Implantable medical devices for tendon and ligament repair: a review of patents and commercial products.

INTRODUCTION: 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 and limitations. Implantable medical devices have gained more attention as an alternative approach. However, due to the many challenges of the inner body environment (limited available space, chemically aggressive environment, etc), the development of suitable devices is not exempt from practical and technical difficulties. AREAS COVERED: Here, implantable medical devices for tendon and ligaments injuries are reviewed and discussed. Commercially-available products and registered patents are all considered as long as they fit the standard definitions of 'implantable medical devices' (reported in the Introduction). The research was then narrowed down to five commercial products, deemed as the most representative of the whole market. Their effectiveness and performance are analysed, as well as the possible areas of improvement and development. EXPERT OPINION: Commercially available products present overall superior mechanical performances than suture techniques. Nevertheless, these latter ones might be still preferred for their wider range of customization. This aspect, and many others, could represent an area of improvement for implantable medical devices, to further explore their potential for tendon and ligament repair.

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® J750™ 3D Printer was used, combining the Agilus30™ 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' 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 ± 0.17 MPa), maximum strain (1.86 ± 0.05 mm/mm), and tensile strength at break (2.11 ± 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.

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-ε-caprolactone) Blend.

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.

3D printing and testing of rose thorns or limpet teeth inspired anchor device for tendon tissue repair.

PURPOSES: Advancements in medical technology have enabled medical specialists to resolve significant problems concerning tendon injuries. However, despite the latest improvements, surgical tendon repair remains challenging. This study aimed to explore the capabilities of the current state-of-the-art technologies for implantable devices. METHODS: After performing extensive patent landscaping and literature review, an anchored tissue fixation device was deemed the most suitable candidate. This design was firstly investigated numerically, realizing a Finite Element Model of the device anchored to two swine tendons stumps, to simulate its application on a severed tendon. Two different hook designs, both bio-inspired, were tested while retaining the same device geometry and anchoring strategy. Then, the applicability of a 3D-printed prototype was tested on swine tendons. Finally, the device-tendon stumps ensemble was subjected to uniaxial tensile tests. RESULTS: The results show that the investigated device enables a better load distribution during the immobilized limb period in comparison to standard suture-based approaches, yet it still presents several design flaws. CONCLUSIONS: The current implantable solutions do not ensure an optimal result in terms of strength recovery. This and other weak points of the currently available proposals will serve as a starting point for future works on bio-inspired implantable devices for tendon repair.