Self-Driven "Microfiltration" Enabled by Porous Superabsorbent Polymer (PSAP) Beads for Biofluid Specimen Processing and Storage

Abstract

A remote collection of biofluid specimens such as blood and urine remains a great challenge due to the requirement of continuous refrigeration. Without proper temperature regulation, the rapid degradation of analytical targets in the specimen may compromise the accuracy and reliability of the testing results. In this study, we develop porous superabsorbent polymer (PSAP) beads for fast and self-driven "microfiltration" of biofluid samples. This treatment effectively separates small analytical targets (e.g., glucose, catalase, and bacteriophage) and large undesired components (e.g., bacteria and blood cells) in the biofluids by capturing the former inside and excluding the latter outside the PSAP beads. We have successfully demonstrated that this treatment can reduce sample volume, self-aliquot the liquid sample, avoid microbial contamination, separate plasma from blood cells, stabilize target species inside the beads, and enable long-term storage at room temperature. Potential practical applications of this technology can provide an alternative sample collection and storage approach for medically underserved areas.

Figure 1

Schematic of the PSAP beads for the microfiltration of target species in biofluid specimens. The PSAP beads capture small analytical targets while rejecting large undesired components along the water absorption to achieve the self-driven microfiltration. The polymer network of the beads is synthesized by poly(sodium acrylate) (PSA) crosslinked with polyacrylamide (PAM).

Figure 2

Characterization of the PSAP beads. (a) SEM images of PSAP beads polymerized by precursors containing different concentrations of PEG-6000 from 2.5 to 20 wt %. (b) Porosity of the PSAP beads. (c) Average pore diameter of the PSAP beads. (d) Swelling ratio of the PSAP beads in the saline (0.9% NaCl solution).

Figure 3

Microfiltration performance analysis in the saline medium. (a) Catalase recovery and E. coli rejection using the PSAP beads with a PEG content from 2.5 to 20 wt %. (b) Distribution of fluorescent microspheres (red under the fluorescent field) on the cross-section of the PSAP beads after the treatment. (c) Normalized fluorescence intensity from the edge to the core of the beads.

Figure 4

Microfiltration performance of the PSAP beads in biofluid media. (a) Normalized diameter of the PSAP beads in different biofluid media over time. (b) Optical images of the PSAP beads during the swelling process. The scale bar is 2 mm. (c) Recovery efficiency for glucose, catalase, and bacteriophage MS2 after the microfiltration treatment. (d) Bright-field microscopy images of the hydrated PSAP bead after swelling in the bovine blood medium.

Figure 5

Shelf life extension of catalase by the microfiltration treatment against bacterial contamination. (a) Catalase activity in the saline medium dosed with B. subtilis during the 7-day storage at 4, 22, or 35 °C. The initial bacterial dosage is ∼50 CFU mL^–1. (b) Bacterial concentration that is corresponding to the catalase activity in (a) at each sampling time during the 7 days. The dashed line in b indicates no live bacteria are detected in the agar plates. (c) Catalase activity in the hydrated PSAP beads after the microfiltration treatment during the 7-day storage at 4, 22, or 35 °C. (d) Difference interference contrast microscopy images of the liquid control and the hydrated PSAP bead after the 7-day storage at 35 °C.

Figure 6

Shelf life extension of catalase in the plasma medium by microfiltration treatment. (a) Catalase activity in the liquid control during the 7-day storage at 4, 22, or 35 °C. The dashed line in a indicates no active catalase is detected in the spectrophotometric assay. (b) Catalase activity in the hydrated PSAP beads after microfiltration treatment during the 7-day storage at 4, 22, or 35 °C.