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Biomechanics and Medical Engineering
Biomechanics and Medical Engineering are vibrant and rapidly expanding areas, which apply mechanics principles and engineering techniques to improving health and quality of life.  The research spans multiple length and time scales, ranging from molecules through cells to individual organisms and animal group dynamics.  There are six faculties in the Institute of Biomechanics and Medical Engineering in the Department of Mechanics and Engineering Science.  The major research areas include: cell mechanics, bio-computation, bio-solid mechanics, bio-fluid mechanics, mechanobiology, bio-imaging and bioinstrumentation.  Most of the present work makes use of physical principles, with the help of bio-imaging techniques, in vitro and in vivo measurements, and theoretical and numerical analysis, to explain and predict and treat various diseases in quantitative and statistical terms.  We have extensive collaborations with clinical investigators in many departments of Peking University Affiliated Hospitals such as radiology, neurology, cardiology, dentistry, orthopedics, neurosurgery, obstetrics and gynecology, etc. 
Impacts: In recent years, we have achieved a series of excellent work that has approved by peers and published in top journals, e.g., Circ Res, PNAS, Radiology, Biomaterials, Lab on a Chip, Biophys J, AJP-Heart C, J R Soc Interface and so on.  Moreover, more than 20 scientific and engineering research projects have been awarded by the State Key Program, the National Natural Science Foundation of China, the Ministry of Science and Technology, and so on. 
Listed below are selected research achievements in the Program of Biomechanics and Medical Engineering.
a) Researches on Cold Plasma and Electric Pulse Applications to Biological and Medical Engineering
The studies focus on the applications of non-thermal atmospheric-pressure plasma and nano-second electric pulsed technologies to biological and biomedical fields. For dental medicine applications, it includes cold plasma induced/assisted teeth bleaching, surface modification and functionalization of dental materials, and dental bacteria and bacterial biofilm inactivation in root canals, etc. For material and environment applications, the studies include developing cold plasma technique to fabric silver and gold nano particles for biosensors, magnetic nano indicators for MR imaging, and also the cold plasma technique for treatment of exhaust gases. For biological applications in agriculture, the researches include bacterial inactivation on vegetable and fruit surfaces, and the nano-sec pulsed electric stimulations on plants seeds/bodies for faster growth, etc. For cancer therapy in clinic applications, the technique of nano-second pulsed electric filed has been developed to increase drug efficiency on treatments of the cancer cells involved in oral, breast and skin tumors.

Figure 5.1. (A) CSLM images obtained from the midarea of root canals (box). (B) Bacteria in the untreated E. faecalis biofilms, which are all alive (green areas). (C) Bacteria in the treated biofilm, which are all dead after 10 minutes of plasma treatment in the root canal (red areas). The distance between 2 arrows represents the thickness of the biofilm.
b) Researches on Clinical fMRI
The protective effect of collateral circulation influences final clinical outcomes for patients with hemodynamically significant arterial stenosis.  By using non-invasive arterial spin-labeling (ASL) technology, blood in individual or groups of feeding arteries is tagged, and images are acquired that map the vascular distribution of those feeding arteries.

Figure 5.2. Before stent plantation, small parts of right ACA territory were supplied by right ICA (red) or combination of right and left ICA (yellow), while these parts were supplied only by left ICA after stent plantation in left ICA. The territory of left ICA increased after left ICA stent plantation (arrows).
c) Researches on Cell Mechanics
Cell traction forces play an important role in nearly all aspects of cell biology, from cell migration to morphogenesis to cell proliferation.  We develop a new TFM method to determine cell traction forces reliably, accurately, and efficiently.  We investigate the interaction between single cardiac myocyte and the elastic substrate. We evaluate the migration force of tumor cell.

Figure 5.3. Concept of the fluidic electrode based detection of bacteria in DI water suspension. Impedance magnitude spectra of P. gingivalis suspensions in DI water with the cell concentrations in the range of 103 to 109 cells mL1, along with DI water as control
d) Researches on Calcium Signal
“Ca2+ spark” is the elementary event of calcium release in cardiac myocytes. We develop an anomalous sub-diffusion model to simulate Ca2+ spark, which fit perfectly with experimental results, solving the full-width at half maximum paradox. Based on the anomalous sub-diffusion model, Ca2+waves are also investigated. We theoretically and experimentally discover that when the two or three waves in a local region collide, they would not annihilate, but propagate towards other directions where Ca2+ release units have not opened yet. The studies may be used to predict some pathologies, such as fibrillation and arrhythmias.

Figure 5.4. (A) (a) Experimental linescan image of Ca2+ sparks, (b) Simulated Ca2+ spark based on anomalous subdiffusion, (c) Time courses, (d) Spatial profiles; (B) Experimental snapshots of two local Ca2+ waves collision (Snapshots from (a) to (d)).
e) Researches on Cardiovascular Mechanics
Coronary heart disease remains the major cause of morbidity and mortality around the world.  A principal mechanism in this problem is the diseased epicardial coronary artery that blocks the flow and leads to failure of sufficient blood supply to reach the heart muscle for its own metabolic needs.  Given two major risk factors (i.e., abnormal mural and shear stresses) for coronary artery diseases, we carry out the analysis of tissue mechanics and hemodynamics in the study of coronary circulation and diseases.

Figure 5.5. (A) Coronary arterial trees of mice of different ages reconstructed from Micro-CT images, (B) Blood flows in a patient’s LMCA coronary arteries.
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