Biomedical subjects

Yawen Li

Publications and source records attributed to Yawen Li.

5 recordsLinked to original sources

PubMed2007

4-Substituted-alpha,alpha-diaryl-prolinols improve the enantioselective catalytic epoxidation of alpha,beta-enones.

To seek novel metal-free organic catalysts for epoxidation with high stereoselectivity, a series of 4-substituted-alpha,alpha-diaryl-prolinols were synthesized in four steps from trans-4-hydroxyl-L-proline. These prolinol derivatives catalyzed the asymmetric epoxidation of alpha,beta-enones to give the corresponding chiral epoxides in good yields and high enantioselectivities under mild reaction conditions. Studies of substituent effects on enantioselectivity revealed that steric bulk and electronic effect promoted higher enantioselectivity, and prolinol 8a was found to be the best catalyst until now.

Catalysis↗

PubMed2005

In vivo delivery of BCNU from a MEMS device to a tumor model.

A drug delivery micrcoelectromechanical systems (MEMS) device was used to locally deliver a chemotherapeutic agent (BCNU) to an experimental tumor in rats. This MEMS device consists of an array of reservoirs etched into the silicon substrate. The drug release is achieved by the electrochemical dissolution of the gold membranes covering the reservoirs. A new Pyrex package was developed to improve the BCNU release kinetics and enhance device capacity. Co-formulation of BCNU with polyethylene glycol (PEG) led to complete and rapid release of drug in vivo. BCNU delivered from the MEMS device showed dose-dependent inhibiting effect on the tumor growth in the BCNU dosage range of 0.67 approximately 2 mg. BCNU delivered from the activated devices was as effective as equipotent subcutaneous injections of BCNU in inhibiting tumor growth. Further optimization using this MEMS device to deliver BCNU in combination with other therapeutic agents against the tumor challenge is possible because of the unique capability of the device to precisely control the temporal release profiles of multiple substances.

Animals↗

PubMed2004

Repeated in vivo electrochemical activation and the biological effects of microelectromechanical systems drug delivery device.

The repeated activation of a microelectromechanical systems (MEMS) drug delivery device was studied in vivo in rats to examine the effect of implantation on the device operation and the effect of electrochemical activation on the inflammatory and wound-healing response. The MEMS devices were fabricated from a silicon wafer into which reservoirs were etched and covered with gold membranes. The membranes were electrochemically removed when an anodic voltage was applied. Devices were implanted subcutaneously both with and without stainless steel mesh cages for 4, 7, 14, 21, or 28 days before activation. Devices were activated every other day for five activations. Leukocyte concentrations indicated that both the application of voltage and the gold corrosion products elevated the inflammatory response which was resolved within 48 h after each activation. The efficiency of gold membrane removal was not impaired throughout the implantation, although a bimodal distribution of background current densities was observed after long implantation times. The thickness of the fibrous capsule surrounding the MEMS devices was similar between activated and control devices explanted at each time point. It was concluded that the repeated activation of MEMS drug delivery devices was successful and the activation produced an acceptable biological response that resolved promptly.

Animals↗

PubMed2004

In vivo release from a drug delivery MEMS device.

A drug delivery microelectromechanical systems (MEMS) device was designed to release complex profiles of multiple substances in order to maximize the effectiveness of drug therapies. The device is based on micro-reservoirs etched into a silicon substrate that contain individual doses of drug. Each dose is released by the electrochemical dissolution of the gold membrane that covers the reservoir. The first in vivo operation of this device was reported in this study. Subcutaneous release was demonstrated in rats using two tracer molecules, fluorescein dye and radiolabeled mannitol, and one radiolabeled chemotherapeutic agent, carmustine (BCNU). BCNU was chosen because of the need to improve the direct delivery of chemotherapy to malignant tumors. The spatial profile of fluorescein dye release from the drug delivery device was evaluated by fluorimetry, the temporal profile of 14C labeled mannitol release was evaluated by liquid scintillation counting, and the temporal profile of 14C labeled BCNU release was evaluated by accelerator mass spectrometry (AMS). Release profiles obtained from injected controls were compared with those from activated devices. The in vivo dye release results showed high concentration of fluorescein in the flank tissue surrounding the devices 1 h after activation. The 14C labeled mannitol released from the drug delivery devices was rapidly cleared (1 day) from the rat urine. In vivo release of 14C labeled BCNU from activated devices showed slightly slower kinetics than the injected and in vitro controls, and the time to reach the steady-state plasma 14C concentration was on the order of 1 h. All these results demonstrated the capability of this drug delivery device to achieve localized delivery of various compounds with well-defined temporal profiles.

Animals↗

PubMed2004

Electronic MEMS for triggered delivery.

Implantable electronic devices such as pacemakers and neural implants are often used for electrical stimulation. The usage of microfabrication techniques to produce microelectromechanical systems (MEMS) has allowed engineers to address a wider range of clinical indications. A new direction in the area of MEMS technology is the goal of achieving pulsatile drug delivery. The digital capabilities of MEMS may allow greater temporal control over drug release compared to traditional polymer-based systems, while the batch-processing techniques used in the microelectronics industry can lead to greater device uniformity and reproducibility than is currently available to the pharmaceutical industry. A repertoire of structures, including microreservoirs, micropumps, valves, and sensors, is being developed that will provide a strong foundation for the design of integrated, responsive MEMS for drug delivery.

Electronics↗