Tissue Reactions to Injectable Biomaterials: Histopathological Features and Mechanisms; Article Review

Abstract

Injectable biomaterials have a lot of applications in aesthetic medicine, tissue engineering, drug delivery and reconstructive surgery. After injection these materials undergo reactions with the extracellular environment and trigger host reactions that depend on the material's chemical composition, physical properties, degradation properties, injection site and local tissue conditions. The response varies from a short-term inflammatory and remodeling process to a long-term foreign body reaction (FBR) and granuloma formation/fibrosis.

In this review, histopathological features and biological mechanisms involved in tissue reactions to injectable biomaterials are taken into account. Special emphasis is placed on the recruitment of neutrophils, activation of macrophages, development of foreign body giant cells, the involvement of lymphocytes, activation of fibroblasts, deposition of extracellular matrix, and fibrous encapsulation. The tissue properties of material-specific responses to hyaluronic acid, calcium hydroxylapatite, poly-L-lactic acid, polymethyl methacrylate, silicone, and hydrogels are discussed. The review also addresses the difference between pathological inflammatory remodeling, foreign body granulomatous reactions and infectious complications with an emphasis on the need to correlate the histopathological findings with clinical findings and material history. At present, there is evidence that material properties are not the only factors determining the response of tissues, as the properties of the particles, the persistence of the material in the tissue, the local tissue conditions and the host's immune response all play a role. The mechanism of these interactions is crucial for better biomaterial design, histopathological interpretation and the evaluation of biomaterial-associated complications.