The purpose of this study was to provide a clearer understanding of virus adsorption, focusing specifically on the role of electrostatic interactions between virus particles and adsorbent surfaces. The adsorption of poliovirus 1, reovirus types 1 and 3, and coliphages MS-2 and T2 to colloidal silica synthetically modified to carry either positive or negative surface charge was evaluated. Adsorption experiments were performed by combining virus and silica in 0.1-ionic-strength buffers of pH 4.0, 6.4, and 8.5. Samples agitated for specified adsorption periods were centrifuged to pellet adsorbent particles plus adsorbed virus, and the supernatants were assayed for unadsorbed virus. All viruses adsorbed exclusively to negatively charged silica at pH values below their isoelectric points, i.e., under conditions favoring a positive surface charge on the virions. Conversely, all viruses adsorbed exclusively to positively charged silica at pH values above their isoelectric points, i.e., where virus surface charge is negative. Viruses in near-isoelectric state adsorbed to all types of silica, albeit to a lesser degree.

The effects of positively charged nylon and depth (cellulose-diatomaceous earth) filters on endotoxin removal from various solutions were evaluated. The charged filter media removed significant amounts of Escherichia coli and natural endotoxin from tap water, distilled water, sugars, and NaCl solutions; no significant removal of endotoxin was observed with negatively charged filter media. The extent of removal was influenced by pH, the presence of salts, and organic matter. Such media may be useful for the control of endotoxins in raw-product water or solutions used to prepare parenteral drug products or in other fluids where endotoxin control is desired.

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This report demonstrates how electropositive filters can be used to enhance the removal of microorganisms and other negatively charged particles from water. It was shown that electropositive depth filters were capable of adsorbing viruses and endotoxins many times smaller than the average pore size of the filter. Electronegative filters of similar porosity or electropositive filters that had been treated to destroy the positive charge were almost ineffective under similar conditions for the removal of viruses and small latex spheres. The results of this study indicate that electropositive filters are highly effective in the removal of a wide range of contaminants over a wide range of pH values and ionic conditions.

A high level of heparin, infused into blood, often causes severe complications such as hemorrhage, especially when a drug is administered over a long period. The most common way of preventing a patient from bleeding after transfusion is by administering a heparin antagonist such as protamine. The complex molecules formed between heparin and protamine, if left in the bloodstream, may cause hypotension and other side effects. Protamine was immobilized as a bioligand on the affinity matrix formed by grafting an acrylic polymer on cellulose backbone. By flowing blood tangentially along the matrix surface immobilized with protamine, 70-90% heparin reduction was achieved from 1 L of blood containing 10 IU/ml of heparin studied in vitro. The acrylic gel surface avoids lysis of blood, the cellulose support sustains the flow of viscous blood at 50 ml/min, and the tangential flow design permits direct processing of blood without pressure buildup in the system. The example demonstrates the feasibility of applying such a device as a means of immunoadsorptive filter for the selective removal of disease-causing factors from blood.