Developing in vitro assays to quantitatively evaluate the interactions of dressings with wounds.

Evaluating interactions between dressing and wound is important for understanding wound management. This study quantitatively compared four polyurethane foam-based wound dressings for their absorption profile, cell penetration, and adherence using two novel in vitro assays. The dressing with uniform pore sizes varying from 25~75 µm showed the highest absorption of both culture media and serum. The same dressing showed a 1.2- to 3.6-fold lower cell adherence (3 hours) than the other dressings, and ~20-fold lower cell penetration (5 days) than dressings with pore sizes varying from 55 to 343 µm. Additionally, cell and dressing interactions using a 3-dimensional wound healing assay showed that the dressings with the smallest pore size of 25~75 µm maintained the highest cell viability (76.3%) and promoted cell migration into the wound site. This data suggest that polyurethane foam dressing with smaller and evenly distributed pores promotes wound healing with less cellular adhesion and penetration.

Purpose-driven biomaterials research in liver-tissue engineering.

Bottom-up engineering of microscale tissue ("microtissue") constructs to recapitulate partially the complex structure-function relationships of liver parenchyma has been realized through the development of sophisticated biomaterial scaffolds, liver-cell sources, and in vitro culture techniques. With regard to in vivo applications, the long-lived stem/progenitor cell constructs can improve cell engraftment, whereas the short-lived, but highly functional hepatocyte constructs stimulate host liver regeneration. With regard to in vitro applications, microtissue constructs are being adapted or custom-engineered into cell-based assays for testing acute, chronic and idiosyncratic toxicities of drugs or pathogens. Systems-level methods and computational models that represent quantitative relationships between biomaterial scaffolds, cells and microtissue constructs will further enable their rational design for optimal integration into specific biomedical applications.

Galactosylated cellulosic sponge for multi-well drug safety testing.

Hepatocyte spheroids can maintain mature differentiated functions, but collide to form bulkier structures when in extended culture. When the spheroid diameter exceeds 200 µm, cells in the inner core experience hypoxia and limited access to nutrients and drugs. Here we report the development of a thin galactosylated cellulosic sponge to culture hepatocytes in multi-well plates as 3D spheroids, and constrain them within a macroporous scaffold network to maintain spheroid size and prevent detachment. The hydrogel-based soft sponge conjugated with galactose provided suitable mechanical and chemical cues to support rapid formation of hepatocyte spheroids with a mature hepatocyte phenotype. The spheroids tethered in the sponge showed excellent maintenance of 3D cell morphology, cell-cell interaction, polarity, metabolic and transporter function and/or expression. For example, cytochrome P450 (CYP1A2, CYP2B2 and CYP3A2) activities were significantly elevated in spheroids exposed to ß-naphthoflavone, phenobarbital, or pregnenolone-16α-carbonitrile, respectively. The sponge also exhibits minimal drug absorption compared to other commercially available scaffolds. As the cell seeding and culture protocols are similar to various high-throughput 2D cell-based assays, this platform is readily scalable and provides an alternative to current hepatocyte platforms used in drug safety testing applications.