- M. T. McDowellet al.,Nano Lett. 15 , 1264–1271 (2015).
- J. M. Luther, H. Zheng, B. Sadtler, A. P. Alivisatos,J. Am. Chem. Soc.
131 , 16851–16857 (2009). - A. C. Berendset al.,Chem. Mater. 30 , 3836–3846 (2018).
- W.-Y. Wuet al.,Chem. Mater. 28 , 9132–9138 (2016).
- A. G. Butterfield, L. T. Alameda, R. E. Schaak,J. Am. Chem. Soc.
143 , 1779–1783 (2021). - W. Liet al.,Chem. Commun. 47 , 10332–10334 (2011).
- S. Leeet al.,Chem. Mater. 28 , 3337–3344 (2016).
- M. Sakamotoet al.,J. Phys. Chem. C 119 , 11100– 11105
(2015). - G. Cho, Y. Park, Y. K. Hong, D. H. Ha,Nano Converg. 6 , 17
(2019). - X. Liet al.,Matter 2 , 554–586 (2020).
- B. J. Beberwyck, Y. Surendranath, A. P. Alivisatos,
J. Phys. Chem. C 117 , 19759–19770 (2013). - B. C. Steimle, J. L. Fenton, R. E. Schaak,Science 367 , 418– 424
(2020). - Y. Zhai, M. Shim,Chem. Mater. 29 , 2390–2397 (2017).
- Materials and methods are available as supplementary materials.
- X. Maet al.,Nanoscale 10 , 4816–4824 (2018).
- J. N. Wickham, A. B. Herhold, A. P. Alivisatos,Phys. Rev. Lett.
84 , 923–926 (2000).
32. G. D. Moon, S. Ko, Y. Xia, U. Jeong,ACS Nano 4 , 2307– 2319
(2010).
33. B. C. Steimle, R. W. Lord, R. E. Schaak,J. Am. Chem. Soc. 142 ,
13345 – 13349 (2020).
34. B. Sadtleret al.,J. Am. Chem. Soc. 131 , 5285–5293 (2009).
35. J. L. Fenton, B. C. Steimle, R. E. Schaak,J. Am. Chem. Soc.
140 , 6771–6775 (2018).
36. L. Manna, L. W. Wang, R. Cingolani, A. P. Alivisatos,J. Phys.
Chem. B 109 , 6183–6192 (2005).
37. L. Mu, F. Wang, B. Sadtler, R. A. Loomis, W. E. Buhro,ACS
Nano 9 , 7419–7428 (2015).
38. M. von Laue,Z. Kristallogr. Cryst. Mater. 105 , 124–133 (1943).
39. D.-H. Haet al.,Nano Lett. 14 , 7090–7099 (2014).
40. C. G. Sharp, A. D. P. Leach, J. E. Macdonald,Nano Lett. 20 ,
8556 – 8562 (2020).
ACKNOWLEDGMENTS
We thank R. Sato for helpful discussions and M. S. Long from
Edanz Group (https://en-author-services.edanz.com/ac) for
editing a draft of this manuscript.Funding:This research was
supported by the Ministry of Education, Culture, Sports, Science,
and Technology (MEXT)/Japan Society for the Promotion of
Science (JSPS) KAKENHI for Scientific Research S (grantJP19H05634) and Scientific Research for Innovative Areas (grant
JP16H06520, Coordination Asymmetry) (T.T.); Challenging
Research (Exploratory) (grant JP20K21236) (M.S.); a JSPS
Research Fellowship (grant 19J23268) (Z.L.); the International
Collaborative Research Program of the Institute for Chemical
Research, Kyoto University (grant 2020-17) (Y.T. and T.T.); and the
Nanotechnology Platform Program (grants JPMXP09S19NI0009
and JPMXP09S20NI0020).Author contributions:Z.L., M.S., and
T.T. conceived of the concept, designed the experiments, and
wrote the paper. Z.L. synthesized and characterized the samples.
T.A. performed HRTEM and STEM experiments. Y.T. conducted
theoretical calculations.Competing interests:The authors declare
no competing interests.Data and materials availability:All
data are available in the manuscript or the supplementary materials.
SUPPLEMENTARY MATERIALS
science.sciencemag.org/content/373/6552/332/suppl/DC1
Materials and Methods
Figs. S1 to S19
Tables S1 to S5
References ( 41 – 44 )
26 February 2021; accepted 4 June 2021
10.1126/science.abh2741MATERIALS SCIENCE
Wafer-scale heterostructured piezoelectric
bio-organic thin films
Fan Yang1,2,3†, Jun Li^1 †, Yin Long^1 , Ziyi Zhang^1 , Linfeng Wang^1 , Jiajie Sui^1 , Yutao Dong^1 , Yizhan Wang^1 ,
Rachel Taylor^4 , Dalong Ni^5 , Weibo Cai^5 , Ping Wang2,3, Timothy Hacker^4 , Xudong Wang^1 *
Piezoelectric biomaterials are intrinsically suitable for coupling mechanical and electrical energy in biological
systems to achieve in vivo real-time sensing, actuation, and electricity generation. However, the inability to
synthesize and align the piezoelectric phase at a large scale remains a roadblock toward practical applications.
We present a wafer-scale approach to creating piezoelectric biomaterial thin films based ong-glycine
crystals. The thin film has a sandwich structure, where a crystalline glycine layer self-assembles and
automatically aligns between two polyvinyl alcohol (PVA) thin films. The heterostructured glycine-PVA films
exhibit piezoelectric coefficients of 5.3 picocoulombs per newton or 157.5 × 10−^3 volt meters per newton
and nearly an order of magnitude enhancement of the mechanical flexibility compared with pure glycine
crystals. With its natural compatibility and degradability in physiological environments, glycine-PVA
films may enable the development of transient implantable electromechanical devices.
P
iezoelectricity is a material property that
couples mechanical energy with elec-
tricity. It is also a relatively common
phenomenon that can be found in many
biological systems ( 1 – 3 ). More than a
century of research on piezoelectric materials
has led to advancements in inorganic piezoelec-
tric crystals in terms of processing techniques,
property enhancement, and multifunctional-
ity. This group of materials is used in a broad
range of electromechanical systems for sensing,
acoustics, imaging, actuation, and energy har-
vesting ( 4 – 8 ). For use in biotechnology, these
materials must also show flexibility, biocom-
patibility, and biodegradability ( 9 , 10 ). Unfor-
tunately, inorganic piezoelectric materials are
intrinsically rigid, brittle, and challenging to
process and may contain toxic elements. Even
synthetic piezoelectric polymers, such as poly-
vinylidene difluoride (PVDF), are not able to
satisfy many requirements, particularly those
for flexibility and degradability.
Piezoelectric biomaterials—for example, silk
( 11 , 12 ), collagen ( 13 , 14 ), amino acids ( 15 , 16 ),
chitin ( 17 ), cellulose ( 18 ), and viral particles
( 19 )—can naturally offer many potentially
beneficial properties of biomaterials such as
reliability, biocompatibility, reproducibility,
and flexibility. They are mostly biodegradable,
and their production is considered environ-
mentally sustainable. However, because of
the lack of large-scale assembly and domain
aligning, studies of their piezoelectricity are
still primarily at the conceptual level. Within
this intriguing group of piezoelectric biomate-rials, glycine, the simplest amino acid, stands
out with a high piezoelectric coefficient (d 33 up
to 10 pC/N) and exceptional stability (g-glycine)
( 20 ). Nevertheless, similar to many inorganic
molecules, pure glycine tends to form fragile
bulk crystals with a very high Young’s mod-
ulus (~30 GPa). Moreover, glycine requires an
extremely high electric field (more than GV/m)
to align the domains, which makes it rather
challenging for its polycrystalline film to exhibit
macroscopic piezoelectricity.
We report a self-assembly strategy for wafer-
scale synthesis of heterostructured piezoelectric
glycine thin films. The films have a polyvinyl
alcohol (PVA)–glycine-PVA sandwich structure,
where the hydrogen bonding between PVA and
glycine at the interface leads to the formation
and self-alignment ofg-glycine crystals across
theentirefilm.Theas-synthesizedfilmex-
hibits a superb, stable, and uniform piezo-
electric property, as well as excellent flexibility
and biocompatibility.
Glycine-PVA films were synthesized by di-
rect solidification from their mixture solution
at 60°C (Fig. 1A; detailed synthesis procedures
are included in the materials and methods sec-
tion of the supplementary materials). Because
of the low surface tension, the solution evenly
dispersed on the supporting surface, forming a
uniform liquid film. As the solvent evaporated,
the liquid film crystalized from the edges and
expanded rapidly across the entire area within
30 min (movie S1). Through this approach, the
solidified film could reach a fairly large area,
which was only limited by the size of the sup-
porting surface. The film could be directly
peeled off from the surface, exhibiting excel-
lent uniformity, integrity, and flexibility (inset
of Fig. 1A and movie S2). A cross-sectional
scanning electron microscopy (SEM) image
revealed that the as-received film had a three-
layer structure with an overall thickness ofSCIENCEsciencemag.org 16 JULY 2021•VOL 373 ISSUE 6552 337
(^1) Department of Materials Science and Engineering, University
of Wisconsin–Madison, Madison, WI 53706, USA.^2 School of
Civil Engineering, Southwest Jiaotong University, Chengdu
610031, China.^3 Key Laboratory of High-speed Railway
Engineering, Ministry of Education, Chengdu 610031, China.
(^4) Cardiovascular Research Center, University of Wisconsin–
Madison, Madison, WI 53705, USA.^5 Department of
Radiology and Medical Physics, University of Wisconsin–
Madison, Madison, WI 53705, USA.
*Corresponding author. Email: [email protected]
†These authors contributed equally to this work.
RESEARCH | REPORTS