Culture and in situ H2O2-mediated electrochemical study of cancer cells using three-dimensional scaffold based on graphene foam coated with Fe3O4 nanozyme.

For real-time evaluation of the cell behavior and function under in vivo-like 3D environment, the 3D functionalized scaffolds simultaneously integrate the function of 3D cell culture, and electrochemical sensing is a convincing candidate. Herein, Fe3O4 nanoparticles as the nanozyme (peroxide oxidase mimics) were modified on graphene foam scaffold to construct a 3D integrated platform. The platform displayed a wide linear range of 100 nM to 20 µM and a high sensitivity of 53.2 nA µM-1 toward detection of hydrogen peroxide (H2O2) under the working potential of + 0.6 V (vs. Ag/AgCl). The obtained 3D scaffold also displayed satisfactory selectivity toward the possible interferents that appeared in the cell culture environment. Furthermore, the cells still maintained high cell viability (almost 100%) after their growth and proliferation on the scaffold for 7 days. With the superior performance on cell culture and electrochemical monitoring, the functions on the 3D culture of MCF-7 or HeLa cells and in situ monitoring of cell-released H2O2 was easily achieved on this 3D platform, which show its great application prospects on further cancer-related disease diagnosis or drug screening. A nanozyme-based three-dimensional graphene scaffold was successfully constructed for cell culture and identification of cancer cells through in situ electrochemical monitoring of the cell-released H2O2.

Integrating Flexible Electrochemical Sensor into Microfluidic Chip for Simulating and Monitoring Vascular Mechanotransduction.

As an interface between the blood flow and vessel wall, endothelial cells (ECs) are exposed to hemodynamic forces, and the biochemical molecules released from ECs-blood flow interaction are important determinants of vascular homeostasis. Versatile microfluidic chips have been designed to simulate the biological and physiological parameters of the human vascular system, but in situ and real-time monitoring of the mechanical force-triggered signals during vascular mechanotransduction still remains a significant challenge. Here, such challenge is fulfilled for the first time, by preparation of a flexible and stretchable electrochemical sensor and its incorporation into a microfluidic vascular chip. This allows simulating of in vivo physiological and biomechanical parameters of blood vessels, and simultaneously monitoring the mechanically induced biochemical signals in real time. Specifically, the cyclic circumferential stretch that is actually exerted on endothelium but is hard to reproduce in vitro is successfully recapitulated, and nitric oxide signals under normal blood pressure, as well as reactive oxygen species signals under hypertensive states, are well documented. Here, the first integration of a flexible electrochemical sensor into a microfluidic chip is reported, therefore paving a way to evaluate in vitro organs by built-in flexible sensors.

Conductive Polymer Coated Scaffold to Integrate 3D Cell Culture with Electrochemical Sensing.

Remarkable progresses have been made in electrochemical monitoring of living cells based on one-dimensional (1D) or two-dimensional (2D) sensors, but the cells cultured on 2D substrate under these circumstances are departed from their three-dimensional (3D) microenvironments in vivo. Significant advances have been made in developing 3D culture scaffolds to simulate the 3D microenvironment yet most of them are insulated, which greatly restricts their application in electrochemical sensing. Herein, we propose a versatile strategy to endow 3D insulated culture scaffolds with electrochemical performance while granting their biocompatibility through conductive polymer coating. More specifically, 3D polydimethylsiloxane scaffold is uniformly coated by poly(3,4-ethylenedioxythiophene) and further modified by platinum nanoparticles. The integrated 3D device demonstrates desirable biocompatibility for long-term 3D cell culture and excellent electrocatalytic ability for electrochemical sensing. This allows real-time monitoring of reactive oxygen species release from cancer cells induced by a novel potential anticancer drug and reveals its promising application in cancer treatment. This work provides a new idea to construct 3D multifunctional electrochemical sensors, which will be of great significance for physiological and pathological research.

A Stretchable Electrochemical Sensor for Inducing and Monitoring Cell Mechanotransduction in Real Time.

Existing methods offer little direct and real-time information about stretch-triggered biochemical responses during cell mechanotransduction. A novel stretchable electrochemical sensor is reported that takes advantage of a hierarchical percolation network of carbon nanotubes and gold nanotubes (CNT-AuNT). This hybrid nanostructure provides the sensor with excellent time-reproducible mechanical and electrochemical performances while granting very good cellular compatibility, making it perfectly apt to induce and monitor simultaneously transient biochemical signals. This is validated by monitoring stretch-induced transient release of small signaling molecules by both endothelial and epithelial cells cultured on this sensor and submitted to stretching strains of different intensities. This work demonstrates that the hybrid CNT-AuNT platform offers a versatile and highly sensitive way to characterize and quantify short-time mechanotransduction responses.

Conductive Polymer-Coated Carbon Nanotubes To Construct Stretchable and Transparent Electrochemical Sensors.

Carbon nanotube (CNT)-based flexible sensors have been intensively developed for physical sensing. However, great challenges remain in fabricating stretchable CNT films with high electrochemical performance for real-time chemical sensing, due to large sheet resistance of CNT film and further resistance increase caused by separation between each CNT during stretching. Herein, we develop a facile and versatile strategy to construct single-walled carbon nanotubes (SWNTs)-based stretchable and transparent electrochemical sensors, by coating and binding each SWNT with conductive polymer. As a polymer with high conductivity, good electrochemical activity, and biocompatibility, poly(3,4-ethylenedioxythiophene) (PEDOT) acting as a superior conductive coating and binder reduces contact resistance and greatly improves the electrochemical performance of SWNTs film. Furthermore, PEDOT protects the SWNTs junctions from separation during stretching, which endows the sensor with highly mechanical compliance and excellent electrochemical performance during big deformation. These unique features allow real-time monitoring of biochemical signals from mechanically stretched cells. This work represents an important step toward construction of a high performance CNTs-based stretchable electrochemical sensor, therefore broadening the way for stretchable sensors in a diversity of biomedical applications.

Stretchable Electrochemical Sensor for Real-Time Monitoring of Cells and Tissues.

Stretchable electrochemical sensors are conceivably a powerful technique that provides important chemical information to unravel elastic and curvilinear living body. However, no breakthrough was made in stretchable electrochemical device for biological detection. Herein, we synthesized Au nanotubes (NTs) with large aspect ratio to construct an effective stretchable electrochemical sensor. Interlacing network of Au NTs endows the sensor with desirable stability against mechanical deformation, and Au nanostructure provides excellent electrochemical performance and biocompatibility. This allows for the first time, real-time electrochemical monitoring of mechanically sensitive cells on the sensor both in their stretching-free and stretching states as well as sensing of the inner lining of blood vessels. The results demonstrate the great potential of this sensor in electrochemical detection of living body, opening a new window for stretchable electrochemical sensor in biological exploration.

An artificial blood vessel implanted three-dimensional microsystem for modeling transvascular migration of tumor cells.

Reproducing a tumor microenvironment consisting of blood vessels and tumor cells for modeling tumor invasion in vitro is particularly challenging. Here, we report an artificial blood vessel implanted 3D microfluidic system for reproducing transvascular migration of tumor cells. The transparent, porous and elastic artificial blood vessels are obtained by constructing polysaccharide cellulose-based microtubes using a chitosan sacrificial template, and possess excellent cytocompatibility, permeability, and mechanical characteristics. The artificial blood vessels are then fully implanted into the collagen matrix to reconstruct the 3D microsystem for modeling transvascular migration of tumor cells. Well-defined simulated vascular lumens were obtained by proliferation of the human umbilical vein endothelial cells (HUVECs) lining the artificial blood vessels, which enables us to reproduce structures and functions of blood vessels and replicate various hemodynamic parameters. Based on this model, the adhesion and transvascular migration of tumor cells across the artificial blood vessel have been well reproduced.

Engineering interconnected 3D vascular networks in hydrogels using molded sodium alginate lattice as the sacrificial template.

Engineering 3D perfusable vascular networks in vitro and reproducing the physiological environment of blood vessels is very challenging for tissue engineering and investigation of blood vessel function. Here, we engineer interconnected 3D microfluidic vascular networks in hydrogels using molded sodium alginate lattice as sacrificial templates. The sacrificial templates are rapidly replicated in polydimethylsiloxane (PDMS) microfluidic chips via Ca⁺²-crosslinking and then fully encapsulated in hydrogels. Interconnected channels with well controlled size and morphology are obtained by dissolving the monolayer or multilayer templates with EDTA solution. The human umbilical vein endothelial cells (HUVECs) are cultured on the channel linings and proliferated to form vascular lumens. The strong cell adhesion capability and adaptive response to shear stress demonstrate the excellent cytocompatibility of both the template and template-sacrificing process. Furthermore, the barrier function of the endothelial layer is characterized and the results show that a confluent endothelial monolayer is fully developed. Taken together, we develop a facile and rapid approach to engineer a vascular model that could be potentially used in physiological studies of vascular functions and vascular tissue engineering.