Constructing and probing biomimetic models of the actin cortex with holographic optical tweezers

The actin cortex is an adaptive chemo-mechanical polymer network located beneath the cell membrane. A thin, quasi two-dimensional (2D) network, the actin cortex plays a leading role in controlling cellular viscoelasticity, shape, and motility. Regulated by internal and external stimuli, the actin cortex varies its properties with controlled polymerization and depolymerization of actin. For constructing and probing biomimetic actin networks we combined three different techniques to achieve complete spatial, visual and chemical control of the microenvironment: 1) dynamic holographic optical tweezers (HOTs) which produce and independently steer one to hundreds of optical traps, 2) fluorescence microscopy for imaging of actin and 3) a specially-designed microfluidic system, which precisely controls the chemical environment. Using this system, we take two approaches to construct biomimetic 2D actin networks. First HOTs micropattern surfaces with microspheres onto which actin can the be grown. Secondly, HOTs in combination with a multi channel microfluidic system are used to coat optically-trapped microsphere arrays with actin