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. Impact statement This review considers the range of materials that have been used to investigate fibroblast behavior in three-dimensional (3D) culture. It evaluates the merits of each material, the results gained, and the evolving rationale behind the presented studies. We highlight aspects of 3D culture from porosity to polarity and their varied impact on fibroblast behavior. Understanding fibroblast behavior and mechanisms of control in vitro not only serves as a direct therapeutic opportunity in diseases from cancer to fibrosis but also can facilitate progress for future regenerative therapies.