Studies on small (<350 ?m) alginate-poly-L-lysine microcapsules. V. Determination of carbohydrate and protein permeation through microcapsules by reverse-size exclusion chromatography

Abstract

Membrane molecular weight (MW) cut-off is a critical factor for immunoprotection of transplanted microencapsulated cells as well as for graft survival. Our goal was to study dextran and protein permeation through small (<350 microm in diameter) alginate-poly-L-lysine microcapsules made with an electrostatic system. Microcapsules were packed into a column, and gel-sieving chromatography was performed with proteins and dextrans of known MW. The objectives of this study were (1) to validate this approach for the assessment of the MW cut-off of <350 microm-in-diameter microcapsules and (2) to evaluate the effect on MW cut-off of changes in experimental conditions. Elution profiles of proteins suggest that the MW cut-off of our small microcapsules lies between 14,500 and 44,000 Da whereas dextrans > or =19,000 Da were excluded. The increase in poly-L-lysine (PLL) concentration from 0.02 to 0.08% reduced the MW cut-off. Increasing the PLL MW from 11.6 to 69.6 kDa induced no change in the MW cut-off. The results also show that the method can be used to discriminate between adsorption and absorption and that insulin diffuses freely across the microcapsule membrane. This method will be useful in establishing the ideal MW cut-off, in optimizing microcapsule characteristics, and in performing routine quality controls.

Effects of PEG hydrogel crosslinking density on protein diffusion and encapsulated islet survival and function

“…However, relative to proteins which are monodisperse, the polymers used to synthesize encapsulation barriers are polydisperse, further complicating the concept of a gel MWCO and contributing to very broad MWCO ranges. Alginate‐poly‐ L ‐Lysine capsules have been synthesized with a MWCO between 14,500 and 44,000 g/mol, as determined by measuring the diffusion of linear dextran molecules and model proteins 21. Other natural and synthetic polymer membrane studies have targeted a MWCO of 50,000 g/mol 22–27…”

Robust Microcapsules with Controlled Permeability from Silk Fibroin Reinforced with Graphene Oxide

“…The highly aggregated surface of the microcapsules suggested a potentially porous morphology of the LbL shells. Thus, we examined the permeability of the composite (SF‐PL/GO) 3.5 microcapsules at different pH conditions by employing green fluorescent FITC‐dextrans with various molecular weights as probes ( Figure ) . Instead of investigating the effect of shell thickness on permeability which is well known for LbL shells, we focused on studying shell permeability as a function of the surrounding pH since the silk ionomer component is pH‐sensitive.…”

Considerations in binding diblock copolymers on hydrophilic alginate beads for providing an immunoprotective membrane

“…The PLL that is subsequently added is binding to constitutive alginate molecules in a highly cooperative manner to form a strong, rigid membrane. The degree of cross‐linking determines the mechanical stability and permeability of the membrane …”

“…Polyamino acids such as PLL and polyornithine typically need 10 min to provide a permeability to retain molecules larger than 120 kDa . Such a long incubation period is desired since it allows for versatility and fine tuning of the membrane permeability for different applications . On the other hand, due to larger chain lengths, the adsorption of diblock copolymers is slower and requires longer time periods.…”

“…Also the type of polycation has been shown to be an essential factor in the success and failure of capsules . The reason for application of polyamino acid is to decrease the permeability of the capsules and to improve their mechanical properties . Different polyamino acids have been tested and PLL proved to be the best available option .…”