Biotechnology Letters Vol.4 No.9 511-614 (1982) PHYSICAL PROPERTIES OF POLYETHYLENEIMINE-ALGINATE GELS Suhaila Mohamed* (Fakulti Sains dan Teknologi Makanan) and Abu Bakar Salleh (Jabatan Biokimia dan Mikrobiologi) Universiti Pertanian Malaysia, Serdang, Malaysia SUI~IARY The procedure for preparation of polyethyleneimine (PEl)-alginate gel and some of its physical properties are presented. The rigidity modulus (G) of the gel appears to increase to the second power of PEI concentration. Shrinkage is linearly related to pH up to pH 6.0. G increases as the pH is lowered, and decreases after freezing. The gels does not dissolve on heating and are strong, but fairly brittle. They are resistant to proteolytic enzymes. INTRODUCTION The ability of gelatin to form thermostable gels with alginate esters was first reported by Agfa (1964) in their patent and used in the Photographic Industries. Unilever (1976) took the idea to patent food gels for human consumption. Ranganayaki (1976) improved the method for gel formation. Only certain proteins can form thermostable gels with alginates and the properties of these gels have been studied by Suhaila (1981). The possibility of covalently immobilising various enzymes on gelatin-alginate gels has been investigated (Salleh & Suhaila, 1982). This paper reports on the physical properties of p01yethyleneimine-alginate gels with regards to potential uses in immobilisation of enzymes and cells. MATERIALS AND METHODS Preparation of Gel 50% aqueous solution of polyethyleneimine (PEI) (Sigma, USA) was suitably diluted with 0.1M, pH 9.6 carbonate/bicarbonate buffer. To this was added equal volumes 4% (w/v) aqueous solution propylene glycol alginate (PGA) (ICN Pharmaceutical Inc., USA) and immediately mixed in a food processor (or any strong, fast stirrer) for about 5 seconds. The gel sets almost instantly. Rigidity of PEl~Alginate Gels Dilutions of PEI: buffer of various propor- tions were made and reacted with PGA as above. The rigidity modulus of these gels were then determined using the Instron Universal Testing Machine Model 1140 (Suhaila, 1981). The most suitable dilution of the required gel strength in the order of 104 Nm-2 was then used in the following experiments. Effects of pH PEl-alginate gels of final concentration 0.25% (w/v) PEI, were cut up into suitable pieces and dialysed in 0.1M citrate phosphate (Mcllvaine) buffers (Dawson, et al, 1969) of pH 3.0, 4.0, 5.0, 6.0 and 7.0. The buffers were changed on the 3rd day and the gel was weighed on the 5th day. The rigidity modulus from 3.0 - 7.0 was measured as above. Effect of Temperature The gels which were dialysed at various pH values f0r 5 days were frozen at - 18°C, defrosted and their rigidity modulus measured. Similarly, gels were immersed in the above buffers for 30 minutes and heated at 90°C for 2 hours. 611