Enhancing Adhesion of Fibrin-Based Hydrogel to Polythioether Polymer Surfaces.

The development of stable (bio)hybrid constructs composed of scaffolds and (bio)matrices is a major challenge in the field of tissue engineering. In the present work, the adhesion of fibrin-based hydrogels to the surface of polythioether-based polymers relevant to the 3D printing of polymer scaffolds produced by thiol-ene click chemistry was investigated. Adhesion properties were characterized by single-lap tensile shear testing. Both the sample preparation and the test method were optimized for the analysis of fibrin gel bonding to the polythioether surface. Our experimental results show that even without further modification, an adhesion between the fibrin hydrogel and polythioether is substantial, with an adhesion strength of 4.9 ± 1.0 kPa. To further improve the bonding, linear functional poly(N-vinylpyrrolidone-co-glycidyl methacrylate) (PVP-co-GMA) copolymers were used that are known for covalently binding to fibrin. The maximum adhesion strength in our study was found to be 18.4 ± 3.4 kPa. The pure PVP-co-GMA copolymers also demonstrate covalent binding to the thiol-ene-based polymers with a maximum adhesion strength of 32.2 ± 2.7 kPa. Therefore, compared to pure fibrin, the presence of copolymer coating both on the polythioether surface and in the fibrin gel led to a significant increase of the adhesion strength by a factor of 1.6.

New stereolithographic resin providing functional surfaces for biocompatible three-dimensional printing.

Stereolithography is one of the most promising technologies for the production of tailored implants. Within this study, we show the results of a new resin formulation for three-dimensional printing which is also useful for subsequent surface functionalization. The class of materials is based on monomers containing either thiol or alkene groups. By irradiation of the monomers at a wavelength of 266 nm, we demonstrated an initiator-free stereolithographic process based on thiol-ene click chemistry. Specimens made from this material have successfully been tested for biocompatibility. Using Fourier-transform infrared spectrometry and fluorescent staining, we are able to show that off-stoichiometric amounts of functional groups in the monomers allow us to produce scaffolds with functional surfaces. We established a new protocol to demonstrate the opportunity to functionalize the surface by copper-catalyzed azide-alkyne cycloaddition chemistry. Finally, we demonstrate a three-dimensional bioprinting concept for the production of potentially biocompatible polymers with thiol-functionalized surfaces usable for subsequent functionalization.

Microstructured Hydrogel Templates for the Formation of Conductive Gold Nanowire Arrays.

Microstructured hydrogel allows for a new template-guided method to obtain conductive nanowire arrays on a large scale. To generate the template, an imprinting process is used in order to synthesize the hydrogel directly into the grooves of wrinkled polydimethylsiloxane (PDMS). The resulting poly(N-vinylimidazole)-based hydrogel is defined by the PDMS stamp in pattern and size. Subsequently, tetrachloroaurate(III) ions from aqueous solution are coordinated within the humps of the N-vinylimidazole-containing polymer template and reduced by air plasma. After reduction and development of the gold, to achieve conductive wires, the extension perpendicular to the long axis (width) of the gold strings is considerably reduced compared to the dimension of the parental hydrogel wrinkles (from ≈1 µm down to 200-300 nm). At the same time, the wire-to-wire distance and the overall length of the wires is preserved. The PDMS templates and hydrogel structures are analyzed with scanning force microscopy (SFM) and the gold structures via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The conductivity measurements of the gold nanowires are performed in situ in the SEM, showing highly conductive gold leads. Hence, this method can be regarded as a facile nonlithographic top-down approach from micrometer-sized structures to nanometer-sized features.

Exploiting Electrostatic Interactions in Polymer-Nanoparticle Hydrogels.

Shear-thinning injectable hydrogels exploit dynamic noncovalent cross-links to flow upon applied stress and rapidly self-heal once the stress is relaxed. These materials continue to gather interest as they afford minimally invasive deployment in the body for a variety of biomedical applications. Here, we present rationally engineered polymer-nanoparticle (PNP) interactions based on electrostatic forces for the fabrication of self-assembled hydrogels with shear-thinning and self-healing properties. The selective adsorption of negatively charged biopolymers, including hyaluronic acid (HA) and carboxymethylcellulose (CBMC), to biodegradable nanoparticles comprising poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) is enhanced with a positively charged surfactant, cetyltrimethylammonium bromide (CTAB). We demonstrate that, in this manner, electrostatic interactions can be leveraged to fabricate PNP hydrogels and characterize the viscoelastic properties of the gels imparted by CBMC and HA. This work introduces PNP hydrogels that use common biopolymers without the need for chemical modification, yielding extremely facile preparation and processing, which when coupled with the tunability of their properties are distinguishing features for many important biomedical and industrial applications.

On the incorporation of functionalities into hydroxyapatite capsules.

Nature is capable of building materials with tailor-made properties under ambient conditions for specific applications. We apply some of the basic building principles of biomineralization in this paper: we stabilize an oil/water emulsion with the protein hydrophobin and mineralize this emulsion, resulting in hollow mineral capsules. The use of an emulsion as a liquid template enables precise size control over the final capsules. We mimic nature by using complexing agents and surfactants as additives to alter the properties of the growing mineral. We also modify the mineral itself by addition of different cations. Furthermore, we show the inclusion of silver into the capsules. This should add antibacterial properties to the capsules and shows exemplarily that catalytically active metals can be included. While the manual process needs numerous working steps and long waiting times, we ease the whole process by automation and use phosphatases to shorten synthesis time. Our experiments show the flexibility and adaptability of our system, making it an ideal platform for various possible applications such as drug transport and especially as microreactors.