Poly microcapsule membranes

In this paper, we report some experimental results of the studies for the permeability characteristics, particle size, and charge density of poly(L-lysine-a/r-terephthalic acid) microcapsule membrane. On the basis of such information, we shall discuss die pH- and ionic strength- induced structural change of these microcapsules. 

We measured permeation of anionic and cationic electrolyte ions through poly(L-lysine-fl/r-terephthalic acid) microcapsule membranes as a function of pH of the medium at different ionic strengths. The solutes used were 5-sulfosalicylic acid as an anion and phenyltrimethylammonium chloride as a cation. We suspended water-loaded poly(L-lysine-a/r-terephthalic acid) microcapsules in a buffer solution and mixed this with a 5-sulfosalicylic acid solution or phenyltrimethylammonium chloride solution. The final concentration of the microcapsules is 20 % (v/v). We determined the solute concentration in the suspension medium spectrophotometrically at suitable time intervals after separating microcapsules by centrifugation and filtration through a Millipore filter. 

These observations Aat Ae membrane becomes transparent and Aat the size of microcapsules increases in alkaline medium suggest that poly(L-lysine-a/t-terephthalic acid) microcapsule membranes have a gel-like structure and undergo a volume transition at a pH value between 4 and 6, as usually seen in ionic hydrogels. This pH-driven volume transition is considered to be due to the change of Ae charge density in Ae microcapsule membrane. 

To study the electric properties of these microcapsule membranes, we measured the electrophoretic mobility of poly(L-lysine-a/r-terephthalic acid) microcapsules. 

Figure 5 shows the relationship l tween pH and the electrophoretic mobility of the microcapsules at various ionic strengths. It is observed that poly(L-lysine-a/r-terephdidic acid) microcapsule membranes have their isoelectric points between pH... 

As was described before, both the size and the permeability of poly(L-lysine-a/r-terephthaUc acid) microcapsules show a drastic and discontinuous change in a narrow pH range between 4 and 6 at all ionic strengths. At pH 4, the permeability of poly(L-lysine-a/r-terephthalic acid) microcapsules is minimum and the microcapsule size becomes smallest by shrinking. The isoelectric point of the microcapsules lies between 2.3 and 2.6. This implies that there are 5.5 times or 3.2 times more -COO" than -NH3+ in the microcapsule membranes at pH 4 so that the microcapsulc membrane is negatively charged. The deviation of the pH value at... 

Sawhney, A.S. and Hubbell, J.A., Poly(ethylene oxide)-graft-poly(L-lysine) copolymers to enhance the biocompatibility of poly(L-lysine)-alginate microcapsule membranes. Biomaterials, 13, 863 870, 1992. 

Microcapsules can be used for mammalian cell culture and the controlled release of drugs, vaccines, antibiotics and hormones. To prevent the loss of encapsulated materials, the microcapsules should be coated with another polymer that forms a membrane at the bead surface. The most well-known system is the encapsulation of the alginate beads with poly-L-lysine. 

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

The membranes of the thermosensitive controlled-release microcapsules were constructed by a random mixing Aquacoat (Table 1) with the latex particles having poly(EA/MMA/2-hydroxyethyl methacrylate) core and poly(A-isopropylacrylamide (NIPAAm)) shell. This is an example where the membrane has the random two-phase structure as shown in Fig. 5. The microcapsules exhibited a thermosensitive release of water-soluble drug. The mechanism is explained in Fig. 6. When the temperature was changed in a stepwise manner between 30 and 50°C, the microcapsules showed an on-off pulsatile release. This on-off response was reversible. 

Ichikawa, H. Fukumori, Y. A novel positively thermosensitive controlled-release microcapsules with membrane of nano-sized poly(V-isopropylacrylamide) gel dispersed in ethylcellulose matrix. J. Controlled Release 2000, 63, 107-119. 

The formation of microcapsules Is only one example of the use of polyelectrolyte complexes. Another example Is the formation of a permselective membrane around live cells by a complex formed between alginate and poly(L-lys1ne)(55). This complex 1s formed under mild conditions so as not to harm the cells, and the membrane can be tailored so that It 1s permeable to cell nutrients, but Impermeable to the cellular products. This process 1s of interest to those concerned with large-scale cell cultures. 

Alginate-polylysine has been used to encapsulate hepatocytes (32-34), parathyroid cells (35) and growth hormone transfected fibroblasts (36). Poly (acryl-onitrile/vinyl chloride) (PAN/PVC) macrocapsules have been used with PC12 (37, 38), embryonic mesencephalon tissue (39), thymic epithelial cells (40), adrenal chromaffin cells (41) and islets (25) using preformed hollow fibers or more recently coextrusion techniques (41) similar to those we have developed microcapsules cannot be made since DMSO is used as the solvent. All these studies have concluded from the maintenance of viability of the islets or cells that immunoprotection provided by the capsule membrane was compatible with... 

For this purpose, we prepared microcapsules with polyelectrolyte membranes that is, poly(L-lysine-fl/r-terephthalic acid) membranes, through which the permeability of solute was responding to the pH and ionic strength of the dispersing medium. 

For these experiments, in order to protect the cells from environmental shear stress, an 5 p.m thin membrane made of alginate and poly-L-lysine was created around the immobilized micro-carrier [31]. The movement of microcapsules with immobilized chromatophores was observed microscopically in a glass microtube (d = 700 pm 1 = 5 cm) with the magnetic field conduit embedded in the wall. The experimental setup is presented in Figure 32.4. Fluid (L-15 medium) velocities applied were in the range from 1.6 to 6.4mm/s and corresponded to the predicted operational fluid velocities of the biosensor [11]. Fluid flow was provided by microsyringe pump (LabTronix, USA). 

Materials and Methods. Stable microcapsules (mean diameter, 8 10 pm) with a semipermeable membrane of poly(styrene) (PSt) were prepared by depositing the polymer around emulsified aqueous droplets using the following three procedures (i) primary emulsification of an aqueous solution of sodium dodecylbenzenesulfonate or Triton X-100 as an emulsifier in dichloromethane containing PSt with a homoblender ... 

Methods for forming microparticles containing encapsulated cells have been described. The cells may be encapsulated in a microcapsule that includes an internal cell core containing polysaccharide gum surrounded by a semipermeable membrane (22). The microcapsule is made from alginate in combination with polylysine, poly-omithine. 

Microcapsules with a narrow size distribution containing oily core material can be prepared by a Shirazu porous glass (SPG) emulsification technique, followed by a suspension polymerization process. The SPG membrane is a special porous glass membrane with very uniform pore size. Guang Hui Ma et al. have reported the preparation of microcapsules containing hexadecane (oil core) using poly(styrene-... 

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