(380x) Hot Melt Extrusion of Enzyme-Loaded Hydrogel Membranes for CO2 Capture

Hot melt extrusion, (HME), is a common industrial manufacturing technique used to produce a wide range of products, from polymer coatings, to tubing/pipes, to various sized films, and many more. In HME, a thermoplastic polymer is heated and sheared to produce a melt phase, conveyed via rotating screws, and then forced out through a die, allowing for geometric control of the final product.

In recent years, there has been interest in HME for various biological and medical applications, due to the technology’s high throughput, (hundreds to thousands of kg of material per hour), and high encapsulation of active products such as drugs and enzymes, (theoretical efficiency up to 100%). In these applications, the goal is often to generate affordable devices for accurate drug delivery via dissolution of the polymer. With these traits in mind, HME for membrane manufacturing presents an exciting, scalable route for production of biocatalytic membranes, trapping the active agent in the polymer rather than releasing it over time.

This presentation will discuss the design of polyethylene oxide, (PEO), hydrogels loaded with bovine carbonic anhydrase enzyme, (CA), with application for CO₂ capture from flue gas. Hydrogel membranes, by design, are swollen polymer networks that can handle feeds with high water vapor content like that seen in combustion waste gas streams. Additionally, CA is an attractive tool for CO₂ capture applications due to its speed converting between CO₂ and HCO₃^-. Loading CA into hydrogel membranes has been shown to dramatically improve gas separation performance.

This talk will focus on ensuring high enzyme loading and enzyme activity is maintained following HME and hydrogel swelling. Bovine carbonic anhydrase is known to lose catalytic activity in solution around 70 °C, well below typical PEO melt-processing conditions. Controlling variables including PEO molecular weight, processing temperature, and moisture content allows for dramatic increases in protein stability, with the enzyme surviving temperatures as high as 190 °C. Enzyme activity assays and circular dichroism spectroscopy demonstrate that the enzyme recovered after HME is unaffected by the harsh environments. These, as well as mechanistic explanations, will be highlighted.

Additionally, high enzyme loading is achieved via control of the hydrogel nanostructure. Enzyme immobilization within a hydrogel can be achieved in many ways, including covalent attachment and enzyme adhesion. However, these techniques are often detrimental to enzyme activity. Entrapping the enzyme within the hydrogel matrix allows for high enzyme loading without large decreases in enzyme activity. By varying the PEO crosslinking conditions, tremendous control over the polymer mesh size is achieved, allowing for tuning of the mesh size to that of CA. This is confirmed via protein quantification assays, activity assays, and membrane permeability measurements, demonstrating functional CA entrapped within a PEO hydrogel membrane.