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Studies on small (<350 microm) alginate-poly-L-lysine microcapsules. V. Determination of carbohydrate and protein
R Robitaille1, F A Leblond, Y Bourgeois
1Centre de Recherche Guy-Bernier, Hôpital Maisonneuve-Rosemont, 5415 boulevard de l'Assomption, Montréal, Québec, H1T 2M4, Canada.
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.
Insights
Determining membrane molecular weight (MW) cut-off is vital for transplanted cell immunoprotection. This study validated a gel-sieving method for small microcapsules, finding the MW cut-off between 14,500-44,000 Da.
Area of Science:
- Biomaterials Science
- Cell Encapsulation Technology
- Transplantation Immunology
Background:
- Membrane molecular weight (MW) cut-off is crucial for immunoprotection and graft survival in transplanted microencapsulated cells.
- Alginate-poly-L-lysine (PLL) microcapsules are widely used for cell encapsulation, but their precise MW cut-off needs careful characterization.
Purpose of the Study:
- To validate a gel-sieving chromatography method for assessing the MW cut-off of small (<350 micrometers) alginate-PLL microcapsules.
- To evaluate how experimental conditions, such as poly-L-lysine (PLL) concentration and MW, affect the microcapsule MW cut-off.
- To establish a reliable method for quality control and optimization of microcapsule characteristics.
Main Methods:
- Utilized gel-sieving chromatography with proteins and dextrans of known molecular weights (MW) to analyze permeation through microcapsules packed in a column.
- Assessed elution profiles to determine the MW exclusion limit of the microcapsules.
- Varied poly-L-lysine (PLL) concentration and MW to observe their impact on the MW cut-off.
Main Results:
- The MW cut-off for the small microcapsules was determined to be between 14,500 and 44,000 Da for proteins, with dextrans ≥19,000 Da being excluded.
- Increased PLL concentration (0.02% to 0.08%) reduced the MW cut-off, while increasing PLL MW (11.6 to 69.6 kDa) had no significant effect.
- The method successfully differentiated between adsorption and absorption, and confirmed free diffusion of insulin.
Conclusions:
- The gel-sieving chromatography method is effective for assessing and optimizing the MW cut-off of small alginate-PLL microcapsules.
- Microcapsule MW cut-off can be modulated by adjusting PLL concentration, impacting suitability for different cell transplantation applications.
- This validated method provides a valuable tool for routine quality control in microencapsulation technology.