In the long-term natural selection and evolution, the organization and properties of organism constituent materials have been continuously optimized and improved, so that simple mineral and organic materials are used to meet complex mechanical and functional requirements. The principle is to make best adaptation to the living environment. Nature is a mentor of mankind.
The superior properties of natural biomaterials can provide useful insights into the optimal design of man-made materials, especially the development of high-performance biomimetic materials. Among them, functional gradient design is one of the basic performance optimization strategies that are commonly used in biomaterials. Revealing the gradient design criteria in nature and the corresponding performance optimization mechanism are of great significance for guiding the design and promotion of high performance biomimetic gradient materials.
Recently in a study, Zhang Zhefeng, Department of Materials Fatigue and Fracture Research, Shenyang Institute of Materials Science, Chinese Academy of Sciences, collaborated with Robert O. Ritchie, professor at the University of California at Berkeley, and Marc A. Meyers, professor at the University of California, San Diego, revealed that the gradient structure orientation features are widely existed in biological tissues and materials. They also proposed a new idea of bionic design to improve the contact damage resistance of materials. The mechanical properties of gradient changes are obtained by controlling the orientation of microstructures to achieve local stiffness. The optimal distribution and matching of strength and toughness improve the overall mechanical properties, as shown in Figure 1. Through mechanical analysis and numerical simulation, they established the quantitative relationship between structural orientation and various mechanical properties, clarified the mechanism of material damage resistance improvement, and pointed out the design method of corresponding biomimetic gradient structure.
On this basis, they further summarized the basic functional gradient material design forms and principles commonly found in nature, and took typical biological materials as examples, according to composition and composition, organizational structure (including the arrangement of structural units, spatial distribution, scale and orientation), interface and different types of gradients in the multi-level structure scale combination and matching ideas to concretely describe and analyze the gradient in biomaterials, summed up the role and corresponding mechanism of gradient design in material performance optimization.
At the same time, they summarized the recent progress in the design and application of biomimetic gradient materials, especially the application of new material preparation technologies, such as 3D printing in the field of biomimetic gradient materials, and pointed out the future scientific issues and challenges that need to be addressed in natural and biomimetic gradient materials studies.
The research was funded by the Institute of Metals, the introduction of outstanding scholars, and the Multidisciplinary University Research Initiative project of the US Air Force Scientific Research Office. Related results were recently published in Acta Biomaterialia 44 (2016) 31-40 and Progress in Materials Science (doi: https://doi.org/10.1016/j.pmatsci.2017.04.013).
About natural materials
Biomaterials can be classified into two main groups: synthetic and natural biomaterials. The latter exhibit several advantages over the former, such as biocompatibility, inherent biodegradability, remodeling and critical biological functions. Therefore, natural biomaterials are usually applied in the repair or replacement of damaged human tissues and organs. They have the ability to adequately support cell adhesion, migration, proliferation and differentiation. For example, natural polymers have been used to make natural hydrogels as extracellular matrix that mimic the biological milieu to bridge the gap between conventional cell cultures and complex native in vivo environments. Cellulose, a polysaccharide mainly found in plants can promote bone regeneration. Another example is the silk fiber produced by spiders, its biodegradability is ideal for applications like surgical suture and drug delivery.
In Matexcel, our selection of naturally biomaterials and their derivatives includes DNA and protein-based biomaterials (collagen, gelatin, fibrin, silk, elastin) and polysaccharide-based biomaterials (cellulose, chitin/chitosan, glucose, alginate, hyaluronic acid).