No abstract

Commonly used endoprostheses in the orthopedic industry are those made of Ti6Al4V titanium alloy. Unfortunately, this material has low abrasion resistance, and therefore methods of their modification are still sought. A sensible approach is coating the alloy with a layer of a polymer having higher abrasion resistance. The adhesion of polymers to alloy is low, therefore the alloy requires prior modification. In this work, the alloy was modified with three types of diazonium salt and the influence of substituent on the effectiveness of modification was determined. Then, five or ten polyurethane layers were attached to the surface of the modified alloy. Using Raman mapping, the uniform distribution of layers was proved. Layers are stable in simulated human body fluids. The effectiveness of attaching subsequent layers of polyurethane was also confirmed by nanoindentation. The main focus of this work was to improve the wear resistance of the titanium alloy. The obtained results indicate that the titanium alloy with a polyurethane layer has almost ten times lower coefficient of friction compared to pure alloy. Such a low value has not been described in the literature so far. These results are the first step for obtaining endoprostheses with very high abrasion resistance.

Resurfacing hip and knee endoprostheses are generally embedded in shallow, prepared areas in the bone and secured with cement. Massive cement penetration into periarticular bone, although it provides sufficient primary fixation, leads to the progressive weakening of peri-implant bone and results in failures. The aim of this paper was to investigate in an animal model the first biomimetic fixation of components of resurfacing arthroplasty endoprostheses by means of the innovative multispiked connecting scaffold (MSC-Scaffold). The partial resurfacing knee arthroplasty (RKA) endoprosthesis working prototype with the MSC-Scaffold was designed for biomimetic fixation investigations using reverse engineering methods and manufactured by selective laser melting. After Ca-P surface modification of bone contacting surfaces of the MSC-Scaffold, the working prototypes were implanted in 10 swines. Radiological, histopathological, and micro-CT examinations were performed on retrieved bone-implant specimens. Clinical examination confirmed very good stability (4 in 5-point Likert scale) of the operated knee joints. Radiological examinations showed good implant fixation (radiolucency less than 2 mm) without any signs of migration. Spaces between the MSC-Scaffold spikes were penetrated by bone tissue. The histological sections showed newly formed trabecular bone tissue between the spikes, and the trabeculae of periscaffold bone were seen in contact with the spikes. The micro-CT results showed the highest percentage of bone tissue ingrowths into the MSC-Scaffold at a distance of 2.5÷3.0 mm from the spikes bases. The first biomimetic fixation for resurfacing arthroplasty was successfully verified in 10 swines investigations using RKA endoprosthesis working prototypes. The performed research shows that the MSC-Scaffold allows for cementless and biomimetic fixation of resurfacing endoprosthesis components in periarticular cancellous bone.

The multispiked connecting scaffold (MSC-Scaffold) prototype, inspired by the biological system of anchorage of the articular cartilage in the periarticular trabecular bone by means of subchondral bone interdigitations, is the essential innovation in fixation of the bone in resurfacing arthroplasty (RA) endoprostheses. The biomimetic MSC‐Scaffold, due to its complex geometric structure, can be manufactured only using additive technology, for example, selective laser melting (SLM). The major purpose of this work is determination of constructional possibilities for the structural-geometric functionalization of SLM‐manufactured MSC‐Scaffold prototype, compensating the reduced ability—due to the SLM technological limitations—to accommodate the ingrowing bone filling the interspike space of the prototype, which is important for the prototype bioengineering design. Confocal microscopy scanning of components of the SLM‐manufactured prototype of total hip resurfacing arthroplasty (THRA) endoprosthesis with the MSC‐Scaffold was performed. It was followed by the geometric measurements of a variety of specimens designed as the fragments of the MSC-Scaffold of both THRA endoprosthesis components. The reduced ability to accommodate the ingrowing bone tissue in the SLM‐manufactured prototypes versus that in the corresponding CAD models has been quantitatively determined. Obtained results enabled to establish a way of compensatory structural‐geometric functionalization, allowing the MSC‐Scaffold adequate redesigning and manufacturing in additive SLM technology.

Our team has been working for some time on designing a new kind of biomimetic fixation of resurfacing endoprostheses, in which the innovative multi-spiked connecting scaffold (MSC-Scaffold) that mimics the natural interface between articular cartilage and periarticular trabecular bone in human joints is the crucial element. This work aimed to develop a numerical model enabling the design of the considered joint replacement implant that would reflect the mechanics of interacting biomaterials. Thus, quantitative micro-CT analysis of density distribution in bone material during the embedding of MSC-Scaffold in periarticular bone was applied. The performed numerical studies and corresponding mechanical tests revealed, under the embedded MSC-Scaffold, the bone material densification affecting its mechanical properties. On the basis of these findings, the built numerical model was modified by applying a simulated insert of densified bone material. This modification led to a strong correlation between the re-simulation and experimental results (FVU = 0.02). The biomimetism of the MSC-Scaffold prototype that provided physiological load transfer from implant to bone was confirmed based on the Huber–von Mises–Hencky (HMH) stress maps obtained with the validated finite element (FE) model of the problem. The micro-CT bone density assessment performed during the embedding of the MSC-Scaffold prototype in periarticular bone provides insight into the mechanical behaviour of the investigated implant-bone system and validates the numerical model that can be used for the design of material and geometric features of a new kind of resurfacing endoprostheses fixation.