Crosby Research Group

Bioinspired Adhesion & Friction

Nature has beautiful examples of organisms that use adhesion for locomotion. We are developing fundamental knowledge of how these systems work in Nature, as well as guiding principles for developing synthetic materials that reproduce many of their attractive properties.

We have developed a robust scaling relationship that clearly identifies the key, governing parameters for the maximum force capacity of a reversible adhesive. This scaling relationship has led to new insight into the enabling mechanisms behind natural and synthetic bio-inspired adhesives as well as to the development of a new adhesive technology we call GeckskinTM.

We work with Prof. Duncan Irschick in the Department of Biology at UMass to understand the important lessons that has allowed Nature to scale adhesion across several orders of size, from beetles to geckos---so that we can produce materials with these properties on size scales that society can use!

Growth & Assembly

Materials that possess structural hierarchy have a special range of properties that span across several length scales from the nano- to the macroscale.  A variety of examples are seen in Nature, such as collagen assembling into fibrils, fibers, and extracellular matrices and tissues.  Our goal focuses on developing novel processing methods for fabricating macroscopic hierarchical structures from chemically tailored nanoscale particles and understanding their associated properties.

In collaboration with Prof. Todd Emrick, we exploit functional ligand chemistries to enable the creation of nanoparticle ribbons and fabrics that have excellent structural integrity.  The nanoparticle assemblies are released from their underlying substrate to reveal flexible and robust macroscale structures.  The flexibility is defined by the balance of the particle core size, ligand properties, particle packing, as well as ribbon and fabric geometry.  These materials offer tremendous potential for the design of flexible electronics, new optical devices, membranes, as well as protective coatings and materials for encapsulation and delivery of small objects.

Mechanics of Gels, Tissues and Thin Films

Gels are solids that are composed of a dilute network of material within a liquid domain.  Examples range from familiar items like Jell-O to biomaterials, like the the lens of an eye, to hydrogels, like those found in absorbant diapers.  The mechanical behavior of these materials is key to their utilization in both nature and new technology and is a function of the microstructural make-up of the material.  Currently, our group characterizes this microstructure/property relationship from both design and property measurement perspectives. To this end, we have developed a novel characterization technique we call Cavitation Rheology that is capable of locally quantifing the mechanical properties of soft materials, such as hydrogels.

Cavitation Rheology

Cavitation Rheology takes advantage of the unique elastic instability associated with non-linear elastic materials. This instability is the result of favorable growth for a bubble, or cavity, at some critical pressure related to the local elastic modulus combined with the energetic cost associated with the surface energy of the growing bubble. We are utilizing this technique to probe the mechanical properties of varieties of synthetic materials as well as living tissues.  An example of the latter is shown in the image on the right in which cavitation measurements are being performed in order to correlate disease in mouse skin with mechanical response.  Simultaneously, we characterize the fundamental principles governing a cavitation event under changes in local geometry (e.g.., confinement of the material being tested) and loading conditions (e.g., loading rate) in synthetic hydrogels and soft polymers.

Autonomous and Controlled Movement with Soft Materials

Upon the development of a critical stress, many materials and geometries experience a mechanical instability, which produces significant changes in geometry with small changes in stress. In nature, mechanical instabilities are ubiquitous with well-defined shapes, morphologies, and functions.  For instance, in the emergence of mountains and valleys and at a smaller scale such as fingerprint formation and the snapping of the Venus Flytrap. Inspired by these examples, we are interested in understanding the parameters that influence the evolution of buckled structures and take advantage of their morphologies to control the function of soft polymer surfaces.  

Studying the mechanics of wrinkles and folds, as well as crumpling and snapping surfaces, provide us with fundamental insights of the nonlinear deformation of polymer films. In addition, this knowledge allows for the fabrication of unique patterned surfaces that can be controlled reversibly.

From an application point of view, controlling surface instabilities can be used to tune properties ranging from adhesion to optics. Fundamental knowledge of surface instabilities will also lead to novel technological application relevant in the development of lightweight, flexible electronics and responsive surfaces for biological applications. 

The Crosby Research Group often hosts student and community groups, of all ages (K-12, undergraduate), or participates in science education outreach events. For more information on how we may be able to work with your group's goals, please contact Prof. Crosby at @email.