Prosthetic Socket Research Articles

Finite Element Analysis of Custom Designed and Additive Manufactured Total Surface Bearing Prosthesis for Trans-Tibial Amputees

Our limb prostheses aim to restore Activities of Daily Living (ADLs) for amputees, with the socket being a critical component of trans-tibial prostheses influencing both comfort and functionality. Despite technological advancements, challenges such as fit, weight, and durability remain. This study investigates an additive manufacturing method for Total Surface Bearing (TSB) sockets, leveraging CT scans to create a Computer-Aided Design (CAD) and finite element (FE) model. Biomechanical behavior under static loading conditions were analyzed using FE analysis and resistive-based pressure sensors. The study found consistent pressure distribution across the residual limb, with deviations of 8.53 kPa and 4.46 kPa between FE analysis and experimental measurements. Mean pressures of 44.6 kPa and 22.11 kPa were observed under Full Body Weight (FBW) and Half Body Weight (HBW) conditions, respectively. The FE analysis demonstrated a uniform stress distribution in the prosthetic socket, with a maximum stress of 0.15 MPa and a deformation of 0.008 mm, highlighting the effectiveness of this approach in enhancing socket design.

The Influence of Architecture on the Tensile and Flexural Properties of Single-Polymer Composites

This study investigates the tensile and flexural properties of self-reinforced polylactic acid (SrPLA) and poly(ethylene terephthalate) (SrPET) for prosthetic socket applications. These self-reinforced polymer (srP) composites utilize both a matrix and reinforcement made from the same material, resulting in an optimal matrix–interface bond that significantly enhances mechanical properties compared to traditional bulk polymers and composites. Prosthetic sockets serve as a critical interface between an amputee’s residuum and the prosthetic components, such as pylons and feet. Conventional socket materials, including monolithic high-density polyethylene and polypropylene, as well as advanced fillers reinforced with thermoset resins, often fall short in strength or affordability, particularly for amputees in low- to middle-income countries. In this study, we employed srP composites with various architectural stitch densities, aiming to achieve superior material properties. The results demonstrate that these materials exhibit higher strength and strain capabilities than many existing prosthetic materials. Notably, the low-density srPET composites achieved a tensile strength of 85.11 MPa and a strain of 19.7%, while high-density srPLA exhibited a failure strength of 36.65 MPa and a strain of 1.4%. Additionally, our findings reveal that the stiffness of both srPLA and srPET increases as the density of the reinforcement decreases. Overall, this study suggests that srP composites represent a viable and sustainable alternative for the manufacturing of prosthetic sockets, offering both enhanced performance and cost-effectiveness.

Development of a silicone rubber nanocomposite for prosthetic socket liners with enhanced mechanical and antibacterial properties

Development of a silicone rubber nanocomposite for prosthetic socket liners with enhanced mechanical and antibacterial properties

Skin adaptation in lower limb amputees assessed through Raman spectroscopy and mechanical characterization.

Following lower limb amputation residuum skin from the lower leg is used to reconstruct the residual limb. Unlike skin on the sole of the foot (plantar skin), leg skin is not inherently load bearing. Despite this, leg skin is required to be load bearing in the prosthetic socket. Current hypotheses propose that lower limb amputee skin can adapt to become load bearing with repeated prosthesis use. Here, we show using confocal Raman spectroscopy, mechanical characterization and cytokine analysis that adaptations occur which actually result in impaired barrier function, higher baseline inflammation, increased coefficient of friction and reduced stiffness. Our results demonstrate that repeated frictional trauma does not confer beneficial adaptations in amputee skin. We hypothesize that non-plantar skin lacks the biological capabilities to respond positively to repeated mechanical trauma in the same manner observed in plantar skin. This finding highlights the need for improved therapies as opposed to current mechanical conditioning or product solutions that directly relate to improving load-bearing capacity on the skin of lower limb amputees. This study also highlights the importance of measuring multiple parameters of application-specific skin at different scales for skin tribology applications.

Design of semi-open prosthetic socket with constant force for lower limb.

Prosthetic socket is a key component of the prosthesis for clinical application; its performance directly affects the adaptation of the residual limb to the prosthetic socket. There are long-term and short-term volume fluctuation of the residual limb. The volume fluctuation of the residual limb will lead to the pressure mismatch at the interface of the residual limb and the prosthetic socket, which will cause a series of skin and fit problems. The volume fluctuation of the residual limb is considered a key factor for the successful application of the prosthetic socket; its solution is imminent. The purpose of this paper is to design a prosthetic socket with a constant force unit to solve the problem of volume fluctuation of the residual limb. Constant force extrusion for the residual limb is proposed to solve the problem in this paper. A constant force unit is designed based on the superelasticity of shape memory alloy, and a semi-open prosthetic socket embedded in the constant force unit is designed. The constant force property of prosthetic socket is optimized and verified by finite element analysis. The constant force unit obtains a maximum constant force region of 9.36 mm at 13 mm applied displacement, and the minimum stress amplitude is 0.0264%. The semi-open prosthetic socket may achieve constant pressure at the interface between the residual limb and prosthetic socket within a certain range of the residual limb volume change, and it has a lightweight, good heat dissipation, size adjustability, and constant interface pressure.

"A good socket fit can make you or break you": A multimethod study to explore the perceptions and experiences of socket fitting among people with lower-limb loss in Australia.

Iterative design and modification are used to manufacture lower limb prosthetic sockets that meet users' needs while also fulfilling safety and mobility criteria. Greater understanding of the expectations of prosthesis users regarding prosthetic fit as well as their experiences at the time of socket fitting is needed. Describe lower limb prosthesis user perceptions and experiences of socket comfort and discomfort during their last fitting and compare this to their expectations for a perfectly fitting socket and their satisfaction with the socket they had fitted. Mixed methods (quantitative and qualitative). A questionnaire was designed and administered in consultation with Amputees NSW (an amputee advocacy group) and distributed through their membership database. Qualitative responses were analyzed to explore prosthesis user experiences of socket fitting, general wear, as well as socket comfort, discomfort, and satisfaction. Quantitative responses were analyzed using descriptive, nonparametric methods. Thirty participants with a range of lived experiences completed the questionnaire. Reported comfort and discomfort varied across participants and indicated that expectations and experiences of fit varied and changed over time, with some participants anticipating adjustment over time would be necessary. Qualitative analysis found experiences of prosthesis socket comfort/discomfort on the day of fitting and general experiences of socket comfort related to 2 key factors-the prosthesis itself and the individual prosthesis user. Understanding the experiences and expectations of prosthesis users for comfort and intended activities is central to ensure success of the socket fitting approach. Investigation into fit changes over time could provide insights into follow-up requirements, user education, and funding mechanisms.

3D printing prostheses using additive manufacturing and regenerative engineering

Additive manufacturing is a manufacturing process utilized to make prosthetics. It offers an affordable means to create custom-made prostheses. Yet, the number of studies exploring the domain of 3D printing and bioprinting of prosthetics remains limited. In this paper, we provide a comprehensive review of the current research in additive manufacturing to produce prosthetic limbs, bionic eyes, temporomandibular joints (TMJ), cardiac valves, and skin. We concluded that the research gap lies in the long-term, periodic assessment of 3D-printed prosthetic limbs for durability. 3D-printed prosthetic sockets’ reinforcement materials are a particularly underexplored topic and the main shortcoming of 3D-printed prostheses is their failure under shear stresses. In bioprinting, research must focus on developing tissue-specific bioinks and hydrogels to overcome their existing scarcity. Bioprinting techniques like extrusion, inkjet, and laser-assisted bioprinting subject bioinks to conditions of high temperature and pressure. Bioinks must withstand the printing process and simultaneously retain their rheological properties and cell viability. Moreover, some bioprinting techniques are still quite expensive. However, 3D printing and bioprinting offer the prospect of customization to the patient’s unique anatomy, increasing the wear time of prostheses and offering unique benefits like improved tissue regeneration and adaptability to changing patient anatomy. 3D printing specifically reduces costs, and production time and improves accessibility in war-stricken areas with more amputees.

3D printing prostheses using additive manufacturing and regenerative engineering

Additive manufacturing is a manufacturing process utilized to make prosthetics. It offers an affordable means to create custom-made prostheses. Yet, the number of studies exploring the domain of 3D printing and bioprinting of prosthetics remains limited. In this paper, we provide a comprehensive review of the current research in additive manufacturing to produce prosthetic limbs, bionic eyes, temporomandibular joints (TMJ), cardiac valves, and skin. We concluded that the research gap lies in the long-term, periodic assessment of 3D-printed prosthetic limbs for durability. 3D-printed prosthetic sockets’ reinforcement materials are a particularly underexplored topic and the main shortcoming of 3D-printed prostheses is their failure under shear stresses. In bioprinting, research must focus on developing tissue-specific bioinks and hydrogels to overcome their existing scarcity. Bioprinting techniques like extrusion, inkjet, and laser-assisted bioprinting subject bioinks to conditions of high temperature and pressure. Bioinks must withstand the printing process and simultaneously retain their rheological properties and cell viability. Moreover, some bioprinting techniques are still quite expensive. However, 3D printing and bioprinting offer the prospect of customization to the patient’s unique anatomy, increasing the wear time of prostheses and offering unique benefits like improved tissue regeneration and adaptability to changing patient anatomy. 3D printing specifically reduces costs, and production time and improves accessibility in war-stricken areas with more amputees.

Replication of clinical prosthetic sockets for research purposes.

For research in the field of prosthetics to be representative of clinical realities, studies require inclusion of clinical standard prosthetic sockets. This necessitates involvement of a prosthetist (clinical professional) in any study, which is to truly explore the effectiveness of existing or novel prosthetic technologies. Unfortunately, there is a global shortage of prosthetists. With many technological advances in upper-limb prosthetics coming from engineering focused labs, it is unsurprising that studies are frequently conducted with anatomically intact individuals. In this paper, we present a method to clone the shape of a clinical standard prosthetic socket for research purposes. The technique uses silicone to capture the socket shape; this is then converted into a plaster mold, which can be used to manufacture an identically shaped socket using standard clinical manufacturing techniques. The whole process can be achieved without the involvement of a prosthetist. To validate the proposed technique, molds from an original socket and socket clone were 3D scanned. The distance between the aligned meshes were measured using CloudCompare software. The mean distance between the points on the 2 meshes was 0.16 mm (standard deviation 0.38 mm). This proof-of-concept study demonstrates that the proposed new approach to cloning a clinical standard prosthetic socket is feasible and accurate. This technique will facilitate improvements in the assessment of prosthetic technologies. The process is nondestructive, thus also opening opportunities for socket design and electrode placement research with the removal of confounding factors relating to socket shape.

Self-Reinforced Composite Materials: Frictional Analysis and Its Implications for Prosthetic Socket Design.

Friction and wear characteristics play a critical role in the functionality and durability of prosthetic sockets, which are essential components in lower-limb prostheses. Traditionally, these sockets are manufactured from bulk polymers or composite materials reinforced with advanced carbon, glass, and Kevlar fibres. However, issues of accessibility, affordability, and sustainability remain, particularly in less-resourced regions. This study investigates the potential of self-reinforced polymer composites (SRPCs), including poly-lactic acid (PLA), polyethylene terephthalate (PET), glass fibre (GF), and carbon fibre (CF), as sustainable alternatives for socket manufacturing. The tribological behaviour of these self-reinforced polymers (SrPs) was evaluated through experimental friction tests, comparing their performance to commonly used materials like high-density polyethylene (HDPE) and polypropylene (PP). Under varying loads and rotational speeds, HDPE and PP exhibited lower coefficients of friction (COF) compared to SrPLA, SrPET, SrGF, and SrCF. SrPLA recorded the highest average COF of 0.45 at 5 N and 240 rpm, while SrPET demonstrated the lowest COF of 0.15 under the same conditions. Microscopic analysis revealed significant variations in wear depth, with SrPLA showing the most profound wear, followed by SrCF, SrGF, and SrPET. In all cases, debris from the reinforcement adhered to the steel ball surface, influencing the COF. While these findings are based on friction tests against steel, they provide valuable insights into the durability and wear resistance of SRPCs, a crucial consideration for socket applications. This study highlights the importance of tribological analysis for optimising prosthetic socket design, contributing to enhanced functionality and comfort for amputees. Further research, including friction testing with skin-contact scenarios, is necessary to fully understand the implications of these materials in real-world prosthetic applications.

Design of a custom metamaterial insert for improved pressure distribution within transtibial prosthetic sockets.

Uneven pressure distribution within a transtibial prosthetic socket can lead to discomfort, skin degradation, and suspended prosthesis use. Current custom interfaces to improve pressure distribution are often costly, time-intensive to fabricate, or cannot be incorporated into standard socket fabrication methods. In this technical note, we describe the design and preliminary clinical evaluation of a novel transtibial prosthetic socket insert with modifiable mechanical properties, which can be incorporated into the current clinical cycle of care. The custom insert (termed "inlay") relies on a triangular unit cell, which can be modified based on the desired stiffness profile. Inserts are 3D printed in a soft polymer material and inset into shape-matched voids in a socket creating regions of custom offloading. Preliminary clinical efficacy of the inserts was assessed in a pilot long-term cross-over evaluation. After Institutional Review Board approval, 3 pilot participants wore a shape-matched replica of their habitual socket modified for insert use and a shape-matched socket without. Sockets were worn for 4-week each, and inner socket pressures were measured with thin film pressure sensors at the end of the wear period. Peak pressures within the distal tibial region of interest were decreased for 2 of 3 participants during midstance of level-ground walking when wearing the socket with inlays. The technical methods and results presented provide a new method to address high pressure regions within a transtibial prosthetic socket. The 3D-printed inlays can be rapidly produced allowing for easy modification and replacement without require new socket fabrication.

Design for Disability: Prosthetic BK Socket's Manufacturing with New Digital Methodology

Design for Disability: Prosthetic BK Socket's Manufacturing with New Digital Methodology

Fabrication of a flexible inner prosthetic socket via the FGM technique

Purpose The purpose of this study was to fabricate a flexible inner socket with enhanced stiffness and hardness distribution by using the functional gradient method (FGM). The FGM technique can improve the comfort and flexibility of amputees through the use of a socket that is built via the direct method. Design/methodology/approach Six flexible inner socket samples were fabricated with varying weight fractions of rice husk ash-to-silicone rubber. The tensile strength and hardness of each sample were assessed. Then, numerical analyses were conducted using SOLIDWORKS software to evaluate the pressure distribution on the inner and outer layers of the flexible socket. Findings The hardness and stiffness of the fabricated flexible inner socket gradually increased with the weight ratio of rice husk ash-to-silicone rubber, so when it was in contact with the skin, it approximated the stiffness and hardness of the skin to ensure comfort, and when reaching a higher value in the socket contact layer, it prevented penetration through the flexible inner socket. In addition, the pressure distribution at the external layer of the flexible inner socket has improved. Research limitations/implications A budget of US$500 limited the research to create a flexible inner socket that keeps the socket from penetrating the skin. Practical implications The FGM technique created a flexible inner socket that balances hardness and stiffness to ensure comfort and prevent wounds for its users, lower limb amputees. The commercial value resides in the accessibility of a secure and comfortable flexible inner socket for amputees worldwide, enabling them to overcome the issue of excessive stiffness typically associated with sockets made using the direct method. Originality/value This study introduces the use of FGM to fabricate a flexible inner prosthetic socket with enhanced stiffness and hardness distribution. The approach of using varying weight fractions of rice husk ash-to-silicone rubber to improve the comfort and flexibility of prosthetic sockets is a novel contribution to the field. Given the high stiffness of flexible internal sockets and their ability to maintain flexibility in the part in contact with the skin, such sockets manufactured using this method prevent pain and skin ulcers that previously occurred when sockets are manufactured via the direct method.

A New Socket Prototype Design with a Heat-Exchanging Metal Layer for Individuals with Below-knee Amputation.

Individuals who have undergone lower limb amputation often struggle with excessive heat and sweating in their prosthetic sockets. This is due to the closed environment of the socket, which disrupts the body's natural cooling mechanisms and can lead to increased skin temperature, sweating, and various skin problems. This study aimed to develop a new socket to alleviate heat buildup in those with below-knee amputation. A positive residual limb model of a below-knee amputee was used to create a new socket made of copper metal through electroforming. A cooling system was programmed so that if the temperature exceeded a predetermined threshold, the system would be activated to prevent further temperature increase. The participant wore the conventional and new socket with the cooling system, and his residual limb skin temperature was monitored using a temperature data logger. Implementing the new socket led to a significant 5°C to 6°C reduction in temperature within the socket, greatly enhancing thermal comfort and reducing heat sensation for the users. By incorporating the new socket and cooling system, substantial reductions in heat accumulation within the prosthetic socket can be achieved.

A novel approach for improving material stiffness using a direct method in below-knee prosthetic sockets

The conventional techniques for producing a socket are time-consuming disproportionate to the significant population afflicted by limb amputations. Although the new manufacturing direct method, the modular socket system (MSS) method, involves reduced labor time, the technique produces sockets with high stiffness that cause discomfort for those with lower limb amputations during walking. This study investigated the tensile characteristics of numerous materials in below-knee prosthetic sockets. Initially, a vacuum molding approach was used to produce the sockets, which involved various polymers and composite materials to improve the prosthesis socket properties. An F-socket device was also employed to ensure efficient production and optimized pressure distribution at the interface between the socket and the residual limb. A SOLIDWORKS® software was then applied to determine the numerical analysis (stress distribution and the maximum internal pressure). The samples from Group E involved utilizing a novel mixture compared to the direct and traditional methods of various materials. This study presents a novel prosthetic limb socket made from a mixture of four carbon fiber layers, utilizing 20% polyurethane resin and 80% acrylic as the matrix. The resulting material demonstrated acceptable stiffness, extended socket life, and reduced curing time. During the patient's gait cycle, peak pressure of 300 KPa was recorded using the F-socket, while SOLIDWORKS® software indicated an internal pressure of 343 KPa, aligning closely with F-socket measurements. The new direct-fit socket design prioritizes comfort and flexibility using materials with reduced stiffness.

Innovations in Additive Manufacturing for Socket Fabrication: An Overview

Additive Manufacturing (AM) has transformed the prosthetics industry, particularly in socket production, which plays a critical role in the comfort, fit, and functionality of prosthetic limbs. This article examines the latest advancements in AM technologies and their applications in socket fabrication. Key techniques like stereolithography (SLA), selective laser sintering (SLS), and fused deposition modeling (FDM) have facilitated the production of highly personalized, lightweight, and durable prosthetic sockets. These methods not only improve design precision but also allow for the use of biocompatible, flexible materials, enhancing both comfort and functionality. Digital design tools have streamlined the production process, reducing lead times and costs, while improving accuracy and repeatability in socket manufacturing. This review explores the current state of AM in prosthetic socket development, emphasizing the benefits, challenges, and future directions of this fast-evolving field. By analyzing recent research and case studies, the article provides insights into how AM is reshaping prosthetics, offering more accessible solutions for individuals needing prosthetic limbs. It also discusses the challenges of material selection, regulatory considerations, and the potential for scaling production for broader use.

Comparative biomechanical analysis of a conventional/novel hip prosthetic socket.

The aim of this study was to investigate and compare the biomechanical properties of the conventional and novel hip prosthetic socket by using the finite element and gait analysis. According to the CT scan model of the subject's residual limb, the bones, soft tissues, and the socket model were reconstructed in three dimensions by using inverse modeling. The distribution of normal and shear stresses at the residual limb-socket interface under the standing condition was investigated using the finite element method and verified by designing a pressure acquisition module system. The gait experiment compared and analyzed the conventional and novel sockets. The results show that the simulation results are consistent with the experimental data. The novel socket exhibited superior stress performance and gait outcomes compared to the conventional design. Our findings provide a research basis for evaluating the comfort of the hip prosthetic socket, optimizing and designing the structure of the socket of the hip.

AI-Driven Precision: Transforming Below-Knee Amputation Care in Modern Healthcare

Recently, three-dimensional models 3DM in the prosthetics field gained popularity, especially in the context of residual limb shape creation resulting from collecting medical images in Digital Imaging and Communications in Medicine DICOM format from a magnetic resonance imaging MRI after image processing accurately. In this study, a three-dimensional model of the residual limb for a patient with transtibial amputation was realized with the integration of artificial intelligence and a computer vision approach demonstrating the benefits of AI segmentation tools and artificial algorithms to generate higher accuracy three-dimensional model before prosthetic socket design or in case of comparison the 3D model generated from MRI with another 3D model generated from another technique, where a residual limb of a 23 years old male patient with amputation in the left leg wearing a prosthetic socket liner, and having 62 kg weight, 168 cm height, with high activity level. The patient was scanned using GE Medical Systems, 1,5 Tesla Signa Excite. MRI images in DICOM format were read to retrieve essential metadata such as pixel spacing and slice thickness. These images were processed to obtain a model that reflects the real shape of the residual limb using a specific algorithm, and the 3D model was extracted using AI segmentation tools. The obtained 3D model result with high resolution proves the potential of the artificial intelligence approach with deep learning to reconstruct 3D models concluding that AI has an instrumental role in medical image analysis, particularly in the areas of organ and tissue classification and segmentation., thus generating automatic and repetitive a 3D model.

The effect of nanocellulose and silica filler on the mechanical properties of natural fiber polymer matrix composites

Natural fiber-reinforced polymer matrix composites recently got great attention in biomedical applications due to their inherent characteristics such as biocompatibility, lightweight, and biodegradability. However, natural fiber composites suffer from poor mechanical properties and weak interfacial adhesion. It is well documented that the addition of nanofiller has improved the mechanical properties of different synthetic fibers such as glass and carbon composites. The main objective of this paper is to study nanofillers' effect on the mechanical properties of unidirectional false banana fibers reinforced polymer composites. The filler materials, crystalline nanocellulose fibrils, and crystalline nanosilica particles were extracted from sugarcane bagasse and its byproducts. The composite samples were fabricated by adding the nanofillers in unidirectional natural fibers arranged in four fiber orientations (0°, 0o/90o ±45o, and quasi-isotropic), and their tensile, flexural, compression strength, thermal stability, and void content were measured following ASTM standards. The results revealed that adding nanofillers increased the tensile, flexural, and compressive strengths by 16 % (98.83 Mpa), 11 % (161.60 Mpa), and 23 % (114.62 Mpa), respectively. Similarly, at 0° orientation, the addition of nanoparticles enhances the tensile, bending, and compressive modulus by 30 % (15.43 Gpa), 12 % (13.52 Gpa), and 60 % (42.6 Gpa), respectively. On the other hand, the void content was reduced with the addition of nanofillers. The results also revealed that composites with crystalline nanosilica particle fillers had superior thermal stability compared to crystalline nanocellulose fibril fillers. The overall results of this research give the confidence that nano particle-filled natural fiber composites can be used for bio-based engineering applications, such as prosthetic sockets.

Restoration of grasping in an upper limb amputee using the myokinetic prosthesis with implanted magnets.

The loss of a hand disrupts the sophisticated neural pathways between the brain and the hand, severely affecting the level of independence of the patient and the ability to carry out daily work and social activities. Recent years have witnessed a rapid evolution of surgical techniques and technologies aimed at restoring dexterous motor functions akin to those of the human hand through bionic solutions, mainly relying on probing of electrical signals from the residual nerves and muscles. Here, we report the clinical implementation of an interface aimed at achieving this goal by exploiting muscle deformation, sensed through passive magnetic implants: the myokinetic interface. One participant with a transradial amputation received an implantation of six permanent magnets in three muscles of the residual limb. A truly self-contained myokinetic prosthetic arm embedding all hardware components and the battery within the prosthetic socket was developed. By retrieving muscle deformation caused by voluntary contraction through magnet localization, we were able to control in real time a dexterous robotic hand following both a direct control strategy and a pattern recognition approach. In just 6 weeks, the participant successfully completed a series of functional tests, achieving scores similar to those achieved when using myoelectric controllers, a standard-of-care solution, with comparable physical and mental workloads. This experience raised conceptual and technical limits of the interface, which nevertheless pave the way for further investigations in a partially unexplored field. This study also demonstrates a viable possibility for intuitively interfacing humans with robotic technologies.