Dendritic cells required materials

The size and extent of many neurons presents a special set of challenges. Since protein synthesis for the entire neuron takes place in the cell body, which may represent only 0.1% of the total cell volume, growth and maintenance of neuronal processes requires timely, efficient delivery of material to axonal and dendritic domains. The idea that materials must be transferred from cell body to axon was suggested by Ramon y Cajal and other pioneers during the early part of this century. For many years, the existence of such transport processes could only be inferred. 

In genera] secondary cells have more stringent requirements for separator materials than primary cells. RAM cells typically apply two components, a non woven absorbent and a barrier material. The absorbent material used is formulated fiom polyvinyl alcohol and rayon fibers, acts as mechanical spacer between anode and cathode and provides as an electrolyte reservoir. The barrier is unglycerinated cellulose and prevents zinc dendrites from causing cell shorts. Prior to insertion into the cell the two materials are wound into a tube. Separator materials are selected which are not subject to oxidation in the alkaline electrolyte even at elevated temperatures and which combine chemical and mechanical stability with long life expectancy. 

In lithium-based cells, the essential function of battery separator is to prevent electronic contact, while enabling ionic transport, between the positive and negative electrodes. It should be usable on high-speed winding machines and possess good shutdown properties. The most commonly used separators for primary lithium batteries are microporous polypropylene membranes. Microporous polyethylene and laminates of polypropylene and polyethylene are widely used in lithium-ion batteries [85]. These materials are chemically and electrochemically stable in secondary lithium batteries. A key requirement for the separators for lithium primary batteries is that their pore size be small enough to prevent dendritic lithium penetration through them. 

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