Fibrin Film by Heat

Treatmentat 100°C., Moisture Content 70%. When water-equilibrated film, containing 30 % fibrin, is treated for one second with boiling water or steam, irreversible contraction takes place in the plane of the film, as described above the opacity persists, and the tensile strength drops to a small fraction of its original value. The water content remains at 70%. The consistency of the product resembles that of boiled egg white. 

Treatment Dry at 170°. When dry film is heated in vacuo at 170° for 1.6 hours, it develops a yellow color, and the evolution of gaseous decomposition products indicates considerable chemical change. The treated film, when equilibrated in water, has a fibrin content of 58%, and a tensile strength comparable with that of unmodified film, but a much lower elongation (60% at break). 

Properties of Steam-Treated Film, The properties of film treated with saturated steam at 121 for 20 minutes, the moisture content during treatment being 25%, have been examined in more detail. Compared with unmodified film, it has a lower affinity for water, as evidenced by its high water-equilibrated fibrin content of 57 %, as well as lower water sorption at different relative humidities. Several properties of the water-equilibrated film are directly attributable to its high fibrin content. Thus its opacity is quite low (optical density per mm. of 0.1 to 0.2, compared with 3.0 for water-equilibrated unmodified film) but unmodified film at the same fibrin content (Fig. 32) has a comparable opacity (0.5). Also, the stress-strain curve shows a high initial slope, the mechanical character being tough rather than rubbery it closely resembles the curve for unmodified film at the same fibrin content. 

This similarity in mechanical properties indicates that the density of cross-linking in the two films at a fibrin content of 57 % is roughly the same. However, in the unmodified film many of the cross-links are secondary bonds, since they are broken upon immersion in water while in the steam-treated film they are evidently bonds of a more permanent nature. The existence of a permanent, dense network in the treated film is further indicated by the observations that it swells much less in dilute acid and alkali, and that it is impermeable to hemoglobin. 

That chemical changes accompany the cross-linking is shown by alteration of the affinities of the protein for various dyes. The initial contact with steam increases the affinity for both acid and basic dyes as the treatment is prolonged, the affinity for acid dye decreases, while that for bade dye continues to increase (see below). 

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