Laser-engineered topography: correlation between structure dimensions and cell control

Cell Type-Specific Adhesion and Migration on Laser-Structured Opaque Surfaces

Cytocompatibility is essential for implant approval. However, initial in vitro screenings mainly include the quantity of adherent immortalized cells and cytotoxicity. Other vital parameters, such as cell migration and an in-depth understanding of the interaction between native tissue cells and implant surfaces, are rarely considered. We investigated different laser-fabricated spike structures using primary and immortalized cell lines of fibroblasts and osteoblasts and included quantification of the cell area, aspect ratio, and focal adhesions. Furthermore, we examined the three-dimensional cell interactions with spike topographies and developed a tailored migration assay for long-term monitoring on opaque materials. While fibroblasts and osteoblasts on small spikes retained their normal morphology, cells on medium and large spikes sank into the structures, affecting the composition of the cytoskeleton and thereby changing cell shape. Up to 14 days, migration appeared stronger on small spikes, probably as a consequence of adequate focal adhesion formation and an intact cytoskeleton, whereas human primary cells revealed differences in comparison to immortalized cell lines. The use of primary cells, analysis of the cell-implant structure interaction as well as cell migration might strengthen the evaluation of cytocompatibility and thereby improve the validity regarding the putative in vivo performance of implant material.

Laser Surface Microstructuring of a Bio-Resorbable Polymer to Anchor Stem Cells, Control Adipocyte Morphology, and Promote Osteogenesis

New strategies in regenerative medicine include the implantation of stem cells cultured in bio-resorbable polymeric scaffolds to restore the tissue function and be absorbed by the body after wound healing. This requires the development of appropriate micro-technologies for manufacturing of functional scaffolds with controlled surface properties to induce a specific cell behavior. The present report focuses on the effect of substrate topography on the behavior of human mesenchymal stem cells (MSCs) before and after co-differentiation into adipocytes and osteoblasts. Picosecond laser micromachining technology (PLM) was applied on poly (L-lactide) (PLLA), to generate different microstructures (microgrooves and microcavities) for investigating cell shape, orientation, and MSCs co-differentiation. Under certain surface topographical conditions, MSCs modify their shape to anchor at specific groove locations. Upon MSCs differentiation, adipocytes respond to changes in substrate height and depth by adapting the intracellular distribution of their lipid vacuoles to the imposed physical constraints. In addition, topography alone seems to produce a modest, but significant, increase of stem cell differentiation to osteoblasts. These findings show that PLM can be applied as a high-efficient technology to directly and precisely manufacture 3D microstructures that guide cell shape, control adipocyte morphology, and induce osteogenesis without the need of specific biochemical functionalization.

A silicone fiber coating as approach for the reduction of fibroblast growth on implant electrodes

In cochlear implant (CI) patients, an increase in electrode impedance due to fibrotic encapsulation is frequently observed. Several attempts have been proposed to reduce fibroblast growth at the electrode contacts, but none proved to be satisfactory so far. Here, a silicone fiber coating of the electrode contacts is presented that provides a complex micro-scale surface topography and increases hydrophobicity to inhibit fibroblast growth and adhesion. A silicone fiber electrospinning process was developed to create a thin and porous fiber mesh. Fiber coatings were applied on graphite specimen holders, glass cover slips and CI electrode contacts. For characterization of the coating's pore distribution, water contact angle and electrical impedance were analyzed. Cytotoxicity and in vitro fibroblast growth were evaluated to assess biological efficacy of the coatings. It could be shown that the silicone fiber mesh itself had only minor influence on electrode impedance. A uniform, hydrophobic fiber coating could be achieved that decreased fibroblast growth without showing toxic effects. Finally, CI electrode contacts were successfully coated in order to present this promising approach for a long-term improvement of CI electrodes. We are one of the first groups that could successfully adapt the electrospinning technique on the utilization of silicone. Silicone was chosen because of its high hydrophobicity, chemical stability and excellent biocompatibility and as it is one of the biomaterials already used in CIs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2574-2580, 2017.

Impact of laser-structured biomaterial interfaces on guided cell responses

To achieve a perfect integration of biomaterials into the body, tissue formation in contact with the interface has to be controlled. In this connection, a selective cell control is required: fibrotic encapsulation has to be inhibited, while tissue guidance has to be stimulated. As conventional biomaterials do not fulfil this specification, functionalization of the biointerface is under development to mimic the natural environment of the cells. One approach focuses on the fabrication of defined surface topographies. Thereby, ultrashort pulse laser ablation is very beneficial, owing to a large variety of fabricated structures, reduced heat-affected zones, high precision and reproducibility. We demonstrate that nanostructures in platinum and microstructures in silicon selectively control cell behaviour: inhibiting fibroblasts, while stimulating neuronal attachment and differentiation. However, the control of fibroblasts strongly correlates with the created size dimensions of the surface structures. These findings suggest favourable biomaterial interfaces for electronic devices. The mechanisms which are responsible for selective cell control are poorly understood. To give an insight, cell behaviour in dependence of biomaterial interfaces is discussed-including basic research on the role of the extracellular matrix. This knowledge is essential to understand such specific cell responses and to optimize biomaterial interfaces for future biomedical applications.