Purification of crosslinked, highly viscous and viscoelastic hyaluronic acid hydrogels by dynamic diafiltration

Abstract

The current study shows a new possibility to purify crosslinked hydrogels based on hyaluronic acid (HA) to remove the residual crosslinking agent 1,4 - butanediol diglycidyl ether (BDDE) and its byproduct 1,4-butanediol di-(propan-2,3-diolyl) ether (EPD) using a crossflow filtration (CFF) device. Therefore, a dynamic crossflow-filtration (DCF) device with rotating and semipermeable ceramic filter discs (5 nm, 60 nm, 2000 nm) was used. No negative impacts on the thermal stability and rheological characteristics of the biopolymer could be shown. Furthermore, it was discovered, that 7 diafiltration volumes (DV) are sufficient to reduce the residual contaminants to < 0.1 % from the initial concentration and that the hyaluronic acid (HA) rejection coefficient (R) is 0.99 regardless of the chosen membrane pore size, while the permeability of BDDE and EPD remains at almost 100 %. No correlation between the membrane pore size and the flux could be found. For all membranes, the flux is surprisingly dropping after 0.5 DV was processed, which could be linked to the HA swelling and membrane pore blocking effects. The highest flux was determined for the 60 nm membrane with 32 Lm-2h−1 at steady state. The stability of the biopolymer is neither negatively influenced by the applied shear forces due to the rotational membrane velocity, nor by the applied thermal stress conditions for 6 months at 25 °C, 60 % relative humidity (r.h.) and 40 °C, 75 % r.h. The presented results show that a dynamic diafiltration can be regarded as a promising alternative to conventional purification methods.