Effects of Curing on Photosensitive Resins in {SLA} Additive Manufacturing

Different mechanical properties characterise the materials of 3D printed components, depending on the specific additive manufacturing (AM) process, its parameters, and the post-treatment adopted. Specifically, stereolithography (SLA) uses a photopolymerisation technique that creates solid components through selective solidification. In this study, 72 specimens were 3D printed using 12 commercial-grade methacrylate resins and tested under uniaxial tensile loads. The resin specimens were evaluated before and after curing. The recommended cure temperature and time were followed for all materials. The stress-strain curves measured during the testing campaign were evaluated in terms of maximum tensile strength, Young’s modulus, ductility, resilience, and toughness. The results reveal that the curing process increases the material stiffness and resistance to tensile loads. However, it was found that the curing process generally reduces the plasticity of the resins, causing a more or less marked brittle behaviour. This represents a potential limitation to the use of SLA 3D printing for structural elements which require some plasticity to avoid dangerous sudden failures

Effects of Curing on Photosensitive Resins in {SLA} Additive Manufacturing

Different mechanical properties characterise the materials of 3D printed components, depending on the specific additive manufacturing (AM) process, its parameters, and the post-treatment adopted. Specifically, stereolithography (SLA) uses a photopolymerisation technique that creates solid components through selective solidification. In this study, 72 specimens were 3D printed using 12 commercial-grade methacrylate resins and tested under uniaxial tensile loads. The resin specimens were evaluated before and after curing. The recommended cure temperature and time were followed for all materials. The stress-strain curves measured during the testing campaign were evaluated in terms of maximum tensile strength, Young’s modulus, ductility, resilience, and toughness. The results reveal that the curing process increases the material stiffness and resistance to tensile loads. However, it was found that the curing process generally reduces the plasticity of the resins, causing a more or less marked brittle behaviour. This represents a potential limitation to the use of SLA 3D printing for structural elements which require some plasticity to avoid dangerous sudden failures

Effects of the Manufacturing Methods on the Mechanical Properties of a Medical-Grade Copolymer Poly(L-Lactide-co-D,L-Lactide) and Poly(L-Lactide-co-ɛ-Caprolactone) Blend

11openopenMariana Rodriguez Reinoso; Marco Civera; Vito Burgio; Annalisa Chiappone; Oliver Grimaldo Ruiz; Alessandra D'Anna; Carmela Riccio; Ignazio Roppolo; Alberto Frache; Paola Antonaci; Cecilia SuraceRODRIGUEZ REINOSO, Mariana; Civera, Marco; Burgio, Vito; Chiappone, Annalisa; GRIMALDO RUIZ, Oliver; D'Anna, Alessandra; Riccio, Carmela; Roppolo, Ignazio; Frache, Alberto; Antonaci, Paola; Surace, Cecili

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

Three-dimensional Printing of a multi-material model of the Knee Joint

Abstract: Three-dimensional printing (3D) is an additive manufacturing technology based on material deposition layer by layer for 3D object construction. Every year, 3D Printing offers more alternatives and solutions in the healthcare field. Nowadays, applications such as 3D Printing labs in hospitals, low-cost patient-specific prosthetics, customized medical implants and manufacture of anatomical models with high dimensional accuracy are the most immediate emerging trends. Indeed, 3D Printing application is the convergence of multiple factors, including improvements in medical software, 3D printers evolution and new printing materials. In particular, anatomical models manufacturing is becoming increasingly popular and accessible due to its application in medical training and pre-operative planning. Anatomical models manufacturing is based on several data acquisition techniques such as computed tomography (CT), optical coherence tomography (OCT), magnetic resonance imaging (MRI) or 3D solid modeling through computer-aided-design (CAD) and anatomical structures 3D scanning. The Shirley Ryan Abilitylab research hospital has a full-color multi-material 3D printer Stratasys J750™. It uses Photopolymer jetting (Polyjet™ technology) for manufacture of highly realistic and functional 3D models in a wide range of colors and materials with variable durometers. Materials and methods: Polygonal mesh files (*.hm) corresponding to a finite elements (FE) model of the right knee joint reported by Dhaher et al. 2014 were the basis of this study. The 3D model included femur, tibia, patella, fibula, ligaments, articular cartilage, menisci, retinacula, patella and quadriceps tendons (PT-QT). Three anatomical models were projected and printed achieving the following objectives. (1) 3D model improvement of the right knee joint emulating the hierarchical structure of the collagen fibers matrix of the tendons and ligaments. (2) Anterior cruciate ligament reconstruction (ACL-R) model manufacturing using a bone-patellar-tendon-bone (BPTB) auto-graft and pre-operative planning to improve surgery outcomes, incorporating key surgical elements, such as orientation-architecture of the femoral and tibial tunnels and auto-graft dimensions reported by Dhaher et al. 2014. The surgical planning considers single bundle (SB) reconstruction and includes a customized surgical guide (SG) based on PT anatomy (it used in the graft harvest). The SG requirements followed the indications reported by Wang et al. 2017 with the aim to avoid graft tunnel length mismatch. (3) Total knee replacement (TKR) model manufacturing considering a cruciate sacrificing (CS) implant with customized design of symmetric tibial bearing, adjustment and assembly of standard prosthetic components in the improved 3D model emulating a TKR procedure. The selection process and printing materials matching with anatomical structures was based on stiffness and elastic modulus analysis of different Agilus30 printing material combinations. Mechanical uni-axial tensile tests were conducted in Northwestern University Kaiser Lab using an Instron S3300, Canton, MA Uniaxial Testing Instrument following ASTM test designation D412-C. The combinations No 1-4 were the most similar to real materials with elastic modulus of 1.8-0.7 and Pearson coefficients of the linear region of 0.980-0.991 respectively

Multi-color and Multi-Material 3D Printing of Knee Joint models = Impresión 3D multicolor y multimaterial de modelos de articulación de rodilla

Abstract: Objective: This study reports on a new method for the development of multi-color and multi-material realistic Knee Joint anatomical models with unique features. In particular, the design of a fibers matrix structure that mimics the soft tissue anatomy. Methods: Various Computer-Aided Design (CAD) systems and the PolyJet 3D printing were used in the fabrication of three anatomical models wherein fibers matrix structure is mimicked: (i) Anterior cruciate ligament reconstruction (ACL-R) model used in the previous study. (ii) ACL-R model, incorporating orientations, directions, locations, and dimensions of the tunnels, as well as a custom-made surgical guide (SG) for avoiding graft tunnel length mismatch. (iii) Total knee arthroplasty (TKA) model, including custom-made implants. Before models 3D printing, uni-axial tensile tests were conducted to obtain the mechanical behaviors for individual No. 1 (A60-A50), No. 2 (A50-A50), No. 3 (A50-A40), and No. 4 (A70-A60) soft tissue-mimicking polymers. Each material combination represents different shore-hardness values between fiber and matrix respectively. Results: We correlated the pattern of stress-strain curves in the elastic region, stiffness, and elastic modulus of proposed combinations with published literature. Accordingly, material combinations No. 1 and No. 4 with elastic modules of 0.76-1.82 MPa were chosen for the soft tissues 3D printing. Finally, 3D printing Knee Joint models were tested manually simulating 50 flexo-extension cycles without presenting ruptures. Conclusion: The proposed anatomical models offer a diverse range of applications. These may be considered as an alternative to replacing cadaver specimens for medical training, pre-operative planning, research and education purposes, and predictive models validation. The soft tissue anatomy-mimicking materials are strong enough to withstand the stretching during the flexo-extension. The methodology reported for the design of the fiber-matrix structure might be considered as a start to develop new patterns and typologies that may mimic soft tissues

Finite element analysis of the flexor digitorum profundus tendon during a passive rehabilitation protocol = Análisis de elementos finitos del tendón flexor profundo durante un protocolo de rehabilitación pasiva

Abstract: The present study aims to create a patient-specific hand model to simulate the passive rehabilitation on the index finger, quantifying the flexor digitorum profundus (FDP) tendon excursion and the stress experienced during simulated flexion. The computational model used in this analysis was created from an unknown patient dataset available in the Embodi3d online library. The segmentation, three-dimensional reconstruction, and modeling of the structures involved were performed using Materialise Mimics and Rhino3D. The FDP tendon excursion and stress values present in the model were calculated in the ANSYS environment. Based on the finite-element simulation, the FDP tendon presents an excursion of 10.1 mm during passive postoperative flexion. The highest-stress values were observed between the pulleys-FDP tendon contact surfaces. In particular, the pulley A1 exhibited the máximum principal stress of the model with a 58.7 MPa. The pulley A3 showed the same stress distribution pattern that A1 Pulley, but with the lowest values. The FDP Tendon excursión obtained is consistent with the results reported in the literature, which vary from 8 to 11 mm. The stress values found in the model explain the importance of the pulley mechanism keeping the FDP tendon attached to the finger bone during the range of motion experienced. The silico model proposed may potentially be used in the assessment of new medical device proposals in the field of hand reconstructive surgery

Correction: Riccio et al. Effects of Curing on Photosensitive Resins in SLA Additive Manufacturing. Appl. Mech. 2021, 2, 942–955

The Authors of the paper &ldquo;Effects of Curing on Photosensitive Resins in SLA Additive Manufacturing&rdquo; [...

Design and Mechanical Characterization Using Digital Image Correlation of Soft Tissue-Mimicking Polymers

Present and future anatomical models for biomedical applications will need bio-mimicking three-dimensional (3D)-printed tissues. These would enable, for example, the evaluation of the quality-performance of novel devices at an intermediate step between ex-vivo and in-vivo trials. Nowadays, PolyJet technology produces anatomical models with varying levels of realism and fidelity to replicate organic tissues. These include anatomical presets set with combinations of multiple materials, transitions, and colors that vary in hardness, flexibility, and density. This study aims to mechanically characterize multi-material specimens designed and fabricated to mimic various bio-inspired hierarchical structures targeted to mimic tendons and ligaments. A Stratasys&reg; J750&trade; 3D Printer was used, combining the Agilus30&trade; material at different hardness levels in the bio-mimicking configurations. Then, the mechanical properties of these different options were tested to evaluate their behavior under uni-axial tensile tests. Digital Image Correlation (DIC) was used to accurately quantify the specimens&rsquo; large strains in a non-contact fashion. A difference in the mechanical properties according to pattern type, proposed hardness combinations, and matrix-to-fiber ratio were evidenced. The specimens V, J1, A1, and C were selected as the best for every type of pattern. Specimens V were chosen as the leading combination since they exhibited the best balance of mechanical properties with the higher values of Modulus of elasticity (2.21 &plusmn; 0.17 MPa), maximum strain (1.86 &plusmn; 0.05 mm/mm), and tensile strength at break (2.11 &plusmn; 0.13 MPa). The approach demonstrates the versatility of PolyJet technology that enables core materials to be tailored based on specific needs. These findings will allow the development of more accurate and realistic computational and 3D printed soft tissue anatomical solutions mimicking something much closer to real tissues