Fickian-Based Empirical Approach for Diffusivity Determination in Hollow Alginate-Based Microfibers Using 2D Fluorescence Microscopy and Comparison with Theoretical Predictions

Abstract

Hollow alginate microfibers (od = 1.3 mm, id = 0.9 mm, th = 400 µm, L = 3.5 cm) comprised of 2% (w/v) medium molecular weight alginate cross-linked with 0.9 M CaCl2 were fabricated to model outward diffusion capture by 2D fluorescent microscopy. A two-fold comparison of diffusivity determination based on real-time diffusion of Fluorescein isothiocyanate molecular weight (FITC MW) markers was conducted using a proposed Fickian-based approach in conjunction with a previously established numerical model developed based on spectrophotometric data. Computed empirical/numerical (Dempiricial/Dnumerical) diffusivities characterized by small standard deviations for the 4-, 70- and 500-kDa markers expressed in m2/s are (1.06 × 10−9 ± 1.96 × 10−10)/(2.03 × 10−11), (5.89 × 10−11 ± 2.83 × 10−12)/(4.6 × 10−12) and (4.89 × 10−12 ± 3.94 × 10−13)/(1.27 × 10−12), respectively, with the discrimination between the computation techniques narrowing down as a function of MW. The use of the numerical approach is recommended for fluorescence-based measurements as the standard computational method for effective diffusivity determination until capture rates (minimum 12 fps for the 4-kDa marker) and the use of linear instead of polynomial interpolating functions to model temporal intensity gradients have been proven to minimize the extent of systematic errors associated with the proposed empirical method.

Synthetic poly(ethylene glycol)-based microfluidic islet encapsulation reduces graft volume for delivery to highly vascularized and retrievable transplant site

“…Internal fluorescence was quantified as demonstrated by intensity histograms (Figure A) and change of intensity over time (Figure B). Finite element modeling of diffusivity via parametric sweeps and sum of the squares analysis against measured values (Figure S1) provided diffusivity values comparable to those determined by others and demonstrated comparable diffusivities between PEG and alginate hydrogels (Figure C).…”

Small-Scale Fluidized Bed Bioreactor for Long-Term Dynamic Culture of 3D Cell Constructs and in vitro Testing

“…These rates are a function of the diameter, composition and mechanical properties of the hydrogel, as well as, of the size of the diffusing particles and thus, smaller molecules could diffuse at the same rate as larger ones for hydrogels of different compositions (Gautier et al, 2011;Sun et al, 2018). Of note, the physical barrier imposed by the hydrogel did not impair mass transfer of 150 kDa dextran, reinforced by studies demonstrating alginate permeability to large molecules up to 500 kDa (Khalil et al, 2001;Mobed-Miremadi et al, 2014). Design parameters of fluidized bed bioreactors can also influence mass transfer: increasing the number of holes and pressure drop across the distributor increases the mass transfer coefficient (Kalaga et al, 2014).…”

Effect of artificial cell miniaturization on urea degradation by immobilizedE. coliDH5α (pKAU17)

“…The 3 X increase in effectiveness factor (g MI /g MA) as a result of miniaturization could be further enhanced by switching from microspheres to microfibers. The ratio of experimentally measured membrane diffusivities for alginate-based MIs [35] and microfibers [57,58] for the 4 kDa fluorescent marker is 264 (2.03 Â 1 0 À11 m 2 /s/7.7 Â 10 À14 m 2 /s). The emergence of composite living microfiber technology in the fields of tissue engineering and regenerative medicine has simultaneously addressed the benefits of increasing the aspect ratio as well overcoming the susceptibility to swelling and degradation.…”