Spatial patterning of nanofibrous collagen scaffolds modulates fibroblast morphology

Cell-Tissue Interaction: The Biomimetic Approach to Design Tissue Engineered Biomaterials

The advancement achieved in Tissue Engineering is based on a careful and in-depth study of cell-tissue interactions. The choice of a specific biomaterial in Tissue Engineering is fundamental, as it represents an interface for adherent cells in the creation of a microenvironment suitable for cell growth and differentiation. The knowledge of the biochemical and biophysical properties of the extracellular matrix is a useful tool for the optimization of polymeric scaffolds. This review aims to analyse the chemical, physical, and biological parameters on which are possible to act in Tissue Engineering for the optimization of polymeric scaffolds and the most recent progress presented in this field, including the novelty in the modification of the scaffolds' bulk and surface from a chemical and physical point of view to improve cell-biomaterial interaction. Moreover, we underline how understanding the impact of scaffolds on cell fate is of paramount importance for the successful advancement of Tissue Engineering. Finally, we conclude by reporting the future perspectives in this field in continuous development.

Assembly of Rolled-Up Collagen Constructs on Porous Alumina Textiles

Developing new techniques to prepare free-standing tubular scaffolds has always been a challenge in the field of regenerative medicine. Here, we report a new and simple way to prepare free-standing collagen constructs with rolled-up architecture by self-assembling nanofibers on porous alumina (Al2O3) textiles modified with different silanes, carbon or gold. Following self-assembly and cross-linking with glutaraldehyde, collagen nanofibers spontaneously rolled up on the modified Al2O3 textiles and detached. The resulting collagen constructs had an inner diameter of approximately 2 to 4 mm in a rolled-up state and could be easily detached from the underlying textiles. Mechanical testing of wet collagen scaffolds following detachment yielded mean values of 3.5 ± 1.9 MPa for the tensile strength, 41.0 ± 20.8 MPa for the Young's modulus and 8.1 ± 3.7% for the elongation at break. No roll-up was observed on Al2O3 textiles without any modification, where collagen did not assemble into fibers, either. Blends of collagen and chitosan were also found to roll into fibrous constructs on silanized Al2O3 textiles, while fibrinogen nanofibers or blends of collagen and elastin did not yield such structures. Based on these differences, we hypothesize that textile surface charge and protein charge, in combination with the porous architecture of protein nanofibers and differences in mechanical strain, are key factors in inducing a scaffold roll-up. Further studies are required to develop the observed roll-up effect into a reproducible biofabrication process that can enable the controlled production of free-standing collagen-based tubes for soft tissue engineering.

Collagen Nanoyarns: Hierarchical Three-Dimensional Biomaterial Constructs

Hierarchical fibrous scaffolds (HFS) consist of nanoscale fibers arranged in larger macroscale structures, much in the same pattern as in native tissue such as tendon and bone. Creation of continuous macroscale nanofiber yarns has been made possible using modified electrospinning set-ups that combine electrospinning with techniques such as twisting, drawing, and winding. In this paper, a modified electrospinning setup was used to create continuous yarns of twisted type I collagen nanofibers, also known as collagen nanoyarns (CNY), from collagen solution prepared in acetic acid. Fabricated CNYs were cross-linked and characterized using SEM imaging and mechanical testing, while denaturation of collagen and dissolution of the scaffolds were assessed using circular dichroism (CD) and UV-vis spectroscopy, respectively. HeLa cells were then cultured on the nanoyarns for 24 h to assess cell adhesion on the scaffolds. Scanning electron micrographs revealed a twisted nanofiber morphology with an average nanofiber diameter of 213 ± 60 nm and a yarn diameter of 372 ± 23 μm that shrank by 35% after covalent cross-linking. Structural denaturation assessment of native collagen using circular dichroism (CD) spectroscopy showed that 60% of the triple-helical collagen content in CNYs was retained. Cross-linking of CNYs significantly improved their mechanical properties as well as stability in buffered saline with no sign of degradation for 14 days. In addition, CNY strength and stiffness increased significantly with cross-linking although in the wet state, significant loss in these properties, with a corresponding increase in elasticity, was observed. HeLa cells cultured on cross-linked CNYs for 24 h adhered to the yarn surface and oriented along the nanofiber alignment axis, displaying the characteristic spindle-like morphology of cells grown on surfaces with aligned topography. Collectively, the results demonstrate the promising potential of collagen nanoyarns as a new class of shapable biomaterial scaffold and building block for generating macroscale fiber-based tissues.

Self-assembled fibrinogen nanofibers support fibroblast adhesion and prevent E. coli infiltration

Fibrinogen nanofibers hold great potential for wound healing applications since they mimic the native blood clot architecture and offer important binding sites to support fibroblast adhesion and migration. Recently, we introduced a new method of salt-induced self-assembly to prepare nanofibrous fibrinogen scaffolds. Here, we present our results on the mechanical properties of these scaffolds and their interaction with 3T3 fibroblasts and E. coli bacteria, which we used as model systems for wound healing. Hydrated, nanofibrous fibrinogen scaffolds showed a Young's modulus of 1.3 MPa, which is close to the range of native fibrin. 3T3 fibroblasts adhered and proliferated well on nanofibrous and planar fibrinogen up to 72 h with a less pronounced actin cytoskeleton on nanofibers in comparison to planar fibrinogen. Fibroblasts on nanofibers were smaller with many short filopodia while larger cells with few long filopodia were found on planar fibrinogen. Live cell tracking revealed higher migration velocities on nanofibers in comparison to planar fibrinogen. The growth of E. coli bacteria on nanofibrous fibrinogen was significantly reduced as compared to agar controls with no bacteria migrating through the nanofibers. In summary, we conclude that self-assembled fibrinogen nanofibers could become highly attractive as future scaffolds for wound healing applications.