[show abstract][hide abstract] ABSTRACT: A three-dimensional micro-scale perfusion-based two-chamber (3D-μPTC) tissue model system was developed to test the cytotoxicity of anticancer drugs in conjunction with liver metabolism. Liver cells with different cytochrome P450 (CYP) subtypes and glioblastoma multiforme (GBM) brain cancer cells were cultured in two separate chambers connected in tandem. Both chambers contained a 3D tissue engineering scaffold fabricated with biodegradable poly(lactic acid) (PLA) using a solvent-free approach. We used this model system to test the cytotoxicity of anticancer drugs, including temozolomide (TMZ) and ifosfamide (IFO). With the liver cells, TMZ showed a much lower toxicity to GBM cells under both 2D and 3D cell culture conditions. Comparing 2D, GBM cells cultured in 3D had much high viability under TMZ treatment. IFO was used to test the CYP-related metabolic effects. Cells with different expression levels of CYP3A4 differed dramatically in their ability to activate IFO, which led to strong metabolism-dependent cytotoxicity to GBM cells. These results demonstrate that our 3D-μPTC system could provide a more physiologically realistic in vitro environment than the current 2D monolayers for testing metabolism-dependent toxicity of anticancer drugs. It could therefore be used as an important platform for better prediction of drug dosing and schedule towards personalized medicine.
[show abstract][hide abstract] ABSTRACT: Polymer nanofoams have recently attracted significant interest in both industry and academia. The unique nanoscaled porous structure could bring unprecedented material properties that have not been seen in conventional or microcellular polymer foams. It has been hypothesized that nanofoams could have a much higher specific strength and toughness as well as significantly improved thermal resistivity. In this research, we study the fabrication and characterization of polyetherimide nanofoams using a supercritical carbon dioxide foaming process. A process map indicating the conditions to obtain various polyetherimide foam structures, including micro-, micro/nano transition, and nanofoams has been established. Two types of nanofoams were observed, one made with high gas concentrations and the other with high foaming temperatures. The one with high gas concentrations exhibited a higher specific modulus than that of unfoamed polyetherimide. Nanofoams generally showed a higher thermal resistivity than microfoams with similar relative densities. It is found that the equilibrium CO2 concentration in polyetherimide under the supercritical conditions does not fit well to the well-known dual-mode sorption model. A new gas concentration model was developed to describe the CO2 uptake under supercritical conditions.
Journal of Cellular Plastics 01/2012; 48(3):239-255. · 0.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: In scaffold-based tissue engineering, the fabrication process is important for producing suitable microstructures for seeded cells to grow and reformulate. In this paper, we present a new approach to scaffold fabrication by combining the solid-state foaming and the immiscible polymer-blending method. The proposed approach has the advantage of being versatile and able to create a wide range of pore size and porosity. The proposed method is studied with polylactic acid (PLA) and polystyrene (PS) blends. The interconnected porous structure was created by first foaming the PLA/PS blend and then extracting the PS phase. The solid-state foaming experiments were conducted under various conditions to achieve the desired pore sizes. It is shown that the PS phase of the PLA/PS blend can be extracted much faster in the foamed samples and the pore size of the scaffolds can be easily controlled with proper gas foaming parameters. The average pore size achieved in the foaming process ranged from 20 to 70 µm. After PS extraction, both pore size and porosity can be further improved. For example, the pore size and porosity increased from 48 µm and 49% to 59 µm and 67%, respectively, after the PS extraction process. The fabricated porous scaffolds were used to culture human osteoblast cells. Cells grew well and gradually formed a fibrous structure. The combined solid-state foaming and immiscible polymer blending method provides a new technique for fabricating tissue-engineering scaffolds.
[show abstract][hide abstract] ABSTRACT: A fabrication process to produce functionally graded porous polymer via supercritical carbon dioxide (ScCO2) foaming is reported in this paper. It utilizes a partial gas saturation technique to obtain non-equilibrium gas concentration profiles in thermoplastic polymer. Once foamed the polymer material obtains a graded foam–solid-foam structure with varying pore size distributions. This functionally graded material fabrication method was studied with polymethyl methacrylate (PMMA) under a ScCO2 saturation condition. A diffusion model was developed to estimate the gas diffusion coefficient and to predict the gas concentration profiles inside the polymer samples. Scanning electron microscopy images were used to analyze the effects of partial saturation on the graded porous structure. Mechanical properties of the foamed samples were characterized using a three-point bending test. It was found that the gas concentration profiles resulted from partial saturation corresponded well to the graded structure after foaming. The proportion of the foam and solid regions inside the polymer sample can be manipulated by controlling the partial saturation profile. The test results also suggested that the graded foam structure could be optimized to achieve desirable mechanical properties.
Composites Part B Engineering 03/2011; 42(2):318-325. · 2.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cell migration under chemoattractant is an important biological step in cancer metastasis that causes the spread of malignant tumor cells. Porous polymeric materials are widely used to mimic the extracellular matrix (ECM) environment for applications such as three dimensional (3D) cell culturing and tissue engineering. In this paper we report a novel 3D cell culture device based on porous polymeric material to study cancer migration. We fabricated a porous channel on a polymeric chip using a selective ultrasonic foaming method. We demonstrate that a chemical concentration gradient could be established through the porous channel due to the slow diffusion process. We show that significant cell migration could be observed through the porous channel within 1-2 weeks of cell culturing when metastatic M4A4-GFP breast cancer cells were induced by 20% fetal bovine serum (FBS).We also developed a mathematical model to evaluate the diffusivity and concentration gradient through the fabricated porous structure.
[show abstract][hide abstract] ABSTRACT: This paper first introduces the broadband multimedia communication satellite idea and the concept of channel assignment. It briefly reviews the history of channel assignment research and mathematically formulates the problem. Classical and neural network methods are applied to the solution of the problem. Simulations of both methods show that neural network method is better in dealing with real world channel assignment problem as that encountered in our satellite system. Finally is the conclusion on how to improve performance and other satellite channel assignment related issues.