Figure 3.

Surface treatment with NaOH results in an increased presence in carboxylic acid chain ends on the surface of the PCL microspheres, allowing better conjugation with EDANS, a fluorescent model molecule for Alendronate. (A) FTIR spectra of PCL. The labelled peaks represent: a. asymmetric CH₂ stretching, b. symmetric CH₂ stretching, c. carbonyl stretching, d. C–O and C–C stretching in the crystalline phase, e. asymmetric COC stretching, f. OC-O stretching and g. symmetric COC stretching. The combined surface of peaks a and b and the combined surface of peaks f and g were used to calculate the CH₂/C–O ratio which could give an indication to the degree of saponification on the PCL microsphere surface. (B) Semiquantitative analysis of the changes in CH₂ and C–O FTIR peak integral ratio as a result of exposure to 0.1 ​M NaOH for varying durations (n ​= ​3). (C) PCL microspheres prepared by sonication induced emulsification show no apparent sign of agglomeration or shape-loss after 30 ​min of exposure to 0.1 ​M NaOH. NaOH exposure does not result in observable changes to the surface morphology of the microspheres. (D) Molecular structure of ALN and its fluorescent model EDANS. The primary amine on the short carbohydrate tether in both molecules result in similar EDC/NHS based conjugation to the surface of carboxylated PCL microspheres. (E) Conjugation procedure of EDANS to a PCL surface enriched with carboxylic acid groups by NaOH induced saponification. After EDC/NHS activation of surface carboxylic acids, the fluorescent ALN model molecule EDANS was conjugated to the PCL microsphere surface. (F) Fluorescent intensity of the surface conjugated EDANS molecules on PCL microspheres after varying NaOH saponification times and EDC/NHS activation of surface carboxylic acids. FTIR, Fourier transform infrared spectroscopy; PCL = poly(ɛ-caprolactone); ALN = alendronate; EDC, 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide; NHS = N-hydroxysuccinimide; EDNAS = (5-((2-Aminoethyl)amino)naphthalene-1-sulfonic acid).