Electron beam treated injectable agarose/alginate beads prepared by electrospraying.

Granular hydrogels have evolved into an innovative technology for biomedicine. Unlike conventional hydrogels, granular hydrogels display dynamic properties like injectability and porosity, making them feasible for applications in 3D bioprinting and tissue engineering. High-energy electron irradiation combines sterilization and tuning of hydrogel properties without adding potentially cytotoxic chemicals. In this study, granular agarose/alginate hydrogels are prepared by electrospraying. Utilizing 10 MeV electron irradiation, the granular hydrogels are treated in a dose range of 0 kGy-30 kGy relevant for sterilization. Herein, a size reduction of the microparticles is observed. Mechanical properties of individual agarose/alginate beads are examined using AFM measurements revealing a gel softening attributed to radiation induced chain scission. Shear-thinning and self-healing characteristics of the entire granular hydrogel are studied employing rheology. Although viscoelasticity changes under irradiation, shear-thinning and self-healing prevails. These dynamic properties enable injection, which is demonstrated for 27 G needles. This study presents a mechanical characterization of high-energy electron irradiated granular agarose/alginate hydrogels that extends the diversity of available injectable hydrogels and provides a basis for biomedical applications of this scaffold.

A Versatile Macromer-Based Glycosaminoglycan (sHA3) Decorated Biomaterial for Pro-Osteogenic Scavenging of Wnt Antagonists.

High serum levels of Wnt antagonists are known to be involved in delayed bone defect healing. Pharmaceutically active implant materials that can modulate the micromilieu of bone defects with regard to Wnt antagonists are therefore considered promising to support defect regeneration. In this study, we show the versatility of a macromer based biomaterial platform to systematically optimize covalent surface decoration with high-sulfated glycosaminoglycans (sHA3) for efficient scavenging of Wnt antagonist sclerostin. Film surfaces representing scaffold implants were cross-copolymerized from three-armed biodegradable macromers and glycidylmethacrylate and covalently decorated with various polyetheramine linkers. The impact of linker properties (size, branching) and density on sHA3 functionalization efficiency and scavenging capacities for sclerostin was tested. The copolymerized 2D system allowed for finding an optimal, cytocompatible formulation for sHA3 functionalization. On these optimized sHA3 decorated films, we showed efficient scavenging of Wnt antagonists DKK1 and sclerostin, whereas Wnt agonist Wnt3a remained in the medium of differentiating SaOS-2 and hMSC. Consequently, qualitative and quantitative analysis of hydroxyapatite staining as a measure for osteogenic differentiation revealed superior mineralization on sHA3 materials. In conclusion, we showed how our versatile material platform enables us to efficiently scavenge and inactivate Wnt antagonists from the osteogenic micromilieu. We consider this a promising approach to reduce the negative effects of Wnt antagonists in regeneration of bone defects via sHA3 decorated macromer based macroporous implants.

Employing Nanostructured Scaffolds to Investigate the Mechanical Properties of Adult Mammalian Retinae Under Tension.

Numerous eye diseases are linked to biomechanical dysfunction of the retina. However, the underlying forces are almost impossible to quantify experimentally. Here, we show how biomechanical properties of adult neuronal tissues such as porcine retinae can be investigated under tension in a home-built tissue stretcher composed of nanostructured TiO2 scaffolds coupled to a self-designed force sensor. The employed TiO2 nanotube scaffolds allow for organotypic long-term preservation of adult tissues ex vivo and support strong tissue adhesion without the application of glues, a prerequisite for tissue investigations under tension. In combination with finite element calculations we found that the deformation behavior is highly dependent on the displacement rate which results in Young's moduli of (760-1270) Pa. Image analysis revealed that the elastic regime is characterized by a reversible shear deformation of retinal layers. For larger deformations, tissue destruction and sliding of retinal layers occurred with an equilibration between slip and stick at the interface of ruptured layers, resulting in a constant force during stretching. Since our study demonstrates how porcine eyes collected from slaughterhouses can be employed for ex vivo experiments, our study also offers new perspectives to investigate tissue biomechanics without excessive animal experiments.

Multifunctional coatings combining bioactive peptides and affinity-based cytokine delivery for enhanced integration of degradable vascular grafts.

Insufficient endothelialization of cardiovascular devices is a high-risk factor for implant failure. Presentation of extracellular matrix (ECM)-derived coatings is a well-known strategy to improve implant integration. However, the complexity of the system is challenging and strategies for applying multifunctionality are required. Here, we engineered mussel-derived surface-binding peptides equipped with integrin (c[RGDfK]) and proteoglycan binding sites (FHRRIKA) for enhanced endothelialization. Surface-binding properties of the platform containing l-3,4-dihydroxyphenylalanine (DOPA) residues were confirmed for hydrophilized polycaprolactone-co-lactide scaffolds as well as for glass and polystyrene. Further, heparin and the heparin-binding angiogenic factors VEGF, FGF-2 and CXCL12 were immobilized onto the peptide in a modular assembly. Presentation of bioactive peptides greatly enhanced human umbilical vein endothelial cell (HUVEC) adhesion and survival under static and fluidic conditions. In subsequent investigations, peptide-heparin-complexes loaded with CXCL12 or VEGF had an additional increasing effect on cell viability, differentiation and migration. Finally, hemocompatibility of the coatings was ensured. This study demonstrates that coatings combining adhesion peptides, glycosaminoglycans and modulators are a versatile tool to convey ECM-inspired multifunctionality to biomaterials and efficiently promote their integration.

Endothelialization of Titanium Surfaces by Bioinspired Cell Adhesion Peptide Coatings.

Common interventional therapies for cardiovascular occlusive diseases, such as the implantation of stents, are at risk of complications like thrombosis or restenosis. Drug-eluting stents have improved patency but simultaneously worsen the endothelialization of the implant. Here, we present a novel peptide coating derived from three proteins of the extracellular matrix named fibronectin, laminin, and elastin. Their active sequences RGD, SIKVAV, and VGVAPG were immobilized onto titanium surfaces by a carrier peptide containing l-3,4-dihydroxyphenylalanine (DOPA). Simultaneous functionalization of the carrier peptide with cyclic c[RGDfK] and SIKVAV had the most potent influence on adhesion, proliferation, viability, and angiogenesis of endothelial cells. By presentation of two adhesion peptides in one molecule, a synergistic enhancement of cell-surface interactions was achieved. Overall, this work clearly demonstrates the advantages of spatially defined peptide coatings for the endothelialization of titanium and thus describes a promising approach for the coating of stents.

Regeneration of TiO2 Nanotube Arrays after Long-Term Cell and Tissue Culture for Multiple Use - an Environmental Scanning Electron Microscopy (ESEM) Survey of Adult Pig Retina and beyond.

Long-term organotypic culture of adult tissues not only open up possibilities for studying complex structures of explants in vitro, but also can be employed e.g. to investigate pathological changes, their fingerprints on tissue mechanics, as well as the effectiveness of drugs. While conventional culture methods do not allow for survival times of more than a few days, we have demonstrated recently that TiO2 nanotube arrays allow to maintain integrity of numerous tissues, including retina, brain, spline and tonsils, for as long as 2 weeks in vitro. A mystery in culturing has been the interaction of tissue with these substrates, which is also reflected by tissue debris after liftoff. As the latter reveals fingerprints of tissue adhesion and impedes with nanotube array reuse, we address within the present environmental scanning electron study debris nature and the effectiveness of cleaning approaches of distinct physical and chemical methods, including UV-light irradiation, O2 plasma treatment and application of an enzyme-based buffer. This will lays the foundation for large-scale regeneration and reuse of nanotube arrays in science and clinical research.