Analyses of ancient dog DNA suggest that dogs were likely domesticated from Eurasian wolves around 23,000 years ago, possibly in Siberia.
Image credit: Pixabay/Chiemsee2016.
Edited* by William D. Nix, Stanford University, Stanford, CA, and approved January 9, 2014 (received for review August 12, 2013)
Significance
It has been a long-standing effort to create materials with low density but high strength. Technical foams are very light, but compared with bulk materials, their strength is quite low because of their random structure. Natural lightweight materials, such as bone, are cellular solids with optimized architecture. They are structured hierarchically and actually consist of nanometer-size building blocks, providing a benefit from mechanical size effects. In this paper, we demonstrate that materials with a designed microarchitecture, which provides both structural advantages and size-dependent strengthening effects, may be fabricated. Using 3D laser lithography, we produced micro-truss and -shell structures from ceramic–polymer composites that exceed the strength-to-weight ratio of all engineering materials, with a density below 1,000 kg/m3.
Abstract
To enhance the strength-to-weight ratio of a material, one may try to either improve the strength or lower the density, or both. The lightest solid materials have a density in the range of 1,000 kg/m3; only cellular materials, such as technical foams, can reach considerably lower values. However, compared with corresponding bulk materials, their specific strength generally is significantly lower. Cellular topologies may be divided into bending- and stretching-dominated ones. Technical foams are structured randomly and behave in a bending-dominated way, which is less weight efficient, with respect to strength, than stretching-dominated behavior, such as in regular braced frameworks. Cancellous bone and other natural cellular solids have an optimized architecture. Their basic material is structured hierarchically and consists of nanometer-size elements, providing a benefit from size effects in the material strength. Designing cellular materials with a specific microarchitecture would allow one to exploit the structural advantages of stretching-dominated constructions as well as size-dependent strengthening effects. In this paper, we demonstrate that such materials may be fabricated. Applying 3D laser lithography, we produced and characterized micro-truss and -shell structures made from alumina–polymer composite. Size-dependent strengthening of alumina shells has been observed, particularly when applied with a characteristic thickness below 100 nm. The presented artificial cellular materials reach compressive strengths up to 280 MPa with densities well below 1,000 kg/m3.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: jens.bauer{at}kit.edu.
Author contributions: J.B., I.T., and O.K. designed research; J.B., S.H., and R.S. performed research; J.B., S.H., I.T., and O.K. analyzed data; and J.B. wrote the paper.
The authors declare no conflict of interest.
↵*This Direct Submission article had a prearranged editor.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1315147111/-/DCSupplemental.
Freely available online through the PNAS open access option.
High-strength 3D microarchitectures
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Pollen seasons have lengthened by 20 days and pollen concentrations have increased by 21% from 1990 to 2018 in North America, and anthropogenic climate change is a likely factor.
Image credit: William R. L. Anderegg.
Conservation efforts must be better coordinated across national borders, and the impacts of border barriers on species must be mitigated as the climate changes.
Image credit: Stephen G. Willis.
Vaccination efforts must be coupled with aggressive community-based COVID point-of-care testing so that cases of asymptomatic infection are rapidly identified.
Image credit: Shutterstock/zstock.
The innovative solution entails simply drying and using whole bacteria, with no need to separate and purify the reagent products.
Image credit: Shutterstock/motorolka.