On March 29, the latest issue of "Science" published a lengthy article co-authored by Associate Researcher Zhang Hanyue from the School of Biological Sciences and Medical Engineering and Professor Xiong Rengen from the School of Chemistry and Chemical Engineering at Southeast University. The team innovatively combined ferroelectric chemistry with bioelectronics, developing a biodegradable organic ferroelectric crystal, 2,2,3,3,4,4-hexafluoro-1,5-pentanediol (HFPD), which exhibits a piezoelectric response d33 of 138 pC/N, directly comparable to inorganic ceramic barium titanate (BTO) (Science 2024, 383, 1492–1498).
Reportedly, this marks a significant milestone since 1880 when the Curie brothers discovered the piezoelectric effect. Zhang Hanyue is the joint first author and corresponding author, and Southeast University is the first corresponding institution.
With the continuous development of science and technology in China, there's an increasing demand for medical health. Research on implantable piezoelectric biomedical devices is thriving, promising to greatly improve people's quality of life. Piezoelectric materials are capable of converting mechanical stress into electrical signals. Currently, inorganic piezoelectric ceramics and piezoelectric polymers dominate applications, but they are not biodegradable. Therefore, implantable electronic devices made from these traditional piezoelectric materials face the risk of secondary surgery for removal when applied in the human body. Consequently, implantable transient electronic devices based on biodegradable materials are expected to bring about significant changes in the medical field.
These electronic devices can operate for a controllable period and self-dissolve in the body after completing their tasks, without producing toxic substances. Natural piezoelectric biological materials exhibit many advantages in this aspect. However, their piezoelectric performance is poor, with a piezoelectric coefficient d33 mostly below 10 pC/N, greatly limiting their application in biomedicine. Molecular ferroelectric materials have unique advantages such as simple synthesis, easy processing, lightweight, good biocompatibility, and tunable physical properties, making them ideal candidates for implantable transient electronic devices. Therefore, there is an urgent need to develop biodegradable molecular ferroelectric materials with high piezoelectric properties.
Over the past decade, Professor Xiong Rengen's team has focused on the chemical design and research of molecular ferroelectric materials. This year, based on the ferroelectric chemistry's hydrogen/fluorine substitution strategy and crystal engineering, the team mimicked the b phase structure of PVDF, using a limited odd number (n = 3) of –CF2– groups, combined with hydrogen bond interactions (similar to tie-bars) to form an infinitely long chain structure, developing an organic small molecule ferroelectric material. The team reduced the structural units of PVDF from thousands to 3, achieving a four-fold increase in small molecule piezoelectric performance (with a piezoelectric response d33 of 138 pC/N), playing a significant role (Figure 1A).
This discovery brings the piezoelectric performance of implantable materials to new heights. The ferroelectricity of the compound was systematically characterized by piezoresponse force microscopy (PFM) and electric hysteresis loop testing systems (Figures 1C and D). The two-dimensional hydrogen bond network formed between adjacent molecules through O–H···O hydrogen bond interactions makes the HFPD crystal easily soluble in various solvents (especially body fluids), facilitating the compound's degradation in the body (Figure 1B). The compound possesses good biocompatibility, bio-compatibility, and biodegradability.
Considering the brittleness and rigidity of crystals, the team prepared a flexible piezoelectric composite film of HFPD-polyvinyl alcohol (PVA) with a d33 of 34.3 pC/N using the solution evaporation method. Based on this piezoelectric composite film, the team also assembled a controllable transient electromechanical device and confirmed its excellent biosensing performance (Figures 1E and F). This research provides promising candidate materials for degradable implantable electronic medical devices and offers important application prospects for molecular piezoelectric materials closely related to human health.
Related paper information: https://www.science.org/doi/10.1126/science.adj1946
