Andrew J. Lee

Optimizing the structure and contractility of engineered skeletal muscle thin films

An experimental system was developed to tissue engineer skeletal muscle thin films with well-defined tissue architecture and to quantify the effect on contractility. Using the C2C12 cell line, the authors tested whether tailoring the width and spacing of micropatterned fibronectin lines can be used to increase myoblast differentiation into functional myotubes and maximize uniaxial alignment within a 2-D sheet. Using a combination of image analysis and the muscular thin film contractility assay, it was demonstrated that a fibronectin line width of 100μm and line spacing of 20μm is able to maximize the formation of anisotropic, engineered skeletal muscle with consistent contractile properties at the millimeter length scale. The engineered skeletal muscle exhibited a positive force-frequency relationship, could achieve tetanus and produced a normalized peak twitch stress of 9.4±4.6kPa at 1Hz stimulation. These results establish that micropatterning technologies can be used to control skeletal muscle differentiation and tissue architecture and, in combination with the muscular thin film contractility, assay can be used to probe structure-function relationships. More broadly, an experimental platform is provided with the potential to examine how a range of microenvironmental cues such as extracellular matrix protein composition, micropattern geometries and substrate mechanics affect skeletal muscle myogenesis and contractility.

3D Printing PDMS Elastomer in a Hydrophilic Support Bath via Freeform Reversible Embedding

Polydimethylsiloxane (PDMS) elastomer is used in a wide range of biomaterial applications including microfluidics, cell culture substrates, flexible electronics, and medical devices. However, it has proved challenging to 3D print PDMS in complex structures due to its low elastic modulus and need for support during the printing process. Here we demonstrate the 3D printing of hydrophobic PDMS prepolymer resins within a hydrophilic Carbopol gel support via freeform reversible embedding (FRE). In the FRE printing process, the Carbopol support acts as a Bingham plastic that yields and fluidizes when the syringe tip of the 3D printer moves through it, but acts as a solid for the PDMS extruded within it. This, in combination with the immiscibility of hydrophobic PDMS in the hydrophilic Carbopol, confines the PDMS prepolymer within the support for curing times up to 72 h while maintaining dimensional stability. After printing and curing, the Carbopol support gel releases the embedded PDMS prints by using phosphate buffered saline solution to reduce the Carbopol yield stress. As proof-of-concept, we used Sylgard 184 PDMS to 3D print linear and helical filaments via continuous extrusion and cylindrical and helical tubes via layer-by-layer fabrication. Importantly, we show that the 3D printed tubes were manifold and perfusable. The results demonstrate that hydrophobic polymers with low viscosity and long cure times can be 3D printed using a hydrophilic support, expanding the range of biomaterials that can be used in additive manufacturing. Further, by implementing the technology using low cost open-source hardware and software tools, the FRE printing technique can be rapidly implemented for research applications.

Real-time deformation invariant optical pattern recognition using coordinate transformations

The well-known scale and rotation invariant polar-logarithmic coordinate transformation is used to achieve in-plane distortion invariant pattern recognition. The coordinate transform is produced by a computergenerated hologram on a laser printer. Attention is given to weighting terms in the output and their effect on resolution and the number of input plane pixels removed near the origin. The optically produced coordinate transformed input pattern is interfaced to a correlator by a pocket liquid crystal TV to provide real-time processing. Experimental results are included.

Computer generated hologram recording using a laser printer

The use of a laser printer for recording various types of computer generated holograms is discussed, and initial results are presented.

Diffraction pattern sampling using a computer-generated hologram

A grating computer-generated hologram (CGH) to perform wedge and ring detector diffraction pattern sampling is discussed. Undesirable effects that result due to the nonparallel light incident on a Fourier transform plane CGH are addressed, and several optical system solutions are suggested. Experimental demonstrations are provided.

Estimating Object Rotation And Scale Using Correlation Filters

Recently, much attention has been paid to designing correlation filters that provide distortion-invariant pattern recognition. However, optical correlators can also be used to estimate the orientation and scale change in the object being observed. This paper presents two new methods for designing correlation filters that are aimed at determining the in-plane rotation and scale changes present in the input image (relative to a reference image). These methods assume that a known object is present in the input plane and that its rotation and scale are to be estimated. The first method is capable of determining both rotation and scale changes simultaneously. The second method assumes that the scale is fixed and estimates only the in-plane rotation. Both methods should prove useful in applications in which one needs to estimate the object orientation. Several simulation results are included to quantify the estimation accuracies and the computational complexities of the two methods.

Optical relational-graph rule-based processor for structural-attribute knowledge bases

An optical relational-graph or decision-net processor is advanced, and one optical system design for such a processor is provided. The general description of this processor is provided as well as two designs for a specific case study. A rule-based design of a knowledge base of facts using structural rather than functional attributes of the object is detailed. A general technique is advanced to organize a fact-based knowledge base into a rule-based knowledge base using structural rather than functional attributes. A multiclass 3-D distorted object identification and classification problem is considered as our case study. A general relational-graph design methodology is advanced, and specific designs for our case study are then presented. Multidecision and binary relational-graph designs are advanced, and impressive initial simulation results with each are noted.

A Feature Space Rule-Based Optical Relational Graph Processor

A rule-based optical symbolic and inference processor concept using a relational graph is described. The architecture and its design are discussed and detailed for one example. The system uses a Fourier/polar/Mellin/Fourier transform representation space and the case studies addressed involve aircraft identification and classification. However, the basic rule-based optical-inference relational graph processor concept and architecture are quite general purpose.

Estimating Satellite Pose And Motion Parameters Using A Novelty Filter And Neural Net Tracker

A system for determining the position, orientation and motion of a satellite with respect to a robotic spacecraft using video data is advanced. This system utilizes two levels of pose and motion estimation: an initial system which provides coarse estimates of pose and motion, and a second system which uses the coarse estimates and further processing to provide finer pose and motion estimates. The present paper emphasizes the initial coarse pose and motion estimation subsystem. This subsystem utilizes novelty detection and filtering for locating novel parts and a neural net tracker to track these parts over time. Results of using this system on a sequence of images of a spin stabilized satellite are presented.

Correlation filters for orientation estimation

An important task in many vision applications is that of rapidly estimating the orientation of an object with respect to some frame of reference. Because of their speed and parallel processing capabilities, optical correlators should prove valuable in this application. This paper considers two algorithms for object orientation estimation based on optical correlations and presents some initial simulation results.