Fully biodegradable septal defect occluder-a double umbrella design.

Current percutaneous devices for septal defect treatment are made of nondegradable metallic and synthetic fabric materials. These devices are not ideal due to risks of future complications from device erosions and potential obstructed access for future transseptal procedures. The biodegradable double umbrella device was made of fully biodegradable polymers, featured with two discs connected with a stretchable stem. The devices were inserted across the PFO model created on Yorkshire swines through a short sheath by open thoracotomy. Fluoroscopic imaging and echocardiography obtained during the 1-month follow-up study period showed that the devices were in stable position with no shunt. The in-vitro degradation study and post-mortem explantation confirmed that the devices have good integrity and mechanical strength during the 1-month trial. Furthermore, the devices appeared to be well endothelialized after 1 month. These results showed clearly that it is feasible to replace the current nondegradable devices with the new generation biodegradable PFO occluders. This work studied and proved the feasibility of interventional closure of patent foramen ovale (PFO) with a fully biodegradable device, that we call the "double umbrella" (DU) for its symbolic design. © 2010 Wiley-Liss, Inc.

Realistic simulations of combined DNA electrophoretic flow and EOF in nano-fluidic devices.

We present a three-dimensional dissipative particle dynamics model of DNA electrophoretic flow that captures both DNA stochastic motion and hydrodynamics without requiring expensive molecular dynamics calculations. This model enables us to efficiently and simultaneously simulate DNA electrophoretic flow and local EOF (generated by counterions near the DNA backbone), in mesoscale (~microm) fluidic devices. Our model is used to study the electrophoretic separation of long DNA chains under entropic trapping conditions [Han and Craighead, Science 2000, 288, 1026-1029]. Our simulation results are in good agreement with experimental data for realistic geometries (tapered walls) and reveal that wall tapering in entropic traps has a profound impact in the DNA trapping behavior, an effect which was largely ignored in previous modeling.

A novel biodegradable septal defect occluder: the "Chinese Lantern" design, proof of concept.

OBJECTIVE: Atrial septal defect (ASD) is a general term used to describe an opening in the atrial septum that divides the two atria; unless the hole is occluded, it can give rise to serious complications. Given the need for percutaneous deployment for ASD or patent foramen ovale (PFO) occluders, all currently available devices are made of metals (specifically nitinol) and synthetic fabric. However, their permanent presence in the human body is not desirable due to the risks of long-term allergy, toxicity, and complications such as thrombus formation, device arm fracture, and nickel allergy. Once the hole is covered by a newly regenerated tissue, the device is no longer needed; thus it is ideal if the device is fully absorbed by the body when healing is completed. METHODS: The "Chinese Lantern" device is made of fully biodegradable polymers featured with a unique pull-fold mechanism. The device was inserted across the ASD/PFO model created on Yorkshire swines through a short sheath by hybrid open surgery. X-ray imaging, echocardiography, and postmortem histopathology were obtained during the 1-month follow-up study period. RESULTS: X-ray imaging showed that the devices were in satisfactory position and stable. Echocardiography showed that there is no shunting from the right atrium to the left atrium, indicating excellent sealing. The in vitro degradation study and postmortem explantation study confirmed that the devices have good integrity during the 1-month trial. Furthermore, the devices appeared to be completely endothelialized after 1 month. CONCLUSIONS: This work proves the feasibility of interventional closure of ASD or PFO with an innovative biodegradable device, which we call the "Chinese Lantern" for its symbolic design.

Electrostatic binding of nanoparticles to mesenchymal stem cells via high molecular weight polyelectrolyte chains.

Combining stem cell transplantation with nanoparticle-mediated delivery of drugs and pharmaceuticals is envisioned to be one of the next major developmental steps in regenerative medicine. However, a major challenge would be to keep nanoparticles co-localized with stem cells upon transplantation or transfusion in situ. Since nanoparticles are physically much smaller in size than cells and would not specifically bind to extracellular matrix, it is easier for them to disperse from the transplantation site via the blood circulation. Conjugating nanoparticles directly to the cell membrane can potentially interfere with cellular function by physically obstructing cell surface receptors from interacting with the extracellular matrix, various growth factors and cytokines and other cells. Moreover, drug-loaded nanoparticles may be internalized into the cytoplasm via endocytosis or phagocytosis, which may wreak damage on the cellular machinery, leading to impaired physiological function or cell death. A novel solution may be to utilize high molecular weight polyelectrolyte chains to electrostatically bind nanoparticles to cells. For this purpose, hyaluronan, poly-L-lysine and chitosan are of special interest, because these molecules are generally recognized to be biocompatible for application in various pharmaceutical and surgical products. This study investigated the use of these molecules to bind nanoparticles to mesenchymal stem cells (MSCs), and a novel technique of conjugating half the cell surface with nanoparticles through the use of polyelectrolyte chains was also developed. This would avoid blocking MSC interaction with cytokines, growth factors, extracellular matrix and other cells within the recipient tissue/organ upon delivery in situ.