Magnetic Field-Induced Alignment of Nanofibrous Supramolecular Membranes: A Molecular Design Approach to Create Tissue-like Biomaterials

Magnetically induced anisotropic structure in an injectable hydrogel for skeletal muscle regeneration

Skeletal muscle integrity and its intrinsic aligned architecture are crucial for locomotion, postural support, and respiration functions, impacting overall quality of life. However, volumetric muscle loss (VML) can exceed intrinsic regenerative potential, leading to fibrosis and impairments. Autologous muscle grafting, the current gold standard, is constrained by tissue availability and success rates. Therefore, innovative strategies like cell-based therapies and scaffold-based approaches are needed. Our minimally invasive approach involves a tunable injectable hydrogel capable of achieving an aligned architecture post-injection via a low-intensity static magnetic field (SMF). Our hydrogel formulation uses gellan gum as the backbone polymer, enriched with essential extracellular matrix components such as hyaluronic acid and collagen type I, enhancing bio-functionality. To achieve an aligned architectural biomimicry, collagen type I is coupled with iron oxide magnetic nanoparticles, creating magnetic collagen bundles (MagC) that align within the hydrogel when exposed to a SMF. An extensive study was performed to characterize MagC and assess the hydrogel's stability, mechanical properties, and biological response in vitro and in vivo. The proposed system, fully composed of natural polymers, exhibited mechanical properties similar to human skeletal muscle and demonstrated effective biological performances, supporting its potential as a safe and patient-friendly treatment for VML.

Decoupling Charge and Side Chain Effects in Hierarchical Organization of Cationic PFX Peptide and Alginate

We have successfully created self-assembled membranes by combining positively charged (Pro-X-(Phe-X)5-Pro) PFX peptides with negatively charged alginate. These PFX/alginate membranes were formed by three different peptides that contain either X = Arginine (R), Histidine (H), or Ornithine (O) as their charged amino acid. The assemblies were compared to membranes that were previously reported by us composed of X = lysine (K). This study enabled us to elucidate the impact of amino acids' specific interactions on membrane formation. SEM, SAXS, and cryo-TEM measurements show that although K, R, H, and O may have a similar net charge, the specific traits of the charged amino acid is an essential factor in determining the hierarchical structure of alginate/PFX self-assembled membranes.

Side-Chain Chemistry Governs Hierarchical Order of Charge-Complementary β-sheet Peptide Coassemblies

Self-assembly of proteinaceous biomolecules into functional materials with ordered structures that span length scales is common in nature yet remains a challenge with designer peptides under ambient conditions. This report demonstrates how charged side-chain chemistry affects the hierarchical co-assembly of a family of charge-complementary β-sheet-forming peptide pairs known as CATCH(X+/Y-) at physiologic pH and ionic strength in water. In a concentration-dependent manner, the CATCH(6K+) (Ac-KQKFKFKFKQK-Am) and CATCH(6D-) (Ac-DQDFDFDFDQD-Am) pair formed either β-sheet-rich microspheres or β-sheet-rich gels with a micron-scale plate-like morphology, which were not observed with other CATCH(X+/Y-) pairs. This hierarchical order was disrupted by replacing D with E, which increased fibril twisting. Replacing K with R, or mutating the N- and C-terminal amino acids in CATCH(6K+) and CATCH(6D-) to Qs, increased observed co-assembly kinetics, which also disrupted hierarchical order. Due to the ambient assembly conditions, active CATCH(6K+)-green fluorescent protein fusions could be incorporated into the β-sheet plates and microspheres formed by the CATCH(6K+/6D-) pair, demonstrating the potential to endow functionality.

Self-assembly at the interface of λ-carrageenan and amphiphilic and cationic peptides: More than meets the eye

Self-assembly of macroscopic membranes at the interface between self-assembling peptides and aqueous polymer solutions of opposite charge has been explored mostly due to the membranes' unique hierarchical structure of three distinct regions, including a layer of perpendicular fibers. We report here on the formation and characterization of self-assembled membranes made with λ-carrageenan and the cationic β-sheet peptides, Pro-Lys-(Phe-Lys)5-Pro (PFK). Using SAXS, SEM, ITC, and rheology, we compared these membranes' morphology and physical properties to membranes made with alginate. We recognized that the polysaccharide's single chain conformation, its solution's viscosity, the potential of hydrogen bonding and electrostatic interactions between the polysaccharides and the peptides charged groups, and the strength of these interactions all affect the properties of the resulting membranes. As a result, we identified that an interplay between the polymer-peptide strength of interactions and the stiffness of the polysaccharide's single chain could be used as a route to control the structure-function relationship of the membranes. These results provide valuable information for creating guidelines to design self-assembly membranes with specific properties.

Strategies for Anisotropic Fibrillar Hydrogels: Design, Cell Alignment, and Applications in Tissue Engineering

Efficient cellular alignment in biomaterials presents a considerable challenge, demanding the refinement of appropriate material morphologies, while ensuring effective cell-surface interactions. To address this, biomaterials are continuously researched with diverse coatings, hydrogels, and polymeric surfaces. In this context, we investigate the influence of physicochemical parameters on the architecture of fibrillar hydrogels that significantly orient the topography of flexible hydrogel substrates, thereby fostering cellular adhesion and spatial organization. Our Review comprehensively assesses various techniques for aligning polymer fibrils within hydrogels, specifically interventions applied during and after the cross-linking process. These methodologies include mechanical strains, precise temperature modulation, controlled fluidic dynamics, and chemical modulators, as well as the use of magnetic and electric fields. We highlight the intrinsic appeal of these methodologies in fabricating cell-aligning interfaces and discuss their potential implications within the fields of biomaterials and tissue engineering, particularly concerning the pursuit of optimal cellular alignment.

Small-angle scattering techniques for peptide and peptide hybrid nanostructures and peptide-based biomaterials

The use of small-angle scattering (SAS) in the study of the self-assembly of peptides and peptide conjugates (lipopeptides, polymer-peptide conjugates and others) is reviewed, highlighting selected research that illustrates different methods and analysis techniques. Both small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) are considered along with examples that exploit their unique capabilities. For SAXS, this includes the ability to perform rapid measurements enabling high throughput or fast kinetic studies and measurements under dilute conditions. For SANS, contrast variation using H2O/D2O mixtures enables the study of peptides interacting with lipids and TR-SANS (time-resolved SANS) studies of exchange kinetics and/or peptide-induced structural changes. Examples are provided of studies measuring form factors of different self-assembled structures (micelles, fibrils, nanotapes, nanotubes etc) as well as structure factors from ordered phases (lyotropic mesophases), peptide gels and hybrid materials such as membranes formed by mixing peptides with polysaccharides or peptide/liposome mixtures. SAXS/WAXS (WAXS: wide-angle x-ray scattering) on peptides and peptide hybrids is also discussed, and the review concludes with a perspective on potential future directions for research in the field.

Magnetic Fields Reduce Apoptosis by Suppressing Phase Separation of Tau-441

The biological effects of magnetic fields (MFs) have been a controversial issue. Fortunately, in recent years, there has been increasing evidence that MFs do affect biological systems. However, the physical mechanism remains unclear. Here, we show that MFs (16 T) reduce apoptosis in cell lines by inhibiting liquid-liquid phase separation (LLPS) of Tau-441, suggesting that the MF effect on LLPS may be one of the mechanisms for understanding the "mysterious" magnetobiological effects. The LLPS of Tau-441 occurred in the cytoplasm after induction with arsenite. The phase-separated droplets of Tau-441 recruited hexokinase (HK), resulting in a decrease in the amount of free HK in the cytoplasm. In cells, HK and Bax compete to bind to the voltage-dependent anion channel (VDAC I) on the mitochondrial membrane. A decrease in the number of free HK molecules increased the chance of Bax binding to VDAC I, leading to increased Bax-mediated apoptosis. In the presence of a static MF, LLPS was marked inhibited and HK recruitment was reduced, resulting in an increased probability of HK binding to VDAC I and a decreased probability of Bax binding to VDAC I, thus reducing Bax-mediated apoptosis. Our findings revealed a new physical mechanism for understanding magnetobiological effects from the perspective of LLPS. In addition, these results show the potential applications of physical environments, such as MFs in this study, in the treatment of LLPS-related diseases.

Recent progress in the manipulation of biochemical and biophysical cues for engineering functional tissues

Tissue engineering (TE) is currently considered a cutting-edge discipline that offers the potential for developing treatments for health conditions that negatively affect the quality of life. This interdisciplinary field typically involves the combination of cells, scaffolds, and appropriate induction factors for the regeneration and repair of damaged tissue. Cell fate decisions, such as survival, proliferation, or differentiation, critically depend on various biochemical and biophysical factors provided by the extracellular environment during developmental, physiological, and pathological processes. Therefore, understanding the mechanisms of action of these factors is critical to accurately mimic the complex architecture of the extracellular environment of living tissues and improve the efficiency of TE approaches. In this review, we recapitulate the effects that biochemical and biophysical induction factors have on various aspects of cell fate. While the role of biochemical factors, such as growth factors, small molecules, extracellular matrix (ECM) components, and cytokines, has been extensively studied in the context of TE applications, it is only recently that we have begun to understand the effects of biophysical signals such as surface topography, mechanical, and electrical signals. These biophysical cues could provide a more robust set of stimuli to manipulate cell signaling pathways during the formation of the engineered tissue. Furthermore, the simultaneous application of different types of signals appears to elicit synergistic responses that are likely to improve functional outcomes, which could help translate results into successful clinical therapies in the future.

An Overview of the Supramolecular Systems for Gene and Drug Delivery in Tissue Regeneration

Tissue regeneration is a prominent area of research, developing biomaterials aimed to be tunable, mechanistic scaffolds that mimic the physiological environment of the tissue. These biomaterials are projected to effectively possess similar chemical and biological properties, while at the same time are required to be safely and quickly degradable in the body once the desired restoration is achieved. Supramolecular systems composed of reversible, non-covalently connected, self-assembly units that respond to biological stimuli and signal cells have efficiently been developed as preferred biomaterials. Their biocompatibility and the ability to engineer the functionality have led to promising results in regenerative therapy. This review was intended to illuminate those who wish to envisage the niche translational research in regenerative therapy by summarizing the various explored types, chemistry, mechanisms, stimuli receptivity, and other advancements of supramolecular systems.

Microfabrication of peptide self-assemblies: inspired by nature towards applications

Peptide self-assemblies show intriguing and tunable physicochemical properties, and thus have been attracting increasing interest over the last two decades. However, the micro/nano-scale dimensions of the self-assemblies severely restrict their extensive applications. Inspired by nature, to genuinely realize the practical utilization of the bio-organic super-architectures, it is beneficial to further organize the peptide self-assemblies to integrate the properties of the individual supermolecules and fabricate higher-level organizations for smart functional devices. Therefore, cumulative studies have been reported on peptide microfabrication giving rise to diverse properties. This review summarizes the recent development of the microfabrication of peptide self-assemblies, discussing each methodology along with the diverse properties and practical applications of the engineered peptide large-scale, highly-ordered organizations. Finally, the current limitations of the state-of-the-art microfabrication strategies are critically assessed and alternative solutions are suggested.

Magnetic Control over the Fractal Dimension of Supramolecular Rod Networks

Controlling supramolecular polymerization is of fundamental importance to create advanced materials and devices. Here we show that the thermodynamic equilibrium of Gd³⁺-bearing supramolecular rod networks is shifted reversibly at room temperature in a static magnetic field of up to 2 T. Our approach opens opportunities to control the structure formation of other supramolecular or coordination polymers that contain paramagnetic ions.

Recent Progress in Ionic Coassembly of Cationic Peptides and Anionic Species

Peptide assembly has been extensively exploited as a promising platform for the creation of hierarchical nanostructures and tailor-made bioactive materials. Ionic coassembly of cationic peptides and anionic species is paving the way to provide particularly important contribution to this topic. In this review, the recent progress of ionic coassembly soft materials derived from the electrostatic coupling between cationic peptides and anionic species in aqueous solution is systematically summarized. The presentation of this review starts from a brief background on the general importance and advantages of peptide-based ionic coassembly. After that, diverse combinations of cationic peptides with small anions, macro- and/or oligo-anions, anionic polymers, and inorganic polyoxometalates are described. Emphasis is placed on the hierarchical structures, value-added properties, and applications. The molecular design of cationic peptides and the general principles behind the ionic coassembled structures are discussed. It is summarized that the combination of interesting and unique characteristics that arise both from the chemical diversity of peptides and the wide range of anionic species may contribute in a variety of output, including drug delivery, tissue engineering, gene transfection, and antibacterial activity. The emergent new phenomena and findings are illustrated. Finally, the outlook for the peptide-based ionic coassembly systems is also presented.

Time matters for macroscopic membranes formed by alginate and cationic β-sheet peptides

Hierarchically ordered planar and spherical membranes (sacs) were constructed using amphiphilic and cationic β-sheet peptides that spontaneously assembled together with negatively charged alginate solution. The system was found to form either a fully developed membrane structure with three distinct regions including characteristic perpendicular fibers or a non-fully developed contact layer lacking these standing fibers, depending on the peptide age, membrane geometry and membrane incubation time. The morphological differences were found to strongly depend on fairly-long incubation time frames that influenced both the peptide's intrinsic alignment and the reaction-diffusion process taking place at the interface. A three-stage mechanism was suggested and key parameters affecting the development process were identified. Stability tests in biologically relevant buffers confirmed the suitability of these membranes for bio applications.

Unravelling the Enzymatic Degradation Mechanism of Supramolecular Peptide Nanofibers and Its Correlation with Their Internal Viscosity

Enzyme-responsive supramolecular peptide biomaterials have attracted growing interest for disease diagnostics and treatments. However, it remains unclear whether enzymes target the peptide assemblies or dissociated peptide monomers. To gain further insight into the degradation mechanism of supramolecular peptide amphiphile (PA) nanofibers, cathepsin B with both exopeptidase and endopeptidase activities was exploited here for degradation studies. Hydrolysis was found to occur directly on the PA nanofibers as only surface amino acid residues were cleaved. The number of cleaved residues and the degradation efficiency was observed to be negatively correlated with the internal viscosity of the PA nanofibers, quantified to be between 200-800 cP (liquid phase) using fluorescence lifetime imaging microscopy combined with an environmentally sensitive molecular rotor, BODIPY-C10. These findings enhance our understanding on the enzymatic degradation of supramolecular PA nanofibers and have important implications for the development of PA probes for the real-time monitoring of disease-related enzymes.

Synergistic Fabrication of Dose-Response Chitosan/Dextran/β-Glycerophosphate Injectable Hydrogel as Cell Delivery Carrier for Cardiac Healing After Acute Myocardial Infarction

The human mesenchymal stem cells (hMSCs) therapy offering an encouraging the new methods to establish the conveying on the chitosan (C)/dextran (D)/β-glycerophosphate (β-GP) loaded with hMSCs to enhance the acute myocardial infarctions. The synthesized hMSCs-CD@β-GP system displayed the ratio of determination modules, size of the pore, absorbency, and the swellings ratio in the assortment of the 65 ka, 149 ± 39.8 µm, 92.2%, 42 ± 1.38, and 29 ± 1.9, respectively. The fabricated hMSCs-CD@β-GP was highly stable and physicochemical investigated and confirmed the suitability of the materials for cardiac regeneration applications. The in vitro examinations of the injectable hydrogels with hMSCs-CD@β-GP have recognized that the improved survival rate of the cells, increased the pro-inflammatory expressions factors, pro-angiogenic factors analysis confirmed the promising results of the ejection of fractions, fibrosis area, vessel density with decreased infractions size, with suggesting that the remarkable improvement of the heart regenerative function after myocardial infarctions. The new synergistic approach of the injectable hydrogels with hMSCs could able appropriate for the effective treatment of cardiac therapies after acute myocardial infarctions.