Here, we developed highly sensitive piezoelectric sensors in which flexible membrane components were harmoniously integrated. An electrospun nanofiber mat of poly(vinylidenefluoride-co-trifluoroethylene) was sandwiched between two elastomer sheets with sputtered electrodes as an active layer for piezoelectricity. The developed sensory system was ultrasensitive in response to various microscale mechanical stimuli and able to perceive the corresponding deformation at a resolution of 1 μm. Owing to the highly flexible and resilient properties of the components, the durability of the device was sufficiently stable so that the measuring performance could still be effective under harsh conditions of repetitive stretching and folding. When employing spin-coated thin elastomer films, the thickness of the entire sandwich architecture could be less than 100 μm, thereby achieving sufficient compliance of mechanical deformation to accommodate artery-skin motion of the heart pulse. These skin-attachable film- or sheet-type mechanical sensors with high flexibility are expected to enable various applications in the field of wearable devices, medical monitoring systems, and electronic skin.

A novel hybrid construct was developed by combining aligned fibers (AFs) and random fibers (RFs) to form a scaffolding system. Homogeneous fiber-based structures were fabricated by electrospinning, which produced both random and aligned fiber mats depending on the collection method. The upper part of the scaffold contained an AF layer, which possessed a well-organized configuration that provided uniaxial topographic guidance. For mechanical stability and support, the lower part of the scaffold was composed of an RF layer. Despite the presence of randomly distributed RFs, desirable alignment and differentiation could be achieved in cultured C2C12 myoblasts by controlling the density of AF layer. The fibrous structure of the hybrid scaffold also exhibited high porosity and therefore reasonable permeability. Owing to the structural stability provided by the underlying RFs, the cell-laden fibrous scaffolds were amenable to physical manipulation, such as multilayering. Collectively, the morphological features and manipulable architecture of the developed scaffolds suggest that they would perform well in practical applications.

Despite the usefulness of hydrogels for cell-based bioprinting, the fragility of their resulting constructs has hindered their practical applications in tissue engineering research. Here, we suggest a hybrid integration method based on cell-hydrogel bioprinting that includes alternate layering of flexible nanofiber (NF) sheets. Because the bioprinting was implemented on a nanofibrous surface, the hydrogel-based materials could be printed with enhanced shape resolution compared to printing on a bare hydrogel. Furthermore, the insertion of NF sheets was effective for alleviating the shrinkage distortion of the hydrogel construct, which is inherently generated during the crosslinking process, thereby enhancing shape fidelity throughout the three-dimensional (3D) architecture. In addition to the structural precision, the NF-embedded constructs improved the mechanical properties in terms of compressive strength, modulus, and resilience limit (up to four-fold enhancement). With structural and mechanical supports, we could 3D fabricate complex constructs, including fully opened internal channels, which provided a favorable perfusion condition for cell growth. We confirmed the enhanced bioactivity of the NF-embedded bioprinted construct via cell culture experiments with 80% enhanced proliferation compared to the monolithic one. The synergistic combination of the two flexible materials, NFs and hydrogels, is expected to have extensive applicability in soft tissue engineering.

Three-dimensional (3D) printing, combined with medical imaging technologies, such as computed tomography and magnetic resonance imaging (MRI), has shown a great potential in patient-specific tissue regeneration. Here, we successfully fabricated an ultrathin tubular free-form structure with a wall thickness of several tens of micrometers that is capable of providing sufficient mechanical flexibility. Such a thin geometry cannot easily be achieved by 3D printing alone; therefore, it was realized through a serial combination of processes, including the 3D printing of a sacrificial template, the dip coating of the biomaterial, and the removal of the inner template. We demonstrated the feasibility of this novel tissue engineering construct by conducting bile duct surgery on rabbits. Moving from a rational design based on MRI data to a successful surgical procedure for reconstruction, we confirmed that the presented method of fabricating scaffolds has the potential for use in customized bile duct regeneration. In addition to the specific application presented here, the developed process and scaffold are expected to have universal applicability in other soft-tissue engineering fields, particularly those involving vascular, airway, and abdominal tubular tissues.

We developed a skin-conformal flexible sensor in which three-dimensional (3D) free-form elastomeric sheets were harmoniously integrated with a piezoelectric nanofiber mat. The elastomeric sheets were produced by polydimethylsiloxane (PDMS) molding via using a 3D printed mold assembly, which was adaptively designed from 3D scanned skin surface geometry. The mold assembly, fabricated using a multi-material 3D printer, was composed of a pair of upper/lower mold parts and an interconnecting hinge, with material properties are characterized by different flexibilities. As a result of appropriate deformabilites of the upper mold part and hinge, the skin-conformal PDMS structures were successfully sandwich molded and demolded with good repeatability. An electrospun poly(vinylidene fluoride trifluoroethylene) nanofiber mat was prepared as the piezoelectric active layer and integrated with the 3D elastomeric parts. We confirmed that the highly responsive sensing performances of the 3D integrated sensor were identical to those of a flat sensor in terms of sensitivity and the linearity of the input–output relationship. The close 3D conformal skin contact of the flexible sensor enabled discernable perception of various scales of physical stimuli, such as tactile force and even minute skin deformation caused by the tester’s pulse. Collectively from the 3D scanning design to the practical application, our achievements can potentially meet the needs of tailored human interfaces in the field of wearable devices and human-like robots.