Macroporous click-elastin-like hydrogels for tissue engineering applications

Injectable hydrogels for bone regeneration with tunable degradability via peptide chirality modification

The degradability of hydrogels plays a pivotal role in bone regeneration, yet its precise effects on the bone repair process remain poorly understood. Traditional studies have been limited by the use of hydrogels with insufficient variation in degradation properties for thorough comparative analysis. Addressing this gap, our study introduces the development of matrix metalloproteinase (MMP)-responsive hydrogels engineered with a tunable degradation rate, specifically designed for bone regeneration applications. These innovative hydrogels are synthesized by integrating MMP-sensitive peptides, which exhibit chirality-transferred amino acids, with norbornene (NB)-modified 8-arm polyethylene glycol (PEG) macromers to form the hydrogel network. The degradation behavior of these hydrogels is manipulated through the chirality of the incorporated peptides, resulting in the classification into L, LD, and D hydrogels. Remarkably, the L hydrogel variant shows a significantly enhanced degradation rate, both in vitro and in vivo, which in turn fosters bone regeneration by promoting cell migration and upregulating osteogenic gene expression. This research highlights the fundamental role of hydrogel degradability in bone repair and lays the groundwork for the advancement of degradable hydrogel technologies for bone regeneration, offering new insights and potential for future biomaterials development.

Bioengineering approaches for the endometrial research and application

The endometrium undergoes a series of precise monthly changes under the regulation of dynamic levels of ovarian hormones that are characterized by repeated shedding and subsequent regeneration without scarring. This provides the potential for wound healing during endometrial injuries. Bioengineering materials highlight the faithful replication of constitutive cells and the extracellular matrix that simulates the physical and biomechanical properties of the endometrium to a larger extent. Significant progress has been made in this field, and functional endometrial tissue bioengineering allows an in-depth investigation of regulatory factors for endometrial and myometrial defects in vitro and provides highly therapeutic methods to alleviate obstetric and gynecological complications. However, much remains to be learned about the latest progress in the application of bioengineering technologies to the human endometrium. Here, we summarize the existing developments in biomaterials and bioengineering models for endometrial regeneration and improving the female reproductive potential.

A Factor-Free Hydrogel with ROS Scavenging and Responsive Degradation for Enhanced Diabetic Bone Healing

In view of the increased levels of reactive oxygen species (ROS) that disturb the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), the repair of diabetic bone defects remains a great challenge. Herein, a factor-free hydrogel is reported with ROS scavenging and responsive degradation properties for enhanced diabetic bone healing. These hydrogels contain ROS-cleavable thioketal (TK) linkers and ultraviolet (UV)-responsive norbornene (NB) groups conjugated with 8-arm PEG macromers, which are formed via UV crosslinking-mediated gelation. Upon reacting with high levels of ROS in the bone defect microenvironment, ROS-cleavable TK linkers are destroyed, allowing the responsive degradation of hydrogels, which promotes the migration of BMSCs. Moreover, ROS levels are reduced through hydrogel-mediated ROS scavenging to reverse BMSC differentiation from adipogenic to osteogenic phenotype. As such, a favorable microenvironment is created after simultaneous ROS scavenging and hydrogel degradation, leading to the effective repair of bone defects in diabetic mouse models, even without the addition of growth factors. Thus, this study presents a responsive hydrogel platform that regulates ROS scavenging and stromal degradation in bone engineering.

Contribution of the ELRs to the development of advanced in vitro models

Developing in vitro models that accurately mimic the microenvironment of biological structures or processes holds substantial promise for gaining insights into specific biological functions. In the field of tissue engineering and regenerative medicine, in vitro models able to capture the precise structural, topographical, and functional complexity of living tissues, prove to be valuable tools for comprehending disease mechanisms, assessing drug responses, and serving as alternatives or complements to animal testing. The choice of the right biomaterial and fabrication technique for the development of these in vitro models plays an important role in their functionality. In this sense, elastin-like recombinamers (ELRs) have emerged as an important tool for the fabrication of in vitro models overcoming the challenges encountered in natural and synthetic materials due to their intrinsic properties, such as phase transition behavior, tunable biological properties, viscoelasticity, and easy processability. In this review article, we will delve into the use of ELRs for molecular models of intrinsically disordered proteins (IDPs), as well as for the development of in vitro 3D models for regenerative medicine. The easy processability of the ELRs and their rational design has allowed their use for the development of spheroids and organoids, or bioinks for 3D bioprinting. Thus, incorporating ELRs into the toolkit of biomaterials used for the fabrication of in vitro models, represents a transformative step forward in improving the accuracy, efficiency, and functionality of these models, and opening up a wide range of possibilities in combination with advanced biofabrication techniques that remains to be explored.

"In-situ" formation of elastin-like recombinamer hydrogels with tunable viscoelasticity through efficient one-pot process

Despite the remarkable progress in the generation of recombinant elastin-like (ELR) hydrogels, further improvements are still required to enhance and control their viscoelasticity, as well as limit the use of expensive chemical reagents, time-consuming processes and several purification steps. To alleviate this issue, the reactivity of carboxylic groups from glutamic (E) acid distributed along the hydrophilic block of an amphiphilic ELR (coded as E50I60) with amine groups has been studied through a one-pot amidation reaction in aqueous solutions, for the first time. By means of this approach, immediate conjugation of E50I60 with molecules containing amine groups has been performed with a high yield, as demonstrated by the 1H NMR and MALDI-TOF spectroscopies. This has resulted in the preparation of viscoelastic irreversible hydrogels through the "in-situ" cross-linking of E50I60 with another ELR (coded as VKV24) containing amine groups from lysines (K). The rheology analysis demonstrated that the gelation process takes place following a dual mechanism dependent on the ELR concentration: physical cross-linking of I60 block through the hydrophobic interactions, and covalent cross-linking of E50I60 with VKV24 through the amidation reaction. While the chemical network formed between the hydrophilic E50 block and VKV24 ELR preserves the elasticity of ELR hydrogels, the self-assembly of the I60 block through the hydrophobic interactions provides a tunable physical network. The presented investigation serves as a basis for generating ELR hydrogels with tunable viscoelastic properties promising for tissue regeneration, through an ''in-situ", rapid, scalable, economically and feasible one-pot method.

Vaginal reconstruction with a double-sided biomembrane-a preclinical experimental study on large animals

Tissue engineering techniques bring the promise of vaginal reconstruction with low invasiveness and fewer complications. However, existing biomaterial scaffolds remain limited in efficient vaginal recovery, focusing only on regenerating an epithelial layer, but muscle layers are missing or abnormal. The lack of a multi-tissue hierarchical structure in the reconstructed vagina leads to shrinking, stenosis, and fibrosis. Here, an acellular matrix named a double-sided biomembrane (DBM) is demonstrated for vaginal recovery. The regeneration of epithelial and muscle layers is achieved simultaneously since the smooth side of the DBM is helpful for guiding epithelial cell growth, while its loose and porous side guides muscle cell growth. In addition, the DBM demonstrates excellent mechanical properties similar to vaginal tissue, and hydrophilicity. Therefore, neovaginas were observed in the fourth and twelfth weeks after DBMs were transplanted to repair full-thickness vaginal defects (4 cm) that we established in large animals. The DBMs can effectively promote rapid epithelialization, the formation of large muscle bundles, higher rates of angiogenesis, and the restoration of physiological function in a neovagina. That is, the injured vagina achieves nearly complete recovery in anatomy and function, similar to a normal vagina. These preclinical results indicate that the DBM has prospects for vaginal injury repair.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Protein scaffolds in human clinics

Fundamental clinical areas such as drug delivery and regenerative medicine require biocompatible materials as mechanically stable scaffolds or as nanoscale drug carriers. Among the wide set of emerging biomaterials, polypeptides offer enticing properties over alternative polymers, including full biocompatibility, biodegradability, precise interactivity, structural stability and conformational and functional versatility, all of them tunable by conventional protein engineering. However, proteins from non-human sources elicit immunotoxicities that might bottleneck further development and narrow their clinical applicability. In this context, selecting human proteins or developing humanized protein versions as building blocks is a strict demand to design non-immunogenic protein materials. We review here the expanding catalogue of human or humanized proteins tailored to execute different levels of scaffolding functions and how they can be engineered as self-assembling materials in form of oligomers, polymers or complex networks. In particular, we emphasize those that are under clinical development, revising their fields of applicability and how they have been adapted to offer, apart from mere mechanical support, highly refined functions and precise molecular interactions.

Protein-based nanomaterials: a new tool for targeted drug delivery

Protein nanomaterials are well-defined, hollow protein nanoparticles comprised of virus capsids, virus-like particles, ferritin, heat shock proteins, chaperonins and many more. Protein-based nanomaterials are formed by the self-assembly of protein subunits and have numerous desired properties as drug-delivery vehicles, including being optimally sized for endocytosis, nontoxic, biocompatible, biodegradable and functionalized at three separate interfaces (external, internal and intersubunit). As a result, protein nanomaterials have been intensively investigated as functional entities in bionanotechnology, including drug delivery, nanoreactors and templates for organic and inorganic nanomaterials. Several variables influence efficient administration, particularly active targeting, cellular uptake, the kinetics of the release and systemic elimination. This review examines the wide range of medicines, loading/release processes, targeted therapies and treatment effectiveness.

Design and characterization of an in vivo injectable hydrogel with effervescently generated porosity for regenerative medicine applications

Injectable hydrogels that polymerize directly in vivo hold significant promises in clinical settings to support the repair of damaged or failing tissues. Existing systems that allow cellular and tissue ingrowth after injection are limited because of deficient porosity and lack of oxygen and nutrient diffusion inside the hydrogels. Here is reported for the first time an in vivo injectable hydrogel in which the porosity does not pre-exist but is formed concomitantly with its in situ injection by a controlled effervescent reaction. The hydrogel tailorable crosslinking, through the reaction of polyethylene glycol with lysine dendrimers, allows the mixing and injection of precursor solutions from a dual-chamber syringe while entrapping effervescently generated CO₂ bubbles to form highly interconnected porous networks. The resulting structures allow preserving modular mechanical properties (from 12.7 ± 0.9 to 29.9 ± 1.7 kPa) while being cytocompatible and conducive to swift cellular attachment, proliferation, in-depth infiltration and extracellular matrix deposition. Most importantly, the subcutaneously injected porous hydrogels are biocompatible, undergo tissue remodeling and support extensive neovascularisation, which is of significant advantage for the clinical repair of damaged tissues. Thus, the porosity and injectability of the described effervescent hydrogels, together with their biocompatibility and versatility of mechanical properties, open broad perspectives for various regenerative medicine or material applications, since effervescence could be combined with a variety of other systems of swift crosslinking. STATEMENT OF SIGNIFICANCE: A major challenge in hydrogel design is the synthesis of injectable formulations allowing easy handling and dispensing in the site of interest. However, the lack of adequate porosity inside hydrogels prevent cellular entry and, therefore, vascularization and tissue ingrowth, limiting the regenerative potential of a vast majority of injectable hydrogels. We describe here the development of an acellular hydrogel that can be injected directly in situ while allowing the simultaneous formation of porosity. Such hydrogel would facilitate handling through injection while providing a porous structure supporting vascularization and tissue ingrowth.

Synthetic biology as driver for the biologization of materials sciences

Materials in nature have fascinating properties that serve as a continuous source of inspiration for materials scientists. Accordingly, bio-mimetic and bio-inspired approaches have yielded remarkable structural and functional materials for a plethora of applications. Despite these advances, many properties of natural materials remain challenging or yet impossible to incorporate into synthetic materials. Natural materials are produced by living cells, which sense and process environmental cues and conditions by means of signaling and genetic programs, thereby controlling the biosynthesis, remodeling, functionalization, or degradation of the natural material. In this context, synthetic biology offers unique opportunities in materials sciences by providing direct access to the rational engineering of how a cell senses and processes environmental information and translates them into the properties and functions of materials. Here, we identify and review two main directions by which synthetic biology can be harnessed to provide new impulses for the biologization of the materials sciences: first, the engineering of cells to produce precursors for the subsequent synthesis of materials. This includes materials that are otherwise produced from petrochemical resources, but also materials where the bio-produced substances contribute unique properties and functions not existing in traditional materials. Second, engineered living materials that are formed or assembled by cells or in which cells contribute specific functions while remaining an integral part of the living composite material. We finally provide a perspective of future scientific directions of this promising area of research and discuss science policy that would be required to support research and development in this field.

The role of nanohydroxyapatite on the morphological, physical, and biological properties of chitosan nanofibers

OBJECTIVES

This study aimed to evaluate the effects of nanohydroxyapatite (nHAp) particles on the morphological, chemical, physical, and biological properties of chitosan electrospun nanofibers.

MATERIALS AND METHODS

nHAp particles with a 1.67 Ca/P ratio were synthesized via the aqueous precipitation method, incorporated into chitosan polymer solution (0.5 wt%), and electrospun into nHAp-loaded fibers (ChHa fibers). Neat chitosan fibers (nHAp-free, Ch fibers) were used as the control. The electrospun fiber mats were characterized using morphological, topographical, chemical, thermal, and a range of biological (antibacterial, antibiofilm, cell viability, and alkaline phosphatase [ALP] activity) analyses. Data were analyzed using ANOVA and Tukey's test (α = 0.05).

RESULTS

ChHa fibers demonstrated a bead-like morphology, with thinner (331 ± 110 nm) and smoother (Ra = 2.9 ± 0.3 μm) distribution as compared to the control fibers. Despite showing similar cell viability and ALP activity to Ch fibers, the ChHa fibers demonstrated greater antibacterial potential against most tested bacteria (except for P. intermedia), and higher antibiofilm activity against P. gingivalis biofilm.

CONCLUSIONS

The incorporation of nHAp particles did not jeopardize the overall morphology, topography, physical, and biological characteristics of the chitosan nanofibers.

CLINICAL RELEVANCE

The combination of nHAp particles with chitosan can be used to engineer bioactive, electrospun composite nanofibers with potential applications in regenerative dentistry.

Controlled Production of Elastin-like Recombinamer Polymer-Based Membranes at a Liquid-Liquid Interface by Click Chemistry

Diffusion of organic and inorganic molecules controls most industrial and biological processes that occur in a liquid phase. Although significant efforts have been devoted to the design and operation of large-scale purification systems, diffusion devices with adjustable biochemical characteristics have remained difficult to achieve. In this regard, micrometer-scale, bioinspired membranes with tunable diffusion properties have been engineered by covalent cross-linking of two elastin-like recombinamers (ELRs) at a liquid-liquid interface. The covalent approach selected provides the desired ELR-based membranes with structural support, and modulation of the concentration of the polypeptides employed confers direct control of the thickness, pore size, and diffusive properties over a broad range of molecular weights (4-150 kDa). The recombinant and versatile nature of the proteinaceous building blocks employed further paves the way to engineering bioactive motifs within the membrane scaffold, thereby widening their applicability in the biological field.

Modified acellular porcine corneal matrix in deep lamellar transplantation of rabbit cornea

This study presents to develop a modified acellular porcine corneal matrix (MAPCM) to maintain high transparency, stability and biocompatibility as a rabbit deep cornea replacement using 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide crosslinking and a mild decellularization technique. Scaffolds are translucent and remain higher amount of glycosaminoglycans after decellularization than acellular porcine corneal matrix (APCM). Enzymatic degradation kinetics and mechanical properties of scaffolds are regulated by 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide -crosslinking density. The porous structure and ultrastructure of collagenous lamellae are maintained, and the pore size of MAPCM crosslinked with 0.5% (w/v) 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide is 13.26 ± 1.65 µm, similar to that of normal porcine cornea. The transmittance of MAPCM gets 79.1 ± 0.45 to 92.7 ± 1.4% in the visible light range. Results from a CCK-8 assay indicate that MAPCM gets higher cell proliferation rate of rabbit corneal stroma cells than APCM. Since collagen fibres structural integrity and regularity of MAPCM are retained after crosslinking, the opacity and stability of MAPCM are better than those of APCM within 4 weeks of animal implantation. In addition, there is no indication of an immune response or neovascularization in or around the transplanted disc. These results reveal that MAPCM may be a more suitable scaffold for corneal substitute construction.

Small Caliber Compliant Vascular Grafts Based on Elastin-Like Recombinamers for in situ Tissue Engineering

Vascular disease is a leading cause of death worldwide, but surgical options are restricted by the limited availability of autologous vessels, and the suboptimal performance of prosthetic vascular grafts. This is especially evident for coronary artery by-pass grafts, whose small caliber is associated with a high occlusion propensity. Despite the potential of tissue-engineered grafts, compliance mismatch, dilatation, thrombus formation, and the lack of functional elastin are still major limitations leading to graft failure. This calls for advanced materials and fabrication schemes to achieve improved control on the grafts' properties and performance. Here, bioinspired materials and technical textile components are combined to create biohybrid cell-free implants for endogenous tissue regeneration. Clickable elastin-like recombinamers are processed to form an open macroporous 3D architecture to favor cell ingrowth, while being endowed with the non-thrombogenicity and the elastic behavior of the native elastin. The textile components (i.e., warp-knitted and electrospun meshes) are designed to confer suture retention, long-term structural stability, burst strength, and compliance. Notably, by controlling the electrospun layer's thickness, the compliance can be modulated over a wide range of values encompassing those of native vessels. The grafts support cell ingrowth, extracellular matrix deposition and endothelium development in vitro. Overall, the fabrication strategy results in promising off-the-shelf hemocompatible vascular implants for in situ tissue engineering by addressing the known limitations of bioartificial vessel substitutes.

Trends in the design and use of elastin-like recombinamers as biomaterials

Elastin-like recombinamers (ELRs), which derive from one of the repetitive domains found in natural elastin, have been intensively studied in the last few years from several points of view. In this mini review, we discuss all the recent works related to the investigation of ELRs, starting with those that define these polypeptides as model intrinsically disordered proteins or regions (IDPs or IDRs) and its relevance for some biomedical applications. Furthermore, we summarize the current knowledge on the development of drug, vaccine and gene delivery systems based on ELRs, while also emphasizing the use of ELR-based hydrogels in tissue engineering and regenerative medicine (TERM). Finally, we show different studies that explore applications in other fields, and several examples that describe biomaterial blends in which ELRs have a key role. This review aims to give an overview of the recent advances regarding ELRs and to encourage further investigation of their properties and applications.

A review on cellulose nanocrystals as promising biocompounds for the synthesis of nanocomposite hydrogels

Hydrogels are hydrophilic cross-linked polymer networks formed via the simple reaction of one or more monomers with the ability to retain a significant extent of water. Owing to an increased demand for environmentally friendly, biodegradable, and biocompatible products, cellulose nanocrystals (CNCs) with high hydrophilicity have emerged as a promising sustainable material for the formation of hydrogels. The cytocompatibility, swellability, and non-toxicity make CNC hydrogels of great interest in biomedical, biosensing, and wastewater treatment applications. There has been a considerable progress in the research of CNC hydrogels, as the number of scientific publications has exponentially increased (>600%) in the last five years. In this paper, recent progress in CNC hydrogels with particular emphasis on design, materials, and fabrication techniques to control hydrogel architecture, and advanced applications are discussed.

Tethering QK peptide to enhance angiogenesis in elastin-like recombinamer (ELR) hydrogels

The development of new capillary networks in engineered constructs is essential for their survival and their integration with the host tissue. It has recently been demonstrated that ELR-based hydrogels encoding different bioactivities are able to modulate their interaction with the host after injection or implantation, as indicated by an increase in cell adhesion and the ability to trigger vascularization processes. Accordingly, the aim of this study was to increase their angiogenic ability both in vitro and in vivo using a small VEGF mimetic peptide named QK, which was tethered chemically to ELR-based hydrogels containing cell-adhesion sequences in their backbone, such as REDV and RGD, as well as a proteolytic site (VGVAPG). In vitro studies were performed using a co-culture of endothelial and fibroblast cells encapsulated into the ELR-based hydrogels in order to determine cell proliferation after 21 days of culture, as well as the number of cell-cell interactions. It was found that although the presence of this peptide does not influence the morphological and rheological properties of these hydrogels, it has an effect on cell behaviour, inducing an increase in cell proliferation and the formation of endothelial cell clusters. In vivo studies demonstrate that the QK peptide enhances the formation of prominent functional capillaries at three weeks post-injection, as confirmed by H&E staining and CD31 immunohistochemistry. The newly formed functional microvasculature ensures perfusion and connection with surrounding tissues. These results show that ELR-QK hydrogels increase capillary network formation and are therefore attractive candidates for application in tissue regeneration, for example for the treatment of cardiovascular diseases such as myocardial infarction or ischemia.

Combining Catalyst-Free Click Chemistry with Coaxial Electrospinning to Obtain Long-Term, Water-Stable, Bioactive Elastin-Like Fibers for Tissue Engineering Applications

Elastic fibers are a fundamental requirement for tissue-engineered equivalents of physiologically elastic native tissues. Here, a simple one-step electrospinning approach is developed, combining i) catalyst-free click chemistry, ii) coaxial electrospinning, and iii) recombinant elastin-like polymers as a relevant class of biomaterials. Water-stable elastin-like fibers are obtained without the use of cross-linking agents, catalysts, or harmful organic solvents. The fibers can be directly exposed to an aqueous environment at physiological temperature and their morphology maintained for at least 3 months. The bioactivity of the fibers is demonstrated with human vascular cells and the potential of the process for vascular tissue engineering is shown by fabricating small-diameter tubular fibrous scaffolds. Moreover, highly porous fluffy 3D constructs are obtained without the use of specially designed collectors or sacrificial materials, further supporting their applicability in the biomedical field. Ultimately, the strategy that is developed here may be applied to other click systems, contributing to expanding their potential in medical technology.