Polylactic acid (PLA) is a biodegradable polyester polymer that is produced from renewable resources, such as corn or other carbohydrate sources. However, its poor toughness limits its commercialization. PLA composites can meet the growing performance needs of various fields, but limited research has focused on their sustainable applications in sports. This paper reviews the latest research on PLA and its composites by describing the characteristics, production, degradation process, and the latest modification methods of PLA. Then, it discusses the inherent advantages of PLA composites and expounds on different biodegradable materials and their relationship with the properties of PLA composites. Finally, the importance and application prospects of PLA composites in the field of sports are emphasized. Although PLA composites mixed with natural biomass materials have not been mass produced, they are expected to be sustainable materials used in various industries because of their simple process, nontoxicity, biodegradability, and low cost.

Driven by various environmental and economic factors, it is emerging to adopt an efficient and sustainable strategy to recycle carbon fibers (rCFs) from carbon fiber-reinforced polymer (CFRP) wastes and reuse them in high-value applications. This review summarized the latest progress of CFRP waste recycling methods (including mechanical, chemical, and thermal methods), discussed their advantages and disadvantages, influence parameters and possible environmental effects, and their potential effects on the mechanical and surface chemical properties of rCFs. In addition, the latest optimization schemes of leading recycling technologies were detailed. According to the literature, CFs are the key points in the structural support of semiconductor-based recyclable photocatalytic systems and the enhancement of performance, which means that rCFs have high reuse potential in sustainable photocatalysis. Therefore, this paper also emphasized the possibility and potential value of reusing recovered fibers for developing recyclable photocatalytic products, which may be a new way of reuse in environmental purification often ignored by researchers and decision-makers in the field of CFs.

Conductive hydrogels demonstrate substantial potential for flexible wearable sensors in motion monitoring, owing to their unique physicochemical properties; however, current implementations still confront persistent challenges in long-term stability, sensitivity, response speed, and detection limits under complex dynamic conditions, which material innovations are urgently required to resolve. Consequently, this paper comprehensively reviews the recent advancements in conductive hydrogel-based flexible wearable sensors for sports applications. The paper examines the conductivity, self-adhesion, self-repair, and biocompatibility of conductive hydrogels, along with detailed analyses of their working principles in resistance, capacitance, piezoelectric, and battery-based sensing mechanisms. Additionally, the paper summarizes innovative strategies to enhance sensor performance through polymer blending, polyelectrolyte doping, inorganic salt doping, and nanomaterial integration. Furthermore, the paper highlights the latest applications of conductive hydrogel flexible wearable sensors in human motion monitoring, electrophysiological signal detection, and electrochemical biosignal monitoring. Finally, the paper provides an in-depth discussion of the advantages and limitations of existing technologies, offering valuable insights and new perspectives for future research directions.

The application of hydrogels in flexible sensing has received increasing attention, but the simultaneous preparation of hydrogels with good structural stability, strain sensing sensitivity, freezing resistance, and drying resistance remains a challenge. Based on this, a GG-nanocellulose/sodium alginate/polyacrylamide composite hydrogel with a hierarchical network structure was constructed by one-step synthesis by incorporating graphene oxide (GO) and glycerol into the hydrogel. The hydrogel remained structurally intact after 100 compression cycles. In addition, the hydrogel was dried at 30 °C for 24 h. The mass retention rate was 48%, the melting peak was as low as −13.87 °C, and the hydrogel remained flexible and stable at low temperatures. GO modulated the network structure arrangement of the hydrogel through various mechanisms, thereby conferring to the hydrogel an excellent sensing performance, with a sensitivity (GF) of 2.21. In conclusion, this hierarchical network hydrogel has good drying, freezing, and sensing properties, which provides a new viable strategy for monitoring motion signals. Moreover, the hydrogel is predicted to function as a dressing, thereby facilitating the absorption of heat from the skin’s surface, with the aim of alleviating the discomfort associated with joint and muscle injuries caused by strenuous exercise.

Skeletal muscles exhibit excellent properties due to their well-developed microstructures. Taking inspiration from nature that thick filaments and thin filaments are linked by “cross-bridges”, leading to good stability and ion transport performance of muscles. In this work, extracted poplar lignin and microcrystalline cellulose (MCC) were connected by biomimetic covalent bonds, akin to biological muscle tissue, in which isophorone diisocyanate was used as the chemical crosslinking agent. Then, poplar lignin–MCC was mixed with polyacrylonitrile to serve as the precursor for electrospinning. The results show that due to the effective covalent-bond connection, the precursor fibers possess excellent morphology, smooth surface, good thermal stability, and high flexibility and toughness (average elongation-at-break is 51.84%). Therefore, after thermal stabilization and carbonization, derived lignocellulose-based carbon fibers (CFs) with a reduced cost, complete fiber morphology with a uniform diameter (0.48 ± 0.22 μm), and high graphitization degree were obtained. Finally, the electrodes fabrication and electrochemical testing were carried out. The results of electrochemical impedance spectroscopy (EIS) indicate that the Rs and Rct values of CFs supercapacitors are 1.18 Ω and 0.14 Ω, respectively. Results of cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) suggest that these CFs demonstrate great application potential in electrochemical materials.

Sports-related injuries involving muscle, tendon, cartilage, ligament, and bone remain challenging because of their heterogeneous mechanisms, high functional demands, and need for timely diagnosis, targeted repair, and rehabilitation monitoring. Musculoskeletal ultrasound (MSKUS) provides real-time, portable, radiation-free, and repeatable evaluation of injured tissues, including lesion location, structural continuity, vascular response, stiffness changes, and healing progression. Protein-based hydrogels, owing to their biocompatibility, tunable mechanics, extracellular matrix-like microenvironments, and capacity for localized bioactive delivery, offer promising platforms for tissue repair and functional recovery. This review summarizes major sports injuries, discusses the diagnostic and monitoring value of MSKUS, and analyzes protein-based hydrogels according to tissue-specific repair requirements. Particular attention is given to the connection between imaging assessment and hydrogel therapy, including ultrasound-guided delivery, lesion localization, post-treatment monitoring of hydrogel retention or degradation, and evaluation of therapeutic response. By linking MSKUS-based lesion assessment with hydrogel selection, image-guided delivery, post-intervention monitoring, and rehabilitation-oriented decision-making, this review outlines a coordinated framework for precise diagnosis and localized biomaterial-assisted repair in sports injury management.