Extra-wide deposition in extrusion additive manufacturing: A new convention for improved interlayer mechanical performance

Recent studies have contested long-standing assumptions that mechanical anisotropy is caused by weak interlayer bonding and demonstrated that microscale geometry (the groove between extruded filaments) is the major cause of anisotropy in extrusion additive manufacturing (AM). Inspired by those finding, this study investigates the potential for a new convention for print-path design to improve mechanical properties by setting extrusion width to be at least 250 % of nozzle diameter. The new convention enabled an almost 50 % improvement in mechanical performance, which was supported by finite element analysis data, whilst simultaneously reducing the printing time by 67 %. Whereas a typical extrusion AM part uses several side-by-side extrusions, here, three 0.4-mm-wide extrusions are replaced with a single extra-wide 1.2-mm extrusion; two 0.6-mm-wide extrusions are also studied. The contact area between layers of the extra-wide extrusion was 90 % as opposed to 63 % for the conventional approach. The improved contact area led to a 40–48 % enhancement of strength, strain-at-fracture and toughness. This study presents a compelling case for a methodological shift to extra-wide extruded-filament deposition and explains the underlying cause of anisotropic strength observed in previous studies. Two case studies demonstrate practical applicability for a print run of 1000 nylon visors and lower-limb polylactide prosthetic sockets, for which extra-wide filaments more than doubled load-bearing capabilities. Polylactide material was used for most of the study; potential for translation to other materials is discussed

Experimental and numerical framework for improved lower-limb prosthetic socket design

Experimental and numerical framework for improved lower-limb prosthetic socket design</p

Structural integrity of 3D-printed prosthetic sockets: an experimental study for paediatric above-knee applications

Introduction of 3D printing into manufacturing of prosthetic sockets raised a question of structural integrity of such products. Prosthetic sockets, as customized products, cannot be directly included in a standardized testing protocol like other major parts of the prosthesis; this makes their mechanical assessment challenging. In this study, a prototype testing rig was developed according to BS EN ISO 10328, able to recreate the loading conditions of the early stance of the amputee gait on a paediatric transfemoral socket. A variety of above-knee prosthetic socket designs were 3D printed in PLA and carbon-fiber-reinforced nylon. The sockets were tested under static compressive load using the developed rig together with a silicone-rubber phantom limb with mechanical properties similar to those of the human tissue. New load requirements were calculated for the case of a 14-year-old male weighting in the 98th percentile. After initial design improvements, the 3D printed sockets were able to sustain loads up to five times the weight of the user without failing.</p

Structural integrity of 3D-printed prosthetic sockets: Experimental study for paediatric applications

Due to unique patient characteristics, prosthetic sockets cannot be included in a standardised testing protocol as the rest major parts of the prosthesis. This makes the mechanical assessment of the socket a difficult process, which still remains crucial, especially nowadays, when new manufacturing technologies, such as additive manufacturing, are gaining ground in the field. In this study, a prototype testing rig was developed according to BS EN ISO 10328 standard, able to recreate the loading conditions of the early stance of the amputee gait on a paediatric transfemoral socket. The load requirements suggested in the standard were recalculated for the case of a 14-year-old male user with their weight in the 98th percentile. A variety of above-knee prosthetic sockets were produced with PLA and carbon-fibre reinforced nylon, using a commercial 3D printer. The sockets were tested under compressive load employing a plaster limb manikin. Video image processing was used to accurately capture the load-displacement relation of the sockets

Mechanical performance of 3D printed prosthetic sockets: an experimental and numerical study

A lower-limb socket is an integral part of a prosthesis with functions to connect the residual limb and transfer the loads to the prosthesis. As a result of long and costly traditional manufacturing methods, assessing the mechanical performance of such products is challenging. With additive manufacturing gaining ground in healthcare and rehabilitation, it is even more important for such products to be analyzed to ensure that they comply with the required safety regulations. In this study, sockets were 3D printed employing PLA from two different manufacturers, and mechanically tested to assess their ultimate strength. Results of finite-element analysis (FEA) informed their redesigns that were created reinforcing the sockets at the stress-concentration areas for improved mechanical performance. It was shown that FEA can assist the development of designs with improved performance. The material choice was found to have the strongest effect; hence, serious considerations need to be taken when selecting the material, especially for healthcare applications, to maintain high safety standards.</p

AM lower-limb prosthetic socket: Using FEA for improved mechanical performance

Prosthetic sockets are bespoke products tailored to the needs of the individual user. Their manufacturing requires many workhours to achieve high quality and comfort. As modern technologies are introduced in healthcare, 3D printing of prosthetic sockets is also gaining ground. Still, prosthetic products made with this manufacturing process are limited and their mechanical performance is mostly unexplored. In this study, prosthetic sockets were 3D printed with PLA, using commercially available filament and printer. The sockets were tested in accordance with BS EN ISO 10328–2006 test instructions for ultimate strength to evaluate their ability to safely bear the loads caused by user's weight and movement. It was found that inconsistent behaviour occurs in materials and caution is advised when choosing them. Still, 3D printed sockets could sustain the required loads and, in some cases, exceed 5000 N (>5fold user's weight). Improved mechanical performance was achieved with a new socket design created utilising the data from finite-element analysis (FEA). The study addresses the challenges of using FEA to develop a 3D printed prosthetic socket and the benefits of the novel process for the healthcare industry

Mechanical assessment of lower-limb prosthetic sockets after printing-path optimization

A conventional way to design and manufacture prosthetic sockets is labor-intensive and time-consuming, as such products are tailored to individual users. Achieving the desired and comfortable fit relies on a prosthetist's expertise and a patient's feedback. To digitalize this process, computer aided design (CAD) methods have been used recently to design the prosthetic socket while novel manufacturing methods such as Additive Manufacturing (AM) have been employed to increase time efficiency. Mechanical performance of products manufactured with this approach is still not fully understood. In this study, above-knee prosthetic sockets were printed with a material-extrusion 3D printing technique using various printing paths with an increased inter-layer contact area. Compliance of AM PLA prosthetic sockets to safety regulations, as described in the BS EN ISO 10328:2006, was achieved, while at the same time the conventional path sockets were outperformed. Understanding the material behavior at the inter-layer bond is a step towards reduced manufacturing times and increased mechanical performance.</p

Ανακύκλωση φωτοβολταϊκών πάνελ

Περίληψη: Με την ραγδαία τεχνολογική εξέλιξη των τελευταίων ετών –ειδικότερα μετά την βιομηχανική επανάσταση- και την ανθρώπινη εξάρτηση από τις μηχανές, η σημερινή κοινωνία καθίσταται αρκετά ενεργοβόρα. Η ενέργεια αντλείται με διάφορους τρόπους από το περιβάλλον. Σε αυτήν όμως την κλίμακα το κόστος εξόρυξης ορυκτών πόρων είναι υπέρογκο και σε συνδυασμό με τους περιβαλλοντικούς κανονισμούς που επιβάλλονται τα τελευταία χρόνια, για την προστασία του πλανήτη, αναζητήθηκαν νέοι τρόποι παραγωγής ενέργειας. Ένας εξ αυτών είναι η χρήση φωτοβολταϊκών πάνελ. Σε αυτή την περίπτωση η ηλιακή ενέργεια συλλέγεται και μετατρέπεται σε ηλεκτρική με μοναδικό κόστος αυτό των δημιουργίας και συντήρησης των κατάλληλων υποδομών. Καθώς όμως εδραιώνεται η χρήση των φωτοβολταϊκών πάρκων ανά τον κόσμο, ένα νέο πρόβλημα που αναδύεται, είναι η διαχείριση των φθαρμένων πάνελ και αυτών που έχουν περατώσει το χρονικό όριο ζωής-λειτουργείας τους. Με γνώμονα την ελαχιστοποίηση του κόστους για την κοινωνία καθώς και για την ορθολογική διαχείριση των μεταλλικών και μη κατάλοιπων κρίνεται απαραίτητη η ανακύκλωση τους. Στην παρούσα εργασία θα επικεντρωθούμε σε ένα συγκεκριμένο τμήμα της διαδικασίας ανακύκλωσης, αυτό της ανάκτησης των επιμεταλλώσεων των φωτοβολταϊκών πάνελ. Θα εξεταστεί μία νέα μέθοδος, που με την χρήση κατάλληλων χημικών διαλυτών και συμπλόκων, σκοπεύει στην μεγαλύτερη δυνατή ανάκτηση των μεταλλικών στοιχείων, χωρίς την παραγωγή βλαβερών για τον άνθρωπο αποβλήτων. Το προτεινόμενο μοντέλο έχει σχεδιαστεί στο καινούριο περιβάλλον του SIEMENS NX 11.

Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects

Abstract Modern developments of biomedical applications demand a better understanding of mechanical behaviour of soft biological tissues. As human soft tissues demonstrate a significant structural and functional diversity, characterisation of their mechanical behaviour still remains a challenge. Limitations related with implementation of mechanical experiments on human participants lead to a use of finite-element models for analysis of mechanical responses of soft tissues to different loads. This study focuses on parameters of numerical simulation considered for modelling of indentation of a human lower limb. Assessment of the effect of boundary conditions on the model size shows that at a ratio of its length to the tissue’s thickness of 1.7 for the 3D model this effect vanishes. The numerical results obtained with models employing various sets of mechanical parameters of the first-order Ogden scheme were compared with original experimental data. Furthermore, high sensitivity of the resulting reaction forces to the indenting direction is demonstrated for cases of both linear and angular misalignments of the indenter. Finally, the effect of changes in material parameters and their domain on their contribution to the reaction forces is discussed with the aim to improve our understanding of mechanical behaviour of soft tissues based on numerical methods. The undertaken research with its results on minimal requirements for finite-element models of indentation of soft tissues can support inverse analysis of their mechanical properties and underpin orthopaedic and medical procedures

Evaluation of MET T1010I and MET rs40239 single-nucleotide polymorphisms in triple-negative breast cancer: a case--control study

Aim: The purpose of this study is to evaluate the role of MET T1010I and MET rs40239 as potential risk factor and/or prognostic markers in patients with triple-negative breast cancer (TNBC). Methods: 114 samples of DNA from paraffin-embedded breast normal tissues of patients with TNBC and 124 samples of healthy controls were collected and analyzed for MET T1010I and MET rs40239 polymorphisms. Results: MET T1010I CT genotype was associated with increased risk of TNBC in both univariate and multivariate analysis. The status of rs40239 was not associated with a higher risk for TNBC at either the univariate or the multivariate analysis. None of the examined polymorphisms was associated with overall survival at the univariate or multivariate Cox regression analysis (adjusted HR=1.35, 95% CI: 0.31–5.97 for MET T1010I CT/TT vs CC; adjusted HR=1.78, 95% CI: 0.73–4.35 for rs40239 AG/GG vs AA). Conclusion: Our case–control study suggests that MET T1010I seems to be a risk factor for TNBC in the Caucasian Greek population, in contrast with MET rs40239, where no correlation was found. © 2019 Kalapanida et al