5 to 1 the semed f forms a structure which approximates dense cobwebs native collagen film wherein the film strength is preserved and the triple helix structure of the collagen polymer is maintained intact can also be used either alone or with a plasticizer incorporated therewith a typical collagen sheet is cast from solution to a thickness of about 1 8 to 2 mm and contains the following composition by weight collagen 70 3 plasticizer typically glycerol or glycerine 16 9 water 9 other 3 8 such a material is available from norwood medical products division of norwood industries inc malverne pa when gelatin or other water soluble forms of collagen are utilized certain advantages are provided in that the material will readily polymerize at body temperatures to form a stable subcutaneous gel in addition when implanted into the body as filler material in the weld joint the polymerized material will become rapidly populated by host fibroblasts thus the material become vascularized and can remain histologically stable for up to 18 months one problem with gelatin material per se however is that it is highly soluble in blood such that the flow of blood across the material will cause it to dissolve thus gelatin or other soluble collagen material when used along as laser weld filler should be limited to areas where direct contact with blood is avoided or minimized it is also possible to use mixtures of the various types of collagen to obtain the most desirable features of each grade for example a 50 50 mixture of semed f and semed s.