Understanding Fibroblast Behavior in 3D Biomaterials

Traditional monolayer culture fails to fully recapitulate the in vivo environment of connective tissue cells such as the fibroblast. When cultured on stiff two-dimensional (2D) plastic, fibroblasts become highly proliferative forming broad lamellipodia and stress fibers. Conversely, in different three-dimensional (3D) culture systems, fibroblasts have displayed a diverse array of features; from an "activated" phenotype like that observed in 2D cultures and by myofibroblasts, to a quiescent state that likely better represents in vivo fibroblasts at rest. Today, a plethora of microfabrication techniques have made 3D culture commonplace, for both tissue engineering purposes and in the study of basic biological interactions. However, establishing the in vivo mimetic credentials of different biomimetic materials is not always straightforward, particularly in the context of fibroblast responses. Fibroblast behavior is governed by the complex interplay of biological features such as integrin binding sites, material mechanical properties that influence cellular mechanotransduction, and microarchitectural features like pore and fiber size, as well as chemical cues. Furthermore, fibroblasts are a heterogeneous group of cells with specific phenotypic traits dependent on their tissue of origin. These features have made understanding the influence of biomaterials on fibroblast behavior a challenging task. In this study, we present a review of the strategies used to investigate fibroblast behavior with a focus on the material properties that influence fibroblast activation, a process that becomes pathological in fibrotic diseases and certain cancers.

Exploiting Substrate Cues for Co-Culturing Cells in a Micropattern

Spatial distribution of cells and their interactions between neighboring cells in native microenvironments are of fundamental importance in determining cell fate decisions such as migration, growth, and differentiation. Controlling the spatial distribution of different cell types in defined geometries can replicate these native environments, which can be a useful model for several studies. While spatiotemporal control over multiple cell arrangements is required to achieve the complex tissue architecture, unfortunately, conventional cell patterning techniques usually allow only single patterning with a single cell type. In the present study, we introduce a simple lithographic method to pattern multiple cell types in a spatially controlled manner by utilizing the biophysical cues present at the corners of the patterned geometry. By fabricating micropatterns of different shapes, we demonstrate how the cell can be constrained to pattern along the corners of patterned geometries owing to the presence of topographical cues, leaving empty voids in the center that can be further utilized for patterning a second cell type. We also demonstrate that the cell alignment along the pattern is a dynamic process and the cells migrate from a more uniform cell-adhesive region toward the topographical cues. The cytoskeleton arrangement was geometry-dependent, which was confirmed through a series of in vitro evaluations, such as scanning electron microscopy and fluorescence microscopy. These findings have not only helped us in exploring the importance of these cues in guiding the cell fate but have also allowed us to develop a technique, which self-patterns the cells without any expensive exogenous cues and can be used as a model protocol to eventually organize cells into a specific pattern with micron-scale precision in vitro.

Hang on tight: reprogramming the cell with microstructural cues

Cells interact intimately with complex microdomains in their extracellular matrix (ECM) and maintain a delicate balance of mechanical forces through mechanosensitive cellular components. Tissue injury results in acute degradation of the ECM and disruption of cell-ECM contacts, manifesting in loss of cytoskeletal tension, leading to pathological cell transformation and the onset of disease. Recently, microscale hydrogel constructs have been developed to provide cells with microdomains to form focal adhesion binding sites, which enable restoration of cytoskeletal tension. These synthetic anchors can recapitulate the complex 3D architecture of the native ECM to provide microtopographical cues. The mechanical deformation of proteins at the cell surface can activate signaling cascades to modulate downstream gene-level transcription, making this a unique materials-based approach for reprogramming cell behavior. An overview of the mechanisms underlying these mechanosensitive interactions in fibroblasts, stem and other cell types is provided to review their effects on cellular reprogramming. Recent investigations on the fabrication, functionalization and implementation of these materials and microtopographical features for drug testing and therapeutic applications are discussed.

Antibacterial titanium nano-patterned arrays inspired by dragonfly wings

Titanium and its alloys remain the most popular choice as a medical implant material because of its desirable properties. The successful osseointegration of titanium implants is, however, adversely affected by the presence of bacterial biofilms that can form on the surface, and hence methods for preventing the formation of surface biofilms have been the subject of intensive research over the past few years. In this study, we report the response of bacteria and primary human fibroblasts to the antibacterial nanoarrays fabricated on titanium surfaces using a simple hydrothermal etching process. These fabricated titanium surfaces were shown to possess selective bactericidal activity, eliminating almost 50% of Pseudomonas aeruginosa cells and about 20% of the Staphylococcus aureus cells coming into contact with the surface. These nano-patterned surfaces were also shown to enhance the aligned attachment behavior and proliferation of primary human fibroblasts over 10 days of growth. These antibacterial surfaces, which are capable of exhibiting differential responses to bacterial and eukaryotic cells, represent surfaces that have excellent prospects for biomedical applications.

Phase-contrast microtomography with synchrotron radiation technology: a new noninvasive technique to analyze the three-dimensional structure of dermal tissues

BACKGROUND

Since the three-dimensional (3-D) structure of dermal tissue has an important role in regulating cell behavior and directing the wound healing process, the characteristic of the 3-D structure of dermal tissue needs to be clarified.

OBJECTIVE

To explore the different 3-D structures between normal and scar dermal tissues.

MATERIAL AND METHODS

Phase-contrast microtomography with synchrotron radiation technology was applied to detect the 3-D structure of dermal tissues.

RESULTS

The normal dermal tissue consists of elliptical structures formed by fiber bundles interwoven in a helical manner. A regular louver-like structure was observed on the fibers. In scar tissue, the fiber bundles were arrayed in parallel, the louver-like structures were disordered.

CONCLUSION

The study demonstrates the mesoscopic difference between normal dermal tissue and scar tissue, suggests that the high level of interweaving capability of collagen is compromised/lost when dermal tissue is injured, and provides a basis for future studies.

In vivo biofunctionality comparison of different topographic PLLA scaffolds

In this work, the in vivo biodegradation of, biocompatibility of, and host response to various topographic scaffolds were investigated. Randomly oriented fibrous poly(L-lactide) (PLLA) nanofibers were fabricated using the electrospinning technique. A PLLA scaffold was obtained by salt leaching. Both the electrospun PLLA nanofibers and the salt-leaching PLLA scaffolds formed three-dimensional pore structures. Cytotoxicity studies, in which rat muscle-derived stem cells (rMDSCs) were grown on electrospun PLLA nanofibers or the salt-leaching PLLA scaffolds, revealed that the rMDSCs cell count on the PLLA nanofibers was slightly higher than that on the salt-leaching PLLA scaffolds. An in vivo study was carried out by implanting the scaffolds subcutaneously into rats to test the biodegradation, biocompatibility, and host response at regular intervals over 0-4 weeks. The degradation of the PLLA nanofibers 1, 2, and 4 weeks after initial implantation was more extensive than that observed for the salt-leaching PLLA scaffolds. PLLA nanofibers seeded the growth of larger fibrous tissue masses due to in vivo cellular infiltration into the randomly oriented fibrillar structures of the PLLA nanofibers. In addition, the inflammatory cell accumulation in PLLA nanofibers was lower than that in the salt-leaching PLLA scaffolds. These results indicate that the electrospun PLLA nanofibers may serve as a good scaffold to elicit fibrous cellular infiltration, to minimize host response, and to enhance tissue-scaffold integration.