Optimization of a Patient-Specific External Fixation Device for Lower Limb Injuries

From MDPI via Jisc Publications RouterHistory: accepted 2021-08-02, pub-electronic 2021-08-10Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; Grant(s): EP/R01513/1Funder: King Saud University; Grant(s): RSP-2021/299The use of external fixation devices is considered a valuable approach for the treatment of bone fractures, providing proper alignment to fractured fragments and maintaining fracture stability during the healing process. The need for external fixation devices has increased due to an aging population and increased trauma incidents. The design and fabrication of external fixations are major challenges since the shape and size of the defect vary, as well as the geometry of the human limb. This requires fully personalized external fixators to improve its fit and functionality. This paper presents a methodology to design personalized lightweight external fixator devices for additive manufacturing. This methodology comprises data acquisition, Computer tomography (CT) imaging analysis and processing, Computer Aided Design (CAD) modelling and two methods (imposed predefined patterns and topology optimization) to reduce the weight of the device. Finite element analysis with full factorial design of experiments were used to determine the optimal combination of designs (topology optimization and predefined patterns), materials (polylactic acid, acrylonitrile butadiene styrene, and polyamide) and thickness (3, 4, 5 and 6 mm) to maximize the strength and stiffness of the fixator, while minimizing its weight. The optimal parameters were found to correspond to an external fixator device optimized by topology optimization, made in polylactic acid with 4 mm thickness

Mechanical, biological and tribological behaviour of fixation plates 3D printed by electron beam and selective laser melting

From Springer Nature via Jisc Publications RouterHistory: received 2019-10-30, accepted 2020-06-22, registration 2020-06-22, pub-print 2020-07, pub-electronic 2020-07-06, online 2020-07-06Publication status: PublishedFunder: University of ManchesterAbstract: Commercially available fixation plates are built using metallic biocompatible materials such as titanium and its alloys and stainless steel. However, these plates show a stiffness mismatch comparing to bone, leading to stress shielding and bone loss. In this paper, we investigate the combined use of topology optimisation and additive manufacturing to print fixation plates with reduced stiffness and improved biological performance. Ti-6Al-4 V plates were topology optimised considering different loading conditions and volume reductions and printed using electron beam melting and selective laser melting. The effect of processing conditions on the mechanical properties, microhardness, wear resistance and surface roughness was analysed. Results show acceptable wear resistance values for a medical device and a reduction of stress shielding by increasing volume reduction. It is also shown that no polishing is required as 3D printed plates are able to support cell attachment and proliferation. In comparison to commercial plates, 3D printed ones show significantly better biological performance. For the same design, SLM plates present higher mechanical properties, while EBM plates present better cell attachment and proliferation

Topology optimization of metallic locking compression plates produced using electron beam melting

Bone fixation plates currently used to treat traumatic fractured bones and to promote fracture healing are built with metallic materials such as stainless steel, cobalt and titanium and its alloys (e.g. CoCrMo and Ti6Al4V). However, due to significant differences between the mechanical properties of these plates and native bone, stress shielding problems causing bone loss lead to deficient orthopedic treatment. This paper describes the use of Topology Optimization and Electron Beam Melting to redesign and fabricate novel plates based on a commercial standard one, minimizing the stress shielding phenomenon, by considering a compliance minimization approach, different mechanical loading conditions (tension and torsion) and volume reduction (25-75%). The optimized plates, present reduced stiffness due to the optimal distribution of material, maintaining their structural integrity. The optimized plates fabricated using additive manufacturing showed adequate shapes and proved the possibility of fabricating designs developed using topology optimization.Published versio

Structural optimisation for medical implants through additive manufacturing

Advanced manufacturing techniques are being explored to fabricate degradable and non-degradable, porous or non-porous implants for medical applications. These implants have been designed using standard computer-aided design (CAD) and computer-aided engineering (CAE) tools and produced in a multitude of materials. The recent use of optimisation tech niques, mainly topology optimisation, allows the development of additive manufactured medical devices with improved performance. This review discusses the combined use of optimisation techniques and additive manufacturing to produce biocompatible and biodegradable scafolds for tissue engineering with improved mechanical and permeability properties; metallic lattice structures with reduced weight and minimal stress shielding efect; and lightweight personalised orthopae dic implants. Three optimisation routes are considered: topology optimisation; triply periodic minimal surfaces that can be manipulated by means of the equations parameters to optimise the overall performance; and the use of repetitive structures that are optimised as unit cells under certain conditions to compose a bulk object. Major limitations and research challenges are highlighted and discussed.info:eu-repo/semantics/publishedVersio

Optimization of a Patient-Specific External Fixation Device for Lower Limb Injuries

The use of external fixation devices is considered a valuable approach for the treatment of bone fractures, providing proper alignment to fractured fragments and maintaining fracture stability during the healing process. The need for external fixation devices has increased due to an aging population and increased trauma incidents. The design and fabrication of external fixations are major challenges since the shape and size of the defect vary, as well as the geometry of the human limb. This requires fully personalized external fixators to improve its fit and functionality. This paper presents a methodology to design personalized lightweight external fixator devices for additive manufacturing. This methodology comprises data acquisition, Computer tomography (CT) imaging analysis and processing, Computer Aided Design (CAD) modelling and two methods (imposed predefined patterns and topology optimization) to reduce the weight of the device. Finite element analysis with full factorial design of experiments were used to determine the optimal combination of designs (topology optimization and predefined patterns), materials (polylactic acid, acrylonitrile butadiene styrene, and polyamide) and thickness (3, 4, 5 and 6 mm) to maximize the strength and stiffness of the fixator, while minimizing its weight. The optimal parameters were found to correspond to an external fixator device optimized by topology optimization, made in polylactic acid with 4 mm thickness

Material Extrusion of Multi-Polymer Structures Utilizing Design and Shrinkage Behaviors: A Design of Experiment Study

Material extrusion (ME) is an additive manufacturing technique capable of producing functional parts, and its use in multi-material fabrication requires further exploration and expansion. The effectiveness of material bonding is one of the main challenges in multi-material fabrication using ME due to its processing capabilities. Various procedures for improving the adherence of multi-material ME parts have been explored, such as the use of adhesives or the post-processing of parts. In this study, different processing conditions and designs were investigated with the aim of optimizing polylactic acid (PLA) and acrylonitrile–butadiene–styrene (ABS) composite parts without the need for pre- or post-processing procedures. The PLA-ABS composite parts were characterized based on their mechanical properties (bonding modulus, compression modulus, and strength), surface roughness (Ra, Rku, Rsk, and Rz), and normalized shrinkage. All process parameters were statistically significant except for the layer composition parameter in terms of Rsk. The results show that it is possible to create a composite structure with good mechanical properties and acceptable surface roughness values without the need for costly post-processing procedures. Furthermore, the normalized shrinkage and the bonding modulus were correlated, indicating the ability to utilize shrinkage in 3D printing to improve material bonding

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population