Temperature and Counterion Effect on Ion Release from Ion-Permeable Microcapsules

Objectives: The objective of this study was to measure the release of calcium and phosphate ions from microcapsules with ion permeable membranes as a function of counterion, concentration and temperature.  Methods: A heterogeneous polymerization technique was utilized to prepare a series of microcapsules based on an ethylene glycol based polyurethane containing different aqueous solutions of potassium phosphate dibasic, sodium phosphate dibasic, potassium phosphate monobasic, calcium nitrate, calcium chloride and calcium acetate.  Ion release profiles were studied as a function of initial ion concentration within the microcapsule, ion type and counterion type, and temperature. Phosphate ion detection was performed by the molybdenum blue method.  Calcium ion release measurements were performed using ion specific electrodes.  Results:   Ion release profiles were studied as a function of initial ion concentration in the microcapsule, ion and counterion identity and temperature.  A table highlighting some of the results is shown below.

Salt Identity	Ion Release Measured	Initial Concentration in microcapsule (M)	0.1 hour (ppm)	20 hours (ppm)	48 hours (ppm)	72 hours (ppm)
Calcium nitrate	Calcium	1	0	4	31	81
Calcium chloride	Calcium	1	2	11	15	24
Calcium acetate	Calcium	1	3	6	18	36
Potassium phosphate dibasic	Phosphate	6	8	600	1982	2028
Potassium phosphate dibasic	Phosphate	3	2	214	897	1392

Conclusions: Ion release profiles were generated for microencapsulated aqueous solutions that contained biologically available ions useful in remineralization.  The preparation of microcapsules with controlled release profiles appears promising based on counterion selection and concentration.  This work is funded in part by Premier Dental Products Incorporated, GL Materials Research LLC and an NSF University-Industry Partnership grant.