Affiliated Faculty: Bhattacharya, Burdick, Dabiri, Dickinson, Fraser, Gharib, Guo, Phillips

The BMBID group in Bioengineering at Caltech develops and utilizes analytical, computational, and experimental tools from mechanics to probe biological function and to design bio-inspired engineering systems with novel function. Research within the group focuses on biological systems ranging in scale from single molecules to whole organisms.

The following research projects illustrate current research activities:

Bacteriophage Mechanics
When bacteriophage lambda ejects its DNA, the entire 48.5 kbp genome emerges from the capsid in a continuous process over about 1.5 s, which we observe using fluorescence microscopy.  The bacteriophage capsid is stuck to the surface of a microscope coverslip, and fluorescent dye allows us to visualize the DNA, stretched out in a flow for the purpose of measuring its length as a function of time.  As the DNA emerges from the capsid, we record a movie with frames every 0.25 s that are displayed here side-by-side.  A quantitative analysis of the translocation velocity of the DNA teaches us about the physics of the highly compressed DNA within the capsid, which involves hydrodynamics and friction at the molecular scale. The results are relevant both for the function of viruses and for the design of DNA handling nanotechnology such as single-molecule sequencing devices.

Mechanics of Embryonic Cardiogenesis
The pattern of blood flow in the developing heart has long been proposed to play a significant role in cardiac morphogenesis. In response to flow-induced forces, cultured cardiac endothelial cells rearrange their cytoskeletal structure and change their gene expression profiles. To link such in vitro data to the intact heart, we performed quantitative in vivo analyses of intracardiac flow forces in zebrafish embryos. Using in vivo imaging, we observed the presence of high-shear, vortical flow at two key stages in the developing heart, and predicted flow-induced forces much greater than might have been expected for micro-scale structures at low Reynolds numbers. To test the relevence of these shear forces in vivo, flow was occluded at either the cardiac inflow or outflow tracts, resulting in hearts with an abnormal third chamber, diminished looping and impaired valve formation. The similarity of these defects to those observed in some congenital heart diseases argues for the importance of intracardiac haemodynamics as a key epigenetic factor in embryonic cardiogenesis.

Mechanics of Insect Flight
Most insects are thought to fly by creating a leading-edge vortex that remains attached to the wing as it translates through a stroke. In the species examined so far, stroke amplitude is large, and most of the aerodynamic force is produced halfway through a stroke when translation velocities are highest. In this work we demonstrated that honeybees use an alternative strategy, hovering with relatively low stroke amplitude and high wingbeat frequency (approximately 90 degrees and 230 Hz, respectively). When measured on a dynamically scaled robot, the kinematics of honeybee wings generate prominent force peaks during the beginning, middle, and end of each stroke, indicating the importance of additional unsteady mechanisms at stroke reversal. When challenged to fly in low-density helium, bees responded by maintaining nearly constant wingbeat frequency while increasing stroke amplitude by nearly 50%. We examined the aerodynamic consequences of this change in wing motion by using artificial kinematic patterns in which amplitude was systematically increased in 5 degrees increments. To separate the aerodynamic effects of stroke velocity from those due to amplitude, we performed this analysis under both constant frequency and constant velocity conditions. The results indicate that unsteady forces during stroke reversal make a large contribution to net upward force during hovering but play a diminished role as the animal increases stroke amplitude and flight power. We suggest that the peculiar kinematics of bees may reflect either a specialization for increasing load capacity or a physiological limitation of their flight muscles.

Curriculum

Students in the BMBID program must demonstrate proficiency in the mechanics of fluids and solids, mathematics, and the application of these tools to biology. First- and second-year coursework in the program is intended to build upon undergraduate training and to complement concurrent research activities. The following table lists the coursework requirements of the BMBID academic program.

BMBID Requirements (Year 1)

Boot Camp:
Prior to first term

Math track (3 terms):
ACM 95/100 abc

Biology track (3 terms):
Bi 145 ab, BE 201 abc

BMBID core I track (3 terms):
Ae/APh/CE/ME 101 abc, ChE 103 abc, ChE 151 ab, ChE 174

BMBID core II track (3 terms):
Ae/AM/CE/ME 102 abc, ChE/Ch 164, Ph 127 abc

Research track:
Optional research rotations BE250

BMBID Requirements (Year 2)

BMBID elective track (2 terms):

An incoming student who demonstrates prior proficiency in any required course can elect to opt out of that course. However, the student must maintain a course load of 36 units each term during the first year, and the student will be responsible for the course material during the Qualifying Exam. The exam will encompass the material from the math track, biology/physiology track, and either the solid or fluid mechanics track (depending on each student’s preference). Students are encouraged to pursue research rotations in several labs during the first year to gain exposure to a number of different research areas before choosing an advisor and settling on a research project.

HomeBDBI Sub-Option
BMBID Sub-Option
SSB Sub-OptionPeopleAcademics SeminarsPositionsAdmissionsContact

BE News & Events
Caltech Home