Research | research

Research Interests

Additive manufacturing (3D printing) is playing important role for scientific research and modern manufacturing and profoundly changing world and people's lives. By employing most advanced Additive Manufacturing (3D Printing) Technologies with Novel Multifunctional Materials, interdisciplinary and influential research can be created for various applications. My research interests focus on different biomedical devices, such as Artificial Organs, Wearable Biosensors, Bionic Systems and Electronics, and Biomimetic Surfaces. The research works are dedicated to impacting and serving the entire scientific and medical fields.

My research interests focus on following main fields:
(1) Wearable Biosensors for Health Monitoring

(2) Bionic Systems and Electronics for Haptics and Human Rehabilitation

(3) Artificial Organs and Organoids for Surgical and Medical Applications
(4) Biomimetic Surfaces for Enhanced Locomotion
Previously, some of my works have resulted in publications in well-known journals and, have been widely funded (such as NIH, Army Research Office, Top Medical Schools, and Industrial Companies) and recognized (such as Nature News, NIH News, Science Daily, Science Newsline, Fox News, and NBC News).

Wearable Biosensors

for Health Monitoring

Artificial Organ Models

for Medical Applications

Bionic Systems for

Human Functions Restoration

Biomimetic Surfaces

for Enhanced Locomotions

Direction : 3D-Printed Wearable Biosensors

Project: 3D-Printed Flexible Microfluidic Health Monitor for In Situ Sweat Analysis and Biomarker Detection

Wearable sweat biosensors have shown great progress in noninvasive, in situ, and continuous health monitoring to demonstrate individuals’ physiological states. Advances in novel nanomaterials and fabrication methods promise to usher in a new era of wearable biosensors. Here, we introduce a three-dimensional (3D)-printed flexible wearable health monitor fabricated through a unique one-step continuous manufacturing process with self-supporting microfluidic channels and novel single-atom catalyst-based bioassays for measuring the sweat rate and concentration of three biomarkers. Direct ink writing is adapted to print the microfluidic device with self-supporting structures to harvest human sweat, which eliminates the need for removing sacrificial supporting materials and addresses the contamination and sweat evaporation issues associated with traditional sampling methods. Additionally, the pick-and-place strategy is employed during the printing process to accurately integrate the bioassays, improving manufacturing efficiency. A single-atom catalyst is developed and utilized in colorimetric bioassays to improve sensitivity and accuracy. A feasibility study on human skin successfully demonstrates the functionality and reliability of our health monitor, generating reliable and quantitative in situ results of sweat rate, glucose, lactate, and uric acid concentrations during physical exercise.

Direction : 3D-Printed Wearable Biosensors

Project: 3D-printed hollow microneedle-based electrochemical sensor for wireless glucose monitoring

Wearable electrochemical sensors have aroused tremendous attention due to their great potential for in situ and continuous assessment for glucose monitoring. The conventional fingerstick test is the easiest and most efficient method for glucose evaluation, but it is invasive and painful. Here we introduce a wearable and user-friendly microneedle-based electrochemical sensor, fabricated via resin 3D printing with an affordable desktop 3D printer and featuring a single-atom nanozyme-modified electrode, offering high sensitivity and superior selectivity for glucose monitoring. This minimally invasive electrochemical sensor demonstrates the capability to extract artificial interstitial fluid using hollow microneedles and a finger-activated pump, enabling continuous monitoring of dynamic glucose concentration changes. This electrochemical sensor exhibits remarkable sensitivity and selectivity, with a linear range of 0.1 μM to 50 mM and a limit of detection of 0.285 μM, attributed to the incorporation of single-atom nanozymes with peroxidase-like enzymatic activity. The glucose concentration data are wirelessly transmitted to a smartphone application in real time, offering user-friendly access and facilitating remote monitoring. The described electrochemical sensor presents the possibilities for point-of-care health monitoring applications.

Direction : 3D-Printed Artificial Organs

Project: Machine Learning Enabled Design and Optimization for 3D-Printing of High-Fidelity Presurgical Organ Models

The development of a general-purpose machine learning algorithm capable of quickly identifying optimal 3D-printing settings can save manufacturing time and cost, reduce labor intensity, and improve the quality of 3D-printed objects. Existing methods have limitations which focus on overall performance or one specific aspect of 3D-printing quality. Here, for addressing the limitations, a multi-objective Bayesian Optimization (BO) approach which uses a general-purpose algorithm to optimize the black-box functions is demonstrated and identifies the optimal input parameters of direct ink writing for 3D-printing different presurgical organ models with intricate geometry. The BO approach enhances the 3D-printing efficiency to achieve the best possible printed object quality while simultaneously addressing the inherent trade-offs from the process of pursuing ideal outcomes relevant to requirements from practitioners. The BO approach also enables us to effectively explore 3D-printing inputs inclusive of layer height, nozzle travel speed, and dispensing pressure, as well as visualize the trade-offs between each set of 3D-printing inputs in terms of the output objectives which consist of time, porosity, and geometry precisions through the Pareto front.

TOC Fig_Machine Learning 3D-Printing Organ Models.png

Direction : 3D Printing of Artificial Organs

Project: 3D Printed Presurgical Prostate Models for Advanced Surgical Rehersal and Quantitative Feedback

Preoperative organ models play very important roles for surgical planning and rehearsal since they can save patient lives in many circumstances. However, previous organ models and their related devices suffer from two main issues. First, although these models exhibit accurate anatomical structures, they mostly lack the precise mimicry of physical properties of organ tissue. This issue limits their effectiveness in preoperative planning, rehearsal with surgical tools, or accurate predicting and replicating of organ physical behavior during surgical handling. Secondly, these 3D printed preoperative organ models lack the functionality to provide quantitative feedback resulting from organ and tissue handling: a function that can aid medical professionals in assessing and controlling their performed task quantitatively. After fully understanding these issues, I led a research team, with 17 researchers across different institutions and departments, and over a dozen of other supporters from both academia and industry, to conduct the interdisciplinary research for developing 3D printed preoperative organ models with physical properties of tissue and integrated soft electronic sensors using custom-formulated polymeric inks. The outcome of this work successfully solved the both aforementioned issues, and received highly positive feedbacks from medical professionals. The work also can be expected to apply for any organ models, such as bionic cardiac models. In addition, a series of novel methodologies, customized inks, and advanced surgical aids have been developed and applied during the research progress, and these efforts are expected to lay solid foundations in many research fields, including 3D printing, tissue characterization, custom ink development, property fidelity analysis, organ model simulations, displacement tracking, 3D printed electronics integration and advanced surgical applications. These efforts, suggest a new paradigm in preoperative practice, which could enable medical professionals to engage in more accurate and helpful surgical planning and rehearsal. This work has been published in Advanced Materials Technologies (2018) and featured in over 50 news outlets. The research paper has also been selected as a Best of 2018 article and the Cover image in Advanced Materials Technologies, as well as the Cover story in Minnesota Business. In addition, a comprehensive review paper for the research progress in the entire field has been presented in the Annual Review of Analytical Chemistry (2018).

Video: 3D Printed Organ Models Introduction

The 3D Printed Organ Model, Along with A Multimaterial 3D Printing System

Fox News Video: 3D Printed Organs Help Doctors Prep for Surgery

Applying an Endoscope in the Urethra of the 3D Printed Organ (Prostate) Model

Organ Physical Behavior Prediction

The 3D Printed Organ Model with Physical Properties of Tissue and Integrated Sensors

3D Printed Organ Model with Integrated Sensors as A Medical Device for Quantitative Feedback

Project: 3D Printed Patient-Specific Aortic Root Models for Minimally Invasive Surgery

Minimally invasive surgeries have numerous advantages, yet complications may arise from limited knowledge about the anatomical site targeted for the delivery of therapy. Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure for treating aortic stenosis. Here, we demonstrate multimaterial three-dimensional printing of patient-specific soft aortic root models with internally integrated electronic sensor arrays that can augment testing for TAVR preprocedural planning. We evaluated the efficacies of the models by comparing their geometric fidelities with postoperative data from patients, as well as their in vitro hemodynamic performances in cases with and without leaflet calcifications. Furthermore, we demonstrated that internal sensor arrays can facilitate the optimization of bioprosthetic valve selections and in vitro placements via mapping of the pressures applied on the critical regions of the aortic anatomies. These models may pave exciting avenues for mitigating the risks of postoperative complications and facilitating the development of next-generation medical devices. This work has been published by Science Advances (2020). The work also involves collaborations with Industrial Company (Medtronic Inc.) & Visible Heart Laboratory at UMN for model applications and device evaluations. The work also has been featured in numerous scientific new outlets.

Structure of the Aortic Root Model

Video: 3D Printed Aortic Root Model

Multi-materials, Multi-nozzles Printing

Internally Integrated Sensor Array

3D Printed Aortic Root Model with

Internally Integrated Sensor Array

Prosthetic Valve Implantation Depth

Project: 3D Bioprinting of Complex Cardiac Tissue with Contiguous, Living Muscle and Pump Function (Led by Dr. Ogle's group)

The design for this project is to 3D bioprint the structurally complex cardiac tissue with contiguous, living muscle and associated pump function using proper bioinks consisting of biomaterials and stem cells . I worked on this project (mainly in 3D bioprinting and some model characterization part) with a close collaboration with researchers from UMN biomedical engineering (led by Prof. Ogle's group) and medical school. The work is expected to lay foundation for the studies of future cardiac tissue and organoid and their biomedical applications. Different bioinks and bioprinting approaches have been explored and developed during the research progress to fabricate the 3D cardiac tissue with functions. This work represents a tangible step forward in evaluating the feasibility of a 3D printed organ graft. The most recent work has been published in Circulation Research (2020) with a Cover and the Best Manuscript Award).

Screen Shot 2020-04-02 at 5.47.04 PM.png

3D Bioprinted Human Muscle Pump

Direction 2: 3D Printed Bionic and Electronic Systems

Project: 3D Printed Stretchable Tactile Sensors (Led by Dr. Guo)

This work was started with the simple idea of 3D printing materials directly on freeform surfaces. As the project progressed, we realized that 3D printing of multifunctional devices could impact different areas ranging from wearable electronics and energy harvesting devices to smart prosthetics and human–machine interfaces. Particularly, novel strategies need to be developed to enable the intimate biointegration of wearable electronic devices with human skin in ways that bypass the mechanical and thermal restrictions of traditional microfabrication technologies. Therefore, we demonstrated the 3D printing of stretchable, conformal tactile sensors on freeform surfaces (such as a model hand) via a multimaterial, multiscale, and multifunctional 3D printing approach (up to 4 materials with different functions) under ambient conditions. The 3D printed sensors showed the capabilities for detecting human movements, including pulse monitoring and finger motions. The work opens new routes for the biointegration of various sensors in wearable electronics systems, and toward advanced bionic skin applications. This work has been published on Advanced Materials (2017) and highlighted in over 50 news outlets. The research paper is also the No. 1 most accessed article in Advanced Materials in May 2017.

A Schematic of 3D Printing Stretchable Tactile Sensors Conformally on a Freeform Surface

Video: Tactile Sensor Directly Printing On Hand Model

3D Printed Tactile Sensors

Tactile Sensor Directly Printing On Hand Model

Four Ink Dispensers for Printing Electronics

Project: 3D Printed Polymer Photodetectors (Led by Dr. Park & Dr. Su)

This project is a collaborative (led by Dr. Park and Dr. Su) project. Extrusion based 3D printing, an emerging technology, has been previously used in the comprehensive fabrication of light emitting diodes using various functional inks, without cleanrooms or conventional microfabrication techniques. Here, polymer based photodetectors exhibiting high performance are fully 3D printed and thoroughly characterized. A semiconducting polymer ink is printed and optimized for the active layer of the photodetector, achieving an external quantum efficiency of 25.3%, which is comparable to that of microfabricated counterparts and yet created solely via a one pot custom built 3D printing tool housed under ambient conditions. The devices are integrated into image sensing arrays with high sensitivity and wide field of view, by 3D printing interconnected photodetectors directly on flexible substrates and hemispherical surfaces. This approach is further extended to create integrated multifunctional devices consisting of optically coupled photodetectors and light emitting diodes, demonstrating for the first time the multifunctional integration of multiple semiconducting device types which are fully 3D printed on a single platform. The 3D printed optoelectronic devices are made without conventional microfabrication facilities, allowing for flexibility in the design and manufacturing of next generation wearable and 3D structured optoelectronics, and validating the potential of 3D printing to achieve high performance integrated active electronic materials and devices. This work has been published on Advanced Materials (2018) and highlighted in Nature, Newsweek, and dozens of other news outlets.

3D Printed Polymer Photodetectors

Video: 3D Printed Prototype Bionic Eye

Customized 3D Printing Systems

The customized 3D printing systems generally include four main subsystems, including motion control subsystem, ink dispensing subsystem, lightning/irradiation subsystem, and monitoring camera subsystem. These components are integrated to advanced systems with high resolution, high precision and high speed. A large number of different materials can be applied for 3D printing in the customized systems, such as thermoplastic polymers, thermoset epoxy, metallic materials , hydrogels and bioinks.

3D Printing System 1

3D Printing System 2

Ph.D. Projects: Biobased and Biodegradable Polymer Nanocomposites

My Ph.D. research at Cornell University focused on Biobased and Biodegradable Polymer Nanocomposites (Ph.D. Dissertation). Different nanomaterials, such as bacterial cellulose, microfibrillated cellulose, halloysite nanotubes, were inserted into biobased and biodegradable polymers for fabricating the polymer nanocomposites. The fabrication approaches include in situ fabrication, dispersion and embedding. The formed polymer nanocomposites showed enhanced mechanical, thermal, and other functional properties for a variety of useful applications. These works were published as paper in many journals, including Fibers (2017), Polymer Reviews (2014), Journal of Polymers and the Environment (2013), Polymer Composites (2013), Composites Science and Technology (2012), Journal of Materials Science (2012) and Carbohydrate Polymers (2008). The works also yielded 2 Book Chapters [Chapter (2015) & Chapter (2014)] and 1 Patent (2016).