The design of implants for tissue transitions remains a major scientific challenge. This is due to gradients in characteristics that need to be restored. The rotator cuff in the shoulder, with its direct osteo-tendinous junction (enthesis), is a prime example of such a transition. Our approach towards an optimized implant for entheses is based on electrospun fiber mats of poly(ε-caprolactone) (PCL) as biodegradable scaffold material, loaded with biologically active factors. Chitosan/tripolyphosphate (CS/TPP) nanoparticles were used to load transforming growth factor-β₃ (TGF-β₃) with increasing loading concentrations for the regeneration of the cartilage zone within direct entheses. Release experiments were performed, and the concentration of TGF-β₃ in the release medium was determined by ELISA. Chondrogenic differentiation of human mesenchymal stromal cells (MSCs) was analyzed in the presence of released TGF-β₃. The amount of released TGF-β₃ increased with the use of higher loading concentrations. This correlated with larger cell pellets and an increase in chondrogenic marker genes (SOX9, COL2A1, COMP). These data were further supported by an increase in the glycosaminoglycan (GAG)-to-DNA ratio of the cell pellets. The results demonstrate an increase in the total release of TGF-β₃ by loading higher concentrations to the implant, which led to the desired biological effect.

Implant‐integrated drug delivery systems that enable the release of biologically active factors can be part of an in situ tissue engineering approach to restore biological function. Implants can be functionalized with drug‐loaded nanoparticles through a layer‐by‐layer assembly. Such coatings can release biologically active levels of growth factors. Sustained release is desired for many in vivo applications. The layer‐by‐layer technique also allows for the addition of extra layers, which can serve as “barriers” to delay the release. Electrospun Polycaprolactone (PCL) fiber mats are modified with a Chitosan (CS) grafted with PCL sidechains (CS‐g‐PCL₂₄) and coated with transforming growth factor beta 3 (TGF‐β₃) loaded Chitosan/tripolyphosphate nanoparticles as a drug delivery system. Additional layers including polystyrene sulfonate, alginate, carboxymethyl cellulose, and liposomes (phosphatidylcholine) are applied. Streaming potential and X‐ray photoelectron spectroscopy (XPS) measurements indicated a strong interpenetration of the chitosan and polyanion layers, while liposomes formed separate layers, which are more promising for sustained release. All samples release TGF‐β₃ at different cumulative levels without altering release kinetics. Variations in layer structure, interpenetration, and stability depending on the chitosan used are observed, which ultimately has minimal impact on the release kinetics. Polyelectrolyte layers strongly interpenetrated the active layers and therefore do not act as effective diffusion barriers, while the liposome layer, though separated, lacked sufficient stability.