No abstract

Explicit antigen–antibody binding has accelerated the development of immunosensors for the detection of various analytes in biomedical and environmental domains. Being a subclass of biosensors, immunosensors have been a significant area of research in attaining high sensitivity and an ultralow sensing limit to detect biological analytes present in trace levels. The highly porous structure, large surface area, and excellent biocompatibility of hydrogels enabling the retainability of the activity and innate framework of the attached biomolecules make them a suitable candidate for immunosensor fabrication. Hydrogels based on polycarboxylate, cellulose, polyaniline, polypyrrole, sodium alginate, chitosan, and agarose are exploited in conjunction with other nanomaterials such as AuNPs, GO, and MWCNTs to augment the electron transfer during the immunosensing mechanism. Surface plasmon resonance, electrochemiluminescence, colorimetric, and electrochemical assays are different strategies utilized for the signal transduction in hydrogel-based immunosensors during the formation of the antigen–antibody complex. These hydrogel-based immunosensors exhibit rapid response, excellent stability, reproducibility, high selectivity and high sensitivity, a broad range of detection, an ultralow limit of detection, and display results similar to those for the ELISA test. This review propounds different hydrogel-functionalized immunosensing platforms classified on the basis of their signal transduction for the detection of disparate cancer biomarkers (tumor necrosis factor, α-fetoprotein, prostate-specific antigen, carbohydrate antigen 24-2, carcinoembryonic antigen, neuron-specific enolase, and cytokeratin antigen 21-1), hormones (cortisol, cortisone, and human chorionic gonadotropin), human IgG, and ractopamine in animal feeds.

Being a bioactive material, hydroxyapatite (HAp) is regarded as one of the most attractive ceramic biomaterials for bone and hard-tissue replacement and regeneration. Despite its substantial biocompatibility, osteoconductivity, and compositional similarity to that of bone, the employment of HAp is still limited in orthopedic applications due to its poor mechanical (low fracture toughness and bending strength) and antibacterial properties. These significant challenges lead to the notion of developing novel HAp-based composites via different fabrication routes. HAp, when efficaciously combined with functionally graded materials and antibacterial agents, like Ag, ZnO, Co, etc., form composites that render remarkable crack resistance and toughening, as well as enhance its bactericidal efficacy. The addition of different materials and a fabrication method, like 3D printing, greatly influence the porosity of the structure and, in turn, control cell adhesion, thereby enabling biological fixation of the material. This article encompasses an elaborate discussion on different multifunctional HAp composites developed for orthopedic applications with particular emphasis on the incorporation of functionally graded materials and antibacterial agents. The influence of 3D printing on the fabrication of HAp-based scaffolds, and the different in vitro and in vivo studies conducted on these, have all been included here. Furthermore, the present review not only provides insights and broad understanding by elucidating recent advancements toward 4D printing but also directs the reader to future research directions in design and application of HAp-based composite coatings and scaffolds.