The Effect of Swelling Ratio on the Coulter Underestimation of Hydrogel Microsphere Diameters

Abstract

It has been demonstrated that the diameters of porous particles are underestimated by Coulter measurements. This phenomenon has also been observed in hydrogel particles, but not characterized. Since the Coulter principle uses the displacement of electrolyte to determine particle size, electrolyte contained within the swelled hydrogel microparticles results in an underestimate of actual particle diameters. The increased use of hydrogel microspheres in biomedical applications has led to the increased application of the Coulter principle to evaluate the size distribution of microparticles. A relationship between the swelling ratio of the particles and their reported Coulter diameters will permit calculation of the actual diameters of these particles. Using polyethylene glycol diacrylate hydrogel microspheres, we determined a correction factor that relates the polymer swelling ratio and the reported Coulter diameters to their actual size.

The effect of polymer molecular weight and cell seeding density on viability of cells entrapped within PEGDA hydrogel microspheres

“…For all hydrogel molecular weights, microsphere diameters ranged in size from 20-3000 mm, with a 130-150 mm median microsphere size (Table 1). For a detailed analysis and characterisation of the polydispersity of these microspheres, refer to (Pellegrini et al 2015). Initially, encapsulated cells at medium and high cell seeding densities (1 Â 10 4 and 2.5 Â 10 4 cells/lL, respectively) showed similar viability, while cells seeded at low cell densities (0.2 Â 10 4 cells/ lL) showed the lowest viability (Figure 1).…”

“…It is possible that large serum proteins could not pass through the smaller mesh size that comprises low molecular weight PEGDA, resulting in the increased cell death observed (Zhang et al 2011). The various mesh sizes were calculated for these hydrogels and found to be 32.3, 28, 16.2 (Pellegrini et al 2015), and 10.8 nm for 20, 10, 5, and 3.4 kDa molecular weight PEGDA, respectively. Bovine serum albumin, the main protein found in FBS, was demonstrated to have dimensions of 14 nm by 4 nm Figure 3.…”

“…Hydrogel mesh sizes (5, 10, and 20 kDa) were determined previously (16.2, 28, and 32.3 nm, respectively); 3.4 kDa hydrogel mesh size was determined in the same manner, where mesh size was characterised via a series of dextran diffusion assays (Pellegrini et al 2015). Briefly, hydrogel sheets 0.08 mm thick were formed by photopolymerising PEGDA prepolymer solution (absent the surfactant pluronic F68) within a 25 Â 75 mm glass mould.…”

Comparing laser diffraction and optical microscopy for characterizing superabsorbent polymer particle morphology, size, and swelling capacity

“…The use of sieves to determine a PSD results in a discontinuous size distribution with large fractional size ranges . Although microscopy techniques are accurate and often used to determine particle sizes, they require image processing, which can be time consuming, and the sample size is limited to the number of particles within a micrograph and the number of micrographs taken. To reduce the time required and increase the sample size, particle size analyzers can be used to obtain accurate PSDs.…”

“…To reduce the time required and increase the sample size, particle size analyzers can be used to obtain accurate PSDs. One method uses the Coulter principle but has been shown to underestimate the particle sizes of hydrogels in the swollen state . DLS and LD are the preferred methods because of their relatively fast analysis time and accuracy.…”