Monday July 23, 2007

Today we are beginning our work on the effect of varying surface tension on wrinkling. First, we learn to use the Tensiometer. This instrument has a precise set up regimen. After turning the instrument on, a microsyringe is filled with the solution to be analyzed (below left).

Then the syringe is inserted into the syringe holder, just to the right of the thermometer. A cuvette has one ml of water added to it, then it is covered with parafilm. A hole is cut into the parafilm so that the tip of the syringe can be inserted into the covered cuvette; all this is done to prevent evaporation of water from the surface of the drop being analyzed during the measuring period. It is critical that the syringe is precisely perpendicular to the water surface, and that the drop is as large as possible without falling off the tip of the syringe.


As is true of every instrument we have encountered in the lab, the Tensiometer is computer driven. The software, SCA20, is initiated and the parameters for the system and for the ambient conditions are entered into the computer. Once the program is set, the computer directs the volumes to be dispensed from the syringe to create the drop to be analyzed (below, left).

The data is recorded 30 times a minute for an hour. It takes some time for the drop to become stable, so the first ten to fifteen minutes of readings are discarded. The readings then become stable and are displayed alphanumerically as well as graphically (above, right). Each of us set up the instrument and software to measure the surface tension of water. We achieved readings of 70, 71, and 72; the expected surface tension was 72. Pretty good!

At the end of the day, we attended a seminar presented by two professors from Tsinghua University in Beijing, considered China's M.I.T., which has a total enrollment of 30,000 students. Dr. Quingling Feng presented her work on :The Fabrication and Characterization of Scaffolds for Tissue Engineering", which explained the use of biomimetic composites to encourage bone growth. The biomimetric composites are based on studies of natural bone; nanohydroxyapatite/collagen can be molded on PLLA to create a bone scaffold very similar in structure to natural bone. In some work, chitin was used instead of hydroxyapatite in conjunction with the collagen, and more crosslinking between molecules (therefore higher compression strength) was found. A combination of the two polymers was used to repair fractures in goat tibia, and the healing time was decreased. The material has received approval for trials in humans in China.


The second presentation was by Professor Guosheng Gai, whose field of expertise is the behavior of fine powders. His current research investigates the construction of composite particles and modification of their shape. He controls the microstructure within the material to affect particle shape. He has been able to create conductive plastics through particle coating. This was hard for me to follow.