A Soft Fluidic Force Microscope Probe for Cellular Force Measurement

Committee:
Todd Sulchek, Ph.D. (Chair and PI), ME
Oliver Brand, Ph.D., ECE
Peter Hesketh, Ph.D., ME
Wilber A. Lam, MD, Ph.D., BME
Hang Lu, Ph.D., ChBE

The focus of this work is on a micro-fabrication technique for batch fabrication of a low stiffness fluid force microscope with direct connection to a microfluidic capillary.  A fluid force microscope is an AFM probe that has a micro-channeled cantilever, giving it the additional capacity to perform contractile and adhesion measurements, perfusion and cellular manipulation.   The abiotic and reversible nature of the device enables decoupling of receptor-ligand associated stimulus responses and enables rapid serial measurements.  The major limitations of current fluidic probes are twofold:  1. Current fabrication techniques disenable force microscopy in the pN range, which is physiologically relevant to cell thrust, early adhesion and contraction.  2.  The fluidic system interface requires destructive modification of the AFM’s costly mounting assembly.  In this work, three enabling design or micro-fabrication techniques are developed and validated:
1. A low stiffness micro-channeled cantilever | The aim is to design and perform both analytical and experimental validation of a thermally decomposable polynorbornene sacrificial resist technique to fabricate low stiffness (<0.1 N/m) cantilever for high resolution at sub-nN force spectroscopy.  Stiffness is first characterized as a function of dimension by a numerical analysis, design and experimental validation follow;
2. A fully integrated microfluidic system | The aim is to design and validate a glass capillary to probe interconnect technique to create a fully integrated fluidic channel avoiding the need for modification of the AFM mounting assembly;
3. A surface to bulk microfluidic channel | The aim is to design and validate a multi-layer and multi-viscosity resist based technique to form a fluidic interface between surface and bulk microfluidic channels for modulation of the pressure at the cantilever terminus.
The probe is then fabricated and characterized.  Biological utility is demonstrated by performing simultaneous measurements showing cell size, adhesion and stiffness on early leukocyte-epithelial cell adhesion and comparing with benchmark technologies.