## 1 Introduction
In the last few years, a number of innovative strategies have been proposed for eardrum replacement and repair, including tissue engineering approaches, 3D-printed eardrums, growth factor injection, and stem cell therapy [17; 18; 19; 20; 21; 22]. From a tissue engineering perspective, three pillars are needed: biomaterials in the form of porous scaffold (usually polymer-based), cells (usually, stem cells), and stimuli (e.g., chemical, mechanical and topographical). Among the many bioresorbable polymers available for tissue engineering scaffolding, star-branched polymers offer novel interesting options. They are made up by several linear polymeric chains centered in a small core unit; as such, their properties may greatly differ from those of their purely linear counterparts with the same molecular weight. The key advantages of star-polymers are their small size, compactness, and 3D structure, which ultimately affect viscosity and large possibilityof functionalization through chain ends [23]. In particular, due to reduced hydrodynamic volume, leading to strong chain entanglement, star-branched poly(\(\varepsilon\)-caprolactone) (*PCL) was found suitable for the electrospinning process [24; 25]. Electrospinning is a nanotechnology platform to produce nonwovens, with fiber size ranging from tens of nanometers up to a few microns, which complies with the dimensions of the protein fibers and fiber bundles present in the connective tissue, such as collagens [26]. Recent strategies of TM tissue engineering have focused on autologous approaches, stressing the use of undifferentiated cell sources, like mesenchymal stem (or stromal) cells (MSCs) [19; 27]. MSCs isolated from the bone marrow have been processed in vitro towards many mature lineages of connective tissue, including fibroblasts, which hold importance for tendon and ligament regeneration [28]. It is widely known that human MSCs (hMSCs) can express collagen type II gene and protein under chondrogenic differentiation [29]. Dynamic culture systems based on bioreactors have been developed for mechanically responsive tissues (e.g., bone) and have shown interesting benefits [30]: they increase cell viability and scaffold spatial colonization due to the damping of mass transfer limitation in vitro, which represents a crucial issue for metabolically active tissues in the absence of blood supply. Additionally, dynamic cultures of tissue engineered constructs containing differentiating MSCs resulted in an enhanced cell maturation, as a direct consequence of the mechanical stimuli; finally, the spatial orientation of cells and extracellular matrix (ECM) components have been strongly related to applied stresses. In a previous study, we proposed electrospun poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) nonwovens, as scaffolds for eardrum regeneration, which were cultured with hMSCs in a TM bioreactor (WO/2015/040554) under non-differentiating conditions, demonstrating increased cell viability and penetration in the mesh thickness [27]. This study aims at the in vitro regeneration of a connective-like tissue mimicking the collagen types of the _lamina propria_ of the _pars tensa_ in a human TM. We used a tissue engineering approach, consisting of (i) a fibrous bioresorbable polymer scaffold; (ii) hMSCs; and (iii) biochemical, physical, and mechanical stimuli to differentiate hMSCs into fibroblasts synthetizing TM-like collagens. The mechanical stimuli are given via a TM bioreactor (WO/2015/040554) able to generate a hydrodynamic pressure and a tangential stress field in a membrane, thus inducing circular and radial strains during hMSC differentiation. Such a stress/deformation field aims to mimic the circular and radial patterns found in TM collagen fibers, thus inducing a physical stimulation over the cells at the scaffold interface.