Liposomal aggregates sustain the release of rapamycin and protect cartilage from friction
Fibrosis, low-grade inflammation, and increased friction are together with degradation of cartilage key culprits for debilitating pain in osteoarthritis (OA), which is one of the most common chronic diseases of todays aging population. Intraarticular administration of bio-lubricants loaded with a pharmaceutically active component recently showed promise to improve therapy. Liposomes have emerged as exceptional lubricant biomaterial, but their small size leads to rapid clearance from the synovium, causing a need for more frequent administration. We recently developed a liposomal drug delivery system based on aggregation of negatively charged liposomes with physiologically present divalent cations. Here, we expanded our platform by replacing calcium with zinc, reported to exert anti-inflammatory action. The liposomal aggregates extend the release of rapamycin (RAPA) beyond the free liposomes and have a diameter of nearly 100 m, which was previously established to improve retention in synovial joints. Electron microscopy showed that RAPA alters the irregular morphology of liposomal clusters, which are irreversible upon dilution. RAPA recently showed great promise both in vitro and in vivo at protecting the joints from inflammation and cartilage from further degradation. Our study adds to this by showing that RAPA is also able to dampen the fibrotic response in human OA synovial fibroblasts. Finally, the tribological properties were assessed on nano- and macro-scales on silicon surface and ex vivo porcine cartilage, which showed an excellent protective ability of the system against friction on both scales. Taken together, our study shows that liposomal aggregates have the potential of improving local OA therapy.