Cell Adhesion Assessment Reveals a Higher Force per Contact Area on Fibrous Structures Compared to Flat Substrates.

The distribution and density of ligands have a determinant role in cell adhesion on planar substrates. At the same time, planar surfaces are nonphysiological for most cells, and cell behavior on planar and topographical surfaces is significantly different, with fibrous structures being the most natural environment for cells. Despite phenomenological examinations, the role of adhesion ligand density in the fibrous scaffold for cell adhesion strength has so far not been assessed. Here, we established a method to measure the amount of cell ligands on biofunctionalized electrospun meshes and planar substrate coatings with the same chemical composition. With this as a basis for systematic comparison and pure polyester as benchmark substrates, we have cultured L929 mouse fibroblasts and measured the adhesion force to surfaces of different chemistry and topography. In every case, having fibrous structures have led to an increased adhesion force per area also at a lower ligand density, which remarks the importance of such structures in a natural extracellular environment. Conversely, cells migrate more on planar surfaces than on the tested fibrous substrates. We thus established a platform to study cell-matrix interactions on different surfaces in a precise and reproducible manner as a new tool to assess and quantify cell-matrix interactions toward 3D scaffolds.

Bioactive Electrospun Fibers: Fabrication Strategies and a Critical Review of Surface-Sensitive Characterization and Quantification.

Fabricating a porous scaffold with high surface area has been a major strategy in the tissue engineering field. Among the many fabrication methods, electrospinning has become one of the cornerstone techniques due to its enabling the fabrication of highly porous fibrous scaffolds that are of natural or synthetic origin. Apart from the basic requirements of mechanical stability and biocompatibility, scaffolds are further expected to embody functional cues that drive cellular functions such as adhesion, spreading, proliferation, migration, and differentiation. There are abundant distinct approaches to introducing bioactive molecules to have a control over cellular functions. However, the lack of a thorough understanding of cell behavior with respect to the availability and spatial distribution of the bioactive molecules in 3D fibrous scaffolds is yet to be addressed. The rational selection of proper sets of characterization techniques would essentially impact the interpretation of the cell-scaffold interactions. In this timely Review, we summarize the most popular methods to introduce functional compounds to electrospun fibers. Thereafter, the strength and limitations of the conventional characterization methods are highlighted. Finally, the potential and applicability of emerging characterization techniques such as high-resolution/correlative microscopy approaches are further discussed.

Prefabricated and Self-Setting Cement Laminates.

Polycaprolactone (PCL) fiber mats with defined pore architecture were shown to provide sufficient support for a premixed calcium phosphate cement (CPC) paste to serve as a flat and flexible composite material for the potential application in 2-dimensional, curved cranial defects. Fiber mats were fabricated by either melt electrospinning writing (MEW) or solution electrospinning (SES) with a patterned collector. While MEW processed fiber mats led to a deterioration of the cement bending strength by approximately 50%, due to a low fiber volume content in conjunction with a weak fiber-matrix interface, fiber mats obtained by solution electrospinning resulted in a mechanical reinforcement of the cement matrix in terms of both bending strength and absorbed fracture energy. This was attributed to a higher fiber volume content and a large contact area between nanosized fibers and cement matrix. Hydrophilization of the PCL scaffolds prior to lamination further improved composite strength and preserved the comparably higher fracture energy of 1.5 to 2.0 mJ/mm². The laminate composite approach from this study was successful in demonstrating the limitations and design options of such novel composite materials. However, fiber-cement compatibility remains an issue to be addressed, since a high degree of hydrophilicity does not necessarily provoke a stronger interface.

A Bone Glue with Sustained Adhesion under Wet Conditions.

Bone glues often suffer from low adhesion to bone under wet conditions. This study aims to improve wet adhesiveness of a bone glue based on a photocurable poly(ethylene glycol) dimethacrylate matrix through in situ interpenetrating network formation by addition of six-armed isocyanate functional star-shaped prepolymers (NCO-sP(EO-stat-PO)). Biodegradable ceramic fillers are added to adjust the paste workability. The 3-point bending strength of the bone glues is in the range of 3.5-5.5 MPa and not significantly affected by the addition of NCO-sP(EO-stat-PO). Storage in phosphate buffered saline (PBS) decreases the bending strength of all formulations to approximately 1 MPa but the adhesion to cortical bone increases from 0.15-0.2 to 0.3-0.5 MPa after adding 20-40 wt% NCO-sP(EO-stat-PO) to the matrix. Bone glues without the NCO-sP(EO-stat-PO) additive lose their adhesiveness to bone after aging in PBS for 7 days, whereas modified glues maintain a shear strength of 0.18-0.25 MPa demonstrating the efficacy of the approach. Scanning electron microscopy and energy-dispersive X-ray spectroscopy investigations of the fracture surfaces prove a high amount of residual adhesive on the bone surface indicating that adhesion to the bone under wet conditions is stronger than cohesion.

Isotropic Versus Bipolar Functionalized Biomimetic Artificial Basement Membranes and Their Evaluation in Long-Term Human Cell Co-Culture.

In addition to dividing tissues into compartments, basement membranes are crucial as cell substrates and to regulate cellular behavior. The development of artificial basement membranes is indispensable for the ultimate formation of functional engineered tissues; however, pose a challenge due to their complex structure. Herein, biodegradable electrospun polyester meshes are presented, exhibiting isotropic or bipolar bioactivation as a biomimetic and biofunctional model of the natural basement membrane. In a one-step preparation process, reactive star-shaped prepolymer additives, which generate a hydrophilic fiber surface, are electrospun with cell-adhesion-mediating peptides, derived from major components of the basement membrane. Human skin cells adhere to the functionalized meshes, and long-term co-culture experiments confirm that the artificial basement membranes recapitulate and preserve tissue specific functions. Several layers of immortalized human keratinocytes grow on the membranes, differentiating toward the surface and expressing typical epithelial markers. Fibroblasts migrate into the reticular lamina mimicking part of the mesh. Both cells types begin to produce extracellular matrix proteins and to remodel the initial membrane. It is shown at the example of skin that the artificial basement membrane design provokes biomimetic responses of different cell types and can thus be used as basis for the future development of basement membrane containing tissues.