Nanostructures formed by self-assembled peptides have been increasingly exploited as functional materials for a wide variety of applications, from biotechnology to energy. However, it is sometimes challenging to assemble free short peptides into functional supramolecular structures, since not all peptides have the ability to self-assemble. Here, we report a self-assembly mechanism for short functional peptides that we derived from a class of fiber-forming amyloid proteins called curli. CsgA, the major subunit of curli fibers, is a self-assembling β-helical subunit composed of five pseudorepeats (R1–R5). We first deleted the internal repeats (R2, R3, R4), known to be less essential for the aggregation of CsgA monomers into fibers, forming a truncated CsgA variant (R1/R5). As a proof-of-concept to introduce functionality in the fibers, we then genetically substituted the internal repeats by a hydroxyapatite (HAP)-binding peptide, resulting in a R1/HAP/R5 construct. Our method thus utilizes the R1/R5-driven self-assembly mechanism to assemble the HAP-binding peptide and form hydrogel-like materials in macroscopic quantities suitable for biomineralization. We confirmed the expression and fibrillar morphology of the truncated and HAP-containing curli-like amyloid fibers. X-ray diffraction and TEM showed the functionality of the HAP-binding peptide for mineralization and formation of nanocrystalline HAP. Overall, we show that fusion to the R1 and R5 repeats of CsgA enables the self-assembly of functional peptides into micron long fibers. Further, the mineral-templating ability that the R1/HAP/R5 fibers possesses opens up broader applications for curli proteins in the tissue engineering and biomaterials fields.

Traditional antibacterial dressings continuously elute biocides, even if there are no bacteria. This unneeded release can cause cytotoxicity, increase costs, and delay healing. We designed a bacteria-responsive nanofibrous wound dressing, which can be degraded in the presence of bacteria to release antimicrobial agents. A model biocide, benzyl dimethyl tetradecyl ammonium chloride (BTAC), was incorporated into bacteria-degradable polymers [polycaprolactone and poly(ethylene succinate)] in two ways: evenly distributed inside the polymers as single nanofibers and encapsulated in a core surrounded by the same polymers as core–shell nanofibers. Because of bacterial activity (both lipase secretion and acidic pH), degradation of the fibers was facilitated and caused the release of incorporated BTAC. BTAC-loaded single and core−shell nanofibers presented >1 log reduction of both Staphylococcus aureus and Escherichia coli within 2 h. Additionally, the core–shell structure provided a more controlled release of BTAC with prolonged antibacterial properties than single nanofibers. The core–shell nanofibers also exhibited minimal cytotoxicity against human fibroblast cells (>80% viable cells after 24 h contact). These nanofibrous mats have the potential to selectively release antibacterial agents to prevent wound infections without delaying wound healing.

Wearable pH sensors are useful tools in the healthcare and fitness industries, allowing consumers to access information related to their health in a convenient manner via the monitoring of body fluids. In this work, we tailored novel protein-textile composites to fluorescently respond to changing pH. To do so, we used amyloid curli fibers, a key component in the extracellular matrix of Escherichia coli, as genetic scaffold to fuse a pH-responsive fluorescent protein, pHuji. Engineered amyloids form macroscopic and environmentally resistant aggregates that we isolated to use as stand-alone hydrogel-based sensors, and that we trapped within textile matrices to create responsive biocomposites. We showed that these composites were mechanically robust and vapor-permeable, thus exhibiting favorable characteristics for wearable platforms. CsgA-pHuji fibers integrated in the textile allowed the final device to respond to pH changes and distinguish between alkaline and acidic solutions. We demonstrated that the resulting composites could sustain their fluorescence response over days, and that their sensing ability was reversible for at least 10 high/low pH cycles, highlighting their potential for continuous monitoring. Overall, we introduced a biosynthesized amyloid-based textile composite that could be used as biosensing patch for a variety of applications in the smart textile industry. Epidermal pH is an effective biomarker for preliminary detection of skin-related ailments such as dermatitis, acne and other bacterial and fungal infections 1. The pH of healthy skin is slightly acidic (pH 4-6.5) due to the presence of an 'acid mantle' , a protective barrier against harsh environmental stresses and invasive organisms 2. Low epidermal pH also promotes vital physiological processes in the skin, including but not limited to, antimicrobial defense, periodic skin differentiation and shedding 3. Monitoring changes in epidermal pH is therefore an essential aspect of skincare and dermatological diagnostics. Wearable sensors that can be directly mounted onto one's body to detect and respond to the physiological status of the wearer's skin are making diagnostic data more accessible 4. Irrespective of their final application, wearable devices are ideally designed to be flexible (in order to blend seamlessly with movements of the body), tunable (to detect diverse physiological signals) and biocompatible 5. However, most platforms for pH sensing currently employ electrodes or organic dyes to detect pH electrochemically or optically 6-9. Using electrodes limits the mechanical flexibility of the system, renders the device sensitive to background motion, and often requires multistep chemical functionalization processes 10. Dyes used in wearable sensors face a major issue of not being easily tunable-requiring complex chemical modifications to detect and bind new analytes. To prevent leaching out from sensors during use, devices often incorporate rigid substrates that are less likely to disintegrate in contact with solvents or diverse chem...

Salinomycin is an antibiotic that has recently been introduced as a novel and effective anti-cancer drug. In this study, PLGA nanofibers (NFs) containing salinomycin (Sali) were fabricated by electrospinning for the first time. The biodegradable PLGA NFs had stability for approximately 30 days and exhibited a sustained release of the drug for at least a 2-week period. Cytotoxicity of the NFs + Sali was evaluated on human glioblastoma U-251 cells and more than 50% of the treated cells showed apoptosis in 48 h. Moreover, NFs + Sali was effective to induce intracellular reactive oxygen species (ROS) leading to cell apoptosis. Gene expression studies also revealed the capability of the NFs + Sali to upregulate tumor suppressor Rbl1 and Rbl2 as well as Caspase 3 while decreasing Wnt signaling pathway. In general, the results indicated anti-tumor activity of the Sali-loaded NFs suggesting their potential applications as implantable drug delivery systems in the brain upon surgical resection of the tumor.

Poly­(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) is a highly conductive, easily processable, self-healing polymer. It has been shown to be useful in bioelectronic applications, for instance, as a biointerfacing layer for studying brain activity, in biosensitive transistors, and in wearable biosensors. A green and biofriendly method for improving the mechanical properties, biocompatibility, and stability of PEDOT:PSS involves mixing the polymer with a biopolymer. Via structural changes and interactions with PEDOT:PSS, biopolymers have the potential to improve the self-healing ability, flexibility, and electrical conductivity of the composite. In this work, we fabricated novel protein–polymer multifunctional composites by mixing PEDOT:PSS with genetically programmable amyloid curli fibers produced byEscherichia coli bacteria. Curli fibers are among the stiffest protein polymers and, once isolated from bacterial biofilms, can form plastic-like thin films that heal with the addition of water. Curli-PEDOT:PSS composites containing 60% curli fibers exhibited a conductivity 4.5-fold higher than that of pristine PEDOT:PSS. The curli fibers imbued the biocomposites with an immediate water-induced self-healing ability. Further, the addition of curli fibers lowered the Young’s and shear moduli of the composites, improving their compatibility for tissue-interfacing applications. Lastly, we showed that genetically engineered fluorescent curli fibers retained their ability to fluoresce within curli-PEDOT:PSS composites. Curli fibers thus allow to modulate a range of properties in conductive PEDOT:PSS composites, broadening the applications of this polymer in biointerfaces and bioelectronics.