Much of biomimicry in the fields of microfluidics and adhesion relies on fabricating and manipulating the surface energy at very small size scales. This patent is for a method that deposits hydrophobic or hydrophilic coating in a very precise way.

We have developed an improved vapor-phase deposition method and apparatus for the application of layers and coatings on various substrates. The method and apparatus are useful in the fabrication of biotechnologically functional devices, Bio-MEMS devices, and in the fabrication of microfluidic devices for biological applications.

Link to patent description

It looks like the first substantive papers on Min Jun Kim’s research are in review at prestigious journals.  Kim has fabricated microfluidics devices that use the bacterial flagellum as a mixing or pumping element.  The downside is the fluid must not only be biocompatible, but it will be scavenged by the bacteria for nutrients.  The upside is the power and size scale of these pumps. 

We were interested in utilizing flagellated bacteria as elements of a microfluidic systems, such as chaotic mixer, fludic pump, and micro-transportation system. Flagellar bacteria are propelled by a number of flagella, which are rotated by a nano-scale molecular motor embedded in the cell body.

In an abstract at the NanoScience and Technology meetings Kim writes -

…we show that (i) the flow-deposition of bacteria can successfully create a live bacterial carpet to generate local fluid motion inside a microfabricated system; (ii), that the carpet-activated microfluidic system can be used not only to enhance mixing in the closed system but also to pump fluid autonomously for several hours and (iii), that the pumping performance of the system changes in response to modifications to the chemical and thermal environment of the bacteria. Such bacterial systems are (to our knowledge) the first demonstrations of biological actuation of an engineered microfluidic system. The robustness, ease of “manufacture” and the ability to genetically modify their behavior make such systems highly attractive for powering microfluidic devices.

Kim’s Publication List

New Scientist article on Kim’s research

NSTI Abstract

Flow through biological nanotubes - blood vessels for example - happens with very little resistance. Imitating this low resistance in very small pipes has been elusive.  Bruce Hinds’ group has made a major advance by treating the nanotube core to make it highly hydrophobic. This apparently changes the flow regime in the tube dropping resistance by 5 fold over expectations from theory.  The tubes do seem to clog up pretty quickly, but this is a very promising first step.

PubMed Abstract

Sometimes I am just going to write about techniques that I think are cool.  Hopefully most will have an obvious relationship to biomimetics research.

First up is a flow visualization tool: the particle image velocimetry (PIV) system operating at the micron scale developed in Juan Santiago’s lab at Stanford.  To perform PIV a fluid is seeded with tiny, light reflective particles. In micro-PIV these particles are 300-500nanometer in diameter. A very thin sheet of laser light illuminates a chamber in which seeded fluid is moving. Sequential video frames (high speed or normal depending on the time resolution eeded) are then compared mathematically to determine how the particles have moved. The result is a field of flow vectors that accurately demonstrate the movement of fluid through the area of interest. 

This system will be important for biomechanists and biomimetics research because it allows visualization of flows at some  difficult to access, but biologically relevant, size scales.  This is the size scale of blood in a capillary, water over a fishes gill and air over a moth’s antenna.  All are areas of active biomimetics research.  

Lab Web Site

This lab’s website has some nice images of the water conducting tissue of plants.  Plants are wonderfl sources for inspiration in the field of bio-microfluidics. They are masters of moving large volume through small diameter tubes with both passive and active control.  The ability of plants to refill water transport structures (xylem) while adjacent tubes are still conducting water under tension is of particular interest. This process of embolism repair would be key to any man-made, real world microfluidics operation.  The image above shows the network of pits that cross the walls of adjacent xylem vessels. 

Lab Web Site 

Microfluidics is concerned with pumping and valving nanoliter volumes of liquids. There are many non-biological approaches but there are also some potentially interesting biomimetic approaches. A discovery phase project involves understanding the seemingly simple transport of water up a tree.  The pipes (xylem) in which water flows do not run the length of the tree.  Xylem cells connect, one with another through pits along their length. In the event that an air embolism appears in one xylem tube it cannot travel to another because each pit has a tiny backflow preventer valve.  When there is a pressure difference between adjacent cells the preventer flops across the pit and stops air from crossing intot he next cell.

Cool images