Aerogel objects inspired by plant cell wall components and structures were fabricated using extrusion-based 3D printing at cryogenic temperatures. The printing process combines 3D printing with the alignment of rod-shaped nanoparticles through the freeze-casting of aqueous inks. We have named this method direct cryo writing (DCW) as it encompasses in a single processing step traditional directional freeze casting and the spatial fidelity of 3D printing. DCW is demonstrated with inks that are composed of an aqueous mixture of cellulose nanocrystals (CNCs) and xyloglucan (XG), which are the major building blocks of plant cell walls. Rapid fixation of the inks is achieved through tailored rheological properties and controlled directional freezing. Morphological evaluation revealed the role of ice crystal growth in the alignment of CNCs and XG. The structure of the aerogels changed from organized and tubular to disordered and flakey pores with an increase in XG content. The internal structure of the printed objects mimics the structure of various wood species and can therefore be used to create wood-like structures via additive manufacturing technologies using only renewable wood-based materials.

In humans, melanin plays an esthetic role, dictating hair and skin color and traits, while keratin is the protein that comprises most of the epidermis layer. Eumelanin and pheomelanin are types of melanin synthesized from the same building blocks via enzymatic oxidation. Pheomelanin has an additional building block, cysteine amino acid, which affects its final structure. Keratin contains high cysteine content, and by exploiting free thiols in hydrolyzed keratin, we demonstrate the formation of keratin-melanin (KerMel) chromophoric submicron particles. Cryo-TEM analyses found KerMel particle sizes to be 100-300 nm and arranged in the form of a central keratin particle with polymerized l-dopa chains. Attenuated total reflection (ATR)-FTIR, UV-vis, and fluorescence measurements identified new chemical bonds, indicating the formation of KerMel particles. Finally, KerMel replicated natural skin tones and proved cytocompatibility for human epidermal keratinocytes at concentrations below 0.1 mg/mL. Taken together, KerMel is a novel, tunable material that has the potential to integrate into the cosmetic industry.

Second skin is a topically applied, skin-conforming material that mimics human skin properties and bears potential cosmetic and e-skin applications. To successfully integrate with natural skin, characteristics such as color and skin features must be matched. In this work, we prepared bio-based skin-like films from cross-linked keratin/melanin films (KMFs), using a simple fabrication method and non-toxic materials. The films retained their stability in aqueous solutions, showed skin-like mechanical properties, and were homogenous and handleable, with non-granular surfaces and a notable cross-linked structure as determined by attenuated total reflection (ATR). In addition, the combination of keratin and melanin allowed for adjustable tones similar to those of natural human skin. Furthermore, KMFs showed light transmittance and UV-blocking (up to 99%) as a function of melanin content. Finally, keratin/melanin ink (KMI) was used to inkjet-print high-resolution images with natural skin pigmented features. The KMFs and KMI may offer advanced solutions as e-skin or cosmetics platforms.

Inappropriate use of antibiotics is one of the leading causes of the increasing numbers of resistant bacteria strains, resulting in 700,000 deaths worldwide each year. Reducing unnecessary use of antibiotics and choosing the most effective antibiotics instead of broad-spectrum drugs will slow the arms race between germs and humans. Urinary tract infections (UTIs) are among the most common bacterial infections. Currently, accurate diagnosis of UTI requires approximately 48 h from the time of urine sample collection until antibiotic susceptibility test (AST) results. This work presents a rapid bacterial detection device that integrates a centrifuge, microscope, and incubator. Two disposable microfluidic chips were developed. The first chip was designed for bacteria concentration, detection, and medium exchange. A second multi-channel chip was developed for AST. This chip contains superhydrophobic and hydrophilic coatings to ensure liquid separation between the channels without the need for valves. The designed chips supported the detection of E. coli at a concentration as low as 5 × 10³ cells/mL within 5 min and AST in under 2 h. AST was also successfully performed with Klebsiella pneumonia isolated from a human urine sample. In addition, machine-learning-based image recognition was shown to reduce the required time for AST and to provide results within 1 h for E. coli cells. Thus, the BactoSpin device can serve as an efficient and rapid platform for UTI diagnostics and AST.

The quest for novel chromophoric materials with tunable properties to match the natural spectrum of skin tones lacks comprehensive solutions, particularly in harnessing natural proteins for pigment synthesis. This research delved into the synthesis of sub‐micron Keratin‐Cysteine particles inspired by natural pigment production pathways. Adjustment of the initial conditions of the water‐based reaction between keratin, tyrosinase and cysteine, yielded Keratin‐Cysteine particles with colors tunable within the light to intermediate skin tone range. A systematic investigation of the reaction conditions through factorial design of experiment (DOE) identified the sequence of addition of tyrosinase and cysteine as the key determinant of color tone. Ultraviolet‐visible (UV‐Vis) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy and color analysis were performed to elucidate the reaction mechanism. This research presents a promising approach to chromophore synthesis for cosmetic and biomedical applications.

Mimicking accurate skin texture through advanced printing technologies holds significant promise for cosmetic, biomedical, and tissue engineering applications. Inkjet printing offers precise control in fabricating skin‐mimicking materials, with keratin emerging as a key component due to its biocompatibility and structural similarity to natural skin. This study focused on developing keratin‐based inks by optimizing the rheological and surface properties to meet inkjet printing requirements. Sodium alginate served as a thickener, while the surfactants SDS, Tween 20, and Tween 80 were investigated to tailor the surface tension. The optimal formulation, containing 0.2% wt sodium alginate and 0.3% wt SDS and Tween 20, demonstrated good printability with minimal defects. SDS exhibited superior performance in reducing surface tension and enhancing electrostatic stabilization, while Tween 20 contributed steric stabilization. Excessive additive concentrations led to high viscosity and nozzle clogging, emphasizing the need for precise formulation control. The findings address critical challenges in keratin‐based ink and highlight the potential of inkjet printing for creating skin‐mimicking materials. This work lays the groundwork for advances in personalized wound care, tissue engineering, and cosmetic applications, promoting future exploration in keratin‐based ink for printing technologies.