Week One - Introduction to BioMEMs
Professor Wole Soboyejo welcomed students in the PUMA Trenton session and introduced them to the field of material science through his research to develop a micromachine that detects cancer at the cellular level for very early detection. Through various labs, the focus of this PUMA session is for Trenton students to explore material science by learning and understanding the engineering of this micromachine.
What
are BioMEMS?MEMS (Micro-Electro-Mechanical Systems) integrate mechanical elements, sensors, and electronics on a silicon substrate. The entire apparatus is less than the thickness of a human hair (100 microns). The micromechanical components are made by either selectively etching away parts of the silicon wafer or adding new layers to form the mechanical and electromechanical devices. BioMEMS uses these devices for biomedical or biological applications.
Kelly States trained students on basic lab conduct and safety measures to understand the potential hazards and emergency procedures, and to prepare them for working in Princeton University labs.
To review graphing basics, students observed a graph of distance vs. time, and using a special sensor to monitor body position, they attempted to make the same plot by moving toward and away from the sensor at different rates. Two student groups even received perfect scores for exactly matching their graphs!
To better understand why attaching a cancer cell to the cantilever tip will affect its frequency of motion, students reviewed the concept of frequency. Students twirled a string above their heads with washers attached to the end and counted the number of revolutions in 30 seconds. Then they calculated the frequency, defined as the number of revolutions per second, and repeated the exercise after adding a different number of washers to the end of the string. Students graphed their data, and observed the relationship between frequency and mass.
Biomedical
and BioMEMS Systems Explored: Microscopy and in-depth Presentation
Members of Professor Soboyejo’s lab described the nuts and bolts
of current experiments in the lab. An undergrad showed students the healthy
and cancerous bone cells they use, and graduate students, Steve Mwenifumbo
and Chris Milburn, presented the following material science problem they
are studying. To program the sophisticated brains of the BioMEMS and cantilever
device, the machine is made of silicon, just like a computer memory chip.
However, the properties of silicon are not compatible with biological
materials, and the cells will not stick to the cantilever.
Knowing that titanium is often used in medical devices, the lab has tried
to coat the machine with titanium, but much like a tidal wave will demolish
a small village, the forces holding the cancer cells to the material were
too weak to withstand the sheer force of moving fluid in a blood sample
or in the human body. Next, the lab is trying to coat the machine in gold,
capable of forming strong bonds with cells, in order to solve the problem.
Students saw first hand how well these bone cells stuck (or didn’t
stick) to silicon, titanium, and gold on three different microscopes:
optical, scanning electron microscope (SEM), and atomic force microscope
(AFM).
The
optical microscope bends the light shined on a sample through a series
of lenses to create a magnified image. Students observed bone cells
magnified up to 400 times. (led by an undergraduate student)- The SEM uses electrons instead of light to create a 3-dimensional image at much higher magnifications and better resolution than an optical microscope. (led by Steve Mwenifumbo)
- The AFM uses a lever probe, not lenses, to measure the attractive or repulsive atomic forces between the tip and the sample to generate an image resembling a topographical map of the sample’s surface. (led by Chris Milburn)
The purpose of this lab was to simulate how an atomic force microscope (AFM) generated a picture of a sample’s surface. The AFM used a lever probe to systematically run along the sample surface and measure the repulsion or attraction of the atoms between the sample and the probe tip. With these measurements, the image is created.
PUMA Trenton students simulated the AFM probe with two strips of magnet. Students ran one strip over the surface of the other magnet strip in a horizontal direction, and then repeated the exercise in a vertical direction. Students felt a force from the atomic arrangement only in one direction, to reveal the atomic alignment. What a first week!