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Excavation of burrows is an extremely physically demanding activity producing a large amount of metabolic heat. Dissipation of its surplus is crucial to avoid the risk of overheating, but in subterranean mammals it is complicated due to the absence of notable body extremities and high humidity in their burrows. IR-thermography in a previous study on two species of African mole-rats revealed that body heat was dissipated mainly through the ventral body part, which is notably less furred. Here, we analyzed the dorsal and ventral skin morphology, to test if dermal characteristics could contribute to higher heat dissipation through the ventral body part. The thickness of the epidermis and dermis and the presence, extent and connectivity of fat tissue in the dermis were examined using routine histological methods, while vascular density was evaluated using fluorescent dye and confocal microscopy in the giant mole-rat Fukomys mechowii. As in other hitherto studied subterranean mammals, no subcutaneous adipose tissue was found. All examined skin characteristics were very similar for both dorsal and ventral regions: relative content of adipose tissue in the dermis (14.4 ± 3.7% dorsally and 11.0 ± 4.0% ventrally), connectivity of dermal fat (98.5 ± 2.8% and 95.5 ± 6.8%), vascular density (26.5 ± 3.3% and 22.7 ± 2.3%). Absence of large differences in measured characteristics between particular body regions indicates that the thermal windows are determined mainly by the pelage characteristics.
Biomaterials are widely used in guided bone regeneration (GBR) and guided tissue regeneration (GTR). After application, there is an interaction between the host immune system and the implanted biomaterial, leading to a biomaterial-specific cellular reaction. The present review focuses on cellular reactions to numerous biomaterials in vivo with consideration of different implantation models and microenvironments in different species, such as subcutaneous implantation in mice and rats, a muscle model in goats and a femur model in rabbits. Additionally, cellular reactions to different biomaterials in various clinical indications within the oro-maxillofacial surgical field were considered. Two types of cellular reactions were observed. There was a physiological reaction with the induction of only mononuclear cells and a pathological reaction with the induction of multinucleated giant cells (MNGCs). Attention was directed to the frequently observed MNGCs and consequences of their appearance within the implantation region. MNGCs have different subtypes. Therefore, the present review addresses the different morphological phenotypes observed within the biomaterial implantation bed and discusses the critical role of MNGCs, their subtypes and their precursors as well as comparing the characteristics and differences between biomaterial-related MNGCs and osteoclasts. Polymeric biomaterials that only induced mononuclear cells underwent integration and maintained their integrity, while polymeric biomaterials that induced MNGCs underwent disintegration with material breakdown and loss of integrity. Hence, there is a question regarding whether our attention should be directed to alternative biological concepts, in combination with biomaterials that induce a physiological mononuclear cellular reaction to optimize biomaterial-based tissue regeneration.