Ney Francisco Ferreira

Tibiofemoral wear in standard and non-standard squat: Implication for total knee arthroplasty

Introduction Due to the more resilient biomaterials, problems related to wear in total knee replacements (TKRs) have decreased but not disappeared. In the design-related factors, wear is still the second most important mechanical factor that limits the lifetime of TKRs and it is also highly influenced by the local kinematics of the knee. During wear experiments, constant load and slide-roll ratio is frequently applied in tribo-tests beside other important parameters. Nevertheless, numerous studies demonstrated that constant slide-roll ratio is not accurate approach if TKR wear is modelled, while instead of a constant load, a flexion-angle dependent tibiofemoral force should be involved into the wear model to obtain realistic results. Methods A new analytical wear model, based upon Archards law, is introduced, which can determine the effect of the tibiofemoral force and the varying slide-roll on wear between the tibiofemoral connection under standard and non-standard squat movement. Results The calculated total wear with constant slide-roll during standard squat was 5.5 times higher compared to the reference value, while if total wear includes varying slide-roll during standard squat, the calculated wear was approximately 6.25 times higher. With regard to non-standard squat, total wear with constant slide-roll during standard squat was 4.16 times higher than the reference value. If total wear included varying slide-roll, the calculated wear was approximately 4.75 times higher. Conclusions It was demonstrated that the augmented force parameter solely caused 65% higher wear volume while the slide-roll ratio itself increased wear volume by 15% higher compared to the reference value. These results state that the force component has the major effect on wear propagation while non-standard squat should be proposed for TKR patients as rehabilitation exercise.

IMPRESSÃO TRIDIMENSIONAL A PARTIR DE REJEITOS DE ÁGATA

This paper presents a technique used to obtain raw material for three-dimensional (3D) printing from agate’s manufacturing wastes. Through the use of appropriate methodology for grinding and classification of waste it was possible to obtain powder with a particle size indicated to the process, approximately 200 mesh, and serves as the basis for the raw material that uses maltodextrin and sugar as a solid binder. Saturation testing and manufacturing of 48 specimens, which were subjected to dimensional analysis and mechanical strength were performed. The test specimens made with 14% liquid saturation, the average strength observed was 5.84 MPa and the dimensional deviation was between 0.2 and 1.2 mm. It was observed that this saturation rate was adequate for manufacture of small parts and with the wall thickness of 5 to 10 mm, with low surface detail. The results presented here serve as a basis for improvement of raw material for development, especially for the finishing of parts, reliability and reproduction of small details and the size of the fabricated parts. The work presents the process of 3D printing as an alternative to the reuse of wastes and adding value to the material before rejected and could not be passed otherwise. Keywords: Three-dimensional printing, gems, development of raw material.