Biomedical subjects

Amy C Richards Grayson

Publications and source records attributed to Amy C Richards Grayson.

6 recordsLinked to original sources

PubMed2006

Biophysical and structural characterization of polyethylenimine-mediated siRNA delivery in vitro.

PURPOSE: The goals of this study were as follows: 1) to evaluate the efficacy of different polyethylenimine (PEI) structures for siRNA delivery in a model system, and 2) to determine the biophysical and structural characteristics of PEI that relate to siRNA delivery. MATERIALS AND METHODS: Biophysical characterization (effective diameter and zeta potential), cytotoxicities, relative binding affinities and in vitro transfection efficiencies were determined using nano-complexes formed from PEI's of 800, 25,000, (both branched) and 22,000 (linear) molecular weights at varying N:P ratios and siRNA concentrations. The HR5-CL11 cell line stably expressing luciferase was used as a model system in vitro. RESULTS: Successful siRNA delivery was observed within a very narrow window of conditions, and only with the 25,000 branched PEI at an N:P ratio of 6:1 and 8:1 and with 200 nM siRNA. While the zeta potential and size of PEI:siRNA complexes correlated to transfection efficacy in some cases, complex stability may also affect transfection efficacy. CONCLUSIONS: The ability of PEI to transfer functionally active siRNA to cells in culture is surprisingly dependent on its biophysical and structural characteristics when compared to its relative success and ease of use for DNA delivery.

Biophysical Phenomena↗

PubMed2005

Size and temperature effects on poly(lactic-co-glycolic acid) degradation and microreservoir device performance.

The component materials of controlled-release drug delivery systems are often selected based on their degradation rates. The release time of a drug from a system will strongly depend on the degradation rates of the component polymers. We have observed that some poly(lactic-co-glycolic acid) polymers (PLGA) exhibit degradation rates that depend on the size of the polymer object and the temperature of the surrounding environment. In vitro degradation studies of four different PLGA polymers showed that 150 microm thick membranes degraded more rapidly than 50 microm thick membranes, as characterized by gel permeation chromatography and mass loss measurements. Faster degradation was observed at 37 degrees C than 25 degrees C, and when the saline media was not refreshed. A biodegradable polymeric microreservoir device that we have developed relies on the degradation of polymeric membranes to deliver pulses of molecules from reservoirs on the device. Earlier molecular release was seen from devices having thicker PLGA membranes. Comparison of an in vitro release study from these devices with the degradation study suggests that reservoir membranes rupture and drug release occurs when a membrane threshold molecular weight of 5000-15000 is reached.

Absorbable Implants↗

PubMed2004

Molecular release from a polymeric microreservoir device: Influence of chemistry, polymer swelling, and loading on device performance.

A polymeric microreservoir device for controlled-release drug delivery relies on the degradation of thin poly(lactic-co-glycolic acid) membranes that seal each reservoir to achieve pulsatile drug delivery. In vitro release studies in which the swelling of the reservoir membranes was measured indicate a correlation between the release times of various radiolabeled molecules from the devices and the time at which the maximum membrane swelling was observed. Varying the chemistry (lipophilicity/hydrophilicity) or molecular weight of the molecules loaded into the devices did not appear to affect the degree of membrane swelling that was observed, or the time at which the molecules were released from the devices. The amount of drug that was loaded into the reservoirs also did not appear to affect the observed release time of the drug from the device, a significant departure from the behavior of many matrix-type polymeric drug delivery systems.

Biocompatible Materials↗

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↗

PubMed2003

Multi-pulse drug delivery from a resorbable polymeric microchip device.

Controlled-release drug delivery systems have many applications, including treatments for hormone deficiencies and chronic pain. A biodegradable device that could provide multi-dose drug delivery would be advantageous for long-term treatment of conditions requiring pulsatile drug release. In this work, biodegradable polymeric microchips were fabricated that released four pulses of radiolabelled dextran, human growth hormone or heparin in vitro. Heparin that was released over 142 days retained on average 96 +/- 12% of its bioactivity. The microchips were 1.2 cm in diameter, 480-560 microm thick and had 36 reservoirs that could each be filled with a different chemical. The devices were fabricated from poly(L-lactic acid) and had poly(D,L-lactic-co-glycolic acid) membranes of different molecular masses covering the reservoirs. A drug delivery system can be designed with the potential to release pulses of different drugs at intervals after implantation in a patient by using different molecular masses or materials for the membrane.

Absorbable Implants↗

PubMedDate not supplied

Kinetic and efficacy analysis of RNA interference in stably and transiently expressing cell lines.

RNA interference, particularly through the use of small interfering RNA (siRNA), has become an important laboratory tool for both fundamental and applied investigations. However, it is currently unknown whether siRNA-mediated knockdown of transiently expressed proteins is an acceptable quantitative surrogate for stably expressed proteins. Further, the best means by which to transfect cells with functionally active siRNA are poorly defined, and determination of the best reagent and transfection conditions for a particular cell line is a burdensome prerequisite for RNA interference studies. We therefore established the optimal transfection conditions for six commercial siRNA delivery reagents in three cell lines (HR5-CL11, HeLa, and NIH/3T3) transiently or stably expressing the firefly luciferase gene. The delivery efficiency, knockdown kinetics, and cytotoxicity of the reagents were evaluated. siPORT Amine, X-tremeGENE, and TransIT-siQUEST achieved the best knockdown and consistency of performance among the three cell lines. Delivery efficiency varied and was cell line dependent in some cases. The knockdown kinetics were reagent-dependent, and knockdown was generally more rapid in the stably transfected cells. Cytotoxicity of the reagents was variable. GeneSilencer was the least cytotoxic reagent for all three cell lines, and TransIT-siQUEST was the most cytotoxic to the HeLa and HR5-CL11 cell lines. These comparative results provide an initial basis for reagent selection and experimental design for RNA interference studies in HeLa, NIH/3T3, and their respective derivative cell lines.

Animals↗