Negative Thermal Expansion Metamaterials: A Review of Design, Fabrication, and Applications

Most materials conventionally found in nature expand with an increase in temperature. In actual systems and assemblies like precision instruments, this can cause thermal distortions which can be difficult to handle. Materials with a tendency to shrink with an increase in temperature can be used alongside conventional materials to restrict the overall dimensional change of structures. Such structures, also called negative-thermal-expansion materials, could be crucial in applications like electronics, biomedicine, aerospace components, etc., which undergo high changes in temperature. This can be achieved using mechanically engineered materials, also called negative thermal expansion (NTE) mechanical metamaterials. Mechanical metamaterials are mechanically architected materials with novel properties that are rare in naturally occurring materials. NTE metamaterials utilize their artificially engineered architecture to attain the rare property of negative thermal expansion. The emergence of additive manufacturing has enabled the feasible production of their intricate architectures. Industrial processes such as laser powder bed fusion and direct energy deposition, both utilized in metal additive manufacturing, have proven successful in creating complex structures like lattice formations and multimaterial components in the industrial sector, rendering them suitable for manufacturing NTE structures. Nevertheless, this review examines a range of fabrication methods, encompassing both additive and traditional techniques, and explores the diverse materials used in the process. Despite NTE metamaterials being a prominent field of research, a comprehensive review of these architected materials is missing in the literature. This article aims to bridge this gap by providing a state-of-the-art review of these metamaterials, encompassing their design, fabrication, and cutting-edge applications

Macular hole-associated retinal detachment in Best vitelliform dystrophy: Series of two cases and literature review

Two eyes of 2 patients with macular hole-associated retinal detachment in clinically diagnosed vitelliruptive stage of Best vitelliform dystrophy were surgically managed by 25-gauge sutureless pars plana vitrectomy, internal limiting membrane (ILM) peeling with inverted ILM flap, and short-acting (SF6) gas tamponade. The patients were assessed with respect to best-corrected visual acuity, color fundus photographs, shortwave fundus autofluorescence, and swept source optical coherence tomography. Surgical intervention led to Type 1 closure of macular hole, resolution of retinal detachment, and improvement in vision in both patients