Novel Composites and Multi-Material Assembly Approaches for Tissue Regeneration

Tissue engineering conventionally relies on the combination of cells and a material scaffold. These scaffolds were originally intended to bear mechanical loads while allowing the cells to create new tissue. Strong porous materials were hence the obvious choice and polymers appeared as ideal candidates due to the ease of processability and of introduction of porosity at desired locations. Controllable biodegradability, and presentation of biochemical stimulants on the scaffold surfaces or in the bulk (when they could be released) gave these scaffolds additional advantages. In recent years, as the importance of cell-extracellular matrix interactions and local mechanical properties, such as stiffness, became fully appreciated, the focus has shifted slightly from hard-polymeric scaffolds that mimic the bulk tissue mechanics to hydrogels that can mimic the local environments for cells. However, one material is often not enough to yield all desirable properties (mechanical, biochemical and structural), and several composites (combination of materials where individual components retain distinct phases, at larger than molecular scales) have been utilized. Composites are in fact what biology often uses to get combinations of properties that cannot exist simultaneously in most materials due to trade-offs. In addition, novel composites that embed a stimuli-responsive phase enabling some form of physical stimulation for cells are also on the rise - for example, the introduction of an electrical conductor or a magnetic phase are being explored for electrical or remote mechanical stimulation of cells, respectively.

In any composite, two factors are of importance - the interface/interaction between the phases and the relative organization of the phases. A strong interaction that allows binding between phases while maintaining the properties of each of the components is required. The relative organization of the phases can be a random and uniform dispersion. For example, one phase can be aligned to be stronger in the load bearing direction or it can follow other patterns such as body centre cubic (BCC), hexagonal, etc. While random, uniform dispersions are easier to generate by mixing and simultaneously depositing the multiple phases, organized phases can sometimes better represent the architectural features of the tissues to be mimicked.

This Research Topic aims at compiling the latest research on the various classes of composite materials that have been used so far in tissue engineering, along with the methods and the engineering challenges to get the right interfacing and relative organization between the component phases, as well as the outcomes of these controlled cell-biomaterial composite interactions. Original research articles and review manuscripts will be considered. Topics of interest will thus revolve around the design, fabrication and application of composite materials (both organic and inorganic) for tissue regeneration including, but not limited to:

-Organic and/or inorganic composite materials for tissue regeneration, preferably material combinations that have not been widely studied previously.
-Self-assembled (multi-material) systems for tissue regeneration.
-Composite materials that mimic the ECM.
-Composite materials as stimulus responsive tissue engineering scaffolds.
-Spatially controlled presentation of bioactive molecules.
-Multi-material scaffold fabrication techniques utilizing multi-scale/hierarchical organization strategies.