Membranes environmentally sensitive

Novel responsive controlled release systems based upon polyelectrolyte-grafted membranes have also been reported. Iwata and Matsuda prepared novel environmentally sensitive membranes by grafting poly(acrylic acid) onto poly(vinylidene fluoride) membranes [382, 383]. Under basic conditions, the... 

Osada et al. [52] have also grafted PMAA to a porous substrate in order to achieve an environmentally sensitive membrane. This sensitivity was termed a chemical valve function because mechanochemical forces caused the pores to enlarge and contract. PMAA was grafted onto poly(vinyl alcohol) (PVA) films which had a mean pore radius of 4 pm. The water permeation of the membrane was strongly affected by the conformational state of the PMAA grafts. At low pH the chains were contracted and the water permeability was... 

Environmentally Sensitive Polymers as Biosensors The Glucose-Sensitive Membrane... 

The design of a polymer-based system requires understanding both the steady state and transient behavior in response to the substrate or analyte of interest. For sensor applications, this information is obtained during the operation of the sensor. However, for other applications of environmentally sensitive polymers, such as drag delivery systems, the polymer response to the substrate/analyte is not usually studied directly. Our work with the pAAm/GO/PR system illustrates the usefulness of an in situ probe to measure what governs the membrane s performance in response to the substrate/analyte and how to analyze it. We continue to use this valuable information in the further... 

Environmental sensitivity of candidate materials must be assessed under conditions of temperattfre, pressure and composition that simulate actual usage. Failure of a material in this context can severely limit the range of applicability of a membrane that otherwise has outstanding properties. 

The membrane potential of individual cells can be monitored with a fluorescence microscope. For this purpose, however, it is preferable to use a permeable redistribution dye with spectral characteristics that have minimal environmental sensitivity. Thus, the fluorescence intensity will reflect the degree of Nemstian accumulation of dye only and can, therefore, be readily interpreted. The plasma membrane potential can be distinguished from the organelle membrane by simply using the microscope to identify appropriate regions of the cell (44). Rhodamine-123 (Chart III) was introduced as a mitochondrial stain by Chen and co-workers (45-47) it has been used largely in qualitative studies of mitochondrial membrane potential and has been especially effective in flow cytometry applications. 

As a third option, a preformed track-etched membrane may be functionalized by binding of initiators followed by controlled or free radical polymerization (Figure 2.11C). Such techniques are described in more detail in Chapter 3. They have been adapted to ion track-etched membranes by various groups. For instance, PHEMA and PNIPAAm were copolymerized by ATRP inside tracks etched into a PET membrane to obtain a membrane with dual environmental sensitivity [46]. 

The membrane with the nanometer-sized holes can be used as template of metallic replicas. The holes are filled up with some metal atoms by electrolysis in a galvanic cell, and after deposition, the membrane is removed mechanically or by a suitable solvent. In these ways, little rods with a few pm length and few times 10 nm diameters are produced (Tagawa et al. 2004 Coqueret 2008). By grafting environmental sensitive polymers on the surface of the holes, the permeability of the membrane can be regulated by external signal (temperature, pH, etc.). The operation of such systems may mimic, the operation of biological membranes. 

Due to the well-known enzymatic lability or environmental sensitivity of proteins, a common characteristic among protein delivery systems is the ability to protect the protein from the external environment. Modes of protection may be chemical or physical. A well-recognized system that provides physical protection of proteins is microcapsules, in which a solid membrane separates the solid contents of the microcapsule from the external environment. An alternative approach would be to replace a solid membrane with a liquid membrane, i.e., multiphase or multiple emulsions. Multiple emulsions may be prepared as either oil-in-water-in-oil (OAV/0) or water-in-oil-in-water (W/OAV) systems. Multiple-emulsion systems, for the purpose of delivering proteins, would be comprised of an interior aqueous phase, containing the water-soluble protein, separated from the external aqueous phase by an oil phase, i.e., W/OAV emulsions (Fig. 1). Multiple emulsions, therefore, provide an alternative technique for the encapsulation of proteins and other materials that would otherwise be metabolized, rapidly cleared, or toxic to the patient. Multiple emulsions have been utilized for parenteral and oral administration (Brodin et al, 1978). Although there is a physical resemblance to microcapsules, multiple... 

Fusion reactions of viruses are mediated by short peptides that fall into two main groups one dependent on a shift to low pH and the other pH-independent [108]. Initial interests here have focused on peptides involved in pH-dependent fusion because of their potential for application in environmentally sensitive, and therefore controllable, model systems. Of the pH-dependent viruses (influenza virus, the vesicular stomatitis virus, the Semliki forest virus and mouse mammary tumor virus [108]), influenza hemagglutinin (HA) is probably the most studied [4]. HA alone is enough to facilitate the fusion of the influenza virus with the host membrane [102,107]. Through the involvement of at least three subunits, it mediates both the initial attachment of the virus to receptors that contain sialic acid [94] and its fusion with the endosomal membrane [57,58]. 

Apparently, a variety of probes sensitive to different environmental aspects are required to obtain an experimental picture of membrane structure and dynamics. 

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