C.V.

EDUCATION:

- 4th Year Ph.D. Candidate, Chemical and Biological Engineering;
  Northwestern University, Evanston, IL, Expected Graduation February 2008
- 2003 M.S., Chemical Engineering; University of Louisville
- 2002 B.S., Chemical Engineering; University of Louisville

PUBLICATIONS:

- Houchin-Ray T, Swift LA, Jang JH, Shea LD. (2007) Patterned PLG substrates for localized DNA delivery and directed neurite extension. Biomaterials (in press).

- Houchin-Ray T, Whittlesey KJ, Shea LD. (2007) Spatially patterned gene delivery for localized neuron survival and neurite extension. Molecular Therapy (in press).

- Jang JH, Bengali Z, Houchin TL, Shea LD. (2006) Surface adsorption of DNA to tissue engineering scaffolds for efficient gene delivery. Journal of Biomedical Materials Research Part A 77A: 50-58.

- Jang JH, Houchin TL, Shea, LD. (2004) Gene delivery from polymer scaffolds for tissue engineering. Expert Reviews in Medical Devices 1: 127-138.

- Shea LD, Houchin TL. (2004) Modular design of non-viral vectors with bioactive components. Trends in Biotechnology 22: 429-431.

RESEARCH SUMMARY:

Spatially Patterned Gene Delivery for Directed Tissue Formation

Natural tissues can have complex architectures characterized by the organization of multiple cell types into structures, such as branching networks of the vascular or nervous systems. This cellular organization arises, in part, from spatial patterns in gene expression, which can create concentration gradients of diffusible factors that direct cellular processes. We believe that engineering patterns of gene expression may provide a means to direct cellular processes (e.g., cell migration, neurite extension) for the regeneration of tissues with complex architectures.

Gene delivery from biomaterial scaffolds for tissue engineering offers the potential to support and direct progenitor cell differentiation and migration into functional tissue replacements. Gene therapy vectors, either virus-derived or non-viral, can be immobilized to tissue culture substrates through either specific (e.g., biotin-avidin) or nonspecific (e.g., electrostatic, van der waals) interactions. This technique, which we have termed substrate-mediated gene delivery, places complexes directly in the cellular microenvironment for efficient internalization, and high transfection efficiencies can be achieved with less DNA as compared to traditional bolus delivery.

Substrate Mediated Gene Delivery

This immobilization of gene therapy vectors provides the means to spatially restrict complex deposition and pattern gene expression. Patterned gene expression may offer significant advantages over protein patterning, which has been widely used to pattern cellular responses. We have developed a system to spatially pattern non-viral DNA complex deposition using soft lithography techniques.

Rhodamine-labeled DNA lipoplexes on polystyrene after localized complex deposition with PDMS microchannels

Pluronic treated PDMS microchannels afforded the ability to deposit active lipoplexes, and produced 1000 to 100 μm wide patterns of transgene expression. Subsequently, the patterned expression system was investigated for the ability to localize cellular processes using a neuronal co-culture model.

Neuronal co-culture model

Neuron survival and neurite outgrowth were assessed within patterns and at specific distances outside patterns of neurotrophic factor expression. Patterned transfection of the diffusible neurotrophic factor, nerve growth factor (NGF) could lead to localized and sustained secretion. Previous efforts to localize neurite outgrowth have focused on the patterning of adhesion molecules (e.g., ECM molecules) to guide cellular adhesion and neurite extension. One challenge to patterning proteins for guiding cellular processes is nonspecific adsorption of serum or cell-secreted proteins that can mask or displace the immobilized proteins. Gene delivery, in contrast, can sustain transgene expression for timescales ranging from days to months, with the persistence of the factors maintaining a stimulus locally to promote the cellular process. We show that the patterned expression of neurotrophic factors provides the stimulus to promote neuron survival and neurite outgrowth, and also the directional cue to orient neurite extension.

Localized neuron survival and neurite extension on patterns of neurotrophic factor expression

We believe the engineering of tissues with complex architectures will require concentrations of inductive factors to be manipulated on small length scales (10-100 µm) in order to direct cellular assembly and tissue formation. Ongoing work in this area is being conducted to apply the two-dimensional system to cell types that secrete inhibitory factors at a nerve injury site. Additionally, we are developing methods to pattern gene delivery within three-dimensional hydrogels.