140 JOURNAL OF COSMETIC SCIENCE will most likely cause less edema, but a larger volume of gel needs to be injected to achieve the same results as a less saturated gel.5,27,28 CONCLUSIONS This review intended to gather the most relevant information on the properties of HA present in available literature. Besides being the most abundant polysaccharide in the human skin, HA as a biomaterial shows a promising role in different areas of medicine (most predominantly from an aesthetic point of view), with HA fillers being used to perform tissue lifting, but also being used as a healing agent, thanks to its effects on fibroblasts and other cells. Therefore, it is crucial to have an intricate understanding of HA’s rheology and physicochemical properties, which will influence its clinical outcomes. There is not one universal dermal filler adequate for all patients and anatomical areas, rather there are multiple products with slight differences in said properties. Viscoelasticity (and especially the elastic modulus—G’), cross-linking, HA concentration, cohesivity, particle size, and hydrophilic expansion are some of the most important and influential factors to consider, especially since they all impact one another. All these factors have a role in defining HA’s longevity, expansion and lifting capacity, biocompatibility, and behavior in the patient’s tissues. Despite this, there is little research that presents a truly detailed and integral description of all of HA’s characteristics. Due to this and the growing concern for aesthetics and effective tissue regeneration methods, it is important for future research to further explore this area and establish better defined protocols. REFERENCES (1) Brandt FS, Cazzaniga A. Hyaluronic acid gel fillers in the management of facial aging. Clin Interv Aging. 2008 3(1):153–159. (2) Zhao X. Synthesis and characterization of a novel hyaluronic acid hydrogel. J Biomater Sci Polym Ed. 2006 17(4):419–433. (3) Lee DY, Cheon C, Song S, et al. Influence of molecular weight on swelling and elastic modulus of hyaluronic acid dermal fillers. Polym Korea. 2015 39(6):80–976. (4) Wu GT, Kam J, Bloom JD. Hyaluronic acid basics and rheology. Facial Plast Surg Clin North Am. 2022 30(3):301–308. (5) Clark CP, III. Animal-based hyaluronic acid fillers: scientific and technical considerations. Plast Reconstr Surg. 2007 120(6)(suppl):27S–32S. (6) Wang HM, Chou YT, Wen ZH, Wang CZ, Chen CH, Ho ML. Novel biodegradable porous scaffold applied to skin regeneration. PLOS ONE. 2013 8(6):e56330. (7) Hashemi SS, Rajabi SS, Mahmoudi R, Ghanbari A, Zibara K, Barmak MJ. Polyurethane/chitosan/ hyaluronic acid scaffolds: providing an optimum environment for fibroblast growth. J Wound Care. 2020 29(10):586–596. (8) Noh I, Kim GW, Choi YJ, et al. Effects of cross-linking molecular weights in a hyaluronic acid- poly(ethylene oxide) hydrogel network on its properties. Biomed Mater. 2006 1(3):116–123. (9) Hu M, Yang J, Xu J. Structural and biological investigation of chitosan/hyaluronic acid with silanized- hydroxypropyl methylcellulose as an injectable reinforced interpenetrating network hydrogel for cartilage tissue engineering. Drug Deliv. 2021 28(1):607–619. (10) Toole BP. Hyaluronan: from extracellular glue to pericellular cue. Nat Rev Cancer. 2004 4(7):528–539.

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