Yonghua Chen
Yonghua Chen, Ph.D.
Associate Professor,
Department of Mechanical Engineering,
The University of Hong Kong
Email: yhchen@hku.hk


Dr. Y.H. Chen is currently an associate professor in the Department of Mechanical Engineering, The University of Hong Kong. He has worked intensively on Additive Manufacturing, CAD/CAM, and Robotics in the past 20 years. Dr. Chen has co-authored more than 200 journal and conference papers, two books, and 5 patents. Recently, he has secured more than $8 million to conduct research on biomimetic and soft robotics. Since 1997, Dr. Chen has organized more than 10 international conferences on manufacturing and automation. He has also served as editorial members for 5 international journals. He is now taking on the challenge of 3D printing smart robotics that could be driven by tissue-engineered muscle.


3D Printing of Thermoplastic Polyurethane Based Shape Memory Polymer for Tissue Scaffolding Applications

Bio-compatible porous polymer structures have been widely used in tissue engineering. Such structures have biodegradability, pore interconnectivity and bioactivity to facilitate tissue ingrowth and provide temporary structural support for cells during the regeneration of target tissues. However, these structures lack the shape changing and recovery properties of Shape Memory Polymers (SMPs) which, in some cases, are highly desirable in tissue implant operations. The tunable biocompatibility, capability of shape recovery at glass transition temperature Tg, together with relatively good mechanical properties of SMPs have induced  growing interest from the tissue engineering research communities. In this paper, the 3D fabrication processes (from pellet to scaffold) of a thermos-plastic polyurethane based SMP material are presented.  The material is developed using the basic synthetic mechanism of reacting isocyanates units with hydroxyls and crosslinking the resulting polyether-based polyurethane by a chain extender. Due to good biocompatibility and biodegradability, this material can be used for tissue implant applications.  

Sample parts are fabricated to evaluate the shape memory behavior of the SMP in terms of shape fixity and shape recovery in a thermo-mechanical cycle. A typical thermo-mechanical cycle consists of 4 primary steps. (1) The SMP part is first heated to a temperature greater than Tg; (2) set the SMP part to the desired shape; (3) cool the SMP part to the ambient temperature; and (4) apply thermal energy to the SMP part so that it is heated to Tg for shape recovery. Porous SMP parts are also designed and 3D printed to evaluate their applicability for medical scaffolds.  These parts can be deformed into a smaller shape for easy insertion into the body using a catheter or other tools. Under body or induction heat, the deformed part can redeploy itself to the customized shape (can be a bone defect void) due to shape recovery effect. This feature is very important for minimally invasive surgery where the incisions are normally very small. In summary, the 3D printing processes of a bio-compatible and degradable shape memory polymer have been developed. Both the mechanical properties and the 3D printing fabrication capabilities of the SMP material are characterized. Sample scaffolds with different shape are fabricated at pore diameter less than 0.6 mm. The shape recovery capability of such scaffolds have been evaluated.

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  September 15, 2017