The crosslinking degree controls the mechanical, rheological, and swelling properties of hyaluronic acid microparticles.

Viscosupplements, used for treating joint and cartilage diseases, restore the rheological properties of synovial fluid, regulate joint homeostasis and act as scaffolds for cell growth and tissue regeneration. Most viscosupplements are hydrogels composed of hyaluronic acid (HA) microparticles suspended in fluid HA. These microparticles are crosslinked with chemicals to assure their stability against enzyme degradation and to prolong the action of the viscosupplement. However, the crosslinking also modifies the mechanical, swelling and rheological properties of the HA microparticle hydrogels, with consequences on the effectiveness of the application. The aim of this study is to correlate the crosslinking degree (CD) with these properties to achieve modulation of HA/DVS microparticles through CD control. Because divinyl sulfone (DVS) is the usual crosslinker of HA in viscosupplements, we examined the effects of CD by preparing HA microparticles at 1:1, 2:1, 3:1, and 5:1 HA/DVS mass ratios. The CD was calculated from inductively coupled plasma spectrometry data. HA microparticles were previously sized to a mean diameter of 87.5 µm. Higher CD increased the viscoelasticity and the extrusion force and reduced the swelling of the HA microparticle hydrogels, which also showed Newtonian pseudoplastic behavior and were classified as covalent weak. The hydrogels were not cytotoxic to fibroblasts according to an MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay.

Metabolic effects of the initial glucose concentration on microbial production of hyaluronic acid.

The objective of the present work was to evaluate the metabolic effects induced by the initial glucose concentration (IGC) on the cultivation of Streptococcus zooepidemicus for the production of hyaluronic acid (HA). These effects were monitored along non-controlled pH cultivations, carried out in 250-mL Erlenmeyer flasks (natural aeration) and in a 3-L bioreactor (forced aeration) as well. Effects of the IGC were observed with focus on the main metabolites, cell growth, production, and average molecular weight of HA. The absence of glucose resulted in a mixed acid metabolism independent of the oxygen supply, while, for IGCs ranging from 5 to 90 g L(-1), the homolactic metabolism was prevalent. The IGC had no influence on the amounts of either biomass or HA produced in the cultivations carried out in flasks; however, cultivations in 3-L bioreactor were found to be strongly dependent on it. The highest concentration of HA (1.21 g L(-1)) was obtained from 25 g L(-1) IGC, the only cultivation where the conversion of glucose to HA was higher than the one of glucose to biomass. Average molecular weight of HA increased concomitant with the IGC, independently of aeration; nevertheless, it decreased along cultivation under forced aeration, due to the shear imparted by stirring.