletal system

The objective of this study is to extend the applications of reverse engineering technology from manufacturing industries to the biomedical industry. By obtaining nearly exact geometric data of human tissues, such as bones, tendons, and ligaments, in a high-speed and inexpensive manner, potentially groundbreaking research becomes possible for applications in injury rehabilitation, injury prevention and strengthening. Previous applications of reverse engineering technologies in the biomedical community have dealt largely with prosthetic design and plastic surgery. This study expands this research to include muscular and skeletal applications. The primary advantage provided by scanning technologies is an improved quality of data. Secondly, the time investment for the medical researcher is greatly reduced. And finally, the use of a scanning technology will occasionally provide a less expensive alternative to the medical imaging counterparts. The goal of the research is to develop guidelines and methodologies for reverse engineering human structures.     

Reduced bacterial adhesion on ceramics used for arthroplasty applications

Orthopaedic-implant-related infections are challenging for clinicians: despite progresses in surgical procedures, the mortality rate of patients experiencing periprosthetic joint infections still ranges from 10 to 18%. Generally, infection starts when planktonic bacteria arising from surgery escape immunological surveillance adhering onto implant surface. Bacterial adhesion depends mainly on material’s intrinsic surface features depending on its chemical and physical properties. This study compares materials used for bearings of total hip arthroplasty, advanced ceramics (alumina and zirconia-platelet toughened alumina composites), metals (cobalt–chromium–molybdenum alloy) and polymers (highly cross-linked polyethylene), in terms of wettability and protein adsorption. Materials were infected with Staphylococcus aureus and Staphylococcus epidermidis biofilm for 24 or 48 h. Bacterial adhesion properties were evaluated by means of biofilm viability, morphology, and thickness, in a worst-case surface roughness condition. Thanks to selective protein adsorption, bioceramics reduced bacterial adhesion and subsequent biofilm formation more effectively in comparison with metal and polymer surfaces.     

骨科植入材料的研究现状及发展趋势

综述了目前临床使用的主要骨科植入材料的研究现状及发展趋势，详细介绍了各种材料的特点、优势和存在的问题，结合各种材料的特点，介绍了它们的主要用途。本文认为目前用于制造骨科植入器械的任何一种材料（无论是金属或合金、陶瓷、高分子材料或碳质材料）均不能同时满足人体生理环境（良好的生物相容性及稳定性、耐腐蚀性）和关节生物力学环境（良好的力学相容性及强韧性、高疲劳性能和耐磨性）的苛刻要求。现有骨科植入器械的有效使用寿命和功能尚不能完全满足患者的要求，有待材料研究专家和临床医学专家共同努力解决。最后，阐述了骨科植入材料的未来发展方向。     

聚氨酯矫形材料的制备与性能的研究

本文对聚氨酯矫形材料的制备方法与性能进行了研究。选择了适宜的催化剂和稳定剂体系,使材料具有较短的固化时间和较长的贮存稳定性。村料的力学性能及对x射线的穿透能力均优于石膏绷带。     

Wear analysis of materials used as orthopaedic implants

In the biomedical field, about 6% of the hip total prostheses must be replaced after 9 years. One of the main causes of the aseptic loosening may be attributed to fretting corrosion between the prosthesis and the bone cement. To understand this degradation, a fretting test between a stainless steel, 316L and PMMA has been used in Ringer solution. Fretting maps for the contact 316L/PMMA were determined in air and in Ringer solution. It has been shown that the lubricant effect of the aqueous environment shifts the gross slip/partial slip transition towards larger normal forces or lower displacements.To understand the fretting degradation behaviour of 316L against PMMA, fretting corrosion experiments have been investigated under constant applied potential. The first conclusion is that the dissipated energy is maximum at about −600 mV/SCE. The wear on PMMA does not depend on the applied potential. Moreover, the wear coefficient is lower than that in air due to the lubricant effect of the Ringer solution. Wear on 316L depends on the applied potential. The wear volume is minimum at −600 mV/SCE although the dissipated energy is maximum. The wear on 316L in Ringer solution is attributed to a dissolution process due to the local destruction of the passive film by fretting. The effect of potential on the wear of 316L may be accounted for by changes in the aqueous environment confined in the contact zone due to a restricted mass transport from the bulk solution and to the large local current densities consecutive to the destruction of the passive film. Accordingly, the wear volume on 316L is correlated to the time. Finally, the proton reduction, inside the contact, is believed to contribute significantly to the dissolution process.