Piezoelectric diphenylalanine peptide nanotubes (PNTs) have recently been demonstrated in energy harvesting applications, typically based on vertically aligned PNTs that generate charge when pressed. In this work, we use a wettability difference and an applied electric field to align PNTs and PNT-based composites on flexible substrates. Open-circuit voltages and short-circuit currents exceeding 6 V and 60 nA, respectively, are achieved by bending the substrate, opening up the use of horizontally aligned PNTs as flexible energy harvesting substrates.

Collagen has emerged as an attractive bioelectronics substrate candidate, given its biological origins as a structural protein found in organisms. Substrates for implantable electronics should be biocompatible and have similar mechanical properties to implant target tissues. Furthermore, the characteristic amino acid sequences in collagen promote cell adhesion, migration, and proliferation, all of which are advantageous when compared to commonly explored cellulose and silk. However, denaturation temperature and swelling in water/vacuum have been fundamental barriers to device fabrication on collagen. It is here described how these problems can be avoided for the fabrication of semiconductor devices on collagen. Transfer printing using a sacrificial layer of germanium oxide is used to fabricate capacitors, transistors, and an integrated inverter transistor circuits on the collagen substrate. The mobility and threshold voltage of the transistors on collagen show only ≈41% and ≈22% drop compared to the ones on rigid silicon substrate. The enzymatic digestion and swelling ratio of collagen can be decreased by 80% and 175%, respectively, via glutaraldehyde cross‐linking, while mechanical stiffness increases by more than 270%. This work demonstrates how collagen can be used as a bioelectronics substrate with tunable properties, thereby expanding its application range from transient to more permanent implantable electronics.

Extruded collagen fibres are a promising platform for tissue engineering applications. Ensuring that the functional properties of the engineered tissues possess similar structural properties as native tissues is important for biomedical applications. Advanced imaging tools including scanning electron microscopy (SEM) and atomic force microscopy (AFM) have revealed the structural features of collagen fibrils within such fibres; however, these techniques often require modification steps that can alter the sample in the process. Here, lateral piezoresponse force microscopy (LPFM), which 2 is sensitive to the polar orientation of piezoelectric collagen fibrils, is demonstrated as a promising tool to assess the width of individual fibrils and moreover map their organisation and polar orientation without altering the sample. Within the fibres studied, the collagen fibrils showed a highly anisotropic arrangement with preferred alignment along the length of the fibre. Fibril widths of 74 ± 18 nm and 73 ± 19 nm in untreated and bleached fibres, respectively, were measured from LPFM amplitude images. These values agreed with values from SEM (70 ± 10 nm) and AFM (71 ± 19 nm) measurements that could only be obtained from bleached fibres.

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