Hydrogels are able to mimic the basic three-dimensional (3D) biological, chemical, and mechanical properties of native tissues. Since hyaluronic acid (HA) is a chief component of human extracellular matrix (ECM), it represents an extremely attractive starting material for the fabrication of scaffolds for tissue engineering. Due to poor mechanical properties of hydrogels, structure fabrication of this material class remains a major challenge. Two-photon polymerization (2PP) is a promising technique for biomedical applications, which allows the fabrication of complex 3D microstructures by moving the laser focus in the volume of a photosensitive material. Chemical modification of hyaluronan allows application of the 2PP technique to this natural material and, thus, precise fabrication of 3D hydrogel constructs. To create materials with tailor-made mechanochemical properties, HA was combined and covalently cross-linked with poly(ethylene glycol) diacrylate (PEGDA) in situ. 2PP was applied for the fabrication of well elaborated 3D HA and HA-PEGDA microstructures. For enhanced biological adaption, HA was functionalized with human epidermal growth factor.

No abstract

Abstract:In this work, we have explored 3-D co-culture of vasculogenic cells within a synthetically modified fibrin hydrogel. Fibrinogen was covalently linked with PEG-NHS in order to improve its degradability resistance and physico-optical properties. We have studied influences of the degree of protein PEGylation and the concentration of enzyme thrombin used for the gel preparation on cellular responses. Scanning electron microscopy analysis of prepared gels revealed that the degree of PEGylation and the concentration of thrombin strongly influenced microstructural characteristics of the protein hydrogel. Human umbilical vein endothelial cells (HUVECs) and human adipose-derived stem cells (hASCs), used as vasculogenic co-culture, could grow in 5:1 PEGylated fibrin gels prepared using 1:0.2 protein to thrombin ratio. This gel formulation supported hASCs and HUVECs spreading and the formation of cell extensions and cell-to-cell contacts. Expression of specific ECM proteins and vasculogenic process inherent cellular enzymatic activity were investigated by immunofluorescent staining, gelatin zymography, western blot and RT-PCR analysis. After evaluation of the optimal gel composition and PEGylation ratio, the hydrogel was utilized for investigation of vascular tube formation within a perfusable microfluidic system. The morphological development of this co-culture within a perfused hydrogel over 12 days led to the formation of interconnected HUVEC-hASC network. The demonstrated PEGylated fibrin microfluidic approach can be used for incorporating other cell types, thus representing a unique experimental platform for basic vascular tissue engineering and drug screening applications.

The two-photon polymerization technique (2PP) uses non-linear absorption of femtosecond laser pulses to selectively polymerize photosensitive materials. 2PP has the ability to fabricate structures with a resolution from tens of micrometers down to hundreds of nanometers. Three-dimensional microstructuring by the 2PP technique provides many interesting possibilities for biomedical applications. This microstructuring technique is suitable with many biocompatible polymeric materials, such as polyethylene glycol, polylactic acid, polycaprolactone, gelatin, zirconium-based hybrids, and others. The process of fabrication does not require clean room conditions and does not use hazard chemicals or high temperatures. The most beneficial property of 2PP is that it is capable of producing especially complex three-dimensional (3-D) structures, including devices with overhangs, without using any supportive structure. The flexibility in controlling geometries and feature sizes and the possibility to fabricate structures without the addition of new material layers makes this technique particularly appealing for fabrication of 3-D scaffolds for tissue engineering.

The clinical success of osseointegrated dental implants depends on the strong attachment of the surrounding hard and soft tissues. Bacterial adhesion on implant surfaces can cause inflammatory reactions and may influence healing and long-term success of dental implants. Promising implant coatings should minimize bacterial adhesion, but allow epithelial and connective tissue attachment. Therefore, the present study has examined the bioactive effect of poly-(4-vinyl-N-hexylpyridiniumbromide) regarding typical oral bacteria as well as cytotoxicitiy to human cells considering different methods of connecting polymers to silicate-containing surfaces. The results revealed that the application of putative antibacterial and biocompatible polymer in coating strategies is affected by a variety of parameters. Published findings regarding reduced bacterial adhesion could not be verified using oral pathogens whereas hexylated polymers seem problematic for strong adhesion of soft tissue. Concerning innovative coatings for dental implants basic aspects (surface roughness, thickness, alkylation, combination with other polymers) have to be considered in further investigations.