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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 targets at many fields, such as Artificial Organs, Wearable Biosensors, Flexible Electronics, and Biomimetic Devices and Soft Robots. The research works are dedicated to significantly impacting and serving the entire scientific and medical fields.  


My research interests focus on following main fields: 
(1) Additive Manufacturing (3D Printing) & Functional Materials

(2) Artificial Organs (Abiotic presurgical organ models & biotic organ models)
(3) Wearable Biosensors and Flexible Electronics
(4)  Biomimetic Devices and Soft Robots

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). 

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Direction 1: 3D Printing of Artificial Organs

Project 1: 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 BusinessIn 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 2: 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. 

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Structure of the Aortic Root Model
Video: 3D Printed Aortic Root Model 
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Multi-materials, Multi-nozzles Printing
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Internally Integrated Sensor Array
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3D Printed Aortic Root Model with
Internally Integrated Sensor Array
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Prosthetic Valve Implantation Depth

Project 3: 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). 

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3D Bioprinted Human Muscle Pump

Direction 2: 3D Printed Smart Electronics

Project 1: 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 outletsThe 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 2: 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

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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)

Bacterial Cellulose Network Structure
Bacterial Cellulose-Modified Soy Flour Composites 
Bacterial Cellulose (BC) Nanofibers Self-Assembled On Sisal Fibers
Bacterial Cellulose Pellicle
BC-Poly(Vinyl Alcohol) Composites
Microfibrillated Cellulose-Poly(Vinyl Alcohol) Composites
Halloysite Nanotube-Poly(Vinyl Alcohol) Composites
Degradation Study for Halloystie Nanotube-Poly(Vinyl Alcohol) Composites
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