Soft pneumatic actuators for wearable systems: a structural classification and integration-oriented evaluation

Soft pneumatic actuators promise gentle, body-safe assistance, yet many fail at the moment of integration: inflation alters geometry, increases profile, and stresses seams and ports. This topical review reframes actuator selection through a structure-first lens that links how an actuator is built to how it deforms and how it embeds in garments. Actuators are classified by structural architecture, deformation behavior, and fabrication method, and evaluated against four integration criteria central to wearable systems: geometric compatibility, fabrication scalability, system integration readiness, and actuation simplicity. A staged selection pathway is proposed and presented as a literature-informed mapping table that links reported wearable application contexts to dominant integration priorities and a practical structural-class starting point. Planar sheet designs can preserve a thin, predictable pressurized envelope at modest pressures when seam paths, constraint layers, and attachment features are co-designed. Pouch and bladder actuators are thin at rest, simple to fabricate, and readily integrated with textiles, but commonly bulge under load without external constraint; envelope control and port or manifold routing frequently limit garment integration. Fiber-constrained actuators deliver high specific force but often require rigid end terminations and elevated pressures. Segmented elastomers provide rich kinematics through chamber layout while tending toward bulging and routing burden in multi-segment formats. Mechanical metamaterials realize geometry-programmed motion when hinge fidelity and pattern alignment are maintained; durability of compliant joints and consistent crease formation set current limits. The resulting synthesis identifies practical priorities for wearable use: preserve thin profiles under load, embed stitchable or bondable attachment features, document reproducible process windows, minimize dead volume, routing, and valve count with compact pneumatic architectures, and target low-pressure operation compatible with lightweight hardware. Framing integration in structural terms standardizes comparison across actuator classes, clarifies the narrow feasible design space for compact, body-conforming devices, and supports deliberate actuator choice for biomedical wearables.