Copper-Free Azide-Alkyne Cycloaddition for Peptide Modification of Alginate Hydrogels

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.

Guanosine-based hydrogel as a supramolecular scaffold for template-assisted macrocyclization

The G-quartet-like supramolecular assembly present in guanosine hydrogel templates macrocyclization between bis-azide and bis-alkyne fragments. The resulting macrocycle enhances viscoelastic properties, and strengthens the hydrogel network. This approach holds potential for the in situ synthesis of drugs and their simultaneous delivery in a stimuli-responsive manner.

Lignocellulosic-biomolecules conjugated systems: green-engineered complexes modified by covalent linkers

Lignocellulosic biomass represents an abundant and eco-friendly material widely explored in recent years. The main lignocellulosic fractions include cellulose, hemicellulose, and lignin. Nonetheless, the heterogeneity and complexity of these components pose challenges in achieving the desired properties. Conversely, their attractive functional groups can covalently link with other biomolecules, facilitating the creation and enhancement of material properties. Lignocellulosic molecules can form different linkages with other biomolecules through classic and modern methods. Bioconjugation has emerged as a suitable alternative to create new nuances, empowering the linkage between lignocellulosic materials and biomolecules through linkers. These conjugates (lignocellulosic-linkers-biomolecules) attract attention from stakeholders in medicine, chemistry, biology, and agriculture. The plural formations of these biocomplexes highlight the significance of these arrangements. Therefore, this review provides an overview of the progress of lignocellulosic-biomolecule complexes and discusses different types of covalent bioconjugated systems, considering the formation of linkers, applicability, toxicity, and future challenges.

A peptide-engineered alginate aerogel with synergistic blood-absorbing and platelet-binding capabilities to rapidly stop bleeding

Polysaccharide matrix infused with hemostasis-stimulating chemistry represents a critical medical need of bleeding management. Herein, we describe the development of a polysaccharide-peptide conjugate platform, an alginate engineered with fibrinogen-derived platelet-binding peptides (APE). The alginate backbone was found to allow for multivalent grafting of the peptides. Processing APE conjugate into crosslinked aerogels promoted platelet accumulation, leading to a significant reduction in the coagulation time of whole rabbit blood and improving the stability of the formed clot. The APE aerogels also exhibited a high porosity and fluid uptake capacity (>90 in weight ratio) as well as good biocompatibility in hemostasis. Furthermore, in vivo studies conducted in rat models of tail cut and hepatic hemorrhage showed that APE aerogels reduced bleeding time by >58 % and blood loss by >61 %. The platelet-enrichment capacity of the APE construct synergized by high absorbency in its aerogel form offers a prototype for customized polysaccharide hemostats.

Versatile click alginate hydrogels with protease-sensitive domains as cell responsive/instructive 3D microenvironments

Alginate (ALG) is a widely used biomaterial to create artificial extracellular matrices (ECM) for tissue engineering. Since it does not degrade in the human body, imparting proteolytic sensitivity to ALG hydrogels leverages their properties as ECM-mimics. Herein, we explored the strain-promoted azide-alkyne cycloaddition (SPAAC) as a biocompatible and bio-orthogonal click-chemistry to graft cyclooctyne-modified alginate (ALG-K) with bi-azide-functionalized PVGLIG peptides. These are sensitive to matrix metalloproteinase (MMP) and may act as crosslinkers. The ALG-K-PVGLIG conjugates (50, 125, and 250 μM PVGLIG) were characterized for peptide incorporation, crosslinking ability (double-end grafting), and enzymatic liability. For producing cell-permissive multifunctional 3D matrices for dermal fibroblast culture, oxidized ALG-K was grafted with PVGLIG and with RGD peptides for cell-adhesion. SPAAC reactions were performed immediately before cell-laden hydrogel formation by secondary ionic-crosslinking, considerably reducing the steps and time of preparation. Hydrogels with intermediate PVGLIG concentration (125 μM) presented slightly higher stiffness while promoting extensive cell spreading and higher degree of cell-cell interconnections, likely favored by cell-driven proteolytic remodeling of the network. The hydrogel-embedded cells were able to produce their own pericellular ECM, expressed MMP-2 and 14, and secreted PVGLIG-degrading enzymes. By recapitulating key ECM-like features, these hydrogels provide biologically relevant 3D matrices for soft tissue regeneration.

Thermo-Responsive Hydrogels Encapsulating Targeted Core-Shell Nanoparticles as Injectable Drug Delivery Systems

As therapeutic agents that allow for minimally invasive administration, injectable biomaterials stand out as effective tools with tunable properties. Furthermore, hydrogels with responsive features present potential platforms for delivering therapeutics to desired sites in the body. Herein, temperature-responsive hydrogel scaffolds with embedded targeted nanoparticles were utilized to achieve controlled drug delivery via local drug administration. Poly(N-isopropylacrylamide) (pNIPAM) hydrogels, prepared with an ethylene-glycol-based cross-linker, demonstrated thermo-sensitive gelation ability upon injection into environments at body temperature. This hydrogel network was engineered to provide a slow and controlled drug release profile by being incorporated with curcumin-loaded nanoparticles bearing high encapsulation efficiency. A core (alginate)-shell (chitosan) nanoparticle design was preferred to ensure the stability of the drug molecules encapsulated in the core and to provide slower drug release. Nanoparticle-embedded hydrogels were shown to release curcumin at least four times slower compared to the free nanoparticle itself and to possess high water uptake capacity and more mechanically stable viscoelastic behavior. Moreover, this therapy has the potential to specifically address tumor tissues over-expressing folate receptors like ovaries, as the nanoparticles target the receptors by folic acid conjugation to the periphery. Together with its temperature-driven injectability, it can be concluded that this hydrogel scaffold with drug-loaded and embedded folate-targeting nanoparticles would provide effective therapy for tumor tissues accessible via minimally invasive routes and be beneficial for post-operative drug administration after tumor resection.

The effect of molecular weight and chemical structure of cross-linkers on the properties of redox-responsive hyaluronic acid hydrogels

In this work, we investigated the effect of the size and the chemical structure of crosslinkers on the properties of hyaluronic acid-based hydrogels prepared via an inverse electron demand Diels-Alder reaction. Hydrogels having loose and dense networks were designed by cross-linkers with and without polyethylene glycol (PEG) spacers of different molecular weights (1000 and 4000 g/mol). The study showed that the properties of hydrogels such as swelling ratios (20-55 times), morphology, stability, mechanical strength (storage modulus in the range 175-858 Pa), and drug loading efficiency (87 % ~ 90 %) were greatly influenced by the addition of PEG and changing its molecular weight in the cross-linker. Particularly, the presence of PEG chains in redox- responsive crosslinkers increased the doxorubicin release (85 %, after 168 h) and the degradation rate (96 %, after 10 d) of hydrogels in the simulated reducing medium (10 mM DTT). The in vitro cytotoxicity experiments conducted for HEK-293 cells revealed that the formulated hydrogels were biocompatible, which could be a promising candidate for drug delivery applications.

Microstructured click hydrogels for cell contact guidance in 3D

The topography of the extracellular matrix (ECM) is a major biophysical regulator of cell behavior. While this has inspired the design of cell-instructive biomaterials, the ability to present topographic cues to cells in a true 3D setting remains challenging, particularly in ECM-like hydrogels made from a single polymer. Herein, we report the design of microstructured alginate hydrogels for injectable cell delivery and show their ability to orchestrate morphogenesis via cellular contact guidance in 3D. Alginate was grafted with hydrophobic cyclooctyne groups (ALG-K), yielding amphiphilic derivatives with self-associative potential and ionic crosslinking ability. This allowed the formation of microstructured ALG-K_H hydrogels, triggered by the spontaneous segregation between hydrophobic/hydrophilic regions of the polymer that generated 3D networks with stiffer microdomains within a softer lattice. The azide-reactivity of cyclooctynes also allowed ALG-K functionalization with bioactive peptides via cytocompatible strain-promoted azide-alkyne cycloaddition (SPAAC). Hydrogel-embedded mesenchymal stem cells (MSCs) were able to integrate spatial information and to mechano-sense the 3D topography, which regulated cell shape and stress fiber organization. MSCs clusters initially formed on microstructured regions could then act as seeds for neo-tissue formation, inducing cells to produce their own ECM and self-organize into multicellular structures throughout the hydrogel. By combining 3D topography, click functionalization, and injectability, using a single polymer, ALG-K hydrogels provide a unique cell delivery platform for tissue regeneration.

A porcine islet-encapsulation device that enables long-term discordant xenotransplantation in immunocompetent diabetic mice

Islet transplantation is an effective treatment for type 1 diabetes (T1D). However, a shortage of donors and the need for immunosuppressants are major issues. The ideal solution is to develop a source of insulin-secreting cells and an immunoprotective method. No bioartificial pancreas (BAP) devices currently meet all of the functions of long-term glycemic control, islet survival, immunoprotection, discordant xenotransplantation feasibility, and biocompatibility. We developed a device in which porcine islets were encapsulated in a highly stable and permeable hydrogel and a biocompatible immunoisolation membrane. Discordant xenotransplantation of the device into diabetic mice improved glycemic control for more than 200 days. Glycemic control was also improved in new diabetic mice "relay-transplanted" with the device after its retrieval. The easily retrieved devices exhibited almost no adhesion or fibrosis and showed sustained insulin secretion even after the two xenotransplantations. This device has the potential to be a useful BAP for T1D.

Alginate as a Promising Biopolymer in Drug Delivery and Wound Healing: A Review of the State-of-the-Art

Biopolymeric nanoparticulate systems hold favorable carrier properties for active delivery. The enhancement in the research interest in alginate formulations in biomedical and pharmaceutical research, owing to its biodegradable, biocompatible, and bioadhesive characteristics, reiterates its future use as an efficient drug delivery matrix. Alginates, obtained from natural sources, are the colloidal polysaccharide group, which are water-soluble, non-toxic, and non-irritant. These are linear copolymeric blocks of α-(1→4)-linked l-guluronic acid (G) and β-(1→4)-linked d-mannuronic acid (M) residues. Owing to the monosaccharide sequencing and the enzymatically governed reactions, alginates are well-known as an essential bio-polymer group for multifarious biomedical implementations. Additionally, alginate’s bio-adhesive property makes it significant in the pharmaceutical industry. Alginate has shown immense potential in wound healing and drug delivery applications to date because its gel-forming ability maintains the structural resemblance to the extracellular matrices in tissues and can be altered to perform numerous crucial functions. The initial section of this review will deliver a perception of the extraction source and alginate’s remarkable properties. Furthermore, we have aspired to discuss the current literature on alginate utilization as a biopolymeric carrier for drug delivery through numerous administration routes. Finally, the latest investigations on alginate composite utilization in wound healing are addressed.

An acid-catalyzed polyol in situ crosslinked alginate ester/Antarctic krill protein composite fiber with improved strength and water resistance

A novel alginate ester/Antarctic krill protein composite fiber with high strength and water resistance that is non-toxic.

Integrin and syndecan binding peptide-conjugated alginate hydrogel for modulation of nucleus pulposus cell phenotype

Biomaterial based strategies have been widely explored to preserve and restore the juvenile phenotype of cells of the nucleus pulposus (NP) in degenerated intervertebral discs (IVD). With aging and maturation, NP cells lose their ability to produce necessary extracellular matrix and proteoglycans, accelerating disc degeneration. Previous studies have shown that integrin or syndecan binding peptide motifs from laminin can induce NP cells from degenerative human discs to re-express juvenile NP-specific cell phenotype and biosynthetic activity. Here, we engineered alginate hydrogels to present integrin- and syndecan-binding peptides alone or in combination (cyclic RGD and AG73, respectively) to introduce bioactive features into the alginate gels. We demonstrated human NP cells cultured upon and within alginate hydrogels presented with cRGD and AG73 peptides exhibited higher cell viability, biosynthetic activity, and NP-specific protein expression over alginate alone. Moreover, the combination of the two peptide motifs elicited markers of the NP-specific cell phenotype, including N-Cadherin, despite differences in cell morphology and multicellular cluster formation between 2D and 3D cultures. These results represent a promising step toward understanding how distinct adhesive peptides can be combined to guide NP cell fate. In the future, these insights may be useful to rationally design hydrogels for NP cell-transplantation based therapies for IVD degeneration.

Biocompatible and Enzymatically Degradable Gels for 3D Cellular Encapsulation under Extreme Compressive Strain

Cell encapsulating scaffolds are necessary for the study of cellular mechanosensing of cultured cells. However, conventional scaffolds used for loading cells in bulk generally fail at low compressive strain, while hydrogels designed for high toughness and strain resistance are generally unsuitable for cell encapsulation. Here we describe an alginate/gelatin methacryloyl interpenetrating network with multiple crosslinking modes that is robust to compressive strains greater than 70%, highly biocompatible, enzymatically degradable and able to effectively transfer strain to encapsulated cells. In future studies, this gel formula may allow researchers to probe cellular mechanosensing in bulk at levels of compressive strain previously difficult to investigate.