Boosting both the lightweight and rebound of a shoe's midsole without compromising its durability is regarded as a challenging aspect of developing excellent running shoes. This study explores the replacement of talc, a conventional reinforcing and nucleating agent for polymers, with multi-walled carbon nanotubes (MWCNTs) derived from plastics in the midsole foam of running shoes to enhance lightweight, rebound, and durability. Two types of MWCNTs, non-functionalized and oxygen-functionalized, derived from upcycling mixed plastics were processed with copolymer of ethyl-vinyl acetate (EVA) to create nanocomposite foams. The foam reinforced with non-functionalized MWCNTs exhibited higher dynamic stiffness and similar energy return to oxygen-functionalized MWCNTs. The running shoe prototypes with EVA midsole foam containing 0.5 wt% MWCNTs was 13 % lighter and returned more than 10 % higher energy than the conventional EVA midsole foam with mineral fillers. Additionally, the midsole foam produced from EVA/MWCNTs demonstrated greater flexibility, and durability after 500 km of dynamic impact cycles. The cost difference per pair of running shoe midsole is merely 0.08 USD, considering the exceptional performance of the EVA/MWCNTs midsole as compared to conventional mineral filled EVA midsole. These findings indicate the potential for commercializing EVA/MWCNTs nanocomposite foam as a viable option for high-performance running shoe midsoles, offering athletes improved running performance.

This study examines the effect of thermoplastic elastomers (TPE) on the physical, mechanical, and dynamic impact properties of ethylene-vinyl acetate (EVA) copolymer foam using traditional chemical blowing process. The blending of EVA with TPE aims to improve both physical and dynamic impact cushioning to achieve optimal energyreturn EVA foam. Comparative analysis reveals that adding a 10-20 wt% fraction of propylene elastomer (POE) to EVA significantly reduces foam density while maintaining dynamic energy absorption and energy return. However, high POE content (30 wt%) leads to inferior mechanical and dynamic impact properties due to excessive softness. Blending EVA with terpolymer elastomer (PTW) enhances compression strength (-16%), hardness (-27%), and dynamic energy return (-9%). EVA/POE/PTW hybrid blend foams display intermediate properties. The impact behaviors of foams vary between high and low dynamic impact loading rates. The presence of TPE enhances cushioning by absorbing impact forces through deformation, with EVA/PTW exhibiting remarkably improved rebound properties. Impact peak force decreases linearly with increasing PTW content. Foam morphology, including phase compatibility, cell size and density, plays a role in determining dynamic impact properties. Hard segmented TPE store more energy and quickly recover, resulting in a higher rebound effect as compared to soft segmented TPE. Incorporating TPE provides the ability to control the EVA foam's dynamic rebound, and impact cushioning, expanding its potential in sports-related applications.

Tissue engineering (TE) is a multidisciplinary field that combines engineering, chemistry and biology to create biological alternatives to restore, maintain, improve, or replace various tissue functions. Its applications include regenerative medicine, pharmaceuticals, diagnostics, and research. TE aims to produce a biomimetic environment by utilizing biomaterials, cells, and biological molecules. Traditional fabrication methods have limits, but additive manufacturing (AM), often known as 3D printing, allows for control over tissue architecture and biological environment. Bioprinting, a subtype of AM, uses cells as building materials. Cell supply, culture conditions, scaffold materials, and fabrication methods all play a role in successful application of AM in TE. This chapter explores two biofabrication approaches: AM-made scaffolds and bioprinted constructs, highlighting on the factors to be considered when applying the two approaches. Both approaches have their own distinct challenges, such as a limited range of available materials and low resolution. However, with collaborative research effort in the development of new materials, processes, and optimization of parameters, AM and bioprinting have immense potential for expanding their scope in tissue engineering.

Fused deposition modeling printing is a material extrusion (MEX) process that has gained popularity over the years due to its increased affordability and greater versatility. There is a wide variety of MEX printing technologies and a broad spectrum of materials that can be 3D printed, ranging from metallic to non-metallic materials. MEX has emerged as the most common technology in consumer-grade, desktop 3D printers for printing thermoplastics, such as acrylonitrile butadiene styrene (ABS) and polylactic acid. High-density polyethylene (HDPE) is a widely used thermoplastic material for product packaging. The sheer availability of recyclable or recycled HDPE (rHDPE) from used packaging has led to efforts to apply it in MEX printing. However, rHDPE presents challenges as a filament material, including issues such as part detachment from the print bed and high warpage. The focus of this study is to determine the optimal conditions that can mitigate, if not eliminate, the print bed adhesion problems associated with printing rHDPE filaments. This was achieved by conducting a series of tests to address these challenges, including part removability relating to the shear strength of print bed adhesion to identify the necessary range of print bed adhesion and corresponding parameters.

Current research investigates the manufacturing and bonding characteristics of wholly thermoplastic composites with thermoplastic fibres and acrylic Elium® resin and toughened Elium®IM with 10% weight acrylonitrile butadiene styrene (ABS) particles under Mode I loading. Ultra-high molecular weight polypropylene (UHMWPP)/Elium® IM and UHMWPP/Elium® composites have shown 43.9% and 24.5% higher critical energy release rate compared to epoxy composite systems, while a similar trend was observed in the case with composites with polyester as the reinforcement system. For ultra-high molecular weight polyethylene (UHMWPE)/Elium®, the increase was only 13.7% but with the use of toughened thermoplastic variant, the increase was found to be 36.8% higher. Detailed microscopic examination reported fibre bridging, pull-out, strong fibre–matrix adhesion, riverlines, and matrix deformation owing to the ductile characteristic of Elium® resin. ABS-modified Elium®IM composites have shown rough matrix fracture surface and there was internal cavitation of ABS particles followed by crack growth and local shear band formation.

The current research presents the details of the impact properties of novel all-thermoplastic composite structures with different thermoplastic fabrics like ultra-high molecular weight polyethylene (PE), ultra-high molecular weight polypropylene (PP), and Polyester (PES) with room temperature curable acrylic Elium (R) (EL) thermo-plastic resin. The low-velocity impact performance is studied at five energy levels (10J-50J), and the perfor-mance is compared to baseline epoxy (EP) composites, and their failure mechanisms are deduced through optical and SEM examination. PP/ELC, PE/ELC and PES/ELC all-thermoplastic composites have shown up to 34.68%, 24.46%, 15.35 % higher load carrying capability and 27%, 11.21%, 8.43% lower absorbed energy compared to PP/EPC, PE/EPC, and PES/EPC composites respectively due to the lesser damage and high toughness of the matrix. The major damage energy was found to be 10.55% higher due to the more elastic and plastic deformation mechanisms before the onset of the damage. PP/ELC, PE/ELC, and PES/ELC have shown 32%, 66.7% and 51% improvement in structural integrity as opposed to epoxy counterparts. ELC composites have shown matrix cracks, and strong fibre matrix adhesion with thermoplastic fibres properly embedded in the acrylic resin, while clean fibre pull-out and bare fibres were observed for EPC composites.

Polymer foam that provides good support with high energy return (low energy loss) is desirable for sport footwear to improve running performance. Ethylene-vinyl acetate copolymer (EVA) foam is commonly used in the midsole of running shoes. However, EVA foam exhibits low mechanical properties. Conventional mineral fillers are usually employed to improve EVA’s mechanical performance, but the energy return is sacrificed. Here, we produced nanocomposite foams from EVA and multi-walled carbon nanotubes (CNT) using a chemical foaming process. Two kinds of CNT derived from the upcycling of commodity plastics were prepared through a catalytic chemical vapor deposition process and used as reinforcing and nucleating agents. Our results show that EVA foam incorporated with oxygenated CNT (O-CNT) demonstrated a more pronounced improvement of physical, mechanical, and dynamic impact response properties than acid-purified CNT (A-CNT). When CNT with weight percentage as low as 0.5 wt% was added to the nanocomposites, the physical properties, abrasion resistance, compressive strength, dynamic stiffness, and rebound performance of the EVA foams were improved significantly. Unlike the conventional EVA formulation filled with talc mineral fillers, the incorporation of CNT does not compromise the energy return of the EVA foam. From the long-cycle dynamic fatigue test, the CNT/EVA foam displays greater properties retention as compared to the talc/EVA foam. This work demonstrates a good balanced of mechanical-energy return properties of EVA nanocomposite foam with very low CNT content, which presents promising opportunities for lightweight–high rebound midsoles for running shoes.

In the current research, the delamination behavior under Mode I and Mode II loading for the hybrid carbon-thermoplastic fabrics in conjunction with novel liquid thermoplastic acrylic Elium® resin processable at ambient conditions was studied. The experimentation by incorporating doublers methodology, studying the performance under Mode I and Mode II loading, and understanding failure mechanisms using surface morphological fractography is deliberated. Hybrid Carbon-Ultra-high molecular weight polyethylene (UHMWPP)/Elium® composite has shown a 22.81% higher GIC and a 22.2% higher GIIC than Carbon-UHMWPP/Epoxy composite. On the contrary, the Carbon_Ultra-high molecular weight polypropylene (UHMWPE)/Elium® has shown an 11.11% higher Mode I critical energy release rate (GIC) and a 7.58% higher Mode II critical energy release rate (GIIC) than Carbon_UHMWPE/Epoxy composite. Hybrid fiber reinforced thermoplastic composites have shown severe plastic deformation of the matrix, rough fracture surface, and micro-cracks on the de-bonding surface, extensive fiber bridging, and crack branching which contributed to the improvement in the delamination behavior. Hybrid fiber architecture is also found to be detrimental by inducing crack arresting mechanisms including the tortuous crack path and the resin-rich pockets path due to the mismatch of the size of the fiber yarns.

The joining of composites can be performed in an extremely short time with more energy-efficient ultrasonic welding techniques. The current research investigated the performance optimization of ultrasonic welding of carbon/Elium® composite to carbon/epoxy composite using a polymethyl methacrylate (PMMA) coupling interlayer. The weld strength was quantified by static lap shear strength (LSS) testing. A new methodology was used by creating a PMMA coupling layer on the epoxy composite adherend to achieve an improved interphase and thus enhance the weld properties. The LSS of Elium (EL)-Epoxy (EP) _0.25_0.25 was found to be 190% higher compared to that of EL-EP, confirming the effectiveness of the strategy used for creating an interlayer thermoplastic coupling layer. The time required for welding was optimized to be 2s as compared to 10 min required for adhesive bonding. Scanning electron microscopic images of epoxy and PMMA/Elium matrix interphase were observed to have a rough surface and remained largely unaffected by welding. There was an interphase change further away from the interphase to a rougher texture. There was little to no effect on the penultimate layer on the weld strength, as no interphase change could be observed after welding. Fractography investigation revealed shear cusps, matrix plastic deformation, fiber imprints, fiber pull-out, and good adhesion between matrix and fiber, features seen for configuration with maximum LSS. The current research findings present a way to join Elium® with epoxy composites that could be used in applications that require a selective strengthening, such as in sporting goods and consumer products. Furthermore, a detailed investigation is ongoing to use different filler particles and coupling layers to reach the maximum welding performance.

Ankle braces typically restrict the functional range of motion. Braces should preferably allow a free functional range of motion during sport while protecting the foot at high-risk positions beyond that range. This could be achieved with 3D printed metamaterial structures that could have varying properties throughout an individual's ankle range of motion. This paper aims to illustrate an exploratory methodology of using an affordable Fused Deposition Modelling 3D printing technology to develop an ankle brace using metamaterial structures. It also showcases the design, manufacturing processes and testing of 3D printed customised ankle brace prototype designs that incorporated metamaterial structures. Initial tests showed that as designed, the prototype braces maintained the full range of motion for plantar flexion angles. Results also showed that the prototypes required one of the lowest moments during functional range of motion while achieving almost twice to thrice the moment required beyond the functional range of motion.

In recent years, Additive Manufacturing (AM) has evolved into a “multi-x” era, such as multi-part design, multi-material, multi-process, multi-mode, multi-scale, multi-dimension, and multi-function. These emerging new features of AM present both tremendous opportunities and challenges for developing and regulating new and novel biomedical materials and devices. This paper focuses on two aspects, namely multi-material and multi-dimension AM. In multi-material 3D printing, the layering step is the key. Modifying the layering method yet without changing the solidifying or bonding principles governing the AM process can enable and significantly advance multi-material 3D printing. In multi-dimensional 3D printing, typically 4D printing and 5D printing, the meaning of “D” is suggested to refer to space–time dimension rather than the number of degrees of freedom in physical space. It is proposed in this paper that an alternative dimension (or 5D) for future 3D printing processes can be that of scale. Scale here refers the different levels of resolution that are used simultaneously within a print. In such a scale dimension, continuous printing of cross-scale or varied resolution design features in a single build process without affecting the overall printing speed and time would be highly desirable. This is probably the first paper reflecting on multi-material 3D printing from the perspective of layering and on multi-dimensional 3D printing with regard to its future development.

Current work presents the first investigation on the Mode II fracture toughness of room temperature curable acrylic Elium® resin and toughened Elium®IM with 10% weight acrylonitrile butadiene styrene (ABS) particle with different thermoplastic fabrics like Ultra-high molecular weight polyethylene (UHMWPE), Ultra-high molecular weight polypropylene (UHMWPP), and polyester. The testing methodology using doublers, performance under Mode II loading and understanding the failure and toughening mechanisms is deliberated. GIIC of UHMWPP/Elium®IM composite was found to be 33.3% higher than that of UHMWPP/Epoxy composite. Polyester/Elium® composites have 27.02% higher GIIC than Polyester/Epoxy composites while Polyester/Elium®IM composites exhibited the highest GIIC which was 17.76% higher than Polyester/Elium® composites. Fractography of toughened Elium®IM composites displayed significant resistance to crack propagation that generated a rough and shear deformed curved layer type of de-bonding surface due to the extra toughening provided by particles which generated the crack deflection and void resulting from cavitation of ABS particles.

Current research investigates the structural damping response of hollow tubular structures with novel acrylic liquid thermoplastic Elium (R) resin (EL) and thin ply carbon(TPC) and woven carbon(WC) as the reinforcement. The results are compared with the baseline tubes manufactured with conventional epoxy (EP) resin systems. The structural damping results have shown 26.7% higher structural damping for TPC/EL and 27.3% higher damping for WC/EL compared to TPC/EP and WC/EP tubular configuration respectively at all the accelerometer positions during the modal analysis tests. The viscoelastic presence in acrylic Elium (R) and its amorphous chemical structure as opposed to the cross-linked state in epoxy resin and good fibre matrix interfacial bonding is the major contributing factor towards this increase. Damping results have also shown that the thickness of the tube has a positive effect of the structural damping (1.6 mm as opposed to 1.1 mm) and on the contrary, an increase in the fibre volume fraction (64% as opposed to 41%) has an adverse effect on the damping phenomenon, 10% higher and 85% lower respectively.

Tubular composites are widely used in many industrial applications, and there is need to use new material and reliable manufacturing processes to improve the performance and process aspects. The current research presents a detailed study to understand the flexure response of rectangular tubular composites based on thin ply carbon fibres and Elium® resin. Another aim was to understand the failure mechanisms of novel tubular thermoplastic composite systems and carry out a baseline comparison with Epoxy-based tubular systems. In the current research, a bladder-assisted resin transfer moulding process was used to manufacture hollow thermoplastic composite tubes, and the bending behaviour of thin ply carbon (TPC) composite parts with novel Elium® (EL) and Epoxy (EP) resin as the matrix material was studied using a detailed experimental study. A testing method with optimized support span and a saddle was used to carry out three-point bending tests on the tubular composite structures. The TPC/EL composite tubes have shown 10% higher bending strength, with a noticeable increase in deformation due the presence of extended plasticity attributes for acrylic Elium resin. Failure mechanisms studied with the detailed microscopic investigation have shown severe catastrophic failure for epoxy-based composite tubes; however, acrylic Elium®-based composite tubes have shown different damage modes such as fibre splitting, resin infragmentation, and fibre resin-interfacial cracking.

Current methods to fabricate customized braces typically require a mold of the foot and often require casts to be pre-manufactured or milled from a solid block. This is time consuming and expensive. However, additive manufacturing opens opportunities for mass customization. Selected regions of customized protection or varying properties for the joint range of motion for braces is also possible with 3D printing solutions. This study explored the use of additive manufacturing for the mass customization of braces, using the ankle brace as an illustration. This paper showcases the methodology of using a glass scanner to obtain individual biomechanics data; incorporating personalized data in a pre-designed brace template; designing mass customized braces using Rhinoceros 6 Grasshopper; and manufacturing of the ankle brace using fused deposition modelling. Initial tests on the dynamometer showed that maximum ankle inversion angle was reduced by almost a third, as compared to barefoot conditions. This potentially will significantly reduce ankle lateral sprain injury risks at ankle inversion positions especially beyond functional range of motion and successfully demonstrated the possibility of using 3D printing solutions for similar mass customized applications.