İmplant malzemelerinin mekanik özelliklerinin geliştirilmesi = Improvement of mechanical properties of implant materials

Abstract

Sağlıklı bir bireyin gün içerisinde yürüme, koşma, eğilme, merdiven inip-çıkma gibi rutin ve aktif hareketlerinde kullandığı uzuv eklemlerdir. Günümüzde hasara uğrayan bu uzuvlar için protez ve ortopedik implant uygulamaları yaş aralığı farketmeksizin sıklıkla gerçekleştirilmektedir. Eklemlerin birbirine girintili ve bağımlı (kompleks) yapısının yanında karşılıklı yüzleri temas halinde iki yüzeyi arasında aşınmayı azaltan yumuşak ve elastik yapıda kıkırdak mevcuttur. İmplantlar için bu doğal yapıya benzetilerek malzeme seçimi yapılmaktadır. İmplant ömrü ve sağlığı açısından kullanılan biyomalzemeler çok önemli rol oynamaktadır. Biyomalzemeler, canlının vücudunda görevini yerine getiremeyen, eksik olan uzuv ve parçalarının yenilenebilir şekilde doğal veya yapay hammaddelerle laboratuvar ortamında hazırlanan malzemelerdir. İmplantlarda karşılaşılan malzeme seçimi, aşınma, gevşeme gibi medikal problemlere karşı implant malzemelerinin özelliklerinin iyileştirilmesi ve geliştirilmesi amaçlanmıştır. Ortopedik implantlarda sıklıkla kullanılan metalik malzemelerinden Ti6Al4V alaşımı ve 316L Paslanmaz Çelik altlıklara biyopolimer olan Ultra Yüksek Moleküler Ağırlıklı Polietilen (UHMWPE) ve biyoseramik olan Al2O3 (Alümina) içeren polimer matrisli kaplamalar yapılmıştır. UHMWPE, UHMWPE-ağ.%0,2 Al2O3 ve UHMWPE-ağ.%2 Al2O3 polimer matrisli kaplamalar 316L paslanmaz çelik ve Ti6Al4V alaşım altlığa daldırma yöntemi ile gerçekleştirilmiştir. Elde edilen kompozit kaplamalar sonucu numuneler üzerine triboloji testi, biyokorozyon testi, biyoyumluluk testleri ve yüzey pürüzlülük ölçümü gerçekleştirilmiştir. Kaplamaların mikroyapı ve organik yapı incelemeleri için (Fourier Dönüşümlü Kızılötesi Spektroskopisi) FTIR, (Taramalı Elektron Mikroskop) SEM ve ( Enerji Dağılım X-Spektroskopisi) EDS analizleri yapılmıştır. Polimer matrisli kaplamalar her iki altlık için de sürtünme katsayısını belirli oranlarda azaltırken UHMWPE-ağ.%2 Al2O3 kaplama ile daha düşük sürtünme katsayısı değeri elde edilmiştir. Ayrıca UHMWPE kaplama yüzey pürüzlülüğünü düşürürken alümina artışına bağlı olarak sırasıyla UHMWPE-ağ.%0,2 Al2O3 ve UHMWPE-ağ.%2 Al2O3 kaplamaları yüzey pürüzlülüğünde artış ölçülmüştür. Biyokorozyon testinde ise her iki altlık için UHMWPE kaplama ile en yüksek korozyon direnci elde edilmiştir. Biyouyumluluk incelemesinde L929 (fare fibroblast) hücreleri üzerinde gerçekleşen test sonucu her bir numune için oldukça iyi oranlarda hücre canlılığı vererek vücut içerisinde kullanılabilir olduğu gözlemlenmiştir. Bu çalışmada biyomedikal alanda sıklıkla kullanılan 316L paslanmaz çelik ve Ti6Al4V üzerine UHMWPE- Al2O3 kompozit kaplamaların verdiği sonuçlar incelenerek litearatüre katkıda bulunulmuştur.

Today, with technological developments in the field of health, positive results such as the prolongation of life span for people and an increase in artificial materials that can replace organs and limbs that have lost their functions have been achieved. The contribution of biomaterials in biomedical applications is also significant in these results. The limbs of a healthy individual that can provide various directions and axes to their movements during their daily activities are joints. When the surgery rates are examined, joint prosthesis/implant operations are at a considerable rate. In the selection of the implant to be applied, the age range of the patients was taken into consideration and the patients had knee joint problems from young to old.In addition to being resistant to wear due to the indented structure of the knee joint, it is also desired to be mechanically durable since it has to carry the body's load. Biomaterials are materials prepared in a laboratory environment with natural or artificial raw materials to replace missing limbs and parts that cannot fulfill their function in the body of a living being. Their functions vary according to their areas of use. Biomaterials are placed invasively and non-invasively according to the area where they are intended to be used in the body. Accordingly, it can interact with the biological environment over time according to its structure and its structure can deteriorate in a way that can harm living tissue. To prevent such undesirable events, various studies are being carried out to ensure that the body responds positively to foreign substances placed from outside. The biomaterials used are metals, ceramics, polymers, and composites. Metals generally used in orthopedics are stainless steel, Ti alloys, and Cobalt alloys. Ceramic biomaterials are calcium phosphate, aluminum oxide, and zirconium dioxide. Polymers are silicone, poly (ethylene), poly (vinyl chloride), and polyurethane. Silk, elastin, collagen, gelatin, and polysaccharides are examples of natural polymers. Although the properties of materials vary according to the human body and the area where they are intended to be used for medical applications, the ideal qualities of biomaterials (Hasırcı and Hasırcı, 2022): biocompatibility, resistance to abrasion, non-corrosion, anti-carcinogenicity, physical-mechanical properties in terms of strength, easy to shape for the desired design, resistance to deterioration, non-toxicity, easy to obtain / easy to transport, low cost. The implant must adapt to the tissue in which it will be located best and maintain its structure over time. As the days go by, orthopedic implant applications cover a wide range of people from young to old, regardless of age. The deformation of the joints that provide direction and axis to movements results in difficulty or inability to perform activities such as standing up, squatting, climbing up and down stairs, standing, walking, and running. Problems encountered in knee joints or orthopedic implants can also cause implant complications such as material selection, faulty design, wear residues, and loosening. While quite successful operations are carried out today to restore patients' health, secondary operations are also needed. Inspired by the natural structure of the knee, a biocompatible, bone-like bioceramic material was selected as a polymeric material to resemble the cartilage in the outermost layer of the joint. It was aimed to improve and develop implant properties (friction coefficient-wear, corrosion resistance, compatibility) with polymer and alumina coating on 316L Stainless Steel and Ti6Al4V alloy substrates, which are frequently used in orthopedic implants. UHMWPE is a polymer with a density of ultra-high molecular weight polyethylene between 0.930–0.935 g/cm3 and molecular weights around (2-2.5) millions. Their molecular weights are due to the tightly packed structure or alignment of the polymer chains. This type of polymer is very hard and the best shock absorber among thermoplastics (Chilukoti and Periyasamy, 2012). Ultra-high molecular weight polyethylene (UHMWPE) is used as a carrier surface for joint arthroplasties. UHMWPE, introduced for the acetabular component in total hip arthroplasty, is a linear and semi-crystalline polymer that promises a friction-reducing surface. It is the preferred material in implant types such as ceramic-ceramic and metal-metal due to its resistance to friction (Wright, 2005). Alumina (Al2O3), Also known as aluminum oxide, alumina naturally contains minerals such as bauxite, cristobalite and diaspore. The compound called corundum is the only aluminum compound found in crystalline form in nature and is known as the hardest mineral after diamond (Devaraju et al., 2013). It is also one of the most stable oxides known with its high energy ionic and covalent bond content between Al-O atoms (Metson, 2011; S. K. Tiwari et al., 2011). Aluminum oxide is a biocompatible and chemically inert ceramic that has been confirmed by clinical studies. Based on the problems encountered, it has affected the properties such as friction coefficient (wear), biocorrosion, surface roughness, FTIR and biocompatibility of the samples that have been treated for improvement. Wear is defined as the rupture, physical or chemical changes caused by the movements of two surfaces in contact with each other under certain forces. Friction is the application of force in the opposite direction to a metal moving in a certain direction (Stachowiak ve Batchelor, 2013). It means that materials undergo physical chemical reactions due to various factors in their environment and undergo deterioration and changes in their structure. The surfaces of implant materials interact with body fluids. According to the DIN 50900 norm, corrosion is the measurable change in the material as a result of the reaction of the material with its environment; for metals, according to TS 5731 EN ISO 8044, it is defined as the electrochemical interaction that occurs between the metal and the environment it is in and causes a change in the properties of the metal (Bıyık, 2013). It is the acceptance of the material to be implanted in the body in the environment fluid and tissue and its positive reaction. It is an undesirable situation for the material to give a potentially harmful reaction in terms of chemical, physical and physicochemical aspects. 316L stainless steel and Ti6Al4V metal substrates were coated with UHMWPE and Alumina using the sol-gel method. The stages of the coating process can be roughly divided into 3 stages. In the first stage, the metal is dipped into the sol at the speed determined by the researcher and kept in the sol for the specified time. It can be expected that the surface area of the dipped metal is coated with sol. Then, the sol accumulated on the surface is pulled upwards at the same speed while the coating is drained from the surface in the direction of movement. During this time, excess sol is separated from the layer in the direction of gravity. The coated surface has a wet gel consistency and it is observed that a thin film is formed, which is expected to be obtained by evaporating the solvent. Three stages were taken into consideration in the dipping technique. Metal substrates are dipped into the sol at the speed determined by the researcher and kept in the sol for the specified time. It should be expected that the surface area of the dipped metal is covered with sol. Then, sol is deposited on the surface and while the metal is pulled upwards at the same speed, the coating is drained to the surface in the direction of the movement. During this time, the excess sol is separated from the layer in the direction of gravity. The coated surface is in the consistency of a wet gel and it is observed that the thin film expected to be obtained by evaporating the solvent is formed. The work carried out in this thesis can be summarized in general as follows: Today, orthopedic implant and joint prosthesis applications are frequently performed surgeries. The aim is to improve the properties of implant materials against problems such as material selection, wear and loosening encountered in implants. The changes in the properties of polymer matrix coatings containing biopolymer UHMWPE and bioceramic Al2O3 applied to Ti6Al4V alloy and 316L Stainless Steel substrates, which are frequently used metallic implant materials in orthopedic implants, were investigated. Polymer matrix composites prepared from UHMWPE, UHMWPE-0.2 wt.% Al2O3 and UHMWPE-2 wt.% Al2O3 were applied to 316L stainless steel and Ti6Al4V alloy substrates by immersion method. Tribological test, biocorrosion test, FTIR, surface roughness measurement, SEM-EDS and biocompatibility tests were performed on the samples obtained as a result of the obtained composite coatings. While the polymer matrix coatings significantly reduced the friction coefficient for both substrates, a better friction coefficient value was obtained with UHMWPE-2 wt.% Al2O3 coating. In addition, while UHMWPE coating reduces surface roughness, an increase in surface roughness was measured for UHMWPE-0.2 wt.% Al2O3 and UHMWPE-2 wt.% Al2O3 coatings due to the increase in alumina. In the biocorrosion test, the highest corrosion resistance was obtained with UHMWPE coating for both substrates. In the biocompatibility examination, the test result performed on L929 (mouse fibroblast) cells showed that each sample could be used in the body by providing very good cell viability. In this study, the results of UHMWPE-Al2O3 composite coatings on 316L stainless steel and Ti6Al4V, which are frequently used in the biomedical field, were examined and a contribution was made to the literature.