Modular assembly of layer-by-layer capsules with tailored degradation profiles

Herein we report the preparation of layer-by-layer (LbL) assembled, biodegradable, covalently stabilized capsules with tunable degradation properties. Poly(L-glutamic acid) modified with alkyne moieties (PGA(Alk)) was alternately assembled with poly(N-vinyl pyrrolidone) (PVPON) on silica particles via hydrogen-bonding. The films were cross-linked with a bis-azide linker, followed by removal of the sacrificial template and PVPON at physiological pH through hydrogen bond disruption, yielding one-component PGA(Alk) capsules. To control the kinetics and location of capsule degradation, a number of approaches were investigated. First, a degradable bis-azide cross-linker was incorporated into the inherently enzymatically degradable capsules. Second, we assembled low-fouling capsules composed of nondegradable poly(N-vinyl pyrrolidone-ran-propargyl acrylate) (PVPON(Alk)) via hydrogen bonding with poly(methacrylic acid) (PMA) and combined this with the aforementioned system (PGA(Alk)/PVPON) to produce stratified hybrid capsules. The degradation profiles of these stratified capsules can be closely controlled by the number as well as the position of nondegradable barrier layers in the systems. The facile tailoring of the degradation kinetics makes this stratified LbL approach promising for the design of tailored drug-delivery vehicles.