Diffusion of Protein Molecules through Microporous Nanofibrous Polyacrylonitrile Membranes

Abstract

Porous nanofibrous membranes have ultrahigh specific surface areas and could be broadly employed in protein purification, enzyme immobilization, and biosensors with enhanced selectivity, sensitivity, and efficiency. However, large biomolecules, such as proteins, have hindered diffusion behavior in the micro-porous media, significantly reducing the benefits provided by the nanofibrous membranes. The study of protein diffusion in polyacrylonitrile (PAN) nanofibrous membranes produced under varied humidity and polymer concentration of electrospinning revealed that heterogeneous structures of the nanofibrous membranes possess much smaller effective pore sizes than the measured pore sizes, which significantly affects the diffusion of large molecules through the system though sizes of proteins and pH conditions also have great impacts. Only when the measured membrane pore size is at least 1000 times higher than the protein size, the diffusion behavior of the protein is predictable in the system. The results provide insights into the design and applications of proper nanofibrous materials for improved applications in protein purification and immobilizations.

Keywords: Micro-porous structure; Nanofibrous membrane; Protein diffusion; Protein-polymer interaction; diffusion coefficient; effective pore size; partition coefficient.

Figure 1.

(a) SEM images of PAN nanofibrous membranes made under different polymer concentrations and relative humidity; and fiber diameters, pore distributions, pore sizes of as-prepared membranes: (b) and (e) fiber diameter, (c) and (f) measured pore distribution, and (d) and (g) measured maximum pore size and average pore size.

Figure 2.

(a) A scheme of a side-by-side chamber used in this study; (b-c) SEM images of the membrane before and after the diffusion test.

Figure 3.

Partition coefficient of proteins inside membranes prepared (a) under different relative humidity conditions and (b) with different polymer concentrations; cumulative amounts of protein in receptor chamber versus time: (c) PAN membranes prepared under different relative humidity (RH) conditions, (d) membranes prepared with different polymer concentrations; and effective diffusion coefficients of membranes prepared (e) under different relative humidity conditions and (f) with different polymer concentrations.

Figure 4.

Measured and predicted results of effective diffusion coefficient ratios of proteins in membranes with different a) protein to measured pore size ratios, and b) protein to fiber diameter ratios

Figure 5.

The impact of pH value on (a) partition coefficient, (b) cumulative amount of BSA in the receptor chamber versus time, and (c) diffusion coefficient of BSA in same PAN nanofibrous membrane

Figure 6.

(a) Partition coefficient of proteins and (b) cumulative amount of protein in the receptor chamber versus time, and (c) diffusion coefficient of four proteins in the same PAN nanofibrous membrane

Scheme 1.

The dynamic transport of proteins in small-pore (a) and large-pore (b) fibrous membranes; (c) diffusion of protein through a pore. Where r_p is the average measured pore size, and r_s is a radius of a spherical protein molecule.