Improving Polysaccharide-Based Chitin/Chitosan-Aerogel Materials by Learning from Genetics and Molecular Biology

Abstract

Improved wound healing of burnt skin and skin lesions, as well as medical implants and replacement products, requires the support of synthetical matrices. Yet, producing synthetic biocompatible matrices that exhibit specialized flexibility, stability, and biodegradability is challenging. Synthetic chitin/chitosan matrices may provide the desired advantages for producing specialized grafts but must be modified to improve their properties. Synthetic chitin/chitosan hydrogel and aerogel techniques provide the advantages for improvement with a bioinspired view adapted from the natural molecular toolbox. To this end, animal genetics provide deep knowledge into which molecular key factors decisively influence the properties of natural chitin matrices. The genetically identified proteins and enzymes control chitin matrix assembly, architecture, and degradation. Combining synthetic chitin matrices with critical biological factors may point to the future direction with engineering materials of specific properties for biomedical applications such as burned skin or skin blistering and extensive lesions due to genetic diseases.

Keywords: aerogel; chitin; chitosan; drosophila; insect; materials; obst-A; proteins; skin substitutes; wound healing.

Figure 1

Schematic drawing presenting selected steps of a workflow of chitin/chitosan-aerogel production. (A) Network formation methods at the molecular level either by covalent bonding or by Van der Waals forces, mainly hydrogen bonding. (B) A general principle workflow of aerogel synthesis includes several steps: network-formation, solvent exchange, and drying. For more details, see [54,114,133].

Figure 2

Synthetic and genetically controlled chitin matrices. (A) Scanning electron microscopy images of aerogel chitosan derivates [133]. Scale bars indicate 2 µm (left) and 0.5 µm (right). (B) 3D-projections of confocal Z-stacks of whole-mount immunostainings showing chitin (green) in late Drosophila embryos. Anterior is left, dorsal is up. An Alexa488-linked chitin-binding probe (green) detects chitin in the tracheal tube lumen. The main tracheal tube (marked by yellow lines) is straight and stable (arrow, left image) in wt but over-elongated and unstable with sinusoidal buckling (arrow, right image) in obstructor (obst)-A null mutants. Inlay, wt embryo shows a bright chitin staining (green) in the tracheal tubes, while the obst-A null mutant embryo contains only weak chitin staining (green), indicating unusual premature degradation of the matrix. The α-Spectrin antibody marks the tracheal cell membranes (red). Scale bars indicate 10 µm (inlay) or 100 µm. (C) Confocal images of ultrathin epidermal sections of larval immunostainings. The wt epidermis (upper image) contains a tight cuticle (indicated by the yellow line) that shapes the straight appearance of the epidermis (arrow) of the animal. In obst-A mutants (lower image), the epidermal chitin matrix (yellow line) lost its stability and integrity, resulting in a fragile, wrinkled epidermis (arrow) with partial lesions between cells and cuticle. The Obst-A and Knickkopf antibodies detect the chitin matrix. The Alexa633 conjugated wheat germ agglutinin (WGA, in blue) is a lectin that marks chitin and membranes. Scale bar indicates 10 µm. (D) Transmission electron microscopy images reveal the soft non-lamellar (upper image, arrows), tracheal and tight lamellar (lower image, arrows point to chitin-lamellae) epidermal chitin matrices. Images were provided by Dr. Dietmar Riedel (Electron Microscopy Group, Max-Planck-Institute for Biophysical Chemistry). Note the fine twisted plywood-like structure of lamellar chitin-protein planes in the epidermis. Red lines indicate epidermal cell surfaces. Scale bar indicates 0.5 µm.

Figure 3

Genetic control of chitin matrix formation in Drosophila melanogaster. The chitin-binding protein Obst-A (CPAP3-A) operates as a hub for chitin matrix formation. Within the assembly zone, Obst-A recruits chitin to a scaffold where it places chitin deacetylases (Serp and Verm) and Knickkopf for chitin matrix assembly and maturation into nanofibrils and the subsequent accumulation into compact fibers of the chitinous procuticle. Obst/CPAP family members act synergistically in this process. The genes and their discussed products, the hub of chitin matrix formation, are evolutionarily conserved among arthropods, indicating their general necessity for cuticle biology.

Figure 4

A conceptual model for the usage of critical proteins that control properties of synthetic chitin matrices. The known functions of the proteins are indicated. The combination of synthetic chitin-based aerogels with proteins controlling the chitin packaging and additional bioactive molecules (discussed in the text) will significantly improve and adjust the properties of the materials for customized biomedical applications. The eco-friendly biodegradability is an additional advantage of these new materials.