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In this study, the ternary alloy ZnMg0.8Sr0.2 (wt%) was pre-exposed in a phosphate buffer solution (PBS) with and without the addition of 1 wt% of bovine serum albumin (BSA) to simulate the early stage of the post-implantation period. We investigated the influence of the presence of BSA in the pre-exposure medium on surface chemistry, roughness topography and cytotoxicity of the pre-exposed materials. This study revealed that the pre-exposure in PBS with the addition of BSA induces the formation of a relatively thick and compact phosphate layer on the sample surface. In contrast, the majority of the surface of the samples pre-exposed in pure PBS appear almost untouched, and only a few small areas covered by eye-visible corrosion products were observed. This resulted in lower ion release (66 µmol/L) and a consequent decrease of the cytotoxicity of the eluates prepared from the samples pre-exposed in the BSA containing media. Together with the knowledge available from the literature, the obtained results indicate that BSA affects the degradation mechanism of the Zn-based alloy, resulting in the formation of zinc-BSA complexes. These complexes stimulate the precipitation of phosphates and a consequent formation of solid corrosion products with a protective function. This partially mimics the surface changes occurring in the early post-implantation period. The aforementioned suggests that a suitable pre-exposure of Zn-based absorbable materials in a protein containing media could be used as an approach to obtain reliable data about cytocompatibility by in vitro tests and reduce the discrepancies with the results obtained in vivo.

Summary Background and objective Because the nucleolar protein nucleostemin is present in bone marrow and neuronal stem cells and malignancies originating thereof we monitored its expression in frozen sections from normal human epidermis, basal cell carcinomas, cultured keratinocytes and cells of the squamous carcinoma line FaDu. In addition, probing the value of this protein as a marker of epidermal stem cells was an aim of this study. Materials and methods To further characterize cell features we added analysis of expression of keratins 10 or 19 as markers of terminal differentiation and Ki67 as marker of proliferating cells as well as three adhesion/growth-regulatory galectins. Results Immunohistochemical monitoring revealed expression of nucleostemin in cells of both Ki67-positive and -negative nuclei regardless of the K10-expression status. Cultured keratinocytes were positive, when they were prepared from hair follicles and cultured in the presence of feeder cells. A small population of these nucleostemin-positive cells also expressed galectin-1 but not galectins-3 and -9 in their nucleoli. Part of these cells also expressed keratin 19. FaDu cells were strongly positive, illustrating expression in malignant cells which require no feeder layer. Of note, the number of galectin-1-positive nucleoli was reduced in the course of culture. Conclusion Nucleostemin positivity cannot be considered as marker for stem cells in skin sections. In cultured cells, nucleostemin is expressed in a distinct population of the epidermal cells from hair follicle kept in the presence of a feeder layer, intimating an association of nucleostemin expression with this type of epithelio-mesenchymal interaction which is not essential during propagation of malignant cells.