Calcium-Triggered Pulsatile Delivery of Parathyroid Hormone from Microbeads for Osteoporosis Treatment

Recombinant human parathyroid hormone 1-34 (rhPTH 1-34) is the most potent anabolic drug recommended for patients with osteoporosis who do not respond to conventional treatment. However, subcutaneous intermittent injection is the only effective regimen due to its unusual action of mechanism. This regimen is inconvenient and is a big hurdle in clinical applications. In this study, we designed polyelectrolyte microbeads that can deliver rhPTH 1-34 in response to Ca²⁺ concentration, which indicates the osteoporotic status. Dextran photopolymer was synthesized, mixed with anionic monoacrylate, and photopolymerized by passing through capillary microfluidics to obtain the microbeads. The anionic property of microbeads was confirmed by toluidine blue staining. One microbead, loaded with a 1 day dose of rhPTH 1-34 (23.4 ± 0.9 μg), released rhPTH 1-34 in a triggered manner following the addition of Ca²⁺ ion. In vitro cell study demonstrated that rhPTH 1-34 released in a pulsatile manner from the microbeads induced osteogenic markers (ALP, RUNX2, and OPN) and precipitated mineral disposition more effectively.