Hassas döküm ile üretilen femoral nakillerin ısıl sprey yöntemleri ile geliştirilmesi

Abstract

Bu çalışmada üç adet femoral implant, duraluminyum, saf demir ve kobalt-krom alaşımı kullanılarak, hassas döküm yöntemi ile üretilmiş, daha sonra bu implant numunelerin biyouyumluluk ve benzeri biyolojik özelliklerini geliştirmek amacıyla plazma sprey kaplaması ve tel sprey, ısıl sprey yöntemleri uygulanmıştır. Çalışmanın temelinde; biyolojik özellikleri vasat olan fakat bağıl olarak ucuz ve yaygın elde edilen malzemeleri, biyolojik olarak üstün özellikler sergileyen ancak bağıl anlamda daha pahalıya elde edilebilen malzemelerle kaplayarak herhangi bir komplikasyona yer vermeyecek ekonomik biyomalzemeler geliştirmek amacıyla üretilmiş implant numunelerin arayüzey morfoloji ve yapısal değişimleri incelenmiştir. Üretilen implant malzemeler, özellikle biyouyumluluk ve vücut içerisindeki sıvıların korozif etkilerine karşı direnç gösterme bakımından üstünlük göstermelidir. Dolayısıyla üretilen ve kaplanan numunelerin titizlikle test edilmesinin önemi, vücut içerisinde yer değişecekleri özgün organ dikkate alındığında daha da artmaktadır. Dünyadaki bu uygulamaların pratiğine bakıldığında en yaygın olarak kullanılan cerrahi nakil malzemeler titanyum ve kobalt bazlı alaşımlar olarak göze çarpmaktadır. Ne var ki, üretim şartları dikkate alındığında özellikle titanyum bazlı nakil malzemelerin maliyetinin oldukça yüksek olduğu bilinmektedir. Eğer numunelere uygulanan kaplamalar biyouyumluluk ve metalurjik açıdan güvenilirlik sağlarsa bu malzemelerin üretim maliyetleri oldukça aşağılara çekilebilir. Biyo malzeme olarak kabul edilen malzemelerin, klinik deneylere tabi tutulmadan kullanıma geçilemeyeceği, en az altı ay, ideal olarak ise bir yıl olmak üzere insan bünyesine simülatif bünyelerde mutlak suretle izlenmesi gereği çalışmanın sonunda belirtilmiştir.

Three Femoral Implants were made by precision casting from Co-Cr Alloy, Pure Iron (ARMCO) and Duraluminium (DURAL). In order to improve the biocharacteristics of these materials, commercially pure (CP) titanium was coated on Co-Cr Alloy and ARMCO specimens by Titanium Wire Injection technique. Aluminium Oxide (AI2O3) was coated onto DURAL specimen by plasma spray coating. The purpose of these applications was to analyse the interface morphology and structural modifications of the specimens which are prepared as surgical biomaterials. Qualitative and Quantative analysis were made after the coating procedures. Implant materials have to be biocompatible and resistant to the effects inside the body. Therefore manufactured and coated samples must be tested properly in order to replace the original component in the body. The quality of endosteal implants is defined by the following properties: - intrinsic biocompatibility - implant material acceptance by the body; - functional biocompatibility - implant ability to fulfill its aim and to resist to work stresses ; ' construction biocompatibility - the effect of the implant design and manufacturing technology on the body; - osteointegration - osseous growing around the implant that removes its mobility. The intrinsic biocompatibility of c.p. titanium is maximum in comparison with titanium base alloys.Aluminium is not strongly diminishing the biocompatibility, while the usual (5 stabilizer elements have more obvious negative effect. It is the reason of the suitability of these alloysin implantology, even if their strength is lower and their brittleness is higher than the usual a alloys. In the world practice, the most widely used materials for surgical implants are Ti- based and Co-based alloys; however, when the manufacturing conditions are considered, the cost of these implants become very high. If the coatings applied to the specimens appear biocompatible and metallurgically safe, production cost can be decreased dramatically. Many people suffers various physical impairments in all over the world. Moreover these impairments are gradually increasing because of sports activities, many different accidents, sophisticated weaponry and so on. With the combined effort of bioengineers, material science engineers and orthopedists variety of biomaterials are improved for the function of disabled people. The life of these people is provided to be ordinary living conditions with these studies. The safety of long term implant is of major concern both to the patient and to the surgeon, only the best implant materials should be chosen for designing and manufacturing hip replacements. Price considerations at the expense of quality in respect of the implant itself should merely play a secondary role when considering the total cost for surgical implants, for this would mean economizing in the wrong place. On the other hand some principles should be remembered in biomaterial study field: the future of the biomaterials should be considered also in the light of scarcity of raw materials as well as the steadily rising price trend of strategically important elements. Therefore we aimed the combination of better biocharacteristics and metallurgical properties by applying coatings to the easily available elements. In recent years, many spectacular improvements have been obtained in the field of orthopedical surgery. The trend of the surgery changed to the repairment of the organ without being lost of its functions. There are two final objectives for the metallic materials used in orthopedic surgery. These are replacement of a skeletal segment i.e. internal prostheses and temporary immobilization of the skeletal segment i.e. materials for osteosynthesis. If we consider the medical aspects of an implant: In order to produce functional implant materials, anatomy and physiology of human body must be understood properly. Related with this, if the reactions of the body costituents is not known after the implantation, some negative effects such as rejection of the material by the tissue around the replaced organ may arise. The mechanical properties of the implant should be manipulated to the mechanical properties of the replaced organ. Otherwise, the results may be very disappointed. Furthermore adapting the mechanical properties of the implant material to the mechanical properties of the replaced organ is one of the most difficult part of the bioengineering study. The most important aspect of such mechanical property adaptation is fixing the implant to the bone. For the mentioned bioengineering aspects, some important characteristics of the bone should be clarified:. Bone includes anisotropic materials;. Bone has viscoelastic behaviour;. Properties of the bone shows variations with mineralisation, histological structure, age, sex and practical functioning conditions. Main conditions for material selection for implants are:. Tolerance between bone and inert material;. Mechanical stability of the implant for short term and for long term service conditions. An ideal implant material must have optimum behaviour in static conditions. This can be obtained by high resistance in certain defined values of elongation, XI good resistance for alternative bendings, and maximum corroison resistance in physiological NaCl solution for various pH degrees. Consequently, dynamic and static conditions of an implant material should have maximum corroison stability under fatigue. Ideal implant material should also have non-toxicity against tissues and shapebility. Finally, it is obvious that the implant material should have reasonable costs. In the light of above explanations this study has been carried out. After coating the specimens by various thermal spray techniques Macro and micro examinations had been made and following results have been obtained. Co -Cr alloy and Armco implant samples have to be wire flame injected in atmosphere controlled environment. Furthermore, they should be coated automatically not manuel because of inhomogeneity of the coating thicknesses and distribution. Although at the end of the study, some oxidation arose. These are not very dangerous according to the biological literature. Altough these oxides are tolerable, for the final considerations they are not wanted. The reason for these phenomenon the place that the samples replaced i.e. human body. Therefore all these additional elements have to be tested biologically before the decision of using these samples in service. For the other sample Duralumimum, the primary coating Nickel performed very good coating characteristics although the main coating material Alumina had, shown poor coating behaviour as the thickness of total application was around 100 microns. When the coating thickness is desired to be higher than 100 microns, the coating behaviour of alumina can be improved. However for the fine coating applications i.e. less than 100 microns, the application could have some difficulties such as wetting and sticking problems and inhomogeneity varying thicknesses along the substrate. Finally the rate of deposition is obviously different between primary nickel and alumina. At the end of this study one thing must be clarified: All these samples can be considered as biomedical implant materials. However before the actual service application, a lot of clinical tests and experiments must be performed. Without investigating the result of these implant materials inside of some experimental conditions (in rats, rabbits, dogs etc.) A proper duration of such experiments is one year. Before observing these materials in different body fluids they can not be considered as ideal biomaterials.