ORCID Profile
0000-0002-8642-1417
Current Organisations
Institute of Bioengineering and Nanotechnology
,
Nanyang Technological University
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Publisher: Informa UK Limited
Date: 09-2010
DOI: 10.2147/LRA.S7977
Publisher: Elsevier BV
Date: 03-2007
DOI: 10.1016/J.JCONREL.2006.11.017
Abstract: The colloidal phenomenon of soft particles is becoming an important field of research due to the growing interest in using polymeric system in drug delivery. Previous studies have focused on techniques that require intermediate process step such as dialysis or centrifugation, which introduces additional errors in obtaining the diffusion kinetic data. In this study, a drug selective electrode was used to directly measure the concentration of procaine hydrochloride (PrHy) released from methacrylic acid-ethyl acrylate (MAA-EA) microgel, thereby eliminating the intermediate process step. PrHy selective membrane constructed using a modified poly (vinyl chloride) (PVC) membrane and poly (ethylene-co-vinyl acetate-co-carbon monoxide) as plasticizer exhibited excellent reproducibility and stability. The response was reproducible at pH of between 3 to 8.5 and the selectivity coefficients against various organic and inorganic cations were evaluated. Drug release was conducted using the drug electrode under different pHs and the release rate increased with pH. The release behavior of the system under different pH exhibited obvious gradient release characteristics.
Publisher: Elsevier BV
Date: 12-2007
DOI: 10.1016/J.EJPS.2007.08.010
Abstract: pH-responsive nanogels consisting of methacrylic acid-ethyl acrylate (MAA-EA) cross-linked with di-allyl phthalate (DAP) were synthesized via the emulsion polymerization process. Delivery systems based on pH-responsive nanoparticles can control the release of rapidly metabolized drugs and/or have the ability to protect sensitive drugs, thereby making them ideal candidates for drug delivery applications. In this study, a drug selective electrode (DSE) was used to directly measure the concentration of procaine hydrochloride (PrHy) and imipramine hydrochloride (IMI) released from MAA-EA nanogels. With a single drug delivery system, drug release for two different drugs loaded via two distinctly different interaction forces was demonstrated. Drug release was conducted using the DSE under different pHs, MAA-EA molar ratio and DAP content. The release rate increased with pH for PrHy loaded nanogels and MAA-EA molar ratio but decreased with pH for IMI loaded nanogels and DAP content. PrHy was found to be hydrophobically bounded, while IMI was found to be electrostatically bounded onto the MAA-EA nanogels, which was further enhanced by hydrogen bonding.
Publisher: Wiley
Date: 25-11-2018
DOI: 10.1002/APP.47284
Publisher: American Chemical Society (ACS)
Date: 27-06-2008
DOI: 10.1021/LA703852P
Abstract: Poly holyte microgels consisting of various compositions of poly(methacrylic acid) and poly(2-(dimethylamino)ethyl methacrylate) (PMAA-PDMA) cross-linked with allyl methacrylate (AM) were synthesized via the inverse microemulsion polymerization (IMEP) technique. To improve colloidal stability at the isoelectric point (IEP), steric stabilization via the grafting of poly(ethylene glycol) methyl ether methacrylate (PEGMA) on the surface of the microgel was performed. Potentiometric and conductometric titration showed good agreement between the targeted and experimental compositions of the microgel systems. The microgel swelled at low and high pH and possessed a compact structure near the IEP, and the diameter were in good agreement with data from the transmission electron microscopic (TEM) analyses. With increasing pH, the mobility decreased from +2 m(2)s(-1)V (1) at pH 2 to -2 m(2)s(-1)V (1) at pH 10. An empirical relationship describing the PMAA composition and IEP was proposed, where the IEP decreased with increasing PMAA content. The microgel exhibited thermal-responsive properties at high pH, which is dictated by the lower critical solution temperature of PDMA.
Publisher: Elsevier BV
Date: 05-06-2008
DOI: 10.1016/J.IJPHARM.2008.01.058
Abstract: pH-responsive nanogels consisting of methacrylic acid-ethyl acrylate (MAA-EA) cross-linked with di-allyl phthalate (DAP) were synthesized via emulsion polymerization. Drug release studies were conducted under different pHs, drug loading and concentration gradient difference. The drug loading capacity depended on the cross-link density and MAA-EA molar content, where a lower cross-link density and higher MAA-EA molar content resulted in higher loading capacity. A drug selective electrode was used to directly measure the concentration of procaine hydrochloride (PrHy) released from MAA-EA nanogels. More than 50 data points were acquired, where the mathematical fitting to the Berens and Hopfenberg model allowed the parameters describing the contributions of chain relaxation and diffusion process to be determined. The release rate increased with pH and concentration gradient difference due to a reduction in diffusion barrier and higher concentration gradient driving force, respectively, but it decreased with drug loading as the nanogel could not relax from the compact structure as evident from the contribution of Fickian diffusion, phi(F), and chain relaxation, phi(R). A balance between chain relaxation and Fickian diffusion process controlled the release of drugs from these pH-responsive nanogels. Exponential relationships could be established between diffusion coefficient, characteristic relaxation time and various physical parameters, where the drug release kinetics could be predicted in a quantitative manner.
Publisher: Elsevier BV
Date: 06-2008
DOI: 10.1016/J.JCONREL.2008.03.012
Abstract: Undesirable burst release phenomenon is commonly encountered in nanostructured delivery systems, and should be addressed. The present study demonstrates a simple and practical way to reduce or minimize high burst release associated with nanoparticulate delivery systems. Drug loaded nanogels of size less than 200 nm were successfully coated with alternating layers of poly(allylamine hydrochloride) (PAH, cationic) and poly(sodium 4-styrenesulfonate) (PSS, anionic) polyelectrolytes. With every layer of polyelectrolyte, the radius increased by 2 nm, and the zeta-potential alternated between positive and negative values. PSS coated nanogels were stable at all pH, while PAH coated nanogels were only stable up to pH of 8. A drug selective electrode (DSE) was used to directly measure the concentration of procaine hydrochloride (PrHy) from MAA-EA coated nanogels. The high burst release was reduced or minimized when the number of layers of polyelectrolyte was increased. An empirical relationship describing the number of polyelectrolyte layers and time to attain steady-state drug concentration (tau(D)) was developed, where tau(D) increased with increasing polyelectrolyte layers.
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