Rheological properties of PLGA film-based implants: correlation with polymer degradation and SPf66 antimalaric synthetic peptide release.
This paper reports on the rheological properties of poly(D,L-lactic-co-glycolic acid) polymers (PLGA) dispersions used to form films and of the implants prepared by compression of SPf66 antimalaric peptide between several films, before application and during drug release. 25% PLGA (M(w)=48,000Da) dispersions in dichloromethane showed viscous Newtonian behaviour, being easy flowing and adaptable to the moulds. Evolution of viscoelastic properties, polymer molecular weight, and SPf66 release pattern from the implants immersed in various media was evaluated. Oscillatory shear test showed that freshly prepared implants have an elastic modulus, G', greater than the viscous modulus, G", being both practically independent of angular frequency. After 6 weeks immersion in a pH 7.4 phosphate buffer, G' and G" increased in almost one order of magnitude, despite of a significant polymer degradation. Polymer molecular weight decreased slowly during the first 10 days of immersion (a similar pattern was obtained at pHs 2 and 7.4) and then the degradation process accelerated (degradation index on day 7 equals to 0.89, and on day 14 equals to 16.5). SPf66 release profile followed a pattern similar to that of the polymer degradation index. These observations are explained in terms of changes in polymer structure and conformation that happen in the implant.
Santoveña
A
A
Facultad de Farmacia, Departamento de Ingeniería Química y Tecnología Farmacéutica, Universidad de La Laguna, 38200 Tenerife, Spain.
Alvarez-Lorenzo
C
C
Concheiro
A
A
Llabrés
M
M
Fariña
J B
JB
D020341:Absorbable Implants; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D004058:Diffusion; D004337:Drug Carriers / Q000737:chemistry*; D004343:Drug Implants / Q000737:chemistry*; D004548:Elasticity; D005240:Feasibility Studies; D019344:Lactic Acid / Q000737:chemistry*; D008422:Materials Testing; D008970:Molecular Weight; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D015800:Protozoan Proteins / Q000008:administration & dosage* / Q000737:chemistry*; D011994:Recombinant Proteins / Q000008:administration & dosage* / Q000737:chemistry*; D012212:Rheology / Q000379:methods; D013223:Statistics as Topic; D013696:Temperature; D014783:Viscosity
D020099:Coated Materials, Biocompatible; D004337:Drug Carriers; D004343:Drug Implants; D011108:Polymers; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C066269:SPf66 protein, Plasmodium; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid