Immobilized carbonic anhydrase on hollow fiber membranes accelerates CO2 removal from blood

Abstract

Current artificial lungs and respiratory assist devices designed for carbon dioxide removal (CO2R) are limited in their efficiency due to the relatively small partial pressure difference across gas exchange membranes. To offset this underlying diffusional challenge, bioactive hollow fiber membranes (HFMs) increase the carbon dioxide diffusional gradient through the immobilized enzyme carbonic anhydrase (CA), which converts bicarbonate to CO2 directly at the HFM surface. In this study, we tested the impact of CA-immobilization on HFM CO2 removal efficiency and thromboresistance in blood. Fiber surface modification with radio frequency glow discharge (RFGD) introduced hydroxyl groups, which were activated by 1M CNBr while 1.5M TEA was added drop wise over the activation time course, then incubation with a CA solution covalently linked the enzyme to the surface. The bioactive HFMs were then potted in a model gas exchange device (0.0084 m2) and tested in a recirculation loop with a CO2 inlet of 50mmHg under steady blood flow. Using an esterase activity assay, CNBr chemistry with TEA resulted in 0.99U of enzyme activity, a 3.3 fold increase in immobilized CA activity compared to our previous method. These bioactive HFMs demonstrated 108 ml/min/m2 CO2 removal rate, marking a 36% increase compared to unmodified HFMs (p < 0.001). Thromboresistance of CA-modified HFMs was assessed in terms of adherent platelets on surfaces by using lactate dehydrogenase (LDH) assay as well as scanning electron microscopy (SEM) analysis. Results indicated HFMs with CA modification had 95% less platelet deposition compared to unmodified HFM (p < 0.01). Overall these findings revealed increased CO2 removal can be realized through bioactive HFMs, enabling a next generation of more efficient CO2 removal intravascular and paracorporeal respiratory assist devices.

A novel technique for the precise measurement of CO2 production rate in small aquatic organisms as validated on Aeshnid dragonfly nymphs

“…S5) arranged in parallel and fitted into a 1/8 inch acrylic tube, similar to previous designs (Kaar et al, 2007;Arazawa et al, 2012). The volume surrounding the fibres (0.6 ml) was perfused with water coming from the measuring chamber that was circulated in a closed loop by a peristaltic pump (Gilson MINIPULS 3, Middleton, WI, USA).…”

“…Water was circulated in a closed loop indicated by the blue arrows, and CO 2 -free purge-gas is represented by the dashed arrows. The interface between water and air was a hollow fibre membrane (HFM) gas exchanger, in which water was circulated on the outside of a bundle of gas permeable fibres and CO 2 -free purge-gas was circulated through the lumen of the fibres in a counter-current fashion, similar to previous designs (Kaar et al, 2007;Arazawa et al, 2012). See Materials and methods, Experimental setup for specifications of system components.…”

Acidic sweep gas with carbonic anhydrase coated hollow fiber membranes synergistically accelerates CO2 removal from blood

“…Previous work by our group to chemically increase trans-HFM CO 2 pressure utilized bioactive CA-HFMs for a 31–37% improvement in blood CO 2 removal efficiency [27], [28]. In this work, the addition of SO 2 to an oxygen sweep gas increased CO 2 removal of unmodified PMP HFMs up to 17%, and for bioactive CA-PMP HFMs up to 109% (Figure 2).…”

“…Our lung tissues face the same diffusional challenges as HFMs, however they employ the enzyme carbonic anhydrase (CA) within red blood cells and on the endothelial surfaces of lung capillaries to accelerate diffusion by catalyzing the reversible dehydration of HCO 3 − (bicarbonate) to gaseous carbon dioxide: ${\text{CO}}_2+{\mathrm{H}}_2\mathrm{normalO}\stackrel{CA}{\iff }{{\text{HCO}}_3}^{-}+{\mathrm{H}}^{+}$. We reported development of CA immobilized bioactive HFMs which converts bicarbonate to CO 2 directly at the HFM surface, restoring the trans-HFM CO 2 gradient as it is depleted in the diffusional boundary layer, and increasing CO 2 removal rates from blood by 36% in model gas exchange devices [27]–[29]. The main impediment to CO 2 removal by bioactive HFMs is diffusional boundary layer resistance which restricts transport of CO 2 and bicarbonate from the bulk fluid to the HFM surface, not the CA catalyzed conversion of bicarbonate to CO 2 [28].…”

Carbonic anhydrase immobilized on hollow fiber membranes using glutaraldehyde activated chitosan for artificial lung applications

“…We previously demonstrated enhanced CO 2 removal by covalently immobilizing CA directly on the surface of hollow fiber membranes (HFMs), which locally converts bicarbonate to gaseous CO 2 at the fiber surface, resulting in increased blood-side CO 2 partial pressure and accelerated CO 2 flux through the membrane [12, 13]. In this work, we developed a new coating technology using glutaraldehyde activated chitosan to covalently tether CA to the surface of HFMs used in a commercial ECCO 2 R device (Hemolung, ALung Technologies).…”