Chitosan-Polylactide/Hyaluronic Acid Complex Microspheres as Carriers for Controlled Release of Bioactive Transforming Growth Factor-β1

Abstract

Chitosan(CH)-polylactide(PLA) copolymers containing varied PLA percentages were synthesized using a group-protection method and one of them with solubility in water-based solvents was used to prepare CH-PLA/hyaluronic acid (HA) complex microspheres for the delivery of transforming growth factor-β1 (TGF-β1). An emulsification processing method was developed for producing TGF-β1-loaded CH-PLA/HA microspheres using sodium tripolyphosphate (TPP) as ionic crosslinker and the size of the microspheres was devised to the micron level in order to achieve high encapsulating efficiency. The encapsulating efficiency, swelling property and release administration of the microspheres could be synergistically regulated by PLA component, the applied TPP dose and the incorporated HA amount. In comparison to CH/HA microspheres, the CH-PLA/HA microspheres had greatly reduced TGF-β1 release rates and were able to administrate the TGF-β1 release at controlled rates over a significant longer period of time. The released TGF-β1 was detected to be bioactive when compared to the free TGF-β1. These results suggest that the presently developed CH-PLA/HA complex microspheres have promising potential in delivering TGF-β1 for cartilage repair applications where the applied TGF-β1 amount in the early stage needs to be low whilst the sustained TGF-β1 release at an appropriate dose in the later stage has to be maintained.

Keywords: chitosan; delivery of bioactive molecules; hyaluronic acid; microspheres; polylactide; transforming growth factor-β1.

Figure 1

Schematic illustration (A) for synthesis of CH-PLA; FTIR spectra (B) of CH and CH-PLA; and ¹H NMR spectra of CH (C) and CH-PLA (D) (PLA content in CH-PLA: 40.7 wt %).

Figure 2

Representative scanning electron microscopy (SEM) micrographs for (A) CH-I; (B) CH/HA-II(b) and (C) CH-PLA/HA-II(b) microspheres (arrows denote the cracked clumps and irregularly shaped beads).

Figure 3

Variations in size-distribution of microspheres in set-one (A) and in set-two (B) (see Table 2 for their compositions).

Figure 4

Release profiles of TGF-β1 from microspheres in set-one (A) and set-two (B) (n = 3).

Figure 5

Percent mink lung cell growth inhibition (A, free TGF-β1 without storing treatment; and B, free TGF-β1 stored in DMEM (dulbecco’s modified eagle medium) at 37 °C for different time intervals changing from 10 to 21 days) of TGF-β1 released from different microspheres during varied periods (n = 3; N.S. no significance; * p < 0.05).