Dynamische Biomaterialien

Friction plays an important role in the adhesion of many climbing organisms, such as the gecko. During the shearing between two surfaces, periodic stick-slip behavior is often observed and may be critical to the adhesion of gecko setae and gecko-inspired adhesives. Here, we investigate the influence of short oligomers and pendent chains on the stick-slip friction of polydimethylsiloxane (PDMS), a commonly used material for bioinspired adhesives. Three different stick-slip patterns were observed on these surfaces (flat or microstructured) depending on the presence or absence of oligomers and their ability to diffuse out of the material. After washing samples to remove any untethered oligomeric chains, or after oxygen plasma treatment to convert the surface to a thin layer of silica, we decouple the contributions of stiffness, oligomers, and pendant chains to the stick?slip behavior. The stick phase is mainly controlled by the stiffness while the amount of untethered oligomers and pendant chains available at the contact interface defines the slip phase. A large amount of oligomers and pendant chains resulted in a large slip time, dominating the period of stick-slip motion.

Porous polyethylene (Medpor®) is commonly used in craniofacial reconstructive surgery. Rapid vascularization and tissue incorporation are crucial for the prevention of migration, extrusion, and infection of the biomaterial. Therefore, we analyzed whether surface modification by plasma etching may improve the early tissue response to Medpor®. Medpor® samples were treated in a plasma chamber at low (20 W; LE-PE) and high energy levels (40 W; HE-PE). The samples and non-treated controls were implanted into mouse dorsal skinfold chambers to analyze angiogenesis, inflammation, and granulation tissue formation over 14 days using intravital fluorescence microscopy, histology, and immunohistochemistry. Scanning electron microscopy (SEM) analyses revealed that elevating energy levels of plasma etching progressively increase the oxygen surface content and surface roughness of Medpor®. This did not affect the leukocytic response to the implants. However, LE-PE and HE-PE samples exhibited an impaired vascularization. This was associated with a reduced formation of a collagen-rich granulation tissue at the implantation site. Additional in vitro experiments showed a reduced cell attachment on plasma-etched Medpor®. Thus, plasma etching may not be recommended to improve the clinical outcome of reconstructive interventions using Medpor®. However, it may be beneficial for temporarily implanted polyethylene-based biomedical devices for which tissue incorporation is undesirable.

In-stent restenosis (ISR) is one of the most common and serious complications observed after stent implantation. ISR is characterized by the inordinate proliferation of smooth muscle cells (SMC) that leads to narrowing of the blood vessels. To achieve a healthy endothelium, it is critical to selectively enhance the growth of endothelial cells (EC) while suppressing the growth of smooth muscle cells, which is still a major challenge and yet to be achieved. In this study, novel surfaces have been developed to support the selective growth of endothelial cells. Micro- and nanostructured Al2O3 surfaces with unique topographical features were fabricated and tested. Surface characterization and cellular response of endothelial cells (HUVEC) as well as smooth muscle cells (HUVSMC) has been investigated at cellular and molecular levels. A topography driven selective cell response of ECs over SMCs was demonstrated successfully. This selective response of ECs was also analyzed at protein levels in order to understand the basic mechanism.

The curing time of an adhesive material is determined by the polymerization and cross-linking kinetics of the adhesive formulation and needs to be optimized for the particular application. Here, we explore the possibility of tuning the polymerization kinetics and final mechanical properties of tissue-adhesive PEG gels formed by polymerization of end-functionalized star-PEGs with catecholamines with varying substituents. We show strong differences in cross-linking time and cohesiveness of the final gels among the catecholamine-PEG variants. Installation of an electron-withdrawing but π-electron donating chloro substituent on the catechol ring resulted in faster and more efficient cross-linking, while opposite effects were observed with the strongly electron-withdrawing nitro group. Chain substitution slowed down the kinetics and hindered cross-linking due either to chain breakdown (beta-OH group, in norepinephrine) or intramolecular cyclization (α-carboxyl group, in DOPA). Interesting perspectives derive from use of mixtures of catecholamine-PEG precursors offering further opportunities for fine-tuning of the curing parameters. These are interesting properties for the application of catecholamine-PEG gels as tissue glues or biomaterials for cell encapsulation.