Medical membrane properties

In this Section, it is implicitly assumed that the mass transport resistance at the fluid-membrane interface on either side of the membrane is negligible. Also the following is information that is made available publicly by the membrane manufacturers, when not otherwise noted. As in technical processes, mass transport across semipermeable medical membranes is conveniently related to the concentration and pressme driving forces according to irreversible thermodynamics. Hence, for a two-component mixture the solute and solvent capacity to permeate a semipermeable membrane under an applied pressure and concentration gradient across the membrane can be expressed in terms of the following three parameters Lp, hydraulic permeability Pm, diffusive permeability and a, Staverman reflection coefficient (Kedem and Katchalski, 1958). All of them are more accurately measured experimentally because a limited knowledge of membrane stmcture means that theoretical models provide rather inaccurate predictions. 

Parameter Lp is the reciprocal membrane hydraulic resistance to solvent (i.e., plasma water or plasma) flow, and is estimated as the initial slope of the solvent filtrate fiux dependence on the applied TMP difference. When pressure drop along the module length on either membrane side cannot be neglected, TMP is often estimated by averaging out the inlet and outlet pressures as follows  

A finite TMP is needed to filter blood across HF membranes to counteract the oncotic pressure of the rejected species that accumulate at the membrane surface. 

Transport models relate Lp to HD membrane stmctore, as follows (Klein et al., 1978)  

Equation (18.2) suggests thatLp increases for membranes featuring higher porosity and pore size but decreases when membrane thickness increases and fluids more viscous than water 

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Polymer vesicles or polymersomes constitute an extremely interesting class of macromolecular self-assembly, and since their first observation 20 years ago [35], they have attracted a rapidly increasing degree of scientific attentirm. This is mainly because of their resemblance to natural cellular membranes, the ability to control their size along with their interactions with the environment, their tailorable membrane properties, as well as their versatile potential applications spanning from (bio-) electronics and catalysis to medical therapy. In the last decade, the... 

The earliest membranes used for medical purposes were prepared with cellulose by exploiting the spinning expertise of the textile industry. Only in the late 1960s, did techniques become available to prepare artificial membranes with the available technical polymers and to exploit the convenient properties of these polymers. Medical membranes have been traditionally classified as either namral or synthetic, depending on whether their backbone was made of cellulose or of a technical polymer, respectively (Klinkmann and Vienken, 1994). The reason for this was that, at that time, the material used was correlated with the membrane separation properties, ceUulosic membranes generally being less... 

The hydrogenated materials have a higher maximum service temperature than the conventional SBS materials and, because of the absence of double bonds in the chain, better weathering properties. Known as SEBs these materials now find use in adhesives, sealants and roofing membrane compounds. These also find use in highly filled automotive acoustic barriers and in medical, sports and leisure applications. 

All polymers utilized in this investigation have been listed in Table 2, along with their supplier and the concentration range over which they were tested. Polymers were either used as received or purified by filtration through a 0.22 or 0.45-pm MiUipore cellulose acetate membrane. For aseptic applications autoclaving was carried out for 20 min at a temperature of 121 °C. Qualitative properties of each polymer are listed in Table 3. For polymers supplied as solutions, dialysis was carried out in membranes (Spectrum Medical Industries, Houston, TX) with a MWCO of 10,000 daltons. 

The final principles of back-pulse filter technology are the nature and properties of the GORE-TEX membrane. The membrane is composed of expanded polytetra-fluoroethylene, or e-PTFE. The membrane traces its roots to the invention of e-PTFE by Robert W. Gore in 1969. Since that time, e-PTFE has found application in many areas including medical devices, electronics, fabrics and fuel cells to name a few. In the filtration area, e-PTFE is used in the form of a membrane to capture and remove particles from both gaseous and liquid streams. 

In light of these constraints, perhaps the best strategy to further improve the properties of CNTs for medical applications could be to exploit the cellular principles as blueprints. Natural systems use lipid membranes as a universal host matrix, which... 

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