Ordered and kinetically discrete sequential protein release from biodegradable thin films

Abstract

Multidrug regimens can sometimes treat recalcitrant diseases when single-drug therapies fail. Recapitulating complex multidrug administration from controlled release films for localized delivery remains challenging because their release kinetics are frequently intertwined, and an initial burst release of each drug is usually uncontrollable. Kinetic control over protein release is demonstrated by cross-linking layer-by-layer films during the assembly process. We used biodegradable and naturally derived components and relied on copper-free click chemistry for bioorthogonal covalent cross-links throughout the film that entrap but do not modify the embedded protein. We found that this strategy restricted the interdiffusion of protein while maintaining its activity. By depositing a barrier layer and a second protein-containing layer atop this construct, we generated well-defined sequential protein release with minimal overlap that follows their spatial distribution within the film.

Keywords: click chemistry; controlled release; drug delivery; polyelectrolyte multilayers; staged release.

Figure 1

Illustration of the proposed assembly and degradation process of multilayer films without (upper panel) and with (lower panel) crosslinking, where the therapeutic (green spheres) is loaded into films composed of polycations (blue) and degradable polyanions (red). Each film undergoes typical LbL film assembly (A), however those films with crosslinking retain their stratified structure while non-crosslinked films are highly interdiffused (B). Surface erosion either degrades a blended film where the therapeutic is distributed throughout the film, or a stratified film with the therapeutic sequestered to where it was deposited (C). The release profiles reflect the effect of crosslinking, and hence interdiffusion, on kinetics of drug release (D).

Figure 2

Depth profiling XPS analysis of sulfur content using a C60⁺ ion bombardment of Lys ^x-linked + 20 Barrier Layer Films. Stacked spectra in the S2p region after 1, 20, 40, 50, 60, and 80 cycles corresponding to probe depths of approximately 7 nm, 131 nm, 263 nm, 328 nm, 394 nm, and 525 nm, respectively (A). Integrated S_2p area counts after every sputter cycle is shown as a function of probe depth from the film surface (B).

Figure 3

The effect of crosslinking and barrier layer thickness on the lysozyme release (a) and rate of fractional lysozyme release (b) into PBS, pH 7.4 at 37°C.

Figure 4

Characteristics of sequential release from composite multilayer films with a schematic view of the proposed film architecture and surface-based erosion (A). Protein release profiles (B) and their rates of fractional release (C) into PBS, pH 7.4 at 37°C.

Scheme 1

Chemical structures of poly(β-L-malic acid) (PMLA) and its derivatives functionalized with an azide moiety (PMLA-Az) and dibenzocyclooctyne moiety (PMLA-DBCO).