| Current prosthesis designs for amputees rely on the stump–socket interface for attachment. Numerous problems are associated with current stump–socket designs. For example, the socket transfers the weight of the patient to the ground via the remainder of the prosthesis. Focal points of increased stress caused by nonuniform pressure distribution can lead to skin-related complications whilst the unnatural microbial environment generated in the socket, is detrimental to the maintenance of healthy stump tissues. Besides, the suspension apparatus will limit the forward movement of lower limb amputees. In recent years, intraosseous transcutaneous amputation prostheses (ITAP) have been studied by many reseachers. A titanium fixture is inserted into the medullary cavity, and then a skin-penetrating abutment on top of the fixture is attached. This new kind of prosthesis could overcome those problems by allowing attachment of the external implant directly to the skeleton. However, loosening of implant and unsealing of implant interface are still the bottleneck of this ITAP at present.A skin-penetrating implant will contact the skin and sub-epithelial soft tissue, so if the implant/ sub-epithelial soft tissue interface could't seal, infection will happen sequently and lead to implant failure. To eliminate the bottleneck, a number of studies home and abroad have mainly focused on the modification of implant surface by employing biological ceramic coatings. Hydroxyapatite (HA), the most frequently studied coating, has been proved to be an ideal material with the osseointegration ability. However, HA coating's clinical application is limited due to the difficulties of controlling its coating thickness, surface roughness and attaching strength. Besides, the coating detached easily with the increases of thickness and roughness. Good solutions to this problem have not been found at home and abroad.Our experiment aimed at the in vivo evaluation of osseointegration and soft tissue attachment to Ti alloy (Ti6Al4V) transcutaneous custom-made implants treated by a micro-arc oxidation (MAO) method.A microarc oxidation device was used to fabricate ceramic coatings on the surface of the Ti6Al4V alloy. MAO of the implants was carried out in an electrolyte containing Ca and P. A stainless steel plate was used as the negative electrode, the implant was used as the positive electrode. The SEM results clearly showed a tight and strong connection between the ceramic and the titanium alloy junction. A coarse and porous ceramic layer was formed with evenly distributed micro-pores. The EDS analysis results showed ceramic is composed mainly of O and Ti. It was also found that ceramic contains P and Ca, which are only present as negative irons in solution. The XRD results showed that the coatings are mainly composed of two types of titanium dioxide, metastable anatase and stable rutile, with predominantly anatase which has been proved to has a better biocompatibilityOur in vivo study consisted of two parts. In the first part, the MAO-treated bone-anchored Ti alloy implants were implanted into the medial aspect of the tibia of mature female goats, with the HA-treated and untreated implants as controls respectively. The animals were euthanized at 8 weeks and the samples harvested and processed for histological analysis. The results showed that contact integrations were formed between MAO-treated implants and the bones. HA-treated implants could also integrate with bones, but there were mainly newborn bones formed at the implant/bone interface. And the untreated implants were not able to integrate well with bones, with obvious crack existing at the implant/bone interface.In the second part, the experimental model comprised implantation of transcutaneous implants [2 groups: MAO and machined (control)] in the medial aspect of the tibia of female goats. The animals were euthanized at 8 weeks and the samples harvested and processed for histological and histomorphometrical analysis of soft tissue attachment to the implant surface. The results showed that around the control implants, the epidermis never contacted the implant surface and terminated within the dermis. While aroud the MAO-treated, implants sub-epithelial tissue integration were observed and some pores in the ceramic layer had been filled fully by sub-epithelial soft tissues. It was also observed that the sub-epithelial soft tissue grew inward the connections between the pores in the ceramic layer.The results of our studies indicated that the micro-pores structure and O, Ca, P, elements are some of the necessary conditions of biological activities of the MAO ceramic coating. The formation principle and elements sources of the MAO ceramic coating explained the coating's good intergration abilily with tissues. Our in vivo experiments have proved that the MAO ceramic coating had high biological activities and could induce the ingrowth of bone and soft tissue. These preliminary findings will provide important experimental evidences for the future clinical research, development and application of ITAP.
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