Journal of Composites Science

Objectives: This systematic review and meta-analysis aimed to evaluate microbial adhesion and biofilm formation on additively manufactured composite-based orthodontic clear aligners compared with thermoformed aligners and other conventional polymeric materials. The influence of material composition, surface roughness, post-processing parameters, and cleaning protocols on microbial colonization was also assessed. Methods: A comprehensive search of PubMed, EMBASE, Scopus, Web of Science, and the Cochrane Library was conducted up to September 2025. Only in vitro studies investigating microbial adhesion, biofilm biomass, or microbiome changes on three-dimensional (3D)-printed aligner composites were included. Primary outcomes consisted of colony-forming units (CFU), optical density (OD) from crystal violet assays, viable microbial counts, and surface roughness. Risk of bias was assessed using the RoBDEMAT tool. Data were narratively synthesized, and a random-effects meta-analysis was performed for comparable datasets. Results: Five studies fulfilled the inclusion criteria, of which two in vitro studies were eligible for meta-analysis. Microbial adhesion and biofilm accumulation were influenced by the manufacturing technique, composite resin formulation, and surface characteristics. Certain additively manufactured aligners exhibited smoother surfaces and reduced bacterial adhesion compared with thermoformed controls, whereas others with increased surface roughness showed higher biofilm accumulation. Incorporating bioactive additives such as chitosan nanoparticles reduced Streptococcus mutans biofilm formation without compromising material properties. The meta-analysis, based on two in vitro studies, demonstrated higher OD values for bacterial biofilm on 3D-printed aligners compared with thermoformed aligners, indicating increased biofilm biomass (p < 0.05), but not necessarily viable bacterial load. Conclusions: Microbial adhesion and biofilm formation on 3D-printed composite clear aligners are governed by resin composition, additive manufacturing parameters, post-curing processes, and surface finishing. Although certain 3D-printed materials display antibacterial potential, the limited number of studies restricts the generalizability of these findings. Clinical Significance: Optimizing composite formulations for 3D printing, alongside careful post-curing and surface finishing, may help reduce microbial colonization. Further research is required before translating these findings into definitive clinical recommendations for clear aligner therapy.

Fibre-reinforced polymer (FRP) composites are key materials used in the fabrication of lightweight and high-performance structures. Thus, a comprehensive understanding of material performance is required to ensure the safe and reliable operation of FRPs across a broad range of temperatures. For example, the application of FRPs in cryogenic environments, especially for lightweight cryogenic fuel storage, is gaining considerable attention. However, obtaining accurate tensile property measurements for FRPs can be challenging, as failure of the test specimen near the grips is common, even at room temperature. Under cryogenic conditions, the increased complexity of the experimental setup further reduces the accuracy and reproducibility of the tensile properties. This paper reviews standard test methods for tensile testing of FRPs and discusses the challenges of performing tensile tests in both room and cryogenic environments. Key experimental design considerations and directions for future research are identified to support the development of reliable tensile test methods that yield accurate and consistent measurements of FRP material properties.

Copper has become more important owing to its eco-friendliness and persistent efficacy against infections. Furthermore, copper has benefits such as safety in use and durability. This study aimed to develop and assess the antibacterial efficacy of stainless steel coated with a composite layer, which is nanostructured and incorporates copper, to create antibacterial surfaces with good adherence and good corrosion resistance. The composite coating was produced using anodic oxidation, with an external copper layer applied via pulse electroplating. The homogenous cauliflower-like covering showed important characteristics, like increased surface roughness, boosted surface free energy, reduced contact angle, and higher hardness. Additionally, the adherence between the composite covering and the substrate was exceptional. Electrochemical experiments indicated aggressive corrosion behavior in chloride-containing settings. Antibacterial tests were conducted on four prevalent bacterial strains: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhimurium—microorganisms often linked to healthcare and environmental pollution. The coating exhibited enhanced antibacterial efficacy relative to untreated steel and anodized steel. Results indicated that the composite coating is an effective and possibly cost-efficient method for controlling the surface proliferation of the mentioned pathogens.