Secondary membrane

Subsurface cisternae are a system of smooth, membrane-bound, flattened cisternae that can be found in many neurons. These structures, referred to as hypolemmal cisternae by Palay and Chan-Palay [1], abut the plasmalemma of the neuron and constitute a secondary membranous boundary within the cell. The distance between these cisternae and the plasmalemma is usually 10-12 nm and, in some neurons, such as the Purkinje cells, a mitochondrion may be found in close association with the innermost leaflet. Similar cisternae have been described beneath synaptic complexes, but their functional significance is not... 

For ultrafiltration, the macromolecular solutes and colloidal species usually have insignificant osmotic pressures. In this case, the concentration at the membrane surface (C ) can rise to the point of incipient gel precipitation, forming a dynamic secondary membrane on top of the primary structure (Figure 7). This secondary membrane can offer the major resistance to flow. 

Studies of concentration polarization such as those illustrated in Figures 6.8-6.10 are usually performed during the first few hours of the membrane use. Compaction of the secondary membrane layer has then only just begun, and membrane fluxes are often high. Fluxes obtained in industrial processes, which must operate for days or weeks without cleaning, are usually much lower. 

Plasma fractionators (secondary membranes) Dideco, Italy Albusave Cellulose diacetate 1.00 0.02 350... 

Figure 18.9 Schematic of a cascade filtration circuit for plasma purification with secondary membrane.

A review of plasma purification using secondary filtration has been presented by Siami et al. [19] and Table 18.4 lists the diseases treated with this technique. Diseases treated include immune-mediated disorders and familial type IIA hypercholesterolemia. These authors concluded that cryoglobulins filters were safe and effective for removing cryoproteins, did not induce complement activation and constituted one of the most promising techniques of secondary membrane application. 

Table 18.4 Diseases treated with secondary membrane filtration (From Siami et al. [8]), with permission.)...

Secondary Membranes for Flux Optimization in Membrane Filtration of Biologic Suspensions... 

In addition, the flux for ultrafiltration was relatively insensitive to changes in the concentration of yeast used during deposition of SMY and to the backflushing strength used to periodically remove the secondary membrane. 

Index Entries Secondary membrane backflushing microfiltration ultrafiltration direct visual observation fouling. 

Marcinkowsky et al. (16) were the first to use dynamic secondary membranes in reverse osmosis for rejection of salts. Giiell et al. (17) later investigated protein transmission and permeate fluxes in microfiltration of protein mixtures using yeast to form a predeposited secondary membrane, and they observed higher flux and protein transmission in the presence of the secondary layer. Kuberkar and Davis (18) also observed higher flux and transmission of BSA in the presence of a cake layer of yeast,... 

In the current work, we employed a modified approach, with predeposition of a secondary membrane of yeast (SMY) before starting the filtration of protein. Backflushing was employed periodically to remove the deposited secondary membrane to recover the flux, and a new secondary membrane was deposited subsequently with the start of each new cycle, prior to restarting the filtration of protein. Microfiltration experiments were performed with yeast as the secondary membrane and BSA-only solutions and yeast-BSA mixtures as the feed. Ultrafiltration experiments were performed with yeast as the secondary membrane deposition medium and cellulase enzyme solutions, used in the conversion of biomass into ethanol, as the feed. In this article, we also present direct visual observation images (19) of the formation of the secondary membrane and its subsequent removal. 

Fig. 2. Direct visual observation pictures of surface of membrane (A) during first cycle of deposition ofSMY,and (B) at end of several cycles ofyeast-BSA microfiltration with a secondary membrane, with the pictures taken just after backflushing portion at end of indicated cycle.

Protein transmission data (Fig. 8) indicate nearly 100% transmission of protein initially, but the fraction of protein transmitted decreased rapidly for forward filtration of a BSA-only solution and appeared to reach a steady value of only 35% transmission after 10,000 s. When a secondary membrane of yeast was deposited at the beginning of each cycle, and then filtration of a BSA solution was carried out, the protein transmission values remained at nearly 100% for about 4000 s and subsequently decreased gradually to about 60% after 18,000 s of filtration. With SMY, the amount of protein recovered in the permeate is more than two times that recovered after filtration of the BSA-only solution after 18,000 s. 

Fig. 9. Permeate flux vs time during ultrafiltration of 5.0 g/L of cellulase. The solid line represents SMY and backflushing with Pf= 30 psi, Ph = 15 psi, f( = 300 s, tsf= 5 s, and tb = 2s the line with short and long dashes represents SMY and backflushing under the same conditions but with t = 10 s. The yeast concentration in the secondary feed was 4.0 g/L. The dashed line is the permeate flux obtained without deposition of a secondary membrane or backflushing. A wall shear rate of 1300 s 1 was used. LMH = L(m2 h).

For the conditions in Fig. 9, improvements of 35-50% in the permeate flux were observed when a secondary membrane was used, owing to a reduction in the protein fouling of the primary membrane. Little or no flux recovery was observed with each backpulse, as might be expected from the relatively low resistance of the yeast layer and the irreversible nature of the protein fouling. The flux continuously declined with time owing to irreversible fouling, though the rate of decline was reduced by the SMY. 

Wang DN, Safferling M, Lemieux Ml, Griffith H, Chen Y, Li XD. Practical aspects of overexpressing bacterial secondary membrane transporters for structural studies. Biochim. Biophys. Acta 2003 1610 23-36. 

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