PLA stereocomplexes for controlled release of somatostatin analogue

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Reversible stereoselective complexes were spontaneously formed from mixing acetonitrile solutions of enantiomeric d-poly(lactide) (d-PLA), l-poly(lactide) (l-PLA), and octreotide (an octapeptide, somatostatin analogue). Hetero-stereocomplexes of poly (d-lactide) and l-octreotide were obtained by spray freezing of solution of d-PLA and octreotide. An additional transition temperature close to the melting point of enantiomeric PLA was observed in DSC thermogram. The same phenomenon was observed in stereocomplex of d-PLA/l-PLA and octreotide. The enthalpy of both transition temperatures correlate with peptide content in the hetero-stereocomplex. The spray method produced compact and smooth micro particles compared to particles formed by precipitation in acetonitrile solution. The particle size of stereocomplexes was in the range of 1.5 to 4 μm for all formations. Increasing peptide concentration in the stereocomplex increases the release rate of the peptide, and increases polymer degradation rate as monitored by lactic acid release form stereocomplexes.

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