Hyaluronan-based hydrogels via ether-crosslinking: Is HA molecular weight an effective means to tune gel performance?

Hyaluronan (HA)-based hydrogels obtained by crosslinking the biopolymer via ether bonds are widely used in clinical practice. There is interest in improving the design of these gels to match specific properties. Here, the possibility to tune HA-hydrogel behavior by adjusting the molecular weight distribution of the biopolymer undergoing crosslinking was investigated. Three HA samples (500, 1100 and 1600 kDa) underwent reaction with 1,4-butandioldiglycidyl-ether(BDDE) under reported conditions and the crosslinked products were characterized for chemical modification extent, swelling, rheological behavior, cohesivity, sensitivity to enzymatic degradation and effect on Human Dermal Fibroblasts (HDF). HA hydrolysis, under the highly alkaline crosslinking conditions, was also studied for the first time. The main achievements are that 1) varying HA chain length affects hydrogel behavior less than expected, due to the de-polymerization occurring alongside crosslinking, that reduces the differences in sample size 2) when differences in chain length persist notwithstanding hydrolysis, lowering HA size is a means to prepare more concentrated formulations, expected to exhibit longer duration and better cohesivity in vivo, while retaining a certain rigidity, preserving biocompatibility and slightly influencing HDF behavior in relation to CollagenI production. The study shed light on aspects concerning BDDE-HA gel manufacturing and contributed to the improvement of their design.

Hyaluronan-based hydrogels as dermal fillers: The biophysical properties that translate into a "volumetric" effect.

Biophysical and biochemical data on hyaluronan (HA)-based dermal fillers strongly support their optimal use and design to meet specific requisites. Here, four commercially available (in Europe) HA "volumetric" fillers, among the most used in the clinical practice, have been characterized in vitro. Analyses revealed the highest amounts of water-soluble HA reported so far and provided hydrodynamic data for these soluble polymeric fractions. Volumetric gels exhibit a wide range of rigidity with most of them showing G' values around 200-300Pa. They greatly differ in cohesivity. 1mL of gel hydrates up to 2.4-3.2mL. The products completely solubilize due to Bovine Testicular Hyaluronidase (BTH)'s action, thus predicting in vivo complete resorption. For the first time, filler degradation due to reactive oxygen species (ROS) was studied by rheological measurements and a rank in stability was established. Studies using Human Dermal Fibroblasts (HDF) indicated a positive biological response to the HA networks. Further, gel capacity to prompt collagen I, elastin and aquaporin3 synthesis was demonstrated, thus suggesting a positive effect on skin elasticity and hydration, besides the physical volumetric action. The findings are the first wide assessment of features for the volumetric class of HA-fillers and include first data on their resistance to degradation by ROS and biological effects on HDF. The study represents a valuable contribution to the understanding of HA-fillers, useful to optimize their use and manufacture.

In Vitro Evaluation of Hybrid Cooperative Complexes of Hyaluronic Acid as a Potential New Ophthalmic Treatment.

PURPOSE: The purpose of this in vitro study was to assess the potential benefits of eye drops based on hybrid cooperative complexes (HCCs) obtained from high and low molecular weight hyaluronic acid (HA). METHODS: Rheological measurements were performed to adjust the HCC concentration toward optimal resistance to drainage from the ocular surface. The viscosity and mucoadhesion profiles of the optimized preparation were derived. Primary porcine corneal epithelial cells were used for biological studies. Cells were exposed to dehydration after being pretreated with the HCC solution, and protection from desiccation was evaluated using cell viability assays. Time-lapse experiments were carried out to evaluate the ability of the HCC preparation to promote corneal wound healing. The characterization studies were performed in comparison with a control HA solution representative of commercial HA-based products. RESULTS: The HCC formulation is able to deliver twice the amount of biopolymer compared with conventional products while avoiding discomfort due to excessive viscosity. The viscosity and mucoadhesion profiles allowed the authors to predict the longer in vivo retention and, therefore, an improved HCC formulation bioavailability. The new preparation also proved superior in protecting porcine corneal epithelial cells from desiccation and in hastening corneal cell wound repair in vitro. CONCLUSIONS: The results suggest that the developed formulation may be a promising topical ophthalmic medical treatment.

Optimization of hyaluronan-based eye drop formulations.

Hyaluronan (HA) is frequently incorporated in eye drops to extend the pre-corneal residence time, due to its viscosifying and mucoadhesive properties. Hydrodynamic and rheological evaluations of commercial products are first accomplished revealing molecular weights varying from about 360 to about 1200kDa and viscosity values in the range 3.7-24.2mPa s. The latter suggest that most products could be optimized towards resistance to drainage from the ocular surface. Then, a study aiming to maximize the viscosity and mucoadhesiveness of HA-based preparations is performed. The effect of polymer chain length and concentration is investigated. For the whole range of molecular weights encountered in commercial products, the concentration maximizing performance is identified. Such concentration varies from 0.3 (wt%) for a 1100kDa HA up to 1.0 (wt%) for a 250kDa HA, which is 3-fold higher than the highest concentration on the market. The viscosity and mucoadhesion profiles of optimized formulations are superior than commercial products, especially under conditions simulating in vivo blinking. Thus longer retention on the corneal epithelium can be predicted. An enhanced capacity to protect corneal porcine epithelial cells from dehydration is also demonstrated in vitro. Overall, the results predict formulations with improved efficacy.