Improving the packing density of an enzyme/block-copolymer conjugate as a reactive layer to design an anti-endotoxin water purification membrane

Abstract

<p>Purified water is the most abundant raw material used in the formulation, cleaning, and manufacturing of pharmaceutical products, analytical reagents, intermediates, biomedical devices, and active pharmaceutical ingredients (API). The United State Pharmacopeia monograph &lt;1231&gt; establishes distinct classifications of water quality that must be used in a biotechnological facility. Membrane technology is an important application employed to produce water with a high-standard quality level.</p>

<p>The membrane separation field for water purification applications are evolving toward developing bio-functional interfaces. The permi-selective barrier that separates the unclean to the clean passage is primarily driven by the size exclusion principle in most filtration systems. In addition to this approach, we aimed to design an <em>in-situ</em> response of the membrane to biodegrade unwanted molecules, particularly those from bacterial origin (i.e. endotoxins), using an active interface at the surface of a nano-porous barrier. In pursuit of that vision, we fostered path-breaking scientific discovery via working with bio-reactive membrane separation sciences to address this challenge and thus provide water with a higher quality level.</p>

<p>This research sought to understand the fundamental aspects related to the packing density of a nano-porous polymeric active layer. The porous layer results from the self-assembly properties of the di-block copolymer (BCP) polystyrene-b-poly(4 vinyl pyridine) (PS-bP4VP) that results in cylindrical domains. The PS_40.5K-b-P4VP_16.5K and PS_17K-b-P4VP_49K forms supramolecular immiscible assemblies that have been previously studied in the bulk. Additionally, in recent studies, the complexes of this system have been also investigated ix via phase inversion and as thin films by spin coating techniques to produce thin-porous layers. Moreover, we looked forward to attaching lipase b from <em>Candida Antarctica</em> (CALB) enzyme within the polymeric matrix prepared from the aforementioned methods to add functional properties by means of an enzymatic reaction activity. In this work, CALB was initially attached via physical adsorption and later covalently attached to the self-assembled PS-b-P4VP block copolymer thin-film. The attachment was then characterized via atomic force microscopy (AFM), scanning electron microscopy (SEM), FTIR, hydrolytic activity, among other techniques. For the adsorbed lipase above the thinfilm model, the adsorption of the enzyme was successfully achieved onto the polymeric matrix with average pore size of 19.4 &plusmn; 2.0 nm. Results also demonstrated a relative activity of the immobilized enzyme up to 90.5 &plusmn; 3.7 %. For the covalently attached method, the immobilized enzyme was able to retain 97% of its enzymatic activity when using 4- nitrophenyl acetate (pNPA) and up to 74% when biodegrading LPS. The observed average pore size at the final constructed enzymatic thin-film composite (E-TFC) membrane was 91.8 &plusmn; 29.6 nm. The prepared reactive enzymatic active layer serves as a model and proofof-concept to develop further reactive layers for TFC membranes that finds suitability in water purification applications.</p>