Concentrating aqueous dispersions of Staphylococcus Epidermidis bacteria by swelling of thermosensitive poly [(N-isopropylacrylamide)-co-(acrylic acid)] hydrogels

A novel method for concentrating: of bacteria dispersions without loss of b acterial viability has been developed. Bioseparation was facilitated by the swelling of a thermoresponsive hydrogel in a dilute bacterial dispersion. Hydrogels were prepared by free radical copolymerization in aqueous solutio n of N-isopropylacrylamide (NIPA) and acrylic acid (AA) with N,N'-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels of a single comonomer compo sition and three concentrations of BIS were employed. The potential of the corresponding xero-gels as bioseparation devices was assessed by swelling t o equilibrium at 5 degreesC in aqueous dispersions of the bacterium Staphyl ococcus Epidermidis. The resultant increase in concentration of dispersion, the concentrated dispersion being commonly termed the 'raffinate', was mea sured by the spread plate technique. An efficiency of separation eta was ob tained from this increase, coupled with that calculated from the measured d egree of swelling. It has been shown that high values of eta can be achieve d. It has also been shown that separation efficiency is dependent on the pr ocedure employed in the sampling of the concentrated dispersion. Without ag itation of the swollen hydrogel/raffinate prior to sampling no concentratio n increase was measured, i.e. eta was 0%. However, eta increased to values of 50-80% on agitation (via a vortex mixer) of the hydrogel/raffinate prior to raffinate sampling. The need for agitation and the reduction in the val ue of II from its theoretical maximum (100%) may indicate the adsorption of the bacteria onto the surface of the hydrogel. The effect of the bacterial dispersion on the swelling properties of the hydrogels was also investigat ed It was found that the swelling ratio (= mass of hydrogel/mass of xerogel ) and lower critical swelling temperature of the hydrogels in the bacterial dispersion and pure water were identical.