Alessandro Guzzini

The growing importance of non-contact humidity sensors in various industries like healthcare and agriculture gained prominence during the COVID pandemic. This accompanies the demand for sensor technologies to be non-toxic, biocompatible, sustainable and affordable, to reduce environmental impact and e-waste, while not being burdened by an increase in cost. In this study we explored the viability of applying the inkjet technique for sensor fabrication to waste biomaterials, as the technique is efficient, scalable, and adaptable. Our target materials were eumelanin from black soldier flies (BSF-EuM) and keratin (Ker) from feathers of two types: one produced by steam explosion (KerST) and the other by chemical extraction (KerBS). These materials, when mixed together at different relative weight ratios, demonstrate impedance responsiveness to humidity, making them effective for the engineering of impedance-based humidity sensors. Moreover, depending on the application, we found that it was possible to select different ratios of biomaterials, to detect different humidity ranges or customize the response time for the requirements of different humidity-sensing applications. Overall, the best compromise at RT (T=25°C) to gain device homogeneity and the maximum frequency range (1.0 kHz) at the lowest attainable humidity level (RH(%) = 30%) was obtained by mixing BSF-EuM and KerBS at a ratio of BSF-EuM:KerBS = 1:4 in weight. Further experimental findings showcase the sensor’s negligible hysteresis, rapid response times, and competitive performance in comparison to commercial humidity sensors and similar research-based designs. Ultimately, this work aims to contribute to sustainable sensor technology, integrating circular economy principles and enhancing humidity sensing for diverse applications.

The growing demand for increasingly sustainable chemical processes continues to stimulate organic chemistry to develop highly efficient, low-energy-consuming new reactions that require minimal effort to isolate intermediates and produce reduced waste. In this context, two-step reactions play an important role, and a good approach is the two-step synthesis, in which reagents and catalysts or promoters are introduced sequentially. Among these, the Pictet–Spengler-type cyclization (PS) is a powerful stepwise strategy for the synthesis of heterocyclic compounds. This article presents a novel and environmentally friendly two-step strategy for the Pictet–Spengler reaction, employing graphene oxide and Amberlyst 15 as acid promoters that yields a diverse product library (up to 92% yield) without the need for further purification. Both promoters can be reused over multiple reaction cycles, maintaining high efficiency. The methodology demonstrates broad functional group tolerance and provides a sustainable route to various tetrahydro-β-carbolines (THβCs), including biologically relevant compounds, and, above all, avoids negative interference between the two acidic promoters.

This study investigates the effects of repeated mechanical recycling on the structural, thermal, mechanical, and aesthetic properties of poly(butylene succinate) (PBS), a commercially available bio-based and biodegradable aliphatic polyester. PBS production scraps were subjected to five consecutive recycling cycles through semi-industrial extrusion compounding followed by injection molding to simulate realistic mechanical reprocessing conditions. Melt mass-flow rate (MFR) analysis revealed a progressive increase in melt fluidity. Initially, the trend of viscosity followed the melt flow rate; however, increasing the reprocessing number (up to 5) resulted in a partial recovery of viscosity, which was caused by chain branching mechanisms. The phenomenon was also confirmed by data of molecular weight evaluation. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed the thermal stability of the polymer, with minimal shifts in glass transition, crystallization, and degradation temperatures during the reprocessing cycles. Tensile tests revealed a slight reduction in strength and stiffness, but an increase in elongation at break, indicating improved ductility. Impact resistance declined moderately from 8.7 to 7.3 kJ/m² upon reprocessing; however, it exhibited a pronounced reduction to 1.8 kJ/m² at −50 °C, reflecting brittle behavior under sub-ambient conditions. Despite these variations, PBS maintained excellent color stability (ΔE < 1), ensuring aesthetic consistency while retaining good mechanical and thermal properties.

In the framework of the Circular Economy this study provides a detailed analysis of water-based suspensions of two biopolymers derived by sustainable processes: eumelanin from insect farming and keratin from chicken feathers. The latter material was obtained via two different extraction procedures. Colloidal-like suspensions were produced in water either as a single component system or a mixture of both in selected ratios, taking advantage of their high solubility. The suspensions were examined using a comprehensive set of chemical, structural and dielectric techniques to gather information on their properties. Small-Angle x-ray Scattering results provided insights into the elemental polymer sections within the suspension, while Transmission Electron Microscopy images indicate that keratin is the component driving the shape of the aggregation structure in a colloidal environment, and, in some cases, eumelanin internalization. Furthermore, the co-presence of both polymers in water determines the aggregation dimensions and shapes. The discussion focuses on the influence of the aggregation on the dielectric proper-ties by comparing the former to the AC dynamic response returned by Broadband Dielectric Spectroscopy (BDS). Within the BDS framework various items are highlighted including dielectric relaxations, screening effects, counterion condensation and ionic charge transport. The results shown in this work let to foresee the adoption of water or biofriendly aqueous BSF-EuM:Keratin suspensions in the production of devices and sensors with low environmental impact.

Protein gels prepared by keratin extracted from chicken feathers show potential applications as engineered materials. Feathers are an abundant waste material, whose principal component is keratin, which may have gelling properties not yet sufficiently studied so far which are strongly dependent on the extraction method adopted. The aim of the study is to explore the properties of gels obtained through mercaptoethanol extraction and dialysis process and to evaluate their structural characteristics. The keratin hydrogels were characterized with Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy through which it was possible to identify the secondary structure of the protein on hydrated and dry gel. Moreover, the morphological analysis by scanning electron microscopy (SEM) combined with the rheological analysis showed how the consistency of the gels is maintained on a wide range of loads and frequencies. Furthermore, the biocompatibility of the gels was investigated for the release of subcutaneous drugs using curcumin, an antioxidant polyphenol compound. The fastest release was obtained at pH 7.4, corresponding to physiological conditions.

Natural and renewable sources of calcium carbonate (CaCO₃), also referred to as “biogenic” sources, are being increasingly investigated, as they are generated from a number of waste sources, in particular those from the food industry. The first and obvious application of biogenic calcium carbonate is in the production of cement, where CaCO₃ represents the raw material for clinker. Overtime, other more added-value applications have been developed in the filling and modification of the properties of polymer composites, or in the development of biomaterials, where it is possible to transform calcium carbonate into calcium phosphate for the substitution of natural hydroxyapatite. In the majority of cases, the biological structure that is used for obtaining calcium carbonate is reduced to a powder, in which instance the granulometry distribution and the shape of the fragments represent a factor capable of influencing the effect of addition. As a result of this consideration, a number of studies also reflect on the specific characteristics of the different sources of the calcium carbonate obtained, while also referring to the species-dependent biological self-assembly process, which can be defined as a more “biomimetic” approach. In particular, a number of case studies are investigated in more depth, more specifically those involving snail shells, clam shells, mussel shells, oyster shells, eggshells, and cuttlefish bones.

In this work, the characteristic structure of keratin extracted from two different kinds of industrial waste, namely sheep wool and chicken feathers, using the sulfitolysis method to allow film deposition, has been investigated. The structural and microscopic properties have been studied by means of scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), and infrared (IR) spectroscopy. Following this, small-angle X-ray scattering (SAXS) analysis for intermediate filaments has been performed. The results indicate that the assembly character of the fiber can be obtained by using the most suitable extraction method, to respond to hydration, thermal, and redox agents. The amorphous part of the fiber and medium range structure is variously affected by the competition between polar bonds (reversible hydrogen bonds) and disulfide bonds (DB), the covalent irreversible ones, and has been investigated by using fine structural methods such as Raman and SAXS, which have depicted in detail the intermediate filaments of keratin from the two different animal origins. The preservation of the secondary structure of the protein obtained does offer a potential for further application of the waste-obtained keratin in polymer films and, possibly, biocomposites.