External compression-induced fracture patterning on the surface of poly(dimethylsiloxane) cubes and microspheres

Ordered surface crack patterns in situ formed under confinement on fluidic microchannel boundaries in polydimethylsiloxane

We present ordered surface crack patterns discovered in microfluidic channels/chambers in polydimethylsiloxane (PDMS). The cracks are formed in situ under confinement due to compression applied following an oxygen plasma step in a soft lithography process. The crack patterns are noticeable only after fluorescent labeling and vary with fluidic layout as well as material compliance.

Fracture-based fabrication of normally closed, adjustable, and fully reversible microscale fluidic channels

Adjustable fluidic structures play an important role in microfluidic systems. Fracture of multilayered materials under applied tension has been previously demonstrated as a convenient, simple, and inexpensive approach to fabricate nanoscale adjustable structures; here, it is demonstrated how to extend this concept to the microscale. This is achieved by a novel pairing of materials that leverages fracture mechanics to limit crack formation to a specified region, allowing to create size-controllable and adjustable microfluidic structures. This technique can be used to fabricate "normally closed" microfluidic channels that are completely reversible, a feature that is challenging to achieve in conventional systems without careful engineering controls. The adjustable microfluidic channels are then applied to mechanically lyse single cells, and subsequently manipulate the released nuclear chromatin, creating new possibilities for epigenetic analysis of single cells. This simple, versatile, and robust technology provides an easily accessible pathway to construct adjustable microfluidic structures, which will be useful in developing complex assays and experiments even in resource-limited settings.

Defined topologically-complex protein matrices to manipulate cell shape via three-dimensional fiber-like patterns

Culturing cells in three-dimensional (3D) environments has been shown to significantly influence cell function, and may provide a more physiologically relevant environment within which to study the behavior of specific cell types. 3D tissues typically present a topologically complex fibrous adhesive environment, which is technically challenging to replicate in a controlled manner. Micropatterning technologies have provided significant insights into cell-biomaterial interactions, and can be used to create fiber-like adhesive structures, but are typically limited to flat culture systems; the methods are difficult to apply to topologically-complex surfaces. In this work, we utilize crack formation in multilayered microfabricated materials under applied strain to rapidly generate well-controlled and topologically complex 'fiber-like' adhesive protein patterns, capable of supporting cell culture and controlling cell shape on three-dimensional patterns. We first demonstrate that the features of the generated adhesive environments such as width, spacing and topology can be controlled, and that these factors influence cell morphology. The patterning technique is then applied to examine the influence of fiber structure on the nuclear morphology and actin cytoskeletal structure of cells cultured in a nanofibrous biomaterial matrix.

One-dimensional patterning of cells in silicone wells via compression-induced fracture

We have adapted our existing compression-induced fracture technology to cell culture studies by generating linear patterns on a complex cell culture well structure rather than on simple solid constructs. We present a simple method to create one-dimensional (1D), submicron, and linear patterns of extracellular matrix on a multilayer silicone material. We identified critical design parameters necessary to optimize compression-induced fracture patterning on the wells, and applied stresses using compression Hoffman clamps. Finite-element analyses show that the incorporation of the well improves stress homogeneity (stress variation = 25%), and, thus, crack uniformity over the patterned region. Notably, a shallow well with a thick base (vs. deeper wells with thinner bases) reduces out-of-plane deflections by greater than a sixth in the cell culture region, improving clarity for optical imaging. The comparison of cellular and nuclear shape indices of a neuroblast line cultured on patterned 1D lines and unpatterned 2D surfaces reveals significant differences in cellular morphology, which could impact many cellular functions. Because 1D cell cultures recapitulate many important phenotypical traits of 3D cell cultures, our culture system offers a simple means to further study the relationship between 1D and 3D cell culture environments, without demanding expensive engineering techniques and expertise.

Fracture-based micro- and nanofabrication for biological applications

While fracture is generally considered to be undesirable in various manufacturing processes, delicate control of fracture can be successfully implemented to generate structures at micro/nano length scales. Fracture-based fabrication techniques can serve as a template-free manufacturing method, and enables highly-ordered patterns or fluidic channels to be formed over large areas in a simple and cost-effective manner. Such technologies can be leveraged to address biologically-relevant problems, such as in the analysis of biomolecules or in the design of culture systems that imitate the cellular or molecular environment. This mini review provides an overview of current fracture-guided fabrication techniques and their biological applications. We first survey the mechanical principles of fracture-based approaches. Then we describe biological applications at the cellular and molecular levels. Finally, we discuss unique advantages of the different system for biological studies.