Polymer Microneedles for Localized Drug Delivery in Musculoskeletal Tissue Regeneration

Musculoskeletal (MSK) disorders—osteoporosis, osteoarthritis, rheumatoid arthritis, intervertebral disc degeneration, tendinopathy, and skeletal muscle injury—contribute the largest share of years lived with disability worldwide. Conventional therapy relies on systemic dosing or repeated intra-articular and peri-tissue injections, which suffer from off-target toxicity, poor lesional bioavailability, and low adherence. Polymer microneedles (MNs)—micron-scale projections of biodegradable, dissolving, hydrogel-forming, or composite polymers—have rapidly matured into a versatile platform for minimally invasive, spatially localized, and temporally programmable delivery of small molecules, biologics, nucleic acids, extracellular vesicles, and cells to MSK tissues. This review synthesizes 2018–2026 advances in polymer MN systems engineered specifically for MSK regeneration. We classify dominant polymer chemistries and MN architectures; map fit-for-purpose across bone, cartilage, joint, intervertebral disc, tendon, and skeletal muscle; and survey “smart” MN designs that exploit reactive oxygen species, pH, mechanical, triboelectric, optogenetic, and ultrasonic triggers. We close with a concise conclusion and forward perspective that identifies the key design levers—hybrid MN–scaffold combination products, stimuli-responsive platforms tuned to the MSK micro-environment, and cell- and EV-loaded formats—most likely to have clinical impact.