Yasushi Sasai

Plasma Techniques for Preparation of Controlled Drug Release System

Plasma-induced surface radicals formed on a variety of organic polymers have been studied by electron spin resonance (ESR), making it possible to provide a sound basis for future experimental design of polymer surface processing, i.e., plasma treatment. On the basis of the findings from such studies, several pharmaceutical applications in the field of drug engineering have been devised, which include preparation of double-compressed tablets for reservoir-type drug delivery system (DDS) of sustained- and delayed-release, and fabrication of functionalized composite powders applicable for matrix-type DDS by a mechanical application of plasma-irradiated polymer powder.

Addendum - Recent advances in plasma techniques for biomedical and drug engineering

Plasma-induced surface radicals formed on a variety of organic polymers have been studied by electron spin resonance (ESR), making it possible to provide a sound basis for future experimental design of polymer surface processing (i.e., plasma treatment). On the basis of the findings from such studies on the nature of radical formation and radical reactivity, several novel bioapplications in the field of biomedical and drug engineering have been developed. Applications derived from the nature of plasma-induced surface radical formation include the preparation of a reservoir-type drug delivery system (DDS) of sustained and delayed release, and a floating drug delivery system (FDDS) possessing gastric retention capabilities, the combined findings leading to preparation of a novel “patient-tailored DDS” administered under consideration of the fact that the environment (pH and transit time, etc.) in the gastrointestinal (GI) tract varies with each patient. Applications derived from the reactivity of plasma-induced surface radicals include the preparation of composite powders applicable to a matrix-type DDS by making a mechanical application to the surface radical-containing polymer powders with drug powders, plasma-assisted immobilization of oligo-nucleotides (DNA) onto polymer surfaces applicable to constructing a DNA diagnosis system, and basic study of plasma-assisted preparation of a novel functionalized chemo-embolic agent of non-crosslinked hydrogel, vinyl alcohol-sodium acrylate copolymer (PVA-PAANa).

Mechanically-amplified plasma processing for drug engineering

We report here special features of mechanochemical reaction of plasma-irradiated polyethylene (PE), low density PE (LDPE) and high density PE (HDPE). A dangling bond site (DBS) of three component radicals formed on a PE surface by argon plasma-irradiation disappears rapidly by mechanical vibration with a Teflon twin-shell blender, causing successively solid state radical recombination reaction. When mechanical vibration of plasma-irradiated PE is similarly conducted together with a powdered drug, the sustained release powders are obtained due to trapping of drugs into the powder matrix formed by mechanochemical solid state recombination of plasma-induced PE surface radicals.

Novel pH-responsive polymeric micelles prepared through self-assembly of amphiphilic block copolymer with poly-4-vinylpyridine block synthesized by mechanochemical solid-state polymerization.

We fabricated polymeric micelles containing 5-fluorouracil (5-FU) or fluorescein using the amphiphilic block copolymer, poly-4-vinylpyridine-b-6-O-methacryloyl galactopyranose. Although the polymeric micelles were stable at pH 7.4, they readily decomposed at pH 5, resulting in near complete release of 5-FU. Uptake of polymeric micelles containing fluorescein by HepG2 and HCT116 cells was also investigated. With both cell types, strong fluorescence was observed after a 12-h incubation, but the fluorescence weakened after 24 h of incubation. The fluorescein incorporated into the polymeric micelles was released into acidic organelles (endosome and/or lysosome), from which it diffused throughout the cell. The cytotoxicity of polymeric micelles containing 5-FU was evaluated against HepG2 cells using a CCK-8 assay. The results suggest that polymeric micelles containing 5-FU are more cytotoxic to HepG2 cells than free 5-FU.

Novel Synthesis of Macromonomers by Mechanochemical Reaction for the Application to Polymeric Micelles

We have presented the first example of the synthesis of macromonomers by mechanochemical reaction of polymethylmethacrylate (PMMA) and maleic anhydride (MA). The mechanochemical reaction of PMMA and MA was carried out by vibratory ball milling under anaerobic condition. The ESR spectrum of the fractured sample of PMMA and MA showed a broad singlet, which was apparently different from the spectrum of PMMA mechanoradical. Therefore, PMMA mechanoradical would react with MA. We underwent the UV-labeling of the fractured samples of PMMA and MA to confirm the formation of macromonomers. The gel permeation chromatograms of UV-labeled compounds derived from this fractured sample showed a broad peak in a polymer region with refractive index detector and UV detector, which indicates that macromonomers bounding MA would be produced. This method seems to be applicable for a wide variety of polymers to synthesize macromonomers possessing MA. DOI: http://dx.doi.org/10.6000/1927-5951.2011.01.02.06

Synthesis of Amphiphilic Blockcopolymer Using Mechanically Produced Macromonomers Possessing Anhydrate as a Terminal Group and Its Application to Polymeric Micelles

We have synthesized macromonomers by mechanochemical reaction of poly(benzyl methacrylate) (PBzMA) and maleic anhydride (MA). The ESR spectrum of the fractured sample of PBzMA and MA showed a broad singlet, which was apparently different from the spectrum of PBzMA mechanoradical. The amphiphilic blockcopolymer was synthesized with macromonomer of PBzMA and amino-terminated polyethyleneglycol (a-methyl-w-aminopropoxy polyoxyethylene, MEPA). The number average molecular weight of the produced amphiphilic blockcopolymer was 33,000. Polymeric micelles were readily prepared from the present amphiphilic blockcopolymer by a dialysis method. The mean diameter of the micelles measured by dynamic light scattering was about 146 nm. It was shown that the present macromonomer mechanically produced can be used for the synthesis of amphiphilic bockcopolymer to form polymeric micelles.

Cold Plasma Techniques for Pharmaceutical and Biomedical Engineering

Plasmas can be defined as the state of ionized gas consisting of positively and negatively charged ions, free electrons and activated neutral species (excited and radical), and are generally classified into two types, thermal (or equilibrium) plasma and cold (or nonequilibrium) plasma, based on the difference in characteristics. The thermal plasma is the state of fully ionized gas characterized by a high gas temperature and an approximate equality between the gas and electron temperature (Tg ≈ Te) and can be generated under atmospheric pressure. The energetic of this plasma is very high enough to break any chemical bond, so that this type of plasma can be excluded from most of organic chemistry, let alone from the field of pahramceutical science. In contrast, the cold plasma is most characterized by a low gas temperature and a high electron temperature (Tg << Te), and easily generated by electric discharges under reduced pressure. The field of plasma chemistry deals with occurrence of chemical reactions in the cold plasma including atmosphere pressure glow discharge plasma. One of the characteristics of surface treatment by cold plasma irradiation is the fact that it is surface limited (ca. 500-1000 A) so that only the surface properties can be changed without affecting the bulk properties. In recent years, biomedical applications of cold plasma are rapidly growing due to the fact that the use of cold plasmas is very useful to treat heat-sensitive objects such as polymeric materials and biological samples. The demonstrations of plasma technology in the biomedical field have created a new field at the intersection of plasma science and technology with biology and medicine, called “Plasma Medicine”. (Fridman et al., 2008) When the cold plasma is irradiated onto polymeric materials, the plasma of inert gas emits intense UV and/or VUV ray to cause an effective energy transfer to solid surface and gives rise to a large amount of stable free radicals on the polymer surface. In view of the fact that surface reactions of plasma treatment are initiated by such plasma-induced radicals, study of the resulting radicals is of utmost importance for understanding of the nature of plasma treatment. Thus, we have undertaken plasma-irradiation of a wide variety of polymers, synthetic and natural, and the surface radicals formed were studied in detail by electron spin resonance (ESR) coupled with the aid of systematic computer simulations. On the basis

Development of Novel Polymeric Prodrugs Synthesized by Mechanochemical Solid-State Copolymerization of Hydroxyethylcellulose and Vinyl Monomers

Novel polymeric prodrugs were synthesized by mechanochemical solid-state copolymerization of hydroxyethylcellulose and the methacryloyloxy derivative of 5-fluorouracil (5-FU). Copolymerization was about 94% complete after 4 h, and the polymeric prodrug was quantitatively obtained after 14 h of reaction. The number average molecular weight (Mn) and polydispersity (H) of the polymeric prodrug were 39000 g/mol and 6.20, respectively. Mechanical fracturing of the polymer in a stainless steel twin-shell blender improved these properties (Mn=16000 g/mol and H=1.94). 5-FU was sustainably released from the polymeric prodrugs, and the rate was not affected by the molecular weight or molecular weight distribution of the prodrug under the experimental conditions used. These results suggest that novel polymeric prodrugs composed of a polysaccharide and a synthetic polymer can be fabricated by mechanochemical solid-state copolymerization under anaerobic conditions.