Conductive Bioimprint Using Soft Lithography Technique Based on PEDOT:PSS for Biosensing

Culture platform surface topography plays an important role in the regulation of biological cell behaviour. Understanding the mechanisms behind the roles of surface topography in cell response are central to many developments in a Lab on a Chip, medical implants and biosensors. In this work, we report on a novel development of a biocompatible conductive hydrogel (CH) made of poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and gelatin with bioimprinted surface features. The bioimprinted CH offers high conductivity, biocompatibility and high replication fidelity suitable for cell culture applications. The bioimprinted conductive hydrogel is developed to investigate biological cells’ response to their morphological footprint and study their growth, adhesion, cell–cell interactions and proliferation as a function of conductivity. Moreover, optimization of the conductive hydrogel mixture plays an important role in achieving high imprinting resolution and conductivity. The reason behind choosing a conducive hydrogel with high resolution surface bioimprints is to improve cell monitoring while mimicking cells’ natural physical environment. Bioimprints which are a 3D replication of cellular morphology have previously been shown to promote cell attachment, proliferation, differentiation and even cell response to drugs. The conductive substrate, on the other hand, enables cell impedance to be measured and monitored, which is indicative of cell viability and spread. Two dimensional profiles of the cross section of a single cell taken via Atomic Force Microscopy (AFM) from the fixed cell on glass, and its replicas on polydimethylsiloxane (PDMS) and conductive hydrogel (CH) show unprecedented replication of cellular features with an average replication fidelity of more than 90%. Furthermore, crosslinking CH films demonstrated a significant increase in electrical conductivity from 10−6 S/cm to 1 S/cm. Conductive bioimprints can provide a suitable platform for biosensing applications and potentially for monitoring implant-tissue reactions in medical devices.

3D printing of dual cross-linked hydrogel for fingerprint-like iontronic pressure sensor

Hydrogels with intrinsic high stretchability and flexibility are extremely attractive for soft electronics. However, the existing complicated and laborious methods (such as mold curing) to fabricate microstructured hydrogel (MH) still limit the development of hydrogel-based sensors for flexible devices. Herein, we use digital light processing 3D printing technology to rapidly construct double-network (DN) ionic conductive hydrogel, and then design and print fingerprint-like MH film to manufacture an iontronic pressure sensor. In particular, the DN hydrogel consists of acrylamide/acrylic acid to form a covalently cross-linked network, and magnesium chloride is introduced to form an ionic cross-linked physical network in the hydrogel. The printability (with resolution 150 μm) and mechanical property tunability of DN hydrogel enable the convenient fabrication of sensors. With the biomimetic fingerprint MH film, the iontronic pressure sensor not only has a high sensitivity (0.06 kPa-1), but also has a large detection range (26 Pa-70 kPa) and good stability (200 cycles of pressure loading). We demonstrated that our sensor can be applied to realize tactile sensing in a prosthetic application and detect human motion. With the easy strategy of constructing DN hydrogel with microstructures by 3D printing technology, hydrogel-based sensors are anticipated to be employed in more smart electronics.