Controlled Release of IgG from Microspheres

1. Controlled Release of IgG from Microspheres Reference: H. M. Wong, J. Wang, and C.H. Wang, "In Vitro Sustained Release of Immunoglobulin G from Biodegradable Microspheres", I & EC Research, 40, 933-948 (2001).

2. Sustained Release of IgG • Provides a localised delivery of the drug. • Reduces dose handling leading to reduction in side effects. • Decreases treatment frequency. • Reduction in costs. • Improvement of patient compliance.

3. Polymers used • 3 types of polymers • Poly(DL-lactide) (PLA) (MW 90 000-120 000) • Poly(DL-lactide-co-glycolide) 50:50 (PLGA 50:50) (MW 40 000-75 000) • Poly(DL-lactide-co-glycolide) 65:35 (PLGA 65:35) (MW 40 000-75 000) • Degradable by hydrolysis to form innocuous products lactic and glycolic acids. • Exhibits favorable biocompatibility and toxicological characteristics.

4. PROTEIN SOLUTION POLYMER-DCM SOLUTION ADD TO PVA IN WATER & MIX SECONDARY EMULSION (W/O/W) ULTRA SONICATION SOLVENT EVAPORATION PRIMARY EMULSION (W/O) FILTRATION AND DRYING Fabrication of Microspheres Double Emulsion Method

5. Fabrication Parameters

6. Encapsulation Efficiency

7. Mean Particle Size

8. Porosity – Different Polymers

9. Porosity of PLA – Different loading

10. Surface Structure Before Release (a) PLGA 50:50 (b) PLGA 65:35 (c) PLA

11. PLGA 50:50 - BEFORE RELEASE DRUG LOADING 5 % 15 % 26 % SURFACE CROSS-SECTION

12. PLA - BEFORE RELEASE DRUG LOADING 5 % 15 % 26 % SURFACE CROSS-SECTION

13. Morphological Charateristics • Encapsulation efficiency increases when drug loading decreases for all the polymers. • Encapsulation efficiency decreases when the porosity of the microspheres increases. • Particle size of PLA microspheres are greater than that of PLGA microspheres. • Mean particle size of the same type of polymer is not very sensitive to drug loading. • PLA microspheres are more porous than PLGA microspheres at all drug loadings under the same fabrication conditions. • Drug loading does not have a significant effect on porosity.

14. In Vitro Release Curves - FITC-IgG PLGA50:50 • Release profile similar to non-labelled IgG microspheres PLA

15. Laser Scanning Confocal Microscopy (LSCM) • Inverted light microscope adopting the laser scan mode, capable of producing images of specimens that have been labeled with two or more fluorescent dyes. • Use of FITC-IgG in the fabrication of PLGA 50:50 and PLA microspheres. • Examination of drug distribution and extent of drug release.

16. Confocal Laser Scanning Micrographs PLGA 50:50 PLA BLANK FITC-IgG LOADED

17. PLGA 50:50 – Drug Distribution CROSS-SECTION BEFORE RELEASE AFTER 3 WEEKS

18. PLA – Drug Distribution CROSS-SECTION BEFORE RELEASE AFTER 3 WEEKS

19. In Vitro Release Study

20. In Vitro Release Profiles - 15% Drug Loading • 3 types of polymers : PLA, PLGA 50:50, PLGA 65:35. • Initial burst followed by a period of gradual release. • Initial burst and % of IgG released increased with the porosity of the microspheres.

21. In Vitro Release Profiles - PLA • 3 types of drug loading: 5%, 15% & 26%. • Initial burst followed by a period of gradual release. • % of IgG released increased with drug loading at lower loadings. • At higher loadings, possible increased denaturation of drug.

22. In Vitro Release Profiles - Different Loading PLGA 50:50 PLGA 65:35

23. In Vitro Release Profiles - Different Polymer Composition 5% Drug Loading 26% Drug Loading

24. PLGA 50:50 - AFTER 7 WEEKS DRUG LOADING 5 % 15 % 26 % SURFACE CROSS-SECTION

25. PLA - AFTER 7 WEEKS DRUG LOADING 5 % 15 % 26 % SURFACE CROSS-SECTION

26. PLGA 35:65 - 15% Drug Loading SURFACE CROSS-SECTION BEFORE RELEASE AFTER 7 WEEKS

27. Mass Loss Study • Polymer erosion can be characterised by its mass loss. • Mass of blank samples immersed in PBS were measured periodically to analyse their mass loss. • More than 90% of mass remains after 45 days.

28. Model 1: Diffusion controlled • Crank (1975) and Vergnaud (1993) • Non-steady state radial diffusion For constant diffusivity D,

29. Release under perfect sink conditions Model 1a • Assumptions: • Mass transfer coefficient on surface infinite • Constant concentration on surface • I.C. t = 0, r < R, C = Cin • B.C. t > 0, r = R, C = C • t > 0, r = 0, C/ r = 0

30. Release under surface conditions Model 1b • Assumptions: • Mass transfer coefficient on surface finite • Concentration of surrounding atmosphere constant • I.C. t = 0, 0 < r < R, C = Cin • B.C. t > 0, r = 0, C/ r = 0 • t > 0, r = R,

31. Model 1b Release under surface conditions • Where • S = hR/D • n are the roots of n cot n = 1-S

32. Model 2: Dissolution/Diffusion controlled (1) • From J. Control. Release 7, Harland et al.; (1988). • Incorporates a linear first order dissolution term and the transient Fickian diffusion equation.

33. Release under perfect sink conditions Model 2a I.C. t = 0, 0 < r < R, C = Cs B.C.s t > 0, r = 0, C/ r = 0 t > 0, r = R, C = 0 Using the following transformation and dimensionless parameters, C' = Cs - C Dimensionless radial position  = r/R Dimensionless Fourier time  = Dt/R2 Dimensionless concentration  = C'/ Cs = 1 - C/ Cs

34. Release under perfect sink conditions Model 2a Introducing new dimensionless number, dissolution/diffusion number, Di Di = kR2/D Eqn (1) transformed to I.C.  = 0, 0 <  < 1,  = 0 B.Cs  > 0,  = 0,   /   = 0  > 0,  = 1,  = 1

35. Model 2a Release under perfect sink conditions Dimensionless quantity of drug released,

36. Model 2b Release under surface conditions I.C. t = 0, 0 < r < R, C = Cs B.Cs t > 0, r = 0, C/ r = 0 t > 0, r = R, I.C.  = 0, 0 <  < 1,  = 0 B.C.s  > 0,  = 0,   /   = 0  > 0,  = 1,   /   = Sh. 

37. Model 2b Release under surface conditions Sherwood number, Sh = hR/D - relates the rate of mass transfer to the rate of diffusion Dimensionless quantity of drug released, Where n are the roots of nRcot(n R) + Sh -1 = 0

38. Modeling Results - 5% Loading PLA PLGA 50:50 PLGA 65:35

39. Modeling Results - 15% Loading PLA PLGA 50:50 PLGA 65:35

40. Modeling Results - 26% Loading PLA PLGA 50:50 PLGA 65:35

41. Model Parameters

42. Modeling Results • Diffusion/Dissolution model (Model 2) gives a better fit to the experimental data compared to the Diffusion only model (Model 1). • For both models, the infinite mass transfer coefficient case gives a better fit than the finite mass transfer coefficient case. • Values of D obtained from Model 1 is lower than that of Model 2 due to the incorporated effect of dissolution. • Both D and k are generally greater in PLA compared to PLGA polymers.

43. Conclusions • Type of polymer used have marked effects on the morphology and in vitro release characteristics of IgG from microspheres. • The release profiles and morphology of PLGA 50:50 and PLGA 65:35 are similar at higher loadings. • The release profiles show a low initial burst followed by a period of gradual release. • At lower drug loadings, rate of drug release generally increases with the drug loading. • All the polymers used did not show significant extent of erosion within the period of study. • Diffusion coupled with dissolution was found to be the dominant mechanism in the release kinetics.