Comparison of smooth and hairy attachment pads in insects: friction, adhesion and mechanisms for direction-dependence

James M. R. Bullock, Patrick Drechsler and Walter Federle

Purpose:

Biomemitic technologies provide a valuable opportunity to borrow methods and uses from many years of optimization through evolution.  The aim of this study was to compare the performance of smooth and fibrillar systems in insects to clarify the mechanisms of attachment and removal.  This includes determining how smooth versus hairy attachment influences frictional performance, the importance of fluid pad secretion and its role in adhesion, and if there is any mechanism for direction dependence of attachment.

 

Methods:

A force transducer was used to measure friction forces of the insects feet which employed foil strain gauges and a three dimensional DC driven stage. Optical images were obtained using a camera and LabView and Matlab were used for data analysis from the home built system.

 

Key Findings:

1. Direction dependence of adhesion was observed with dramatically decreased adhesion in the distal direction but not the proximal.

2. No load dependence was observed for friction, contact area, or shear stress

3. Smooth/Hairy comparison of attachment found nearly 2x adhesion forces for the hairy system over the smooth

4.  Fluid pad secretion was quickly depleted from the contact zone and provide hydrophobic contacts to promote adhesion.

Diamond FED diodes

Final Paper    Final Paper

Final Presentation     Final Presention

Therapeutic Nanodevices: Drug Delivery

For the paper click here.
For the slides click here.
December 18, 2008

Functionalized Nanomaterials for Medical Applications

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For the paper, click here.

Photovoltaic cells fabricated by electrophoretic deposition

Nathanael J. Smith, Kevin J. Emmett, and Sandra J. Rosenthal

Purpose

The purpose of this paper is to observe the efficiency of photovoltaic cells made with CdSe nanocrystals that have been electrophoretically deposited onto titanium oxide. The efficiency of these cells are lower to other solar cells (~10^-6%).

Methods/Procedures Used

Electrophoresis was used to deposit the CdSe nanocrystals in a fast and non-destructive manner. Rutherford backscattering was used to compare the composition of the films on both the positive and negative electrodes during the deposition.

Key Findings

1. Too much TOPO solvent made electrophoresis difficult. This is due to an effect seen in previous literature where CdSe prefer to stay in solution.
2. An interesting effect was observed where cadmium precursor attaches to the negative electrode during deposition in a greater concentration than onto the positive electrode. This concentration difference was determined by Rutherford backscattering
3. Nanometer thick photovoltaic cells were successfully created within one minute with this technique.

Biomimetic subwavelength antireflective gratings on GaAs

Chih-Hung Sun,

 

1 Brian J. Ho,1 Bin Jiang,2 and Peng Jiang1,*

OPTICS LETTERS / Vol. 33, No. 19 / October 1, 2008 p 2224-2226

Purpose of Study-

The authors developed a simple effective method in order to make a patterned surface that decreases the reflectivity of a surface.  In this manuscript they apply this method to GaAs wafers.

Methods-

Silica colloidal spheres are dispersed on a wafer using a simple spin-coating technique.  The size of the colloids can be controlled by varing the speed of the spin-coater.  In order to apply this method to GaAs surfaces, a single-layer reduction technique was employed.  Once the silica has  been deposited, a PDMS stamp is created.   Using the stamp as a mold, they are able create a template to form a patterned polymer film.

Key Findings-

• Subwavelength antireflective gratings can be easily formed on a variety of substrates.
• Silica colloids can be uniformily dispersed across a substrate, and be used to create a pattern template.

Integrated molecular targeting of IGR1R and HER2 surface receptors and destruction of breast cancer cells using single wall carbon nanotubes

Ning Shao, Shaoxin Lu, Eric Wickstrom, Balaji Panchapakesan, Nanotechnology 18 (2007) 315101 (9pp).

Purpose of the Study:   

Demonstrate the in vitro ability of single walled carbon nanotubes (SWCNT) functionalized with anti-IGF1R and anti-HER2 monoclonal antibodies to destroy breast cancer cells upon excitation with near infrared light (808nm). 

Methods:

 

•  SWCNTs having an average diameter of 1.4nm and lengths ranging from 500nm to 1mm were fabricated with a self-assembled monolayer of polyethylene glycol (PEG) to prevent undesirable binding with other biomolecules.
• Transmission electron micrography was used to characterize the SWCNTs.
• SWCNTs were divided into three groups and functionalized with a non-specific antibody (control), anti-IGF1R antibody, or anti HER2 antibody.
• Cytotoxicity was minimized, consistent with published research, by chemically modifying SWCNT surface with –OH and –COOH groups in addition to the PEG conjugates.
• SWCNTs were mixed with fluorescent dyes (phalloidin 488 & 555) to form fluorescent SWCNT-antibody hybrids.
• SWCNTs were incubated with two different human breast cancer cell lines:  (a) BT474, which exhibit high expression of HER2 receptors and lower expression of IGF1R receptors, and (b) MCF7, which exhibit high expression of IGF1R receptors and lower expression of HER2 receptors.  Each cell line was incubated with both anti-HER2 SWCNTs and anti-IGF1R SWCNTs.
• Confocal fluorescent microscopy was used to characterize the fluorescent SWCNT-antibody hybrids and the cellular uptake thereof.
• An 808nm laser at 800mW cm^-2 and 3 min exposure time was used for the photo-thermal therapy regimen. 
• Trypan blue assay was used to verify and quantify cell death (i.e. cell viability).  

Key Findings:

 

1. SWCNT-receptor specific antibody conjugates were readily internalized into the cells over large areas while the SWCNTs with the non-specific antibody were not.  The authors hypothesize the following mechanism (consistent w/ previous research):  upon receptor-specific attachment, stresses are generated due to free energy release which generates a pressure differential across membrane pores, thereby facilitating endocytosis.
2. Cells receiving only the NIR light without internalized SWCNT survived the photo-thermal therapy whereas those incubated with the SWCNT anti-HER2 and anti-IGF1R conjugates did not survive (100% kill rate).  Those cells to which SWCNT-non specific antibody conjugates were attached, 50% survived (most likely due to fewer attached).
3. Cells were killed due to the localized increase in temperature resulting from high absorption by the SWCNT that occurs with NIR light while normal cells remain transparent to NIR.   
4. The energy used to destroy the cancer cells was estimated to be ~200nW per cell, too low to create any damage to the normal cells.  Due to the high specificity, antibody-directed targeting, the authors were able to use half the laser power of past nanotube based cell killing techniques. 

Definitions:

Her2:  human epidermal growth factor receptor (often over expressed by breast cancer cells)

IGF1R:  insulin-like growth factor receptor (often over expressed by breast cancer cells)