Vol. 3 No. 1 September 2004

The BioTECH Quarterly

BMES J&J Research Award winners showcased their research

Max Cohen ’05, Physics, Biology. “Altered kinetics of platelet adhesion with stenting.” HST Biomedical Engineering Center, Prof. Elazer Edelman.

Sid Puram ’05, Biology, Brain & Cognitive Sciences. “Poly beta-amino ester microspheres as a specific and controlled DNA delivery vector.” MIT Chemical Engineering Robert Langer Laboratory, Steven Little.

Amy Shi ’04, Chemical Engineering. “Demonstration of cell density effects on stem cell kinetics symmetry.” MIT BE Division Sherley Laboratory, Prof. James Sherley.

Julie Tse ’06, Chemical Engineering. “Biocompatibility of polymeric microspheres for intraperitoneal drug delivery.” MIT Chemical Engineering Langer Lab, Dr. Daniel Kohane.

Woon Teck Yap ’05, Biology. “Synthesis of novel hydrogel particles for antigen delivery to and activation of dendritic cells.” Biomaterials and Immune System Bioengineering Lab, Prof. Darrell Irvine.

BMES-J&J Winner: Max Cohen - Altered kinetics of platelet adhesion with stenting

    Endovascular stents are thin metal tubes implanted into the coronary artery to stabilize damaged vessel walls, largely replacing the older technique of balloon angioplasty. Platelet adhesion to damaged vessel walls is a key step in the development of coronary thrombosis, but it is not well understood how post-interventional geometries (ie, the presence of a stent) affect platelet interactions with the damaged vascular wall.

    We have used a bidirectional, pulsatile, closed-loop flow system to investigate the relationship between stent geometry and platelet adhesion under a variety of coronary flow-like conditions. By comparing results from both an experimental fluid-mechanical model and computation finite-element simulations, we’ve been able to examine the delicate and important interplay of flow, transport, and geometry.

"My experience with biomedical engineering research has shown me that there are many different ways to approach each problem. I have enjoyed the variety of disciplines I've been exposed to, but most of all this project has solidified my interest in a career as a biomedical researcher."

BMES-J&J Winner: Sid Puram - Microspheres as a controlled DNA delivery vector

    I work on research using polymer microspheres as a DNA delivery vector. These microspheres are tested on cultured murine and dendritic cells with transfection effeciency studies such as the luciferase assay. Additional work involves activation studies and release characterization for our particles.

    We have also used 3-D Deconvolution to confirm the intracellular release of DNA from our microspheres. These spheres, approximately 1-10 um in diameter, appear to have great promise for use within the clinical setting.

BMES-J&J Winner: Amy Shi - Cell density effects on stem cell kinetics symmetry

   The potential of adult stem cells (ASCs) for medical and research advances is evident. However, the isolation and propagation of pure ACS populations needed for research and therapeutics have proven to be difficult. Instead of dividing exponentially, ASCs cycle with asymmetric kinetics whereby cell division gives rise to (1) another stem cell and (2) a transit cell destined to produce a terminally differentiated lineage. Even starting with a pure population of stem cells, transit cells are soon produced and eventually dominate the cell culture flask. This kinetic barrier to ASC propagation must be overcome in order to successfully maintain wild-type stem cell strains in vitro.

    The goal of this study is to overcome this barrier through investigating a cell-density induced phenomenon observed in the laboratory, where p53-dependent growth regulation is observed to be sensitive to cell density. The purpose of our research is to determine if cell density effects cell kinetics symmetry, and to understand the molecular mechanisms in the hopes of producing on-demand ASC propagation.

    Past studies have found encapsulation of drugs in poly(lactic-co-glycolic) acid (PLGA) microspheres to be a safe and effective drug delivery system. PLGA degrades by hydrolysis into lactic and glycolic acids, which are products of human metabolism and do not cause toxic effects. As the PLGA encapsulation slowly degrades, drug is released over time in a controlled fasion.

    It is hoped that a drug delivery system based on PLGA microspheres will be an effective method of treating ailments in the peritoneum. Drug delivery to the peritoneum is difficult because the peritoneal space is used for dialysis, so drug clearance is rapid. A polymeric microspheres-based drug delivery system would allow for the slow and continual release of medication into the peritoneum. However, it is uncertain whether PLGA microspheres are biocompatible in the peritoneum.

    Our study will attempt to determine the histological effects of PLGA microspheres in the peritoneum, and to assess the effectiveness of a PLGA microspheres-based drug delivery system for the peritoneum. Peritoneal tissue harvested from mice injected with PLGA microspheres varying in size (5 μm to 250 μm) and amounts (25 mg to 100 mg) contained inflammation and adhesions. Nodules of particle residue and adhesions were found in tissue harvested both two days and two weeks following injection. Two different types of sterilization, ethylene oxidation and ethanol wash, were used on the particles prior to injection; neither method mitigated peritoneal adhesions caused by the particles.

    The fact that PLGA microspheres of various sizes and quantities can cause inflammation and peritoneal adhesions leads us to conclude that PLGA microspheres are not biocompatible in the peritoneum. Furthermore, nodules of aggregated particles found in the peritoneum upon dissection suggest that PLGA microspheres are too dense and not buoyant enough to be dispersed within the peritoneum without unwanted settling. Based on our findings, we determined that a PLGA microspheres-based drug delivery system for the peritoneum is neither biocompatible nor effective.

"My involvement with this project has allowed me to learn many of the things necessary to be a successful scientist/engineer. The skills I have learned – how to plan experiments, organize and analyze data, and problem-solve — are essential for whatever career I choose to pursue. Winning the Johnson & Johnson BME Research Prize is definitely only one of the many benefits I've been fortunate to achieve through my research work!"

BMES-J&J Winner: Woon Teck Yap - Novel hydrogel particles for antigen delivery

    Several types of vaccines currently exist, among which are the live/live attenuated vaccines and the subunit vaccines. The main impetus for the development of subunit vaccines stems from the limitation that certain live/live attenuated pathogens are unsuitable for use as vaccines, due to large associated risks.

    Current research in Irvine Lab deals with the synthesis of novel hydrogel particles for the delivery of subunit antigens concurrent with activation signals to dendritic cells (DCs), the immunological sentinels which reside in all tissues of the body and prime naïve T cells at the initiation of an immune response. DC activation is known to be enhanced by unmethylated CpG oligodeoxynucleotide sequences. As such, selected CpG sequences were conjugated to hydrogel particles via methacrylic acid linkers to enhance both the processing of the model antigen ovalbumin (OVA) within DCs and the activation of DCs.

    DC activation was monitored by means of fluorescent flow cytometry (FACS) and enzyme-linked immunosorbent assays (ELISAs). In particular, DCs secreted much higher levels of IL12-p40 when incubated with the CpG-conjugated OVA hydrogel particles than when they were incubated with OVA hydrogel particles. Furthermore, upon incubation of CD4+ OT-II transgenic TCR T cell blasts with DCs that had been pre-incubated with CpG-conjugated OVA hydrogel particles, relatively high levels of IFN-g and IL-2 secretion were observed compared to those with soluble antigen.

    Our work suggests and supports the principle that with the conjugation of suitable ligands to our hydrogel antigen particles, different desired immunological effects can be achieved. This would in turn allow for the development of a novel vaccine that combines both the safety of subunit vaccines and the efficacy of live/live attenuated vaccines.