The structural and mechanical properties of gels formed from biopolymers are discussed both in terms of the techniques used to characterise these systems, and in terms of the systems themselves The techniques included are spectroscopic, chiroptical and scattering methods, optical and electron microscopy, thermodynamic and kinetic methods and rheological characterisation The systems considered are presented in order of increasing complexity of secondary, tertiary and quaternary structure, starting with gels which arise from essentially ‘disordered’ biopolymers via formation of ‘quasicrystalline’ junction zones (eg gelatin, carrageenans, agarose, alginates etc), and extending to networks derived from globular and rod-like species (fibrin, globular proteins, caseins, myosin) by a variety of crosslinking mechanisms Throughout the text, efforts are made to pursue the link (both from experiment and from theory) between the structural methods and mechanical measurements As far as we are aware this is the first major Review of this area since that of J D Ferry in 1948 — The interest shown by polymer physicists in more complex biochemical systems, and the multi-disciplinary approaches now being applied in this area, make the format adopted here, in our opinion, the most logical and appropriate

Structural and mechanical properties of biopolymer gels

The gel-melting temperatures of branched polyethylene–cyclohexane–carbon disulfide gels were measured. Branched polyethylenes having a different number of long-branching points were used. The reciprocal of the gel-melting temperature is a linear function of the logarithm of the polymer concentration. A theory which predicts the gel-melting temperature of branched crystalline copolymers is given. Analysis of the experimental data suggests that the size of the crystalline junction decreases with an increase in the number of long-branching points.

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Melting Temperature of Thermally Reversible Gel. VI. Effect of Branching on the Sol–Gel Transition of Polyethylene Gels

The gel/sol transition temperatures (T

 ) were measured by cooling of thermally reversible methyl cellulose (MC)-water gels using the ten MC samples. A linear relationship between 1/T

 and the logarithm ofv
2
x was found for each MC gel, wherev
2 is the volume fraction of MC andx the degree of polymerization. The X-ray diffraction patterns of both MC films and gels revealed that the network junction points of the MC gels are crystalline and consist of trimethyl glucose units. The heat of fusion of trimethyl cellulose was estimated as 2.6 × 103 J/mol, and entropy of dilution parameter = −1.6 andΘ = 320 K were also evaluated. Using these values, the gel/sol transition temperature was analysed according to our previous theory. It is concluded that the network junction points of MC gels are between 4 and 8 units long and also that the length is in good agreement with the sequence length estimated from the methoxy content of MC.

Melting temperatures of thermally reversible gels IV. Methyl cellulose-water gels

Sol-gel transition of poly(vinyl alcohol)-borate complex

Gelation in an amorphous polymer: a discussion of its relation to membrane formation

The Melting Temperature of Thermally Reversible Gel. I. Poly(vinyl chloride)–Organic Solvent Gels

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We studied whether the infectivity of Cryptosporidium parvum oocysts for suckling mice could be inactivated by copper tubing or by other types of tubing used to construct water distribution systems, including stainless steel, rigid polyvinyl chloride (PVC), PVC-lined steel, polyethylene (PE), cross-linked PE, and polybutene (PB), using glass tubing as the control. Oocysts were incubated in each tubings for 24 hours. The extent of inactivation of infectious oocysts by copper tubing was -1.303 log, which significantly inactivated of infectivity. In contrast, other types of tubing had no significant effect on some oocyst infectivity, although PB did show a maximum inactivation of -0.313 log. 25% of oocysts showed degeneration morphologically after passing through copper tubing, while 0.3% to 1.8% showed degeneration after passing through other tubing. Significant inactivation of infectious oocysts was not caused by water in which copper tubing had been let stand for 24 hours, although it had a cupric ion (Cu2+) concentration of 2.4 mg/L. The direct contact of oocysts with copper surface resulted in a decrease in the recovery percentage of oocysts and generation of hydrogen peroxide (0.5 mg/L) after 24 h of incubation. The percentage of degenerating oocysts was 29%. Such cryptosporidicidal effects of the copper surface on oocysts were completely inhibited by overlaying the surface with a Millipore filter before adding oocysts and incubating oocysts in the presence of catalase, an antioxidant enzyme. These findings suggest that copper tubing inactivates infectious C. parvum oocysts cytotoxically which may be due to oxygen radicals generated by the interaction between Cu2+ and hydrogen peroxide on the tubing surface.

Takeshi Nakamura

Papers

The Melting Temperature of Thermally Reversible Gel. I. Poly(vinyl chloride)–Organic Solvent Gels

Inactivation of Cryptosporidium parvum oocysts in copper tubing