Functional π-Gelators and Their Applications

Poly(lactic-co-glycolic) acid (PLGA) has attracted considerable interest as a base material for biomedical applications due to its: (i) biocompatibility; (ii) tailored biodegradation rate (depending on the molecular weight and copolymer ratio); (iii) approval for clinical use in humans by the U.S. Food and Drug Administration (FDA); (iv) potential to modify surface properties to provide better interaction with biological materials; and (v) suitability for export to countries and cultures where implantation of animal-derived products is unpopular. This paper critically reviews the scientific challenge of manufacturing PLGA-based materials with suitable properties and shapes for specific biomedical applications, with special emphasis on bone tissue engineering. The analysis of the state of the art in the field reveals the presence of current innovative techniques for scaffolds and material manufacturing that are currently opening the way to prepare biomimetic PLGA substrates able to modulate cell interaction for improved substitution, restoration, or enhancement of bone tissue function.

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An Overview of Poly(lactic-co-glycolic) Acid (PLGA)-Based Biomaterials for Bone Tissue Engineering

Over the past century, hydrogels have emerged as effective materials for an immense variety of applications. The unique network structure of hydrogels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimulus-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. In this extensive review, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss the theoretical analysis of hydrogel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we review the many current and proposed applications of these hydrogels in medicine and industry.

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Stimulus-responsive hydrogels: Theory, modern advances, and applications

An injectable and self-healing collagen-gold hybrid hydrogel is spontaneously formed by electrostatic self-assembly and subsequent biomineralization. It is demonstrated that such collagen-based hydrogels may be used as an injectable material for local delivery of therapeutic agents, showing enhanced antitumor efficacy.

An Injectable Self-Assembling Collagen-Gold Hybrid Hydrogel for Combinatorial Antitumor Photothermal/Photodynamic Therapy.

Self-assembled peptide and protein amyloid nanostructures have traditionally been considered only as pathological aggregates implicated in human neurodegenerative diseases. In more recent times, these nanostructures have found interesting applications as advanced materials in biomedicine, tissue engineering, renewable energy, environmental science, nanotechnology and material science, to name only a few fields. In all these applications, the final function depends on: (i) the specific mechanisms of protein aggregation, (ii) the hierarchical structure of the protein and peptide amyloids from the atomistic to mesoscopic length scales and (iii) the physical properties of the amyloids in the context of their surrounding environment (biological or artificial). In this review, we will discuss recent progress made in the field of functional and artificial amyloids and highlight connections between protein/peptide folding, unfolding and aggregation mechanisms, with the resulting amyloid structure and functionality. We also highlight current advances in the design and synthesis of amyloid-based biological and functional materials and identify new potential fields in which amyloid-based structures promise new breakthroughs.

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Self-assembling peptide and protein amyloids: from structure to tailored function in nanotechnology

Hydrogels are polymeric networks, capable of absorbing large amounts of water and biological fluids. They are insoluble due to the presence of chemical or physical cross-links between the constituents. Hydrogels are promising materials for use as injectable biomaterials due to their high water content, tunable viscoelasticity, and biocompatibility. Peptides and proteins are important building blocks in the design of hydrogels, since they are easily degraded by the body and display a high biocompatibility. This review aims to give an overview of hydrogels in which peptides and proteins are structural elements of the polymer network. The review starts with hydrogels derived from naturally occurring structural proteins, followed by all-protein and peptide-based synthetic systems. Next, hybrid hydrogels composed of synthetic polymeric and peptide structural elements will be discussed. The potential of these hydrogels is illustrated with applications that are mainly derived from the field of tissue engineering.

Peptide- and Protein-Based Hydrogels

Poly(lactic-co-glycolic acid) (PLGA) is the most often used synthetic polymer within the field of bone regeneration owing to its biocompatibility and biodegradability. As a consequence, a large number of medical devices comprising PLGA have been approved for clinical use in humans by the American Food and Drug Administration. As compared with the homopolymers of lactic acid poly(lactic acid) and poly(glycolic acid), the co-polymer PLGA is much more versatile with regard to the control over degradation rate. As a material for bone regeneration, the use of PLGA has been extensively studied for application and is included as either scaffolds, coatings, fibers, or micro- and nanospheres to meet various clinical requirements.

Physicochemical Properties and Applications of Poly(lactic-co-glycolic acid) for Use in Bone Regeneration

Strain-Promoted Oxidation-Controlled Cyclooctyne–1,2-Quinone Cycloaddition (SPOCQ) for Fast and Activatable Protein Conjugation

Strain-promoted oxidation-controlled cyclo-octyne-1,2-quinone cycloaddition (SPOCQ) is a fast and activatable cross-linking strategy for hydrogel formation. Gelation is induced by oxidation, which is performed both chemically using sodium periodate and enzymatically using mushroom tyrosinase. Due to the fast reaction kinetics, SPOCQ-formed hydrogels can be functionalized in one-pot with an azido-containing moiety using SPAAC cross-linking.

A Fast and Activatable Cross‐Linking Strategy for Hydrogel Formation

Poly(ethylene)glycol (PEG)-based hydrogels are often used as matrix material for cell culturing. An efficient method to prepare soft PEG gels is by cross-linking via copper-free strain-promoted azide-alkyne cycloaddition (SPAAC). Here, the effect of polymer density and RGDS-content on hydrogel formation and cell adhesion was studied, by varying the total polymer content (10, 20 and 30 mg · mL(-1) ) and the amount of RGDS moieties (0-100%) independently of each other. Rheology studies confirmed the soft nature of the hydrogels (G' = 25-2 298 Pa). HOS cells are able to adhere well to all RGDS-containing gels. Interestingly, both HeLa cells and NIH 3T3 fibroblasts showed substantial adherence to 10 and 20 mg · mL(-1) gels, but with increased hydrogel stiffness (30 mg · mL(-1) ), their cellular adhesion decreased significantly.

Anika M. Jonker

Papers

Peptide- and Protein-Based Hydrogels

Physicochemical Properties and Applications of Poly(lactic-co-glycolic acid) for Use in Bone Regeneration

Strain-Promoted Oxidation-Controlled Cyclooctyne–1,2-Quinone Cycloaddition (SPOCQ) for Fast and Activatable Protein Conjugation

A Fast and Activatable Cross‐Linking Strategy for Hydrogel Formation

Soft PEG-Hydrogels with Independently Tunable Stiffness and RGDS-Content for Cell Adhesion Studies.