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.

Tendon and ligament injuries are a frequent and debilitating issue that affects many patients worldwide. The predominant solution is the suture thread, which is not without potential side effects a...

Biocompatible and biodegradable polymers represent the future in the manufacturing of medical implantable solutions. As of today, these are generally manufactured with metallic components which cannot be naturally absorbed within the human body. This requires performing an additional surgical procedure to remove the remnants after complete rehabilitation or to leave the devices in situ indefinitely. Nevertheless, the biomaterials used for this purpose must satisfy well-defined mechanical requirements. These are difficult to ascertain at the design phase since they depend not only on their physicochemical properties but also on the specific manufacturing methods used for the target application. Therefore, this research was focused on establishing the effects of the manufacturing methods on both the mechanical properties and the thermal behavior of a medical-grade copolymer blend. Specifically, Injection and Compression Molding were considered. A Poly(L-lactide-co-D,L-lactide)/Poly(L-lactide-co-ε-caprolactone) blend was considered for this investigation, with a ratio of 50/50 (w/w), aimed at the manufacturing of implantable devices for tendon repair. Interesting results were obtained.

Nowadays, biopolymers like Poly(lactic acid) (PLA) and Polycaprolactone (PCL) are commonly adopted in several fields of medicine, from orthopaedics to pharmacology. When dealing with medical applications like prostheses or scaffolds, it is crucial to have a deep knowledge of the mechanical properties of such biopolymers. Both biopolymers show a viscoplastic behaviour, namely, their mechanical response depends on the temperature and the velocity at which the loading or the deformation is applied. Currently, several companies commercialise a large variety of PCL and PLA blends with different ratios classified as "medical grade", indicating that such blends are suitable for manufacturing medical devices. The information about the mechanical behaviour of these blends remains unclear, since the datasheets available report information about the Young's Modulus, a limited amount of data considering their full mechanical behaviour. Most of these commercially available biopolymers have not been investigated thoroughly in the past. In this paper two commercially available biopolymers, Resomer®️ LR 704 S and LC 703 S, from Evonik were investigated. Specifically, the original polymers and the following blend combinations were tested: 60:40, 40:60, and 50:50. The original biopolymers and their blend combinations were considered to explore the application of developing two innovative devices for soft tissues repair, T-REMEDIE for tendon repair (Tendon Repair Medical DevIcE) [patent ID: IT202000006967A1]("Device and assembly for the repair of soft tissues, such as tendons and ligaments," 2020) and T-SURE for abdominal hernia repair (Tissue Surgical REpair), under development in the BIOMAST Lab (BIO-MAterials and STructures Laboratory) at the Politecnico di Torino. Experimental tensile tests on dog bone specimens manufactured by compression and injection moulding were evaluated. Based on the experimental results, the constitutive three network model (TNM), the three network viscoplastic (TNV) model and the Flow Evolution Network (FEN) model were implemented in MATLAB and calibrated. This work represents the first time these constitutive laws have been applied to biopolymers. All the models are suitable for biopolymer constitutive modelling, showing promising results. The constitutive material parameters for all the models are reported in the paper.

The Authors of the paper “Effects of Curing on Photosensitive Resins in SLA Additive Manufacturing”