Crystallised amino acid mixture. Image: SPL

Active self-assembly of piezoelectric biomolecular films

14 August 2023

HKUST scientists have devised a new method to overcome the long-standing challenge of synthesising large-scale, high-performance piezoelectric biomaterials. 

Piezoelectric biomaterials are organic materials that can convert mechanical energy into electrical energy and vice versa, making them attractive for use in sensors, actuators, and energy harvesters. A team led Dr Zhengbao Yang of the Department of Mechanical and Aerospace Engineering at HKUST developed a generalisable route to fabricate customizable bio-organic piezoelectric thin films, combining the power of nanoconfinement and in-situ poling.

Nanoconfinement is a process that restricts a material’s particles to a space on the nanometer scale, which can significantly influence the material’s properties. In-situ poling is a technique that involves applying an electric field to a piezoelectric material during its preparation, resulting in a significant improvement in its piezoelectric properties.

The team used a strategy involving nanoconfinement-induced homogeneous nucleation, a phenomenon where a new crystal phase forms uniformly throughout a material. This approach allowed them to align crystal grains in the strongest polarization direction on a large scale. The resulting thin films exhibited uniform piezoelectricity and high thermal stability.

Their chosen biomaterial, β-glycine, was transformed into nanocrystalline films. Nanocrystalline materials have grains on the nanometer scale, which can lead to improved mechanical and electrical properties. These films only exploited a fraction of their potential giant shear piezoelectricity (195 pm V−1), suggesting that rational structural design could further enhance piezoelectric performance.

The resultant β-glycine nanocrystalline films boasted excellent output performance, natural biocompatibility, and biodegradability. Biocompatibility refers to the ability of a material to interact with a biological system without producing an adverse effect, while biodegradability allows a substance to be broken down by biological organisms or their enzymes.

Unlike traditional bottom-up self-assembly methods, this innovative approach is not dependent on interface dependency, meaning the process is not influenced by the properties of the surfaces where the reactions take place. It’s scalable and versatile, allowing for the creation of films with variable dimensions, programmable structures, and diverse material forms, including flexible composites.

The team’s strategy could be applied to design large-scale films of various biomaterials and other piezoelectric materials, such as molecular or organic-inorganic materials. Organic-inorganic materials combine organic and inorganic components, providing a balance between the advantageous properties of both types of materials.

Yang said, “Our study shows uniformly high piezoelectric response and excellent thermostability across the entire β-glycine films.”

As Yang and his colleagues continue their research, the team is hopeful that their method will inspire further advancements in the field and contribute to the development of sustainable and biocompatible technology. This work represents a significant advance in the field of piezoelectric biomaterials.

The research team included collaborators based at the City University of Hong Kong and University of Wollongong in Australia. The research findings were published in Nature Communications.