P-261

Effect of initial calcium concentration on alginate bead stability in vitro

O. Liang, M. Lamb, J. Lakey
University of California Irvine Medical Center, Surgery, Orange, USA

Objective: Sodium alginate is currently being used as an encapsulation method to circumvent the immune system’s response to islet transplant. Traditionally encapsulation protocols maintain capsules in >5mM calcium to ensure integrity, structure and rigidity of the capsules, however interstitial blood calcium concentration is typically lower than this threshold. It was the aim of this study to examine capsule stability and integrity at various calcium concentrations.

Methods: Alginate capsules were made using a 2.1% Pronova UP-LVM alginate/PBS solution (NovaMatrix, Norway) using a 9mV at 2psi electrostatic generator (Nisco, Switzerland) and allowed to crosslink in high (100mM) calcium/diH₂0 solution for 5 ± 0.5 minutes. Capsules were then washed twice in 0.9% Normal Saline before aliquots were cultured at 37^oC in PBS at increasing concentrations of calcium (0mM, 2mM, 2.5mM, 3mM, 5mM, 10mM). Bead integrity, size and degradation (microscopy and SEM) were analyzed over month period in tissue culture.

Results: Capsule size was 500 ± 20um (mean ± SEM) at day 0. Beads cultured at <2.5mM decreased in size to 480 ± 5um, while those > 2.5mM calcium maintained integrity and size at 1 week. Calcium/phosphate precipitate was observed concentrations >0mM, with crystalline structures in 2–5 mM concentrations. Longer culture duration, 2, 3 and 4 weeks, capsules maintained integrity and size without any further significant changes.

Conclusions: These experiments demonstrate alginate capsule integrity can be maintained in vitro longer at lower than expected concentrations of calcium. In vivo transplant studies of these low calcium concentrated alginate capsules will provide further evidence of this observation.

P-261

Effect of initial calcium concentration on alginate bead stability in vitro

O. Liang, M. Lamb, J. Lakey
University of California Irvine Medical Center, Surgery, Orange, USA

Objective: Sodium alginate is currently being used as an encapsulation method to circumvent the immune system’s response to islet transplant. Traditionally encapsulation protocols maintain capsules in >5mM calcium to ensure integrity, structure and rigidity of the capsules, however interstitial blood calcium concentration is typically lower than this threshold. It was the aim of this study to examine capsule stability and integrity at various calcium concentrations.

Methods: Alginate capsules were made using a 2.1% Pronova UP-LVM alginate/PBS solution (NovaMatrix, Norway) using a 9mV at 2psi electrostatic generator (Nisco, Switzerland) and allowed to crosslink in high (100mM) calcium/diH₂0 solution for 5 ± 0.5 minutes. Capsules were then washed twice in 0.9% Normal Saline before aliquots were cultured at 37^oC in PBS at increasing concentrations of calcium (0mM, 2mM, 2.5mM, 3mM, 5mM, 10mM). Bead integrity, size and degradation (microscopy and SEM) were analyzed over month period in tissue culture.

Results: Capsule size was 500 ± 20um (mean ± SEM) at day 0. Beads cultured at <2.5mM decreased in size to 480 ± 5um, while those > 2.5mM calcium maintained integrity and size at 1 week. Calcium/phosphate precipitate was observed concentrations >0mM, with crystalline structures in 2–5 mM concentrations. Longer culture duration, 2, 3 and 4 weeks, capsules maintained integrity and size without any further significant changes.

Conclusions: These experiments demonstrate alginate capsule integrity can be maintained in vitro longer at lower than expected concentrations of calcium. In vivo transplant studies of these low calcium concentrated alginate capsules will provide further evidence of this observation.