Biomedical subjects

Valerie Liu Tsang

Publications and source records attributed to Valerie Liu Tsang.

4 recordsLinked to original sources

PubMed2007

Fabrication of three-dimensional tissues.

The goal of tissue engineering is to restore or replace the lost functions of diseased or damaged organs. Ideally, engineered tissues should provide nutrient transport, mechanical stability, coordination of multicellular processes, and a cellular microenvironment that promotes phenotypic stability. To achieve this goal, many engineered tissues require both macro- (approximately cm) and micro- (approximately 100 microm) scale architectural features. In recent years, techniques from the manufacturing world have been adapted to create scaffolds for tissue engineering with defined three-dimensional architectures at physiologically relevant length scales. This chapter reviews three-dimensional fabrication techniques for tissue engineering, including: acellular scaffolds, cellular assembly, and hybrid scaffold/cell constructs.

Biocompatible Materials↗

PubMed2006

Fabrication of 3D hepatic tissues by additive photopatterning of cellular hydrogels.

We have fabricated a hepatic tissue construct using a multilayer photopatterning platform for embedding cells in hydrogels of complex architecture. We first explored the potential of established hepatocyte culture models to stabilize isolated hepatocytes for photoencapsulation (e.g., double gel, Matrigel, cocultivation with nonparenchymal cells). Using photopolymerizable PEG hydrogels, we then tailored both the chemistry and architecture of the hydrogels to further support hepatocyte survival and liver-specific function. Specifically, we incorporated adhesive peptides to ligate key integrins on these adhesion-dependent cells. To identify the appropriate peptides for incorporation, the integrin expression of cultured hepatocytes was monitored by flow cytometry and their functional role in cell adhesion was assessed on full-length extracellular matrix (ECM) molecules and their adhesive peptide domains. In addition, we modified the hydrogel architecture to minimize barriers to nutrient transport for these highly metabolic cells. Viability of encapsulated cells was improved in photopatterned hydrogels with structural features of 500 microm in width over unpatterned, bulk hydrogels. Based on these findings, we fabricated a multilayer photopatterned PEG hydrogel structure containing the adhesive RGD peptide sequence to ligate the alpha5beta1 integrin of cocultured hepatocytes. Three-dimensional photopatterned constructs were visualized by digital volumetric imaging and cultured in a continuous flow bioreactor for 12 d where they performed favorably in comparison to unpatterned, unperfused constructs. These studies will have impact in the field of liver biology as well as provide enabling tools for tissue engineering of other organs.

Animals↗

PubMed2004

Photo- and electropatterning of hydrogel-encapsulated living cell arrays.

Living cells have the potential to serve as sensors, naturally integrating the response to stimuli to generate predictions about cell fate (e.g., differentiation, migration, proliferation, apoptosis). Miniaturized arrays of living cells further offer the capability to interrogate many cells in parallel and thereby enable high-throughput and/or combinatorial assays. However, the interface between living cells and synthetic chip platforms is a critical one wherein the cellular phenotype must be preserved to generate useful signals. While some cell types retain tissue-specific features on a flat (2-D) surface, it has become increasingly apparent that a 3-D physical environment will be required for others. In this paper, we present two independent methods for creating living cell arrays that are encapsulated within a poly(ethylene glycol)-based hydrogel to create a local 3-D microenvironment. First, 'photopatterning' selectively crosslinks hydrogel microstructures containing living cells with approximately 100 microm feature size. Second, 'electropatterning' utilizes dielectrophoretic forces to position cells within a prepolymer solution prior to crosslinking, forming cell patterns with micron resolution. We further combine these methods to obtain hierarchical control of cell positioning over length scales ranging from microns to centimeters. This level of microenvironmental control should enable the fabrication of next-generation cellular microarrays in which robust 3-D cultures of cells are presented with appropriate physical and chemical cues and, consequently, report on cellular responses that resemble in vivo behavior.

3T3 Cells↗

PubMed2004

Three-dimensional tissue fabrication.

In recent years, advances in fabrication technologies have brought a new dimension to the field of tissue engineering. Using manufacturing-based methods and hydrogel chemistries, researchers have been able to fabricate tissue engineering scaffolds with complex 3-D architectures and customized chemistries that mimic the in vivo tissue environment. These techniques may be useful in developing therapies for replacing lost tissue function, as in vitro models of living tissue, and also for further enabling fundamental studies of structure/function relationships in three dimensional contexts. Here, we present an overview of 3-D tissue fabrication techniques based on methods for: scaffold fabrication, cellular assembly, and hybrid hydrogel/cell methods and review their potential utility for tissue engineering.

Biocompatible Materials↗