Effects of different traditional methods of cleaning skeletal material: Preliminary evaluation based on scanning electron microscopy

Abstract

Biological collections are unique repositories of biodiversity. Ideally, institutions should have standardized protocols for preparation, storage, and conservation of materials, designed to minimize deterioration over time and to ensure that comparable results could be obtained from them. Eleven cleaning treatments, frequently used in scientific collections, were performed on Wistar rat femurs, consisting of burial (60 days), and enzymatic and chemical digestion. For the last two techniques, ten combinations of concentration of the agents (enzymes, potassium hydroxide [KOH]), temperature, and exposure time were tested. After treatment, bone integrity and percentage of surface covered by soft tissues were evaluated using images obtained by scanning electron microscopy. Good results, in terms of cleaning parameters (muscle and fat removal) were obtained with burial and with the KOH 10%/40 °C/2h and KOH 5%/40 °C/4h combinations; however, superficial desquamation, cracking, and porosity (parameters of bone surface damage) were observed in all cases. Other KOH combinations seemed to be less efficient to clean the surface, but the bones were better preserved. In enzymatic treatments, bone integrity was less affected but more residues persisted; the amount of tissue remaining appears to be related to temperature (treatments at 70 °C were more effective than at 25 °C). Damage caused by burial and KOH coincided with that observed by other authors, although enzymatic treatments left greater amounts of tissue than previously reported. The preliminary information gathered provides a starting point to implement conservative cleaning of skeletal material and will surely constitute an important advance for the establishment of protocols in biological collections.