Dual peptide-presenting hydrogels for controlling the phenotype of PC12 cells

Engineering peptide-modified alginate-based bioinks with cell-adhesive properties for biofabrication

Alginate (ALG) and its oxidised form alginate-dialdehyde (ADA) are highly attractive materials for hydrogels used in 3D bioprinting as well as drop-on-demand (DoD) approaches. However, both polymers need to be modified using cell-adhesive peptide sequences, to obtain bioinks exhibiting promising cell-material interactions. Our study explores the modification of ALG- and ADA-based bioinks with the adhesive peptides YIGSR (derived from laminin), RRETEWA (derived from fibronectin) and IKVAV (derived from laminin) for 3D bioprinting. Two coupling methods, carbodiimide and Schiff base reactions, were employed to modify the polymers with peptides. Analytical techniques, including FTIR and NMR were used to assess the chemical composition, revealing challenges in confirming the presence of peptides. The modified bioinks exhibited decreased stability, viscosity, and stiffness, particularly-ADA-based bioinks in contrast to ALG. Sterile hydrogel capsules or droplets were produced using a manual manufacturing process and DoD printing. NIH/3T3 cell spreading analysis showed enhanced cell spreading in carbodiimide-modified ADA, Schiff base-modified ADA, and PEG-Mal-modified ADA. The carbodiimide coupling of peptides worked for ADA, however the same was not observed for ALG. Finally, a novel mixture of all used peptides was evaluated regarding synergistic effects on cell spreading which was found to be effective, showing higher aspect ratios compared to the single peptide coupled hydrogels in all cases. The study suggests potential applications of these modified bioinks in 3D bioprinting approaches and highlights the importance of peptide selection as well as their combination for improved cell-material interactions.

The Role of Extracellular Matrix (ECM) Adhesion Motifs in Functionalised Hydrogels

To create functional tissue engineering scaffolds, biomaterials should mimic the native extracellular matrix of the tissue to be regenerated. Simultaneously, the survival and functionality of stem cells should also be enhanced to promote tissue organisation and repair. Hydrogels, but in particular, peptide hydrogels, are an emerging class of biocompatible scaffolds which act as promising self-assembling biomaterials for tissue engineering and regenerative therapies, ranging from articular cartilage regeneration at joint defects, to regenerative spinal cord injury following trauma. To enhance hydrogel biocompatibility, it has become imperative to consider the native microenvironment of the site for regeneration, where the use of functionalised hydrogels with extracellular matrix adhesion motifs has become a novel, emerging theme. In this review, we will introduce hydrogels in the context of tissue engineering, provide insight into the complexity of the extracellular matrix, investigate specific adhesion motifs that have been used to generate functionalised hydrogels and outline their potential applications in a regenerative medicine setting. It is anticipated that by conducting this review, we will provide greater insight into functionalised hydrogels, which may help translate their use towards therapeutic roles.

Cell guidance on peptide micropatterned silk fibroin scaffolds

Guiding neuronal cell growth is desirable for neural tissue engineering but is very challenging. In this work, a self-assembling ultra-short surfactant-like peptide I₃K which possesses positively charged lysine head groups, and hydrophobic isoleucine tails, was chosen to investigate its potential for guiding neuronal cell growth. The peptides were able to self-assemble into nanofibrous structures and interact strongly with silk fibroin (SF) scaffolds, providing a niche for neural cell attachment and proliferation. SF is an excellent biomaterial for tissue engineering. However neuronal cells, such as rat PC12 cells, showed poor attachment on pure regenerated SF (RSF) scaffold surfaces. Patterning of I₃K peptide nanofibers on RSF surfaces significantly improved cellular attachment, cellular density, as well as morphology of PC12 cells. The live / dead assay confirmed that RSF and I₃K have negligible cytotoxicity against PC12 cells. Atomic force microscopy (AFM) was used to image the topography and neurite formation of PC12 cells, where results revealed that self-assembled I₃K nanofibers can support the formation of PC12 cell neurites. Immunolabelling also demonstrated that coating of I₃K nanofibers onto the RSF surfaces not only increased the percentage of cells bearing neurites but also increased the average maximum neurite length. Therefore, the peptide I₃K could be used as an alternative to poly-l-lysine for cell culture and tissue engineering applications. As micro-patterning of neural cells to guide neurite growth is important for developing nerve tissue engineering scaffolds, inkjet printing was used to pattern self-assembled I₃K peptide nanofibers on RSF surfaces for directional control of PC12 cell growth. The results demonstrated that inkjet-printed peptide micro-patterns can effectively guide the cell alignment and organization on RSF scaffold surfaces, providing great potential for nerve regeneration applications.

Progress and challenges of implantable neural interfaces based on nature-derived materials

Neural interfaces are bioelectronic devices capable of stimulating a population of neurons or nerve fascicles and recording electrical signals in a specific area. Despite their success in restoring sensory-motor functions in people with disabilities, their long-term exploitation is still limited by poor biocompatibility, mechanical mismatch between the device and neural tissue and the risk of a chronic inflammatory response upon implantation.In this context, the use of nature-derived materials can help address these issues. Examples of these materials, such as extracellular matrix proteins, peptides, lipids and polysaccharides, have been employed for decades in biomedical science. Their excellent biocompatibility, biodegradability in the absence of toxic compound release, physiochemical properties that are similar to those of human tissues and reduced immunogenicity make them outstanding candidates to improve neural interface biocompatibility and long-term implantation safety. The objective of this review is to highlight progress and challenges concerning the impact of nature-derived materials on neural interface design. The use of these materials as biocompatible coatings and as building blocks of insulation materials for use in implantable neural interfaces is discussed. Moreover, future perspectives are presented to show the increasingly important uses of these materials for neural interface fabrication and their possible use for other applications in the framework of neural engineering.

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.

Modulating Alginate Hydrogels for Improved Biological Performance as Cellular 3D Microenvironments

The rational choice and design of biomaterials for biomedical applications is crucial for successful in vitro and in vivo strategies, ultimately dictating their performance and potential clinical applications. Alginate, a marine-derived polysaccharide obtained from seaweeds, is one of the most widely used polymers in the biomedical field, particularly to build three dimensional (3D) systems for in vitro culture and in vivo delivery of cells. Despite their biocompatibility, alginate hydrogels often require modifications to improve their biological activity, namely via inclusion of mammalian cell-interactive domains and fine-tuning of mechanical properties. These modifications enable the addition of new features for greater versatility and control over alginate-based systems, extending the plethora of applications and procedures where they can be used. Additionally, hybrid systems based on alginate combination with other components can also be explored to improve the mimicry of extracellular microenvironments and their dynamics. This review provides an overview on alginate properties and current clinical applications, along with different strategies that have been reported to improve alginate hydrogels performance as 3D matrices and 4D dynamic systems.

Alginate Microencapsulation for Three-Dimensional In Vitro Cell Culture

Advances in microscale 3D cell culture systems have helped to elucidate cellular physiology, understand mechanisms of stem cell differentiation, produce pathophysiological models, and reveal important cell-cell and cell-matrix interactions. An important consideration for such studies is the choice of material for encapsulating cells and associated extracellular matrix (ECM). This Review focuses on the use of alginate hydrogels, which are versatile owing to their simple gelation process following an ionic cross-linking mechanism in situ, with no need for procedures that can be potentially toxic to cells, such as heating, the use of solvents, and UV exposure. This Review aims to give some perspectives, particularly to researchers who typically work more with poly(dimethylsiloxane) (PDMS), on the use of alginate as an alternative material to construct microphysiological cell culture systems. More specifically, this Review describes how physicochemical characteristics of alginate hydrogels can be tuned with regards to their biocompatibility, porosity, mechanical strength, ligand presentation, and biodegradability. A number of cell culture applications are also described, and these are subcategorized according to whether the alginate material is used to homogeneously embed cells, to micropattern multiple cellular microenvironments, or to provide an outer shell that creates a space in the core for cells and other ECM components. The Review ends with perspectives on future challenges and opportunities for 3D cell culture applications.

Construction of Biofunctionalized Anisotropic Hydrogel Micropatterns and Their Effect on Schwann Cell Behavior in Peripheral Nerve Regeneration

Hydrogels have promising application in tissue regeneration due to their excellent physicochemical and biocompatible properties, whereas anisotropic micropatterns are been proven to directionally induce cell alignment and accelerate cell migration. However, an effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration has rarely been reported. In this study, the anisotropic polyacrylamide (PAM) hydrogel micropatterns with aligned ridge/groove structures were first prepared via in situ free radical polymerization and micromolding, and then biofunctionalized using YIGSR peptide for better promoting cell growth. The morphology, swelling ratio, wettability, mechanical properties, and stability of the prepared hydrogel were characterized. The successful immobilization of YIGSR peptide on the PAM hydrogel was monitored using FTIR, immunofluorescence staining, and ELISA. The effects on adhesion, directional growth, and biological function of Schwann cells were evaluated. The results displayed that the anisotropic PAM hydrogel micropatterns with inner porous structure possessed good stability, swelling, and mechanical properties. The YIGSR peptide could be well immobilized on hydrogel micropatterns with a percentage of 62.6%. The biofunctionalized anisotropic hydrogel micropatterns could effectively regulate the orientation growth of Schwann cells, and obviously up-regulate BDNF (40%) and β-actin (50%) expression compared with single hydrogel micropatterns, without negatively affecting the normal secretion of neurotropic factors by Schwann cells. To the best of our knowledge, this is the first time to study the construction and effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration, which may provide an experimental and theoretical basis for the design and development of artificial implants for nerve regeneration application.

Engineered materials for organoid systems

Organoids are 3D cell culture systems that mimic some of the structural and functional characteristics of an organ. Organoid cultures provide the opportunity to study organ-level biology in models that mimic human physiology more closely than 2D cell culture systems or non-primate animal models. Many organoid cultures rely on decellularized extracellular matrices as scaffolds, which are often poorly chemically defined and allow only limited tunability and reproducibility. By contrast, the biochemical and biophysical properties of engineered matrices can be tuned and optimized to support the development and maturation of organoid cultures. In this Review, we highlight how key cell-matrix interactions guiding stem-cell decisions can inform the design of biomaterials for the reproducible generation and control of organoid cultures. We survey natural, synthetic and protein-engineered hydrogels for their applicability to different organoid systems and discuss biochemical and mechanical material properties relevant for organoid formation. Finally, dynamic and cell-responsive material systems are investigated for their future use in organoid research.

Specific capture of glycosylated graphene oxide by an asialoglycoprotein receptor: a strategic approach for liver-targeting

In this work, we report the evaluation of lactosylated graphene oxide (GO-AL) as a potential drug carrier targeted at an asialoglycoprotein receptor (ASGPR) from hepatic cancer cells. Structural-modification, safety evaluation, and functional analysis of GO-AL were performed. The structure and morphology of the composite were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while Raman and FTIR spectroscopy were used to track the chemical modification. For the safe application of GO-AL, an evaluation of the cytotoxic effect, hemolytic properties, and specific interactions of the glycoconjugate were also studied. SEM and AFM analysis of the GO showed graphene sheets with a layer size of 2-3 nm, though a few of them reached 4 nm. The Raman spectra presented characteristic peaks of graphene oxide at 1608 cm^-1 and 1350 cm^-1, corresponding to G and D bands, respectively. Besides, Si-O peaks for the APTES conjugates of GO were identified by FTIR spectroscopy. No cytotoxic or hemolytic effects were observed for GO samples, thus proving their biocompatibility. The interaction of Ricinus communis lectin confirmed that GO-AL has a biorecognition capability and an exposed galactose structure. This biorecognition capability was accompanied by the determination of the specific absorption of lactosylated GO by HepG2 cells mediated through the asialoglycoprotein receptor. The successful conjugation, hemolytic safety, and specific recognition described here for lactosylated GO indicate its promise as an efficient drug-delivery vehicle to hepatic tissue.