Chitin, a biopolymer of N-acetylglucosamine, is abundant in invertebrates and fungi, and is an important structural molecule. There has been a longstanding belief that vertebrates do not produce chitin, however, we have obtained compelling evidence to the contrary. Chitin synthase genes are present in numerous fishes and amphibians, and chitin is localized in situ to the lumen of the developing zebrafish gut, in epithelial cells of fish scales, and in at least three different cell types in larval salamander appendages. Chitin synthase gene knockdowns and various histochemical experiments in zebrafish further authenticated our results. Finally, a polysaccharide was extracted from scales of salmon that exhibited all the chemical hallmarks of chitin. Our data and analyses demonstrate the existence of endogenous chitin in vertebrates and suggest that it serves multiple roles in vertebrate biology.

A material inspired by natural insect cuticle and composed of chitosan and fibroin is created. The material exhibits the strength of an aluminum alloy at half its weight, while being clear, biocompatible, biodegradable, and micromoldable. The bioinspired laminate exhibits strength and toughness that are ten times greater than the unstructured component blend and twice that of its strongest constituent.

A general method for construction of three dimensional structures by directed assembly of microscale polymeric sub-units is presented. Shape-controlled microgels are directed to assemble into different shapes by limiting their movement onto a molded substrate. The capillary forces, resulting from the presence of a liquid polymer, assemble the microgels in close contact with the rest of the units and with the free surface, the latter imposing the final geometry of the resulting construct. The result is a freestanding structure composed of one or multiple layers of sub-units assembled in a tightly packed conformation. The applicability of the technique for the construction of scaffolds with cell-laden sub-units is demonstrated. In addition, scaffolds formed by the sequential aggregation of sub-units are produced.The formation of complex structures through self-regulating aggregation of smaller sub-units is a strategy broadly observed in nature; from the cytoskeletal structure within cells to the formation of coral reefs. Self-assembly is driven by the attempt of a system to minimize its energy by spontaneous assembly of individuals units. The process of self-assembly is characterized by the formation of complex structures via the spontaneous combination of discrete small sub-units at an energy minimum.Self-assembly process could be categorized based on the size of the units into "molecular selfassembly" and "mesoscale self-assembly" (MESA) [1]. Technologies based on MESA have emerged as a promising approach for the spontaneous construction of several shapes with a large number of materials. Potential applications include microelectronics, MEMS, sensors and micro-analytical devices [2]. Additionally, tissue engineering can potentially benefit from MESA, where bottom-up assembly of building blocks containing cells can be used to engineer artificial tissues [3]. For example, cell-laden sub-units have been assembled to form tissues with high spatial resolution by using both MESA [4] and microfluidics [5].Most MESA approaches use hydrophilic-hydrophobic interactions to assemble the sub-units. However, a major limitation of this approach is that it can only be used to generate a limited number of shapes that are defined by the boundaries between the different phases [6]. In this work, we introduce a technique where a surface, acting as a template, partially restricts the subunits by confining them and direct the assembly process. In particular, we used polydimethylsiloxane (PDMS), a versatile and widely used elastomeric material that can easily be molded to replicate the shape and topography of many structures in 2D and 3D [7]. As presented in Figure 1, microgels made with specific shapes were mixed in a pre-polymer solution ( Figure 1A) and spread on a PDMS surface ( Figure 1B). During this process, the liquid wets the surface and drags the microgel sub-units as it covers the PDMS template ( Figure 1C). Upon removal of the excess pre-polymer (e.g. by pipetting or by using an absorbent material), microgels assem...