Freeze-thaw cycles for biocompatible, mechanically robust scaffolds of human hair keratins

A facile method to fabricate versatile keratin cryogels for tissue engineering applications

Human hair keratin (HHK) has been extensively explored as a biomaterial for soft tissue regeneration due to their excellent bioactivity and biocompatibility. The possibility to fabricate HHK into three-dimensional (3D) hydrogels with physical properties resembling soft tissues has been well demonstrated. However, conventional keratin hydrogels often exhibit a dense architecture that could hinder cell filtration. In the present study, HHK-based cryogels were fabricated using a freeze-thaw (FT) method, where oxidized dopamine (ODA) was employed to covalently crosslink thiol/amine rich-keratin molecules at sub-zero temperatures. The obtained HHK-ODA cryogels have micron-sized pores ranging between 100 and 200 μm and mechanical properties that can be tuned by varying the crosslinking density between ODA and HHK. Through optimization of the weight content of ODA and the number of FT cycles, the compressive strengths and stiffnesses of these cryogels achieved 15-fold increments from ∼1.5 kPa to ∼22 kPa and ∼300 Pa to ∼5000 Pa, respectively. The HHK-ODA cryogels competently supported human dermal fibroblast spreading and proliferation. Overall, this study exhibited a facile method to fabricate mechanically superior keratin-based cryogels with cell compatible microarchitecture, circumventing the need for complicated chemical modifications and the use of cytotoxic crosslinkers.

Novel Apparatuses for Incorporating Natural Selection Processes into Origins-of-Life Experiments to Produce Adaptively Evolving Chemical Ecosystems

Origins-of-life chemical experiments usually aim to produce specific chemical end-products such as amino acids, nucleic acids or sugars. The resulting chemical systems do not evolve or adapt because they lack natural selection processes. We have modified Miller origins-of-life apparatuses to incorporate several natural, prebiotic physicochemical selection factors that can be tested individually or in tandem: freezing-thawing cycles; drying-wetting cycles; ultraviolet light-dark cycles; and catalytic surfaces such as clays or minerals. Each process is already known to drive important origins-of-life chemical reactions such as the production of peptides and synthesis of nucleic acid bases and each can also destroy various reactants and products, resulting selection within the chemical system. No previous apparatus has permitted all of these selection processes to work together. Continuous synthesis and selection of products can be carried out over many months because the apparatuses can be re-gassed. Thus, long-term chemical evolution of chemical ecosystems under various combinations of natural selection may be explored for the first time. We argue that it is time to begin experimenting with the long-term effects of such prebiotic natural selection processes because they may have aided biotic life to emerge by taming the combinatorial chemical explosion that results from unbounded chemical syntheses.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing-thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Biocompatible, Antioxidant Nanoparticles Prepared from Natural Renewable Tea Polyphenols and Human Hair Keratins for Cell Protection and Anti-inflammation

Excessive reactive oxygen species (ROS) can cause oxidative stress of tissues and adversely influence homeostasis of the body. Epigallocatechin gallate (EGCG) with an antioxidative effect can effectively eliminate the ROS, but an evident weakness associated with it is the relatively poor cytocompatibility. Combining with other biomacromolecules such as human hair keratin (KE) and using nanotechnology to prepare nanoparticles can improve this situation. By covalent bonding, we assembled KE and EGCG into KE-EGCG nanoparticles (NANO) with size of about 50 nm and characterized them by DLS, UV, FTIR, NMR, and XPS. Free radical scavenging experiments show that antioxidant properties of the obtained NANO are superior to that of vitamin C. Cell culture experiments also show that the NANO can effectively protect the proliferation of L929 cells and HUVEC cells. In addition, we also used RAW264.7 cells to establish a H₂O₂-induced cell injury model and an lipopolysaccharide-induced cellular inflammatory model to evaluate the antioxidant and anti-inflammatory properties of NANO. The results show that the NANO can effectively prevent cells from oxidative damage and reduce inflammatory expression of the cells, indicating that the NANO have a good antioxidative and anti-inflammatory effect on cells which can be applied to many diseases related to oxidative stress.

Preparation of PEG-modified wool keratin/sodium alginate porous scaffolds with elasticity recovery and good biocompatibility

To improve mechanical properties of keratin (KR) porous scaffolds, we prepared a PEGylated keratin through thiol-ene click reaction. Several porous scaffolds were prepared by blending PEGylated keratin with sodium alginate (SA). The surface morphology, mechanical properties, and porosity of scaffolds were detailed studied at different KR/SA proportions. The results showed the content of SA had an effect on pore formation and mechanical properties. When the mass ratio of KR to SA was 2:1, the stress of yield point of the keratin porous scaffold reached 1.24 MPa, and also showed good deformation recovery ability. The PEGylated keratin porous scaffold had a high porosity and great cytocompatibility. Its' porosity is up to 81.7% and the cell viability is about 117.78%. This allows it to absorb the simulated plasma quickly (9.20 ± 0.37 g/g). In addition, the structural stability and acid-base stability of the keratin porous scaffold were also improved after PEGylation. Overall, the PEGylated keratin porous scaffold will be promising in tissue materials due to its great physical, chemical, and biological properties.

Hierarchical porosity in additively manufactured bioengineering scaffolds: Fabrication & characterisation

Biomedical scaffolds with a high degree of porosity are known to facilitate the growth of healthy functioning tissues. In this study, scaffolds with hierarchical porosity are manufactured and their mechanical and thermal properties are characterised. Multi-scale porosity is achieved in scaffolds fabricated by Fused Deposition Modelling (FDM) in a novel way. Random intrinsic porosity at micron length scale obtained from particulate leaching is combined with the structured extrinsic porosity at millimeter length scales afforded by controlling the spacing between the struts. Polylactic acid (PLA) is blended with Polyvinyl alcohol (PVA) and an inorganic sacrificial phase, sodium chloride (NaCl), to produce pores at length scales of up to two orders of magnitude smaller than the inter-filament voids within 3D printed lattices. The specific elastic modulus and specific strength are maximised by optimising the polymer blends. The porosity level and pore size distribution of the foamy filaments within lattices are quantified statistically. Compression tests are performed on the porous samples and the observed mechanical response is attributed to the microstructure and density. Simple cellular solid models that possess power law are used to explain the measured trends and the dependence is associated with various mechanisms of elastic deformation of the cell walls. The relationship between pore architecture, pore connectivity, the blend material composition, and mechanical response of produced foams is brought out. Foams obtained using the PLA:PVA:NaCl 42%-18%-40% material blends show relatively high specific elastic modulus, specific strength and strain at failure. A quadratic power law relating the Young's modulus with the relative density is experimentally obtained, which is consistent with theoretical models for open-cell foams. 3D printing with blends, followed by leaching, produces structures with cumulative intrinsic and extrinsic porosity as high as 80%, in addition to good mechanical integrity.

Hair keratin promotes wound healing in rats with combined radiation-wound injury

Keratins derived from human hair have been suggested to be particularly effective in general surgical wound healing. However, the healing of a combined radiation-wound injury is a multifaceted regenerative process. Here, hydrogels fabricated with human hair keratins were used to test the wound healing effects on rats suffering from combined radiation-wound injuries. Briefly, the keratin extracts were verified by dodecyl sulfate polyacrylamide gel electrophoresis analysis and amino acid analysis, and the keratin hydrogels were then characterized by morphological observation, Fourier transform infrared spectroscopy analysis and rheology analyses. The results of the cell viability assay indicated that the keratin hydrogels could enhance cell growth after radiation exposure. Furthermore, keratin hydrogels could accelerate wound repair and improve the survival rate in vivo. The results demonstrate that keratin hydrogels possess a strong ability to accelerate the repair of a combined radiation-wound injury, which opens up new tissue regeneration applications for keratins.