EFFECT OF “FREEZING” TREATMENTS ON THE HYDROTHERMAL STABILITY OF COLLAGEN
STEPHEN L. WILLIAMS, SARAH R. BEYER, & SAMINA KHAN
2 METHOD AND MATERIALS
This study was conducted in April and May 1994 at the Natural Science Research Laboratory of the Museum of Texas Tech University. During the study, ambient temperature and relative humidity were approximately 23°C and 35%, respectively.
Variables affecting results of Ts analyses include species, age, sampling location on skin, treatment, and agents of deterioration (Hobbs 1940; Gustavson 1956; Williams 1991). To focus on the relationships of various treatments, it was essential to know the natural condition of skin, have a fully documented history of treatments, and minimize influential variables. Thus a fresh skin from a single, adult, female, nonlaboratory rodent (Spermophilus tridecemlineatus; voucher reference number, SLW 7204; head and body length, 162 mm) was selected for study.
The middorsal region of the pelt was subdivided into six sectors, five of which were subjected to various desiccation and/or freezing treatments, and one which served as the control. Desiccation was performed in the dark under ambient conditions with the pelt pinned to an Ethafoam block. The time allowed for drying far exceeded limits specified by Michalski (1992). Freezing of encapsulated skin tissue was performed in a standard freezer at −8°C. The results of six different treatments are summarized in table 1. Shrinkage temperature was documented using a microscope (100 × magnification) with a central processor (Mettler FP90), hot-stage (Mettler FP82HT), and a recording printer (Epson FX870). Sample preparations involved presoaking in distilled water and using described methods (Young 1987; Young and Grimstad 1990; Williams 1991). Temperature was increased 2.0°C per minute. Temperature for initial and final shrinkage stages were documented 10 times for each of the 6 groups. Because movement of collagen fibrils may be caused by extraneous factors (Williams 1991), the initial Ts was recorded when simultaneous movement of two or more fibrils was observed in the field of vision. The final Ts was recorded when all movement in the field of vision stopped for at least 10 seconds. Because Ts is properly regarded as a temperature range between the initial and final stages (Gustavson 1956), the midpoint of the range has been used for designating specific temperature values (Von Hippel and Wong 1963); this method facilitated reporting of results in the current study.
TABLE 1 SUMMARY OF TREATMENTS APPLIED TO FRESH SKIN TISSUE
The SPSS program ONEWAY (Norvsis/ SPSS Inc. 1990) was used to obtain standard statistics for the 10 Ts analyses of each group, test homogeneity of variances, and perform analysis of variance between groups. The Student-Newman-Keul procedure of the same program was used to identify nonsignificant subsets between groups.