Self-Assembling Chimeric Protein for the Construction of Biodegradable Hydrogels Capable of Interaction with Integrins Expressed on Neural Stem/Progenitor Cells

Smart bio-gel optofluidic Mach-Zehnder interferometers multiphoton-lithographically customized with chemo-mechanical-opto transduction and bio-triggered degradation

Stimulus-responsive optical polymers, especially gels, are enabling new-concept energy-transducing "smart" optics. Full exploitation of their molecule-derived tuning and integration with traditional micro/nano-optics/optoelectronics rely on the implementation of devices by advanced "intelligent" micro/nano-manufacturing technologies, especially photolithographies with wide compatibility. In light of the increasing need for an organic combination of smart optical materials and digital micro/nano-manufacturing, novel "smart" optical micro-switches, namely, stimulus-actuated Mach-Zehnder interferometers as a proof-of-concept demonstration, were prototyped with protein-based hydrogels via aqueous multiphoton femtosecond laser direct writing (FsLDW). Protein-based Mach-Zehnder-interferometric smart optical devices here display a morphological quality sufficient for optical applications (average surface roughness ≤∼20 nm), nano-precision three-dimensional (3D) geometry of these millimeter-scale devices and purposely structured distribution of photo-crosslinking degree. Moreover, the device configuration was customized with unbalanced branches in which meticulous stimulus-responsive ability can be realized by simply tuning the surrounding chemical stimuli (i.e., Na₂SO₄ concentration here). The "heterogeneous" configuration with unbalanced branches (i.e., different optical and stimulus-responsive features) exhibits as-designed "smart" switching of propagated near-infrared light (∼808 nm). These capabilities, along with total biodegradation, indicate the application promise of this gel-based optic construction strategy towards novel "intelligent", bio/eco-friendly, self-tuning or sensing photonic integrated systems like optofluidics.

Advances in Tissue Engineering and Innovative Fabrication Techniques for 3-D-Structures: Translational Applications in Neurodegenerative Diseases

In the field of regenerative medicine applied to neurodegenerative diseases, one of the most important challenges is the obtainment of innovative scaffolds aimed at improving the development of new frontiers in stem-cell therapy. In recent years, additive manufacturing techniques have gained more and more relevance proving the great potential of the fabrication of precision 3-D scaffolds. In this review, recent advances in additive manufacturing techniques are presented and discussed, with an overview on stimulus-triggered approaches, such as 3-D Printing and laser-based techniques, and deposition-based approaches. Innovative 3-D bioprinting techniques, which allow the production of cell/molecule-laden scaffolds, are becoming a promising frontier in disease modelling and therapy. In this context, the specific biomaterial, stiffness, precise geometrical patterns, and structural properties are to be considered of great relevance for their subsequent translational applications. Moreover, this work reports numerous recent advances in neural diseases modelling and specifically focuses on pre-clinical and clinical translation for scaffolding technology in multiple neurodegenerative diseases.

Hydrogel-assisted neuroregeneration approaches towards brain injury therapy: A state-of-the-art review

Recent years have witnessed the development of an enormous variety of hydrogel-based systems for neuroregeneration. Formed from hydrophilic polymers and comprised of up to 90% of water, these three-dimensional networks are promising tools for brain tissue regeneration. They can assist structural and functional restoration of damaged tissues by providing mechanical support and navigating cell fate. Hydrogels also show the potential for brain injury therapy due to their broadly tunable physical, chemical, and biological properties. Hydrogel polymers, which have been extensively implemented in recent brain injury repair studies, include hyaluronic acid, collagen type I, alginate, chitosan, methylcellulose, Matrigel, fibrin, gellan gum, self-assembling peptides and proteins, poly(ethylene glycol), methacrylates, and methacrylamides. When viewed as tools for neuroregeneration, hydrogels can be divided into: (1) hydrogels suitable for brain injury therapy, (2) hydrogels that do not meet basic therapeutic requirements and (3) promising hydrogels which meet the criteria for further investigations. Our analysis shows that fibrin, collagen I and self-assembling peptide-based hydrogels display very attractive properties for neuroregeneration.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Hydrogels from feather keratin show higher viscoelastic properties and cell proliferation than those from hair and wool keratins

Hydrogel prepared from keratin shows potential applications in tissue engineering. However, the importance of the keratin sources has not been considered. The objectives of this study were to characterize and compare the rheological (storage modulus), physical (porosity, pore size, swelling capacity, and water contact angle) and in vitro cell compatibility of hydrogel scaffolds prepared from various keratin sources. Keratins were characterized by means of their molecular weight, amino acid composition, thermal and conformational properties. Hydrogels from chicken feather keratins demonstrated substantially higher storage modulus (G') than hair and wool keratin hydrogels. However, higher swelling capacity (>3000%) was determined in hair and wool over feather keratin (1500%) hydrogels. Our results suggest that small molecular weight and β-sheet conformation of feather keratin (~10 kDa) facilitated the self-assembly of rigid hydrogels through disulfide bond re-oxidation. Whereas, high molecular weight (10-75 kDa) stretchable α-helix conformation in hair and wool keratins resulted in weaker hydrogels. The cell cultures using fibroblasts showed the highest proliferation rate on chicken feather keratin hydrogel scaffolds. After 15 days of culture, partial breakdown of keratin fibers was observed. Results indicate that stiffer avian keratins can be used to fabricate more mechanically robust biomaterials than mammalian keratins.

Multidisciplinary Perspectives for Alzheimer's and Parkinson's Diseases: Hydrogels for Protein Delivery and Cell-Based Drug Delivery as Therapeutic Strategies

This review presents two intriguing multidisciplinary strategies that might make the difference in the treatment of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. The first proposed strategy is based on the controlled delivery of recombinant proteins known to play a key role in these neurodegenerative disorders that are released in situ by optimized polymer-based systems. The second strategy is the use of engineered cells, encapsulated and delivered in situ by suitable polymer-based systems, that act as drug reservoirs and allow the delivery of selected molecules to be used in the treatment of Alzheimer's and Parkinson's diseases. In both these scenarios, the design and development of optimized polymer-based drug delivery and cell housing systems for central nervous system applications represent a key requirement. Materials science provides suitable hydrogel-based tools to be optimized together with suitably designed recombinant proteins or drug delivering-cells that, once in situ, can provide an effective treatment for these neurodegenerative disorders. In this scenario, only interdisciplinary research that fully integrates biology, biochemistry, medicine and materials science can provide a springboard for the development of suitable therapeutic tools, not only for the treatment of Alzheimer's and Parkinson's diseases but also, prospectively, for a wide range of severe neurodegenerative disorders.

About supramolecular systems for dynamically probing cells

This article reviews the state of the art in the development of strategies for generating supramolecular systems for dynamic cell studies. Dynamic systems are crucial to further our understanding of cell biology and are consequently at the heart of many medical applications. Increasing interest has therefore been focused recently on rendering systems bioactive and dynamic that can subsequently be employed to engage with cells. Different approaches using supramolecular chemistry are reviewed with particular emphasis on their application in cell studies. We conclude with an outlook on future challenges for dynamic cell research and applications.

Hydrolytically degradable poly(ethylene glycol) hydrogel scaffolds as a cell delivery vehicle: characterization of PC12 cell response

The central nervous system (CNS) has a low intrinsic potential for regeneration following injury and disease, yet neural stem/progenitor cell (NPC) transplants show promise to provide a dynamic therapeutic in this complex tissue environment. Moreover, biomaterial scaffolds may improve the success of NPC-based therapeutics by promoting cell viability and guiding cell response. We hypothesized that a hydrogel scaffold could provide a temporary neurogenic environment that supports cell survival during encapsulation, and degrades completely in a temporally controlled manner to allow progression of dynamic cellular processes such as neurite extension. We utilized PC12 cells as a model cell line with an inducible neuronal phenotype to define key properties of hydrolytically degradable poly(ethylene glycol) hydrogel scaffolds that impact cell viability and differentiation following release from the degraded hydrogel. Adhesive peptide ligands (RGDS, IKVAV, or YIGSR), were required to maintain cell viability during encapsulation; as compared to YIGSR, the RGDS, and IKVAV ligands were associated with a higher percentage of PC12 cells that differentiated to the neuronal phenotype following release from the hydrogel. Moreover, among the hydrogel properties examined (e.g., ligand type, concentration), total polymer density within the hydrogel had the most prominent effect on cell viability, with densities above 15% w/v leading to decreased cell viability likely due to a higher shear modulus. Thus, by identifying key properties of degradable hydrogels that affect cell viability and differentiation following release from the hydrogel, we lay the foundation for application of this system towards future applications of the scaffold as a neural cell delivery vehicle.

Improvement of neural stem cell survival in collagen hydrogels by incorporating laminin-derived cell adhesive polypeptides

Cell transplantation is a potential methodology for the treatment of Parkinson's disease. However, the therapeutic effect is limited by poor viability of transplanted cells. To overcome this problem, we hypothesized that a dual step approach, whereby providing an adhesive substrate for transplanted cells and, at the same time, by preventing the infiltration of activated microglia into the site of transplantation promotes the cell survival. To establish above conditions, attempts were made to prepare 3-D matrices using collagen hydrogels that incorporated integrin-binding polypeptides derived from laminin-1. Tandem combinations of laminin globular domains as well as a single globular domain 3 were prepared using recombinant DNA technology as a fusion with hexahistidine and bound to metal chelated surfaces to screen for the adhesion and proliferation of neural stem cells (NSCs). In addition, a small peptide derived from laminin γ1 chain was prepared and heterodimerized with the globular domain-containing chimeric proteins to evaluate for the enhancement of integrin-mediated cell adhesion. As a result, a heterodimer consisting of the globular domain 3 of the laminin α1 chain and the peptide from the laminin γ1 chain was selected as the best candidate among the polypeptides studied here for the incorporation into a collagen hydrogel. It was shown that the survival of NSCs was indeed promoted in the collagen hydrogel incorporating the heterodimer compared to the pure collagen hydrogel.

Self-assembly of coiled coils in synthetic biology: inspiration and progress

Biological self-assembly is very complex and results in highly functional materials. In effect, it takes a bottom-up approach using biomolecular building blocks of precisely defined shape, size, hydrophobicity, and spatial distribution of functionality. Inspired by, and drawing lessons from self-assembly processes in nature, scientists are learning how to control the balance of many small forces to increase the complexity and functionality of self-assembled nanomaterials. The coiled-coil motif, a multipurpose building block commonly found in nature, has great potential in synthetic biology. In this review we examine the roles that the coiled-coil peptide motif plays in self-assembly in nature, and then summarize the advances that this has inspired in the creation of functional units, assemblies, and systems.

Adhesion molecule-modified biomaterials for neural tissue engineering

Adhesion molecules (AMs) represent one class of biomolecules that promote central nervous system regeneration. These tethered molecules provide cues to regenerating neurons that recapitulate the native brain environment. Improving cell adhesive potential of non-adhesive biomaterials is therefore a common goal in neural tissue engineering. This review discusses common AMs used in neural biomaterials and the mechanism of cell attachment to these AMs. Methods to modify materials with AMs are discussed and compared. Additionally, patterning of AMs for achieving specific neuronal responses is explored.