Alginate-Collagen Fibril Composite Hydrogel

Mechanical properties of mandibular and maxillary bone collagen fibrils based on nonlocal elasticity theory

In this paper, the mechanical properties of collagen fibrils in the cortical bone and cortical-trabecular bone interface of the human mandible and maxilla have been investigated. Force-indentation curves on wet collagen fibrils are taken by applying the atomic force microscopy nanoindentation technique, and the elastic modulus is measured. The distribution of stress and strain is determined by considering an elastic medium when it is deformed by a rigid cone. Afterward, by applying the nonlocal elasticity theory and the indentation parameters, the nonlocal parameter of the collagen fibrils is calculated at the nanoscale. Finally, the elastic modulus and nonlocal modulus of the collagen fibrils are compared. According to the results, the highest and lowest values of the elastic modulus of the collagen fibrils are determined in the maxillary cortical-trabecular bone interface (4.16 ± 0.18 MPa) and mandibular cortical bone (2.03 ± 0.14 MPa), respectively. In general, in collagen fibrils, this parameter is higher in the maxillary bone than in the mandibular one. In the upper and lower jaws, the elastic modulus of collagen fibrils in the cortical-trabecular bone interface is higher than that of the cortical bone. In mandibular and maxillary bone collagen fibrils, the range of nonlocal parameter and scaling parameter e0 are computed as (0.430 ± 0.013-0.483 ± 0.011 nm) and (0.269 ± 0.006-0.302 ± 0.006), respectively. Also, the highest value of this parameter is recorded in the maxillary cortical-trabecular bone interface. The difference between the nanoscale modulus of collagen fibrils and the elastic modulus at large length scales is significant.

An Injectable Alginate Hydrogel Modified by Collagen and Fibronectin for Better Cellular Environment

Encapsulating fibroblasts in alginate hydrogels is a promising strategy to promote wound healing. However, improving the cell function within the alginate matrix remains a challenge. In this study, we engineer an injectable hydrogel through mixing alginate function with collagen and fibronectin, creating a better microenvironment for enhancing fibroblast function and cytokine secretion. We systematically analyze microstructure, mechanical properties, and fibroblast behavior of the developed hydrogel and compare it to alginate control. Our results demonstrate that inclusion collagen and fibronectin lead to the formation of fibrils on macroporous structures with pore sizes ranging from 100 to 500 μm. Compared to collagen hydrogel, the composite hydrogel shows approximately 12-fold increase in storage modulus. After encapsulating fibroblasts into the modified hydrogels, we observed increased fibroblast spreading, proliferation, and cytokine secretion when compared to neat alginate hydrogel. In addition, VEGF secretion of encapsulated fibroblasts is upregulated, indicating its pro-angiogenic potential. These findings suggest that the alginate/collagen/fibronectin hydrogel-encapsulated fibroblasts might serve as a promising therapeutic approach for wound healing.

High-Resolution Atomic Force Microscopy Investigation of Alginate Hydrogel Materials in Aqueous Media

Alginate hydrogels are frequently used in 3D bioprinting and tissue repair and regeneration. Establishing the structure-property-performance correlation of these materials would benefit significantly from high-resolution structural characterization in aqueous environments from the molecular level to continuum. This study overcomes technical challenges and enables high-resolution atomic force microscopy (AFM) imaging of hydrated alginate hydrogels in aqueous media. By combining a new sample preparation protocol with extremely gentle tapping mode AFM imaging, we characterized the morphology and regional mechanical properties of the hydrated alginate. Upon cross-linking, basic units of these hydrogel materials consist of egg-box dimers, which assemble into long fibrils. These fibrils congregate and pile up, forming a sponge-like structure, whose pore size and distribution depend on the cross-linking conditions. At the exterior, surface tension impacts the piling of fibrils, leading to stripe-like features. These structural features contribute to local, regional, and macroscopic mechanics. The outcome provides new insights into its structural characteristics from nanometers to tens of micrometers, i.e., at the dimensions pertaining to biomaterial and hydrogel-cell interactions. Collectively, the results advance our knowledge of the structure and mechanics from the nanometer to continuum, facilitating advanced applications in hydrogel biomaterials.

Injectable mineralized Sr-hydroxyapatite nanoparticles-loaded ɛ-polylysine-hyaluronic acid composite hydrogels for bone regeneration

In this study, multifunctional injectable mineralized antibacterial nanocomposite hydrogels were prepared by a homogenous distribution of high content of (up to 60 wt%) Sr-substituted hydroxyapatite (Sr-HAp) nanoparticles into covalently cross-linked ɛ-polylysine (ɛ-PL) and hyaluronic acid (HA) hydrogel network. The developed bone-targeted nanocomposite hydrogels were to synergistically combine the functional properties of bioactive Sr-HAp nanoparticles and antibacterial ɛ-PL-HA hydrogels for bone tissue regeneration. Viscoelasticity, injectability, structural parameters, degradation, antibacterial activity, and in vitro biocompatibility of the fabricated nanocomposite hydrogels were characterized. Physical performances of the ɛ-PL-HA hydrogels can be tailored by altering the mass ratio of Sr-HAp. The nanocomposite hydrogels revealed good stability against enzymatic degradation, which increased from 5 to 19 weeks with increasing the mass ratio of Sr-HAp from 40 % to 60 %. The loading of the Sr-HAp at relatively high mass ratios did not suppress the fast-acting and long-term antibacterial activity of the ɛ-PL-HA hydrogels against S. aureus and E. coli. The cell studies confirmed the cytocompatibility and pre-collagen I synthesis-promoting activity of the fabricated nanocomposite hydrogels.

Zirconium ion mediated collagen nanofibrous hydrogels with high mechanical strength

Low mechanical strength is still the key question for collagen hydrogel consisting of nanofibrils as hard tissue repair scaffolds with no loss of biological function. In this work, novel collagen nanofibrous hydrogels with high mechanical strength were fabricated based on the pre-protection of trisodium citrate masked Zr(SO4)2 solution for collagen self-assembling nanofibrils and then further coordination with Zr(SO4)2 solution. The mature collagen nanofibrils with d-period were observed in Zr(IV) mediated collagen hydrogels by AFM when the Zr(IV) concentration was ≥ 10 mmol/L, and the distribution of zirconium element was uniform. Due to the coordination of Zr(IV) with ─COOH, ─NH2 and ─OH within collagen and the tighter entanglement of collagen nanofibrils, the elastic modulus and compressive strength of Zr(IV) mediated collagen nanofibrous hydrogel were 208.3 and 1103.0 kPa, which were approximate 77 and 12 times larger than those of pure collagen hydrogel, respectively. Moreover, the environmental stability such as thermostability, swelling ability and biodegradability got outstanding improvements and could be regulated by Zr(IV) concentration. Most importantly, the resultant hydrogel showed excellent biocompatibility and even accelerated cell proliferation.

Development of alginate-collagen interpenetrating network for osteoarthritic cartilage by in situ softening

This study presents an alginate-collagen interpenetrating network (IPN) matrix of incorporating collagen fibrils into an alginate hydrogel by physical mixing and controlled gelation. The resulting matrix closely mimics the physiological and pathological stiffness range of the chondrocyte pericellular matrix (PCM). Chondrocytes were cultured within three-dimensional (3D) alginate-collagen IPN matrices with varying stiffness, namely Firm, Medium, and Soft. Alginate lyase was introduced to study the effects of the changes in stiffness of the Firm on chondrocyte response by in situ softening. The developed alginate-collagen IPN matrix displayed good cell-biocompatibility. Compared with stiffer tissue culture plastic (TCP), chondrocytes grown within Firm displayed a stabilized differentiated phenotype characterized by higher expression levels of aggrecan, collagen II, and SOX-9. Moreover, the developed alginate-collagen IPN matrix exhibited a gradually increased percentage of propidium iodide (PI)-positive dead cells with decreasing stiffness. Softer matrices directed cells towards higher proliferation rates and spherical morphologies while stimulating chondrocyte cluster formation. Furthermore, reducing Firm stiffness by in situ softening decreased aggrecan expression, contributing to matrix degradation similar to that seen in osteoarthritis (OA). Hence, the 3D alginate-collagen IPN constructs hold significant potential for in vitro replicating PCM stiffness changes observed in OA cartilage.

Quercetin-loaded sodium alginate/collagen/h-boron nitride potential wound dressings prepared using the Box-Behnken experimental design

BACKGROUND/AIMS

Natural and synthetic biocompatible polymers have received significant attention in the pharmaceutical industry due to their rapid and effective healing properties in the wound healing process. The aim of this study was to optimize the extraction of onions, the preparation of sodium alginate/collagen/hydrogen boron nitride (NaAlg/Col/h-BN) membranes using the Box-Behnken experimental design, and determine the optimal conditions for quercetin release. The study also aimed to investigate the antimicrobial and antioxidant activities of the prepared membranes and their therapeutic properties.

METHODS AND RESULTS

The prepared membranes were characterized by scanning electron microscopy (SEM), fourier transform infrared (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Antimicrobial activities were tested against Gram-negative (Gr-) Escherichia coli ATCC 25922, Klebsiella pneumonia, Enterobacter aerogenes, Gram-positive (Gr+) Staphylococcus aureus ATCC 25923, and Candida albicans ATCC 10231 pathogens. In vitro release studies were conducted to examine the therapeutic properties of the prepared membranes. The optimum conditions for the extraction of onions and the preparation of NaAlg/Col/h-BN membranes were found to be EtOH = 75 mL, t = 2 h, T = 45°C, and NaAlg = 1.0 g, Col = 2.0 g, and h-BN = 6% wt, respectively. The prepared membranes exhibited serious antimicrobial properties against S. aureus and C. albicans. The membranes also promoted the controlled release of quercetin for 24 h in vitro, indicating their potential as a new approach in wound treatment.

CONCLUSION

The study concludes that quercetin-filled NaAlg/Col/h-BN membranes have promising therapeutic properties for wound healing. The membranes exhibited significant antimicrobial and antioxidant properties, and their controlled release of quercetin suggests their potential for use in wound healing applications.

Hierarchical Mechanical Transduction of Precision-Engineered DNA Hydrogels with Sacrificial Bonds

Engineering the response to external signals in mechanically switchable hydrogels is important to promote smart materials applications. However, comparably little attention has focused on embedded precision mechanisms for autonomous nonlinear response in mechanical profiles in hydrogels, and we lack understanding of how the behavior from the molecular scale transduces to the macroscale. Here, we design a nonlinear stress-strain response into hydrogels by engineering sacrificial DNA hairpin loops into model network hydrogels formed from star-shaped building blocks. We characterize the force-extension response of single DNA hairpins and are able to describe how the specific topology influences the nonlinear mechanical behavior at different length scales. For this purpose, we utilize force spectroscopy as well as microscopic and macroscopic deformation tests. This study contributes to a better understanding of designing nonlinear strain-adaptive features into hydrogel materials.

Biomaterials / bioinks and extrusion bioprinting

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

Magnetic Nanofibrous Hydrogels for Dynamic Control of Stem Cell Differentiation

The extracellular matrix in tissue consists of complex heterogeneous soft materials with hierarchical structure and dynamic mechanical properties dictating cell and tissue level function. In many natural matrices, there are nanofibrous structures that serve to guide cell activity and dictate the form and function of tissue. Synthetic hydrogels with integrated nanofibers can mimic the structural properties of native tissue; however, model systems with dynamic mechanical properties remain elusive. Here we demonstrate modular nanofibrous hydrogels that can be reversibly stiffened in response to applied magnetic fields. Iron oxide nanoparticles were incorporated into gelatin nanofibers through electrospinning, followed by chemical stabilization and fragmentation. These magnetoactive nanofibers can be mixed with virtually any hydrogel material and reversibly stiffen the matrix at a low fiber content (≤3%). In contrast to previous work, where a large quantity of magnetic material disallowed cell encapsulation, the low nanofiber content allows matrix stiffening with cells in 3D. Using adipose derived stem cells, we show how nanofibrous matrices are beneficial for both osteogenesis and adipogenesis, where stiffening the hydrogel with applied magnetic fields enhances osteogenesis while discouraging adipogenesis. Skeletal myoblast progenitors were used as a model of tissue morphogenesis with matrix stiffening augmenting myogenesis and multinucleated myotube formation. The ability to reversibly stiffen fibrous hydrogels through magnetic stimulation provides a useful tool for studying nanotopography and dynamic mechanics in cell culture, with a scope for stimuli responsive materials for tissue engineering.

Electrochemical Wearable Biosensors and Bioelectronic Devices Based on Hydrogels: Mechanical Properties and Electrochemical Behavior

Hydrogel-based wearable electrochemical biosensors (HWEBs) are emerging biomedical devices that have recently received immense interest. The exceptional properties of HWEBs include excellent biocompatibility with hydrophilic nature, high porosity, tailorable permeability, the capability of reliable and accurate detection of disease biomarkers, suitable device-human interface, facile adjustability, and stimuli responsive to the nanofiller materials. Although the biomimetic three-dimensional hydrogels can immobilize bioreceptors, such as enzymes and aptamers, without any loss in their activities. However, most HWEBs suffer from low mechanical strength and electrical conductivity. Many studies have been performed on emerging electroactive nanofillers, including biomacromolecules, carbon-based materials, and inorganic and organic nanomaterials, to tackle these issues. Non-conductive hydrogels and even conductive hydrogels may be modified by nanofillers, as well as redox species. All these modifications have led to the design and development of efficient nanocomposites as electrochemical biosensors. In this review, both conductive-based and non-conductive-based hydrogels derived from natural and synthetic polymers are systematically reviewed. The main synthesis methods and characterization techniques are addressed. The mechanical properties and electrochemical behavior of HWEBs are discussed in detail. Finally, the prospects and potential applications of HWEBs in biosensing, healthcare monitoring, and clinical diagnostics are highlighted.

Enhanced growth and differentiation of neural stem cells on alginate/collagen/reduced graphene oxide composite hydrogel incorporated with lithium chloride

Introduction

Cell transplantation with hydrogel-based carriers is one of the advanced therapeutics for challenging diseases, such as spinal cord injury. Electrically conductive hydrogel has received much attention for its effect on nerve outgrowth and differentiation. Besides, a load of neuroprotective substances, such as lithium chloride can promote the differentiation properties of the hydrogel.

Methods

In this study, alginate/collagen/reduced graphene oxide hydrogel loaded with lithium chloride (AL/CO/rGO Li+) was prepared as an injectable cell delivery system for neural tissue regeneration. After determining the lithium-ion release profile, an MTT assay was performed to check neural viability. In the next step, real-time PCR was performed to evaluate the expression of cell adhesion and neurogenic markers.

Results

Our results showed that the combination of collagen fibers and rGO with alginates increased cell viability and the gene expression of collagen-binding receptor subunits such as integrin α1, and β1. Further, rGO contributed to the controlled release of lithium-ion hydrogel in terms of its plenty of negatively charged functional groups. The continuous culture of NSCs on AL/CO/rGO Li+ hydrogel increased neurogenic genes' expressions of nestin (5.9 fold), NF200 (36.8 fold), and synaptophysin (13.2 fold), as well as protein expression of NF200 and synaptophysin after about 14 days.

Conclusion

The simultaneous ability of electrical conduction and lithium-ion release of AL/CO/rGO Li+ hydrogel could provide a favorable microenvironment for NSCs by improving their survival, maintaining cell morphology, and expressing the neural marker. It may be potentially used as a therapeutic approach for stem cell transplantation in a spinal cord injury.

Cross-linked CMC/Gelatin bio-nanocomposite films with organoclay, red cabbage anthocyanins and pistacia leaves extract as active intelligent food packaging: colorimetric pH indication, antimicrobial/antioxidant properties, and shrimp spoilage tests

Multifunctional food packaging films were produced from crosslinked carboxymethyl cellulose/gelatin (CMC/Ge) bio-nanocomposites incorporated with Ge-montmorillonite (OM) nanofiller, anthocyanins (ATH) from red cabbage as colorimetric pH-indicator, and pistacia leaves extract (PE) as active agent. The influence of additives on the structural, physical, and functional properties of the films was investigated. The results showed that ATH and PE caused color alteration and reduced transparency. However, they improved the UV light barrier ability by 98 %, with less impact from OM, despite its well-dispersed state in the matrix. Increasing PE content in the bio-nanocomposite films caused an increase in compactness and surface roughness, reduction in moisture content (15.10-12.33 %), swelling index (354.55-264.58 %), surface wettability (contact angle 80.1-92.49°), water vapor permeability (7.37-5.69 × 10¹⁰ g m^-1s^-1Pa^-1), and nano-indentation mechanical parameters, without affecting the thermal stability. ATH-included films demonstrated color pH-sensitivity with improved ATH color stability through the ATH-Al³⁺ chelates formation. PE-added films exhibited effective antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, reaching 93 % of inhibition, and antimicrobial properties with biocidal effects for PE-rich film. The shrimp spoilage test showed that the T-1.5PE film offered the strongest active intelligent response. The CMC/Ge-based bio-nanocomposite films endowed with antioxidant/antimicrobial properties and colorimetric pH-sensitivity have promising potential for food packaging application.

3D-Printing of Silk Nanofibrils Reinforced Alginate for Soft Tissue Engineering

The main challenge of extrusion 3D bioprinting is the development of bioinks with the desired rheological and mechanical performance and biocompatibility to create complex and patient-specific scaffolds in a repeatable and accurate manner. This study aims to introduce non-synthetic bioinks based on alginate (Alg) incorporated with various concentrations of silk nanofibrils (SNF, 1, 2, and 3 wt.%) and optimize their properties for soft tissue engineering. Alg-SNF inks demonstrated a high degree of shear-thinning with reversible stress softening behavior contributing to extrusion in pre-designed shapes. In addition, our results confirmed the good interaction between SNFs and alginate matrix resulted in significantly improved mechanical and biological characteristics and controlled degradation rate. Noticeably, the addition of 2 wt.% SNF improved the compressive strength (2.2 times), tensile strength (5 times), and elastic modulus (3 times) of alginate. In addition, reinforcing 3D-printed alginate with 2 wt.% SNF resulted in increased cell viability (1.5 times) and proliferation (5.6 times) after 5 days of culturing. In summary, our study highlights the favorable rheological and mechanical performances, degradation rate, swelling, and biocompatibility of Alg-2SNF ink containing 2 wt.% SNF for extrusion-based bioprinting.

Silk Fibroin Bioink for 3D Printing in Tissue Regeneration: Controlled Release of MSC extracellular Vesicles

Sodium alginate (SA)-based hydrogels are often employed as bioink for three-dimensional (3D) scaffold bioprinting. They offer a suitable environment for cell proliferation and differentiation during tissue regeneration and also control the release of growth factors and mesenchymal stem cell secretome, which is useful for scaffold biointegration. However, such hydrogels show poor mechanical properties, fast-release kinetics, and low biological performance, hampering their successful clinical application. In this work, silk fibroin (SF), a protein with excellent biomechanical properties frequently used for controlled drug release, was blended with SA to obtain improved bioink and scaffold properties. Firstly, we produced a printable SA solution containing SF capable of the conformational change from Silk I (random coil) to Silk II (β-sheet): this transition is a fundamental condition to improve the scaffold's mechanical properties. Then, the SA-SF blends' printability and shape fidelity were demonstrated, and mechanical characterization of the printed hydrogels was performed: SF significantly increased compressive elastic modulus, while no influence on tensile response was detected. Finally, the release profile of Lyosecretome-a freeze-dried formulation of MSC-secretome containing extracellular vesicles (EV)-from scaffolds was determined: SF not only dramatically slowed the EV release rate, but also modified the kinetics and mechanism release with respect to the baseline of SA hydrogel. Overall, these results lay the foundation for the development of SA-SF bioinks with modulable mechanical and EV-release properties, and their application in 3D scaffold printing.

Polydopamine-Coated Alginate Microgels: Process Optimization and In Vitro Validation

In the last decade, alginate-based microgels have gained relevant interest as three-dimensional analogues of extracellular matrix, being able to support cell growth and functions. In this study, core-shell microgels were fabricated by self-polymerization of dopamine (DA) molecules under mild oxidation and in situ precipitation of polydopamine (PDA) onto alginate microbeads, processed by electro fluid dynamic atomization. Morphological (optical, SEM) and chemical analyses (ATR-FTIR, XPS) confirmed the presence of PDA macromolecules, distributed onto the microgel surface. Nanoindentation tests also indicated that the PDA coating can influence the biomechanical properties of the microgel surfaces-i.e., σmaxALG = 0.45 mN vs. σmaxALG@PDA = 0.30 mN-thus improving the interface with hMSCs as confirmed by in vitro tests; in particular, protein adsorption and viability tests show a significant increase in adhesion and cell proliferation, strictly related to the presence of PDA. Hence, we concluded that PDA coating contributes to the formation of a friendly interface able to efficiently support cells' activities. In this perspective, core-shell microgels may be suggested as a novel symmetric 3D model to study in vitro cell interactions.

Utilizing Fish Skin of Ikan Belida (Notopterus lopis) as a Source of Collagen: Production and Rheology Properties

Collagen hydrogels have been extensively applied in biomedical applications. However, their mechanical properties are insufficient for such applications. Our previous study showed improved mechanical properties when collagen was blended with alginate. The current study aims to analyze the physico-chemical properties of collagen-alginate (CA) films such as swelling, porosity, denaturation temperature (Td), and rheology properties. Collagen was prepared from discarded fish skin of Ikan Belida (Notopterus lopis) that was derived from fish ball manufacturing industries and cross-linked with alginate from brown seaweed (Sargasum polycystum) of a local species as a means to benefit the downstream production of marine industries. CA hydrogels were fabricated with ratios (v/v) of 1:1, 1:4, 3:7, 4:1, and 7:3 respectively. FTIR spectrums of CA film showed an Amide I shift of 1636.12 cm−1 to 1634.64 cm−1, indicating collagen-alginate interactions. SEM images of CA films show a porous structure that varied from pure collagen. DSC analysis shows Td was improved from 61.26 °C (collagen) to 83.11 °C (CA 3:7). CA 4:1 swelled nearly 800% after 48 h, correlated with the of hydrogels porosity. Most CA demonstrated visco-elastic solid characteristics with greater storage modulus (G′) than lost modulus (G″). Shear thinning and non-Newtonian behavior was observed in CA with 0.4% to 1.0% (w/v) CaCl2. CA hydrogels that were derived from discarded materials shows promising potential to serve as a wound dressing or ink for bio printing in the future.

Simple synthesis of soft, tough, and cytocompatible biohybrid composites

Collagen is the most abundant component of mammalian extracellular matrices. As such, the development of materials that mimic the biological and mechanical properties of collagenous tissues is an enduring goal of the biomaterials community. Despite the development of molded and 3D printed collagen hydrogel platforms, their use as biomaterials and tissue engineering scaffolds is hindered by either low stiffness and toughness or processing complexity. Here, we demonstrate the development of stiff and tough biohybrid composites by combining collagen with a zwitterionic hydrogel through simple mixing. This combination led to the self-assembly of a nanostructured fibrillar network of collagen that was ionically linked to the surrounding zwitterionic hydrogel matrix, leading to a composite microstructure reminiscent of soft biological tissues. The addition of 5-15 mg mL^-1 collagen and the formation of nanostructured fibrils increased the elastic modulus of the composite system by 40% compared to the base zwitterionic matrix. Most notably, the addition of collagen increased the fracture energy nearly 11-fold ([Formula: see text] 180 J m^-2) and clearly delayed crack initiation and propagation. These composites exhibit elastic modulus ([Formula: see text] 0.180 MJ) and toughness ([Formula: see text]0.617 MJ m^-3) approaching that of biological tissues such as articular cartilage. Maintenance of the fibrillar structure of collagen also greatly enhanced cytocompatibility, improving cell adhesion more than 100-fold with >90% cell viability.

Injectable three-dimensional tumor microenvironments to study mechanobiology in ovarian cancer

Epithelial ovarian cancers are among the most aggressive forms of gynecological malignancies. Despite the advent of poly adenosine diphosphate-ribose polymerase (PARP) and checkpoint inhibitors, improvement to patient survival has been modest. Limited in part by clinical translation, beneficial therapeutic strategies remain elusive in ovarian cancers. Although elevated levels of extracellular proteins, including collagens, proteoglycans, and glycoproteins, have been linked to chemoresistance, they are often missing from the processes of drug- development and screening. Biophysical and biochemical signaling from the extracellular matrix (ECM) determine cellular phenotype and affect both tumor progression and therapeutic response. However, many state-of-the-art tumor models fail to mimic the complexities of the tumor microenvironment (TME) and omit key signaling components. In this article, two interpenetrating network (IPN) hydrogel scaffold platforms, comprising of alginate-collagen or agarose-collagen, have been characterized for use as 3D in vitro models of epithelial ovarian cancer ECM. These highly tunable, injection mold compatible, and inexpensive IPNs replicate the critical governing physical and chemical signaling present within the ovarian TME. Additionally, an effective and cell-friendly live-cell retrieval method has been established to recover cells post-encapsulation. Lastly, functional mechanotransduction in ovarian cancers was demonstrated by increasing scaffold stiffness within the 3D in vitro ECM models. With these features, the agarose-collagen and alginate-collagen hydrogels provide a robust TME for the study of mechanobiology in epithelial cancers. STATEMENT OF SIGNIFICANCE: Ovarian cancer is the most lethal gynecologic cancer afflicting women today. Here we present the development, characterization, and validation of 3D interpenetrating platforms to shift the paradigm in standard in vitro modeling. These models help elucidate the roles of biophysical and biochemical cues in ovarian cancer progression. The agarose-collagen and alginate-collagen interpenetrating network (IPN) hydrogels are simple to fabricate, inexpensive, and can be modified to create custom mechanical stiffnesses and concentrations of bio-adhesive motifs. Given that investigations into the roles of biophysical characteristics in ovarian cancers have provided incongruent results, we believe that the IPN platforms will be critically important to uncovering molecular drivers. We also expect these platforms to be broadly applicable to studies involving mechanobiology in solid tumors.

3D Bioprinted Alginate-Silk-Based Smart Cell-Instructive Scaffolds for Dual Differentiation of Human Mesenchymal Stem Cells

Designing smart bioinks, which can provide multifunctionality and instructive cues to cells, is a current need of the tissue engineering field. Addressing these parameters, this work aims at developing a smart dual 3D bioprinted scaffold that is capable of differentiating human mesenchymal stem cells into two different lineages within the same construct without providing any exogenous cues. Here, biocompatible alginate- and silk-based bioinks were developed to print self-standing structures with the ability of spatially controlled differentiation of the encapsulated hMSCs. We present this proof of concept and have demonstrated a smart design where the incorporation of phosphate groups enhanced the osteogenic differentiation, whereas the addition of silk promoted the chondrogenic differentiation. Altogether, the present work suggests the potential of the developed bioinks for use in creating clinically viable osteochondral grafts.

Immunomodulatory Microgels Support Proregenerative Macrophage Activation and Attenuate Fibroblast Collagen Synthesis

Scars composed of fibrous connective tissues are natural consequences of injury upon incisional wound healing in soft tissues.  Hydrogels that feature a sustained presentation of immunomodulatory cytokines are known to modulate wound healing. However, existing immunomodulatory hydrogels lack interconnected micropores to promote cell ingrowth. Other limitations include invasive delivery procedures and harsh synthesis conditions that are incompatible with drug molecules. Here, hybrid nanocomposite microgels containing interleukin-10 (IL-10) are reported to modulate tissue macrophage phenotype during wound healing. The intercalation of laponite nanoparticles in the polymer network yields microgels with tissue-mimetic elasticity (Young's modulus in the range of 2-6 kPa) and allows the sustained release of IL-10 to promote the differentiation of macrophages toward proregenerative phenotypes. The porous interstitial spaces between microgels promote fibroblast proliferation and fast trafficking (an average speed of ≈14.4 µm h^-1 ). The incorporation of hyaluronic acid further enhances macrophage infiltration. The coculture of macrophages and fibroblasts treated with transforming growth factor-beta 1 resulted in a twofold reduction in collagen-I production for microgels releasing IL-10 compared to the IL-10 free group. The new microgels show potential toward regenerative healing by harnessing the antifibrotic behavior of host macrophages.

Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications-Possibilities and Limits

Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on the force between the scanning tip and the sample, interactions have to be taken into account, making the AFM of irregular samples complicated, but on the other hand it allows measurements of more physical parameters than pure topography. This is especially important for biopolymers and hydrogels used in tissue engineering and other biotechnological applications, where elastic properties, surface charges and other parameters influence mammalian cell adhesion and growth as well as many other effects. This review gives an overview of AFM modes relevant for the investigations of biopolymers and hydrogels and shows several examples of recent applications, focusing on the polysaccharides chitosan, alginate, carrageenan and different hydrogels, but depicting also a broader spectrum of materials on which different AFM measurements are reported in the literature.

Recent advances in piezocatalytic polymer nanocomposites for wastewater remediation

Among several forms of water pollutants, common pesticides, herbicides, organic dyes and heavy metals present serious and persistent threats to human health due to their severe toxicity. Recently, piezocatalysis based removal of pollutants has become a promising field of research to combat such pollutions by virtue of the piezoelectric effect. In reality, piezoelectric materials can produce electron-hole separation upon external vibration, which greatly enhances the production of various reactive oxygen species (ROS) and further increases the pollutant degradation rate. Piezocatalysis does not alter the quality or composition of water, like several other conventional techniques (adsorption and photocatalysis), which makes this technique non-invasive. The simplicity and tremendously high efficacy of piezocatalysis have attracted researchers worldwide and thus various functional materials are employed for piezocatalytic wastewater remediation. In this frontier, we highlight and demonstrate recent developments on polymer based piezocatalytic nanocomposites to treat industrial wastewater in a facile manner that holds strong potential to be translated into a clean and green technology.

In-situ stable injectable collagen-based hydrogels for cell and growth factor delivery

Here we report development of in-situ stable injectable hydrogels for delivery of cells and growth factors based on two precursors, alginate, and collagen/calcium sulfate (CaSO4). The alg/col hydrogels were shear-thinning, injectable through commercially available needles and stable right after injection. Rheological measurements revealed that pre-crosslinked alg/col hydrogels fully crosslinked at 37°C and that the storage modulus of alg/col hydrogels increased with increasing the collagen content or the concentration of CaSO4. The viscoelastic characteristics and injectability of the alg/col hydrogels were not significantly impacted by the storage of precursor solutions for 28 days. An osteoinductive bone morphogenic protein-2 (BMP-2) loaded into alg/col hydrogels was released in 14 days. Human mesenchymal stem cells (hMSCs) encapsulated in alg/col hydrogels had over 90% viability over 7 days after injection. The DNA content of hMSC-laden alg/col hydrogels increased by 6-37 folds for 28 days, depending on the initial cell density. In addition, hMSCs encapsulated in alg/col hydrogels and incubated in osteogenic medium were osteogenically differentiated and formed a mineralized matrix. Finally, a BMP-2 loaded alg/col hydrogel was used to heal a critical size calvarial bone defect in rats after 8 weeks of injection. The alg/col hydrogel holds great promise in tissue engineering and bioprinting applications.

Alginate-magnetic short nanofibers 3D composite hydrogel enhances the encapsulated human olfactory mucosa stem cells bioactivity for potential nerve regeneration application

The design of 3D hydrogel constructs to elicit highly controlled cell response is a major field of interest in developing tissue engineering. The bioactivity of encapsulated cells inside pure alginate hydrogel is limited by its relatively inertness. Combining short nanofibers within a hydrogel serves as a promising method to develop a cell friendly environment mimicking the extracellular matrix. In this paper, we fabricated alginate hydrogels incorporating different magnetic short nanofibers (M.SNFs) content for olfactory ecto-mesenchymal stem cells (OE-MSCs) encapsulation. Wet-electrospun gelatin and superparamagnetic iron oxide nanoparticles (SPIONs) nanocomposite nanofibers were chopped using sonication under optimized conditions and subsequently embedded in alginate hydrogels. The storage modulus of hydrogel without M.SNFs as well as with 1 and 5 mg/mL of M.SNFs were in the range of nerve tissue. For cell encapsulation, OE-MSCs were used as a new hope for neuronal regeneration due to their neural crest origin. Resazurin analyses and LIVE/DEAD staining confirmed that the composite hydrogels containing M.SNFs can preserve the cell viability after 7 days. Moreover, the proliferation rate was enhanced in M.SNF/hydrogels compared to alginate hydrogel. The presence of SPIONs in the short nanofibers can accelerate neural-like differentiation of OE-MSCs rather than the sample without SPIONs.

Osteoblastic differentiation of stem cells induced by graphene oxide-hydroxyapatite-alginate hydrogel composites and construction of tissue-engineered bone

This study aimed to investigate the effect of graphene oxide (GO)-hydroxyapatite (HA)-sodium alginate (SA) composite application in the field of bone tissue engineering. Four scaffold groups were established (SA-HA, SA-HA-0.8%GO, SA-HA-1.0%GO and SA-HA-1.2%GO) and mixed with bone marrow mesenchymal stem cells (BMSCs). Hydrogel viscosity was measured at room temperature, and after freeze-drying and Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) to detect substance crystallinity, the printability of each hydrogel type was measured with a printing grid. Scanning electron microscopy (SEM) was used to observe the internal microstructure of the scaffolds and to evaluate the growth and proliferation of cells on the scaffold. A hollow cylinder was printed to compare the forming effect of the hydrogel bioinks, and cell-hydrogel composites were implanted under the skin of nude mice to observe the effect of the hydrogels on osteogenesis in vivo. Increased GO concentrations led to reduced scaffold degradation rates, increased viscosity, increased printability, increased mechanical properties, increased scaffold porosity and increased cell proliferation rates. In vivo experiments showed that hematoxylin and eosin (HE) staining, Alizarin red staining, alkaline phosphatase staining and collagen type I immunohistochemical staining increased as the implantation time increased. These results demonstrate that GO composites have high printability as bioinks and can be used for bioprinting of bone by altering the ratio of the different components.

Tissue mimetic hyaluronan bioink containing collagen fibers with controlled orientation modulating cell migration and alignment

Biofabrication is providing scientists and clinicians the ability to produce engineered tissues with desired shapes and gradients of composition and biological cues. Typical resolutions achieved with extrusion-based bioprinting are at the macroscopic level. However, for capturing the fibrillar nature of the extracellular matrix (ECM), it is necessary to arrange ECM components at smaller scales, down to the micron and the molecular level. Herein, we introduce a bioink containing the tyramine derivative of hyaluronan (HA; henceforth known as THA) and collagen (Col) type 1. In this bioink, similar to connective tissues, Col is present in the fibrillar form, and HA functions as a viscoelastic space filler. THA was enzymatically cross-linked under mild conditions allowing simultaneous Col fibrillogenesis, thus achieving a homogeneous distribution of Col fibrils within the viscoelastic HA-based matrix. The THA-Col composite displayed synergistic properties in terms of storage modulus and shear thinning, translating into good printability. Shear-induced alignment of the Col fibrils along the printing direction was achieved and quantified via immunofluorescence and second-harmonic generation. Cell-free and cell-laden constructs were printed and characterized, analyzing the influence of the controlled microscopic anisotropy on human bone marrow-derived mesenchymal stromal cell (hMSC) migration. Anisotropic HA-Col showed cell-instructive properties modulating hMSC adhesion, morphology, and migration from micropellets stimulated by the presence and the orientation of Col fibers. Actin filament staining showed that hMSCs embedded in aligned constructs displayed increased cytoskeleton alignment along the fibril direction. Based on gene expression of cartilage/bone markers and ECM production, hMSCs embedded in the isotropic bioink displayed chondrogenic differentiation comparable with standard pellet culture by means of proteoglycan production (safranin O staining and proteoglycan quantification). The possibility of printing matrix components with control over microscopic alignment brings biofabrication one step closer to capturing the complexity of native tissues.

Fabrication of Nanofibrous/Xerogel Layer-by-Layer Biocomposite Scaffolds for Skin Tissue Regeneration: In Vitro Study

Skin burn wounds are a crucial issue that could reduce life quality. Although numerous effective skin products have invaded the biomedical market, most of them still demonstrate some limitations regarding their porosity, swelling and degradation behaviors, antibacterial properties, and cytotoxicity. Thus, the aim of this study is to fabricate novel trilayered asymmetric porous scaffolds that can mimic the natural skin layers. In particular, the fabricated scaffold constitutes an upper electrospun chitosan-poly(vinyl alcohol) layer and a lower xerogel layer, which is made of effective skin extracellular matrix components. Both layers are fixed together using fibrin glue as a middle layer. The results of this study revealed promising scaffold swelling capability suitable for absorbing wound exudates, followed by a constant degradable weight over time, which is appropriate for a burn wound environment. Scanning electron microscopy images revealed an average pore diameter in the range of 138.39-170.18 nm for the cross-linked electrospun mats and an average pore size of 2.29-30.62 μm for the fabricated xerogel layers. This further provided an optimum environment for fibroblast migration and proliferation. The electrospun nanofibrous layer was examined for its antibacterial properties and showed expressive complete bacterial inhibition against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains (log reduction = 3 and 2.70, respectively). Next, mouse embryonic fibroblast cytotoxicity and migration rate were investigated against the developed asymmetrical composite to assess its biocompatibility. Tissue culture experiments demonstrated significant cell proliferation and migration in the presence of the constructed scaffold (P < 0.0001). A complete wound closure was observed in vitro in the presence of the three scaffold asymmetrical layers against the mouse embryonic fibroblast. The results of this study proved superior biological characteristics of the innovative asymmetrical composite that could further replace the burned or damaged skin layers with promising potential for clinical applications.

Comparison of the Structural Characteristics of Native Collagen Fibrils Derived from Bovine Tendons using Two Different Methods: Modified Acid-Solubilized and Pepsin-Aided Extraction

Native collagen fibrils (CF) were successfully extracted from bovine tendons using two different methods: modified acid-solubilized extraction for A-CF and pepsin-aided method for P-CF. The yields of A-CF and P-CF were up to 64.91% (±1.07% SD) and 56.78% (±1.22% SD) (dry weight basis), respectively. The analyses of both amino acid composition and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that A-CF and P-CF were type I collagen fibrils. Both A-CF and P-CF retained the intact crystallinity and integrity of type I collagen’s natural structure by FTIR spectra, circular dichroism spectroscopy (CD) and X-ray diffraction detection. The aggregation structures of A-CF and P-CF were displayed by UV–Vis. However, A-CF showed more intact aggregation structure than P-CF. Microstructure and D-periodicities of A-CF and P-CF were observed (SEM and TEM). The diameters of A-CF and P-CF are about 386 and 282 nm, respectively. Although both A-CF and P-CF were theoretically concordant with the Schmitt hypothesis, A-CF was of evener thickness and higher integrity in terms of aggregation structure than P-CF. Modified acid-solubilized method provides a potential non-enzyme alternative to extract native collagen fibrils with uniform thickness and integral aggregation structure.

Characterisation of hydrogels: Linking the nano to the microscale

Hydrogels are water enriched soft materials widely used for applications as varied as super absorbents, breast implants and contact lenses. Hydrogels have also been designed for smart functional devices including drug delivery, tissue engineering and diagnostics such as blood typing. The hydrogel properties and functionality depend on their crosslinking density, water holding capacity and fibre/polymer composition, strength and internal structure. Determining these parameters and properties are challenging. This review presents the main characterisation methods providing both qualitative and quantitative information of the structures and compositions of hydrogel. The length scale of interest ranges from the nano to the micro scale and the techniques and results are analysed in relationship to the hydrogel macroscopic applications. The characterisation methods examined aim at quantifying swelling, mechanical strength, mesh size, bound and free water content, pore structure, chemical composition, strength of chemical bonds and mechanical strength. These hydrogel parameters enable us to understand the fundamental mechanisms of hydrogel formation, to control their structure and functionality, and to optimize and tailor specific hydrogel properties to engineer particular applications.

Nano-fibre Integrated Microcapsules: A Nano-in-Micro Platform for 3D Cell Culture

Nano-in-micro (NIM) system is a promising approach to enhance the performance of devices for a wide range of applications in disease treatment and tissue regeneration. In this study, polymeric nanofibre-integrated alginate (PNA) hydrogel microcapsules were designed using NIM technology. Various ratios of cryo-ground poly (lactide-co-glycolide) (PLGA) nanofibres (CPN) were incorporated into PNA hydrogel microcapsule. Electrostatic encapsulation method was used to incorporate living cells into the PNA microcapsules (~500 µm diameter). Human liver carcinoma cells, HepG2, were encapsulated into the microcapsules and their physio-chemical properties were studied. Morphology, stability, and chemical composition of the PNA microcapsules were analysed by light microscopy, fluorescent microscopy, scanning electron microscopy (SEM), Fourier-Transform Infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The incorporation of CPN caused no significant changes in the morphology, size, and chemical structure of PNA microcapsules in cell culture media. Among four PNA microcapsule products (PNA-0, PNA-10, PNA-30, and PNA-50 with size 489 ± 31 µm, 480 ± 40 µm, 473 ± 51 µm and 464 ± 35 µm, respectively), PNA-10 showed overall suitability for HepG2 growth with high cellular metabolic activity, indicating that the 3D PNA-10 microcapsule could be suitable to maintain better vitality and liver-specific metabolic functions. Overall, this novel design of PNA microcapsule and the one-step method of cell encapsulation can be a versatile 3D NIM system for spontaneous generation of organoids with in vivo like tissue architectures, and the system can be useful for numerous biomedical applications, especially for liver tissue engineering, cell preservation, and drug toxicity study.

Silk fibroin-alginate based beads for human mesenchymal stem cell differentiation in 3D

Lately silk fibroin has gained a lot of popularity as a tissue engineering scaffold due to its exceptional mechanical properties, negligible inflammatory reactions, remarkable biocompatibility, and tunable biodegradability. Nonetheless, 3 dimensional (3D) silk fibroin based scaffolds, which allow simultaneous formation of scaffolds and cell encapsulation with minimal damage to the cells, are unavailable, as most of the methods involve the use of some cell destructive techniques. Thus, cells have to be loaded after the scaffold formation and the study has to rely upon the ability of the cells to penetrate the scaffold to obtain a 3D microenvironment. Hence, these platforms do not allow for a true 3D system replicating the in vivo environment. Here silk fibroin-alginate based beads have been developed, and retain silk fibroin for a longer period of time and allow for simultaneous cell encapsulation as the crosslinking method is cell-compatible. It is demonstrated for the first time that these silk fibroin-alginate beads can be used to encapsulate the cells at varying cell densities depending on the desired application. These beads were further used to study the effect of functional groups on human mesenchymal stem cell (hMSC) differentiation in 3D, by utilizing carboxylic groups naturally present in alginate as well as introducing phosphate groups. The results showed that these beads were able to support the growth and proliferation of hMSCs and induced differentiation solely due to functional groups within 14 days. These beads were better in directing hMSC differentiation into osteogenic and chondrogenic lineages compared to 2D surfaces and differentiation media.

Blended alginate/collagen hydrogels promote neurogenesis and neuronal maturation

Brain extracellular matrix (ECM) is complex, heterogeneous and often poorly replicated in traditional 2D cell culture systems. The development of more physiologically relevant 3D cell models capable of emulating the native ECM is of paramount importance for the study of human induced pluripotent stem cell (iPSC)-derived neurons. Due to its structural similarity with hyaluronic acid, a primary component of brain ECM, alginate is a potential biomaterial for 3D cell culture systems. However, a lack of cell adhesion motifs within the chemical structure of alginate has limited its application in neural culture systems. This study presents a simple and accessible method of incorporating collagen fibrils into an alginate hydrogel by physical mixing and controlled gelation under physiological conditions and tests the hypothesis that such a substrate could influence the behaviour of human neurons in 3D culture. Regulation of the gelation process enabled the penetration of collagen fibrils throughout the hydrogel structure as demonstrated by transmission electron microscopy. Encapsulated human iPSC-derived neurons adhered to the blended hydrogel as evidenced by the increased expression of α1, α2 and β1 integrins. Furthermore, immunofluorescence microscopy revealed that encapsulated neurons formed complex neural networks and matured into branched neurons expressing synaptophysin, a key protein involved in neurotransmission, along the neurites. Mechanical tuning of the hydrogel stiffness by modulation of the alginate ionic crosslinker concentration also influenced neuron-specific gene expression. In conclusion, we have shown that by tuning the physicochemical properties of the alginate/collagen blend it is possible to create different ECM-like microenvironments where complex mechanisms underpinning the growth and development of human neurons can be simulated and systematically investigated.

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Alginate and collagen are blended to create a bespoke hydrogel that mimics aspects of brain ECM.

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Encapsulated human pluripotent stem cell derived neurons adhere to the hydrogel matrix and form 3D neural networks.

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Neuronal differentiation and maturation is promoted within the hydrogel matrix.

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Mechanical properties of the hydrogel can be easily tuned to optimise neurogenesis.

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The hydrogel presents a platform for studying neuronal function and dysfunction in health and disease.

3D Encapsulation Made Easy: A Coaxial-Flow Circuit for the Fabrication of Hydrogel Microfibers Patches

To fully exploit the potential of hydrogel micro-fibers in the design of regenerative medicinal materials, we designed a simple, easy to replicate system for cell embedding in degradable fibrous scaffolds, and validated its effectiveness using alginate-based materials. For scaffold fabrication, cells are suspended in a hydrogel-precursor and injected in a closed-loop circuit, where a pump circulates the ionic cross-linking solution. The flow of the cross-linking solution stretches and solidifies a continuous micro-scaled, cell-loaded hydrogel fiber that whips, bends, and spontaneously assembles in a self-standing, spaghetti-like patch. After investigation and tuning of process- and solution-related parameters, homogeneous microfibers with controlled diameters and consistent scaffolds were obtained from different alginate concentrations and blends with biologically favorable macromolecules (i.e., gelatin or hyaluronic acid). Despite its simplicity, this coaxial-flow encapsulation system allows for the rapid and effortless fabrication of thick, well-defined scaffolds, with viable cells being homogeneously distributed within the fibers. The reduced fiber diameter and the inherent macro-porous structure that is created from the random winding of fibers can sustain mass transport, and support encapsulated cell survival. As different materials and formulations can be processed to easily create homogeneously cell-populated structures, this system appears as a valuable platform, not only for regenerative medicine, but also, more in general, for 3D cell culturing in vitro.

Integrating structural heterogeneity, fiber orientation, and recruitment in multiscale ECM mechanics

Extracellular matrix (ECM) plays critical roles in establishing tissue structure-function relationships and controlling cell fate. However, the mechanisms by which ECM mechanics influence cell and tissue behavior remain to be elucidated since the events associated with this process span length scales from the tissue to molecular level. Entirely new methods are needed in order to better understand the multiscale mechanics of ECM. In this study, a multiscale experimental approach was established by integrating Optical Magnetic Twisting Cytometry (OMTC) with a biaxial tensile tester to study the microscopic (local) ECM mechanical properties under controlled tissue-level (global) loading. Adventitial layer of porcine thoracic artery was used as a collagen-based ECM. Multiphoton microscopy imaging was performed to capture the changes in ECM fiber structure during biaxial deformation. As visualized from multiphoton microscopy images, biaxial stretch induces gradual fiber straightening and the fiber families become evident at higher stretch levels. The OMTC measurements show that the local apparent storage and loss modulus increases with the global biaxial stretch, however there exists a complex interplay among local ECM mechanical properties, ECM structural heterogeneity, and fiber distribution and engagement. The phase lag does not change significantly with global biaxial stretch. Our results also show a much faster increase in global tissue tangent modulus compared to the local apparent complex modulus with biaxial stretch, indicating the scale dependency of ECM mechanics.

In situ fabrication of a composite hydrogel with tunable mechanical properties for cartilage tissue engineering

A composite hydrogel with tunable mechanical properties has been fabricated and characterized in this study.

Cell laden alginate-keratin based composite microcapsules containing bioactive glass for tissue engineering applications

Microcapsules based on alginate-keratin, alginate dialdehyde (ADA)-keratin and ADA-keratin-45S5 bioactive glass (BG) were successfully prepared. The samples were characterized by light microscopy, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that ADA-based materials possess higher degradation rate compared to alginate-based materials. The incorporation of BG particles (mean particle size: 2.0 µm) improved the bioactivity of the materials. Moreover, the biological properties of the samples were evaluated by encapsulating MG-63 osteosarcoma cells into the microcapsules. The cell viability in all samples increased during 21 days of cultivation. However, the presence of 0.5% BG particle seemed to have initial negative effect on cell growth compared to other samples without BG. On the other hand, the positive effect of CaP formation was visible after 3 weeks in the BG containing samples. The results are relevant to consider the development of cell laden bioinks incorporating inorganic bioactive particles for biofabrication approaches.

Enhanced cellular response elicited by addition of amniotic fluid to alginate hydrogel-electrospun silk fibroin fibers for potential wound dressing application

This study aimed to evaluate a novel bioactive wound dressing from alginate hydrogel-electrospun silk fibroin (SF) fibers with the ability to deliver amniotic fluid (AF) to the wound site. AF is highly enriched with multiple therapeutic agents that can promote cellular response and wound healing. In this study, electrospun SF fibers were first fabricated by electrospinning method and then combined with the alginate hydrogel (ALG) containing AF. Different dressings were made by changing the alginate to AF ratio. The scanning electron microscopy images revealed that SF fibers were fully covered with alginate hydrogel. In addition, the modulus of the dressing decreased by lowering ALG/AF ratios, while a reverse trend was observed for the elongation-at-break. In vitro AF release profiles indicated that an increase in the concentration of ALG leads to a reduction in the AF amount. Fibroblast culturing on the fabricated dressings demonstrated that cellular proliferation, spreading, and secretion of collagen enhanced with increasing AF. Taken together, our results provide a novel bioactive dressing with great potentials for speeding up the healing process in severe wounds.

The quest for mechanically and biologically functional soft biomaterials via soft network composites

Developing multifunctional soft biomaterials capable of addressing all the requirements of the complex tissue regeneration process is a multifaceted problem. In order to tackle the current challenges, recent research efforts are increasingly being directed towards biomimetic design concepts that can be translated into soft biomaterials via advanced manufacturing technologies. Among those, soft network composites consisting of a continuous hydrogel matrix and a reinforcing fibrous network closely resemble native soft biological materials in terms of design and composition as well as physicochemical properties. This article reviews soft network composite systems with a particular emphasis on the design, biomaterial and fabrication aspects within the context of soft tissue engineering and drug delivery applications.

Functionalized thermosensitive hydrogel combined with tendon stem/progenitor cells as injectable cell delivery carrier for tendon tissue engineering

Thermosensitive hydrogels have been studied for potential application as promising alternative cell carriers in cell-based regenerative therapies. In this study, a thermosensitive butane diisocyanate (BDI)-collagen hydrogel (BC hydrogel) was designed as an injectable cell delivery carrier of tendon stem/progenitor cells (TSPCs) for tendon tissue engineering. We functionalized the BDI hydrogel with the addition of 20% (v/v) collagen I gel to obtain the thermosensitive BC hydrogel, which was then seeded with TSPCs derived from human Achilles tendons. The BC hydrogel compatibility and TSPC behavior and molecular response to the 3D hydrogel were investigated. Collagen (COL) I gel served as a control group. Our findings demonstrated that the BC hydrogel was thermosensitive, and hardened above 25 °C. It supported TSPC survival, proliferation, and metabolic activity with satisfactory dimension stability and biocompatibility, as revealed by gel contraction assay, live/dead staining, DNA quantification, and resazurin metabolic assay. Phalloidin-based visualization of F-actin demonstrated that the TSPCs were stretched within COL I gel with classical spindle cell shapes; similar cell morphologies were also found in the BC hydrogel. The gene expression profile of TSPCs in the BC hydrogel was comparable with that in COL I gel. Moreover, the BC hydrogel supported capillary-like structure formation by human umbilical vein endothelial cells (HUVECs) in the hydrogel matrix. Taken together, these results suggest that the thermosensitive BC hydrogel holds great potential as an injectable cell delivery carrier of TSPCs for tendon tissue engineering.

Silk fibroin/collagen protein hybrid cell-encapsulating hydrogels with tunable gelation and improved physical and biological properties

Cell encapsulating hydrogels with tunable mechanical and biological properties are of special importance for cell delivery and tissue engineering. Silk fibroin and collagen, two typical important biological proteins, are considered potential as cell culture hydrogels. However, both have been used individually, with limited properties (e.g., collagen has poor mechanical properties and cell-mediated shrinkage, and silk fibroin from Bombyx mori (mulberry) lacks cell adhesion motifs). Therefore, the combination of them is considered to achieve improved mechanical and biological properties with respect to individual hydrogels. Here, we show that the cell-encapsulating hydrogels of mulberry silk fibroin / collagen are implementable over a wide range of compositions, enabled simply by combining the different gelation mechanisms. Not only the gelation reaction but also the structural characteristics, consequently, the mechanical properties and cellular behaviors are accelerated significantly by the silk fibroin / collagen hybrid hydrogel approach. Of note, the mechanical and biological properties are tunable to represent the combined merits of individual proteins. The shear storage modulus is tailored to range from 0.1 to 20 kPa along the iso-compositional line, which is considered to cover the matrix stiffness of soft-to-hard tissues. In particular, the silk fibroin / collagen hydrogels are highly elastic, exhibiting excellent resistance to permanent deformation under different modes of stress; without being collapsed or water-squeezed out (vs. not possible in individual proteins) - which results from the mechanical synergism of interpenetrating networks of both proteins. Furthermore, the role of collagen protein component in the hybrid hydrogels provides adhesive sites to cells, stimulating anchorage and spreading significantly with respect to mulberry silk fibroin gel, which lacks cell adhesion motifs. The silk fibroin / collagen hydrogels can encapsulate cells while preserving the viability and growth over a long 3D culture period. Our findings demonstrate that the silk / collagen hydrogels possess physical and biological properties tunable and significantly improved (vs. the individual protein gels), implying their potential uses for cell delivery and tissue engineering.

STATEMENT OF SIGNIFICANCE

Development of cell encapsulating hydrogels with excellent physical and biological properties is important for the cell delivery and cell-based tissue engineering. Here we communicate for the first time the novel protein composite hydrogels comprised of 'Silk' and 'Collagen' and report their outstanding physical, mechanical and biological properties that are not readily achievable with individual protein hydrogels. The properties include i) gelation accelerated over a wide range of compositions, ii) stiffness levels covering 0.1 kPa to 20 kPa that mimic those of soft-to-hard tissues, iii) excellent elastic behaviors under various stress modes (bending, twisting, stretching, and compression), iv) high resistance to cell-mediated gel contraction, v) rapid anchorage and spreading of cells, and vi) cell encapsulation ability with a long-term survivability. These results come from the synergism of individual proteins of alpha-helix and beta-sheet structured networks. We consider the current elastic cell-encapsulating hydrogels of silk-collagen can be potentially useful for the cell delivery and tissue engineering in a wide spectrum of soft-to-hard tissues.

A tissue-mimetic nano-fibrillar hybrid injectable hydrogel for potential soft tissue engineering applications

While collagen type I (Col-I) is commonly used as a structural component of biomaterials, collagen type III (Col-III), another fibril forming collagen ubiquitous in many soft tissues, has not previously been used. In the present study, the novel concept of an injectable hydrogel with semi-interpenetrating polymeric networks of heterotypic collagen fibrils, with tissue-specific Col-III to Col-I ratios, in a glycol-chitosan matrix was investigated. Col-III was introduced as a component of the novel hydrogel, inspired by its co-presence with Col-I in many soft tissues, its influence on the Col-I fibrillogenesis in terms of diameter and mechanics, and its established role in regulating scar formation. The hydrogel has a nano-fibrillar porous structure, and is mechanically stable under continuous dynamic stimulation. It was found to provide a longer half-life of about 35 days than similar hyaluronic acid-based hydrogels, and to support cell implantation in terms of viability, metabolic activity, adhesion and migration. The specific case of pure Col-III fibrils in a glycol-chitosan matrix was investigated. The proposed hydrogels meet many essential requirements for soft tissue engineering applications, particularly for mechanically challenged tissues such as vocal folds and heart valves.