Roles of Silk Fibroin on Characteristics of Hyaluronic Acid/Silk Fibroin Hydrogels for Tissue Engineering of Nucleus Pulposus

A silk nanofiber and hyaluronic acid composite hemostatic sponge for compressible hemostasis

Uncontrolled traumatic blood loss is a leading cause of hemorrhagic shock and death, highlighting the critical need for compressible and rapid hemostatic first-aid materials. In this study, silk nanofibers (MA-SNFs) were prepared through maleic acid (MA) hydrolysis decorated with enriched carboxyl groups. The MA-SNFs were then combined with hyaluronic acid (HA) through EDC/NHS crosslinking to form a porous sponge (i.e., MA-SNF/HA) through freeze-drying. The fabricated MA-SNF/HA sponges demonstrated excellent blood compatibility (hemolysis ratio < 5 %), outstanding hemocompatibility (blood clotting index (BCI) < 35 % within 60 s), and good cytocompatibility (cell viability >85 %). Among the different sponges prepared, M4-H6 (MA-SNFs: HA = 4:6) exhibited the best liquid reabsorption capacity after 80 % compression, outperforming M6-H4 and M5-H5 sponges. Furthermore, M4-H6 sponge absorbed liquid rapidly (~30 s) while matching the liquid absorption capacity of commercial gelatin sponge (GS), which require over 5 min for similar absorption (2232.84 ± 141.69 %). These findings suggest that M4-H6 sponge is highly suitable for compressible hemostasis applications and provide further insights into its potential hemostatic mechanism.

Facile fabrication of nano-bioactive glass functionalized blended hydrogel with nucleus pulposus-derived MSCs to improve regeneration potential in treatment of disc degeneration by in vivo rat model

Orthopaedic medicine often treats intervertebral disc degeneration (IVDD), which is caused by nucleus pulposus (NP) tissue damage and mechanical stress. Bioactive glasses (BGs), widely used for bone regeneration, can incorporate therapeutic ions into their network. Manganese (Mn) activates human osteoblast integrins, proliferation, and spreading. The CMnBGNPs-NPMSCs are carboxymethyl cellulose hydrogels functionalized with MnBGsNPs and NP-derived mesenchymal stem cells to treat IVDD. To ensure stability and biocompatibility of CMnBGNPs-NPMSCs were characterized for rheological properties like gelation time and swelling ratio. Gene expression analysis of PAX1, FOXF1, CA12, HBB, and OVOS2 via qRT-PCR further assessed the hydrogel's characteristics. Rat models with induced IVDD had hydrogel-MSC composite injected into their intervertebral discs for in vivo studies. Histological examination, immunohistochemical staining for inflammation and disc regeneration markers, and disc height assessments assessed therapeutic efficacy. CMnBGNPs-NPMSCs show promising results for IVDD treatment, offering a novel therapeutic strategy with clinical implications for degenerative disc diseases.

Decellularized Nucleus Pulposus Matrix/Chitosan Hybrid Hydrogels for Nucleus Pulposus Tissue Engineering

STUDY DESIGN

Basic research.

OBJECTIVE

To prepared 3 DNPM/chitosan hybrid hydrogels and chose the best DNPM/chitosan hybrid hydrogel for NP tissue engineering.

METHODS

Three DNPM/chitosan hybrid hydrogels were fabricated by changing the ratio of the decellularized NP matrix to chitosan and crosslinking with genipin. NP stem cells (NPSCs) were cultured on the hybrid hydrogels and their proliferation, morphology, and gene expression were evaluated. Finally, an in vivo experiment was performed to evaluate the immune response to the hydrogels.

RESULTS

The adhered NPSCs proliferated well on the hybrid hydrogel. The gene expression of NP-related collagen type II, aggrecan, and Sox-9 from NPSCs cultured on DNPM/chitosan hybrid hydrogel-1 was greater than from cells cultured on DNPM/chitosan hybrid hydrogel-2 and DNPM/chitosan hybrid hydrogel-3. Few inflammatory cells were observed during the in vivo experiment with DNPM/chitosan hybrid hydrogel-1.

CONCLUSIONS

DNPM/chitosan hybrid hydrogel-1 is a potential candidate scaffold for NP tissue engineering.

Dopamine-dependent functions of hyaluronic acid/dopamine/silk fibroin hydrogels that highly enhance N-acetyl-L-cysteine (NAC) delivered from nasal cavity to brain tissue through a near-infrared photothermal effect on the NAC-loaded hydrogels

Hyaluronic acid/silk fibroin (HA/SF or HS) hydrogels with remarkable mechanical characteristics have been reported as tissue engineering biomaterials. Herein, the addition of dopamine/polydopamine (DA/PDA) to HS hydrogels to develop multifunctional HA/PDA/SF (or HDS) hydrogels for the delivery of drugs such as N-acetyl-L-cysteine (NAC) from nasal to brain tissue is examined. Herein, DA-dependent functions of HDS hydrogels with highly adhesive forces, photothermal response (PTR) effects generated by near infrared (NIR) irradiation, and anti-oxidative effects were demonstrated. An in-vitro study shows that the HDS/NAC hydrogels could open tight junctions in the RPMI 2650 cell line, a model cell of the nasal mucosa, as demonstrated by the decreased values of transepithelial electrical resistance (TEER) and more discrete ZO-1 staining than those for the control group. This effect was markedly enhanced by NIR irradiation of the HDS/NAC-NIR hydrogels. Compared to the results obtained using NAC solution, an in-vivo imaging study (IVIS) in rats showed an approximately nine-fold increase in the quantity of NAC delivered from the nasal cavity to the brain tissue in the span of 2 h through the PTR effect generated by the NIR irradiation of the nasal tissue and administration of the HDS/NAC hydrogels. Herein, dopamine-dependent multifunctional HDS hydrogels were studied, and the nasal administration of HDS/NAC-NIR hydrogels with PTR effects generated by NIR irradiation was found to have significantly enhanced NAC delivery to brain tissues.

Silk-hydrogel functionalized with human decellularized Wharton's jelly extracellular matrix as a minimally invasive injectable hydrogel system for potential nucleus pulposus tissue replacement therapy

Intervertebral disc degeneration is a primary cause for chronic low back pain, a common health problem with high incidence and the leading cause of disability globally. The early stages of disc degeneration in terms of functional and anatomical abnormalities start from the central nucleus pulposus tissue of the intervertebral disc; hence its regeneration has become a prime concern. A plethora of hydrogel systems have been investigated as nucleus pulposus tissue substitute over the years, with limited clinical translation. In the present study, we formulated a minimally invasive injectable cross-linker-free bioactive silk-based hybrid hydrogel system functionalized with decellularized human Wharton's jelly extracellular matrix as an ampule of bioactive cues. The centrifugation based decellularization method removed >92 % of cellular components and preserved >83 % of extracellular matrix composition. The hydrogels were investigated for secondary structure and surface properties through infrared spectroscopy and electron micrographs, respectively. Notably, the developed hydrogels were found to mimic the rheological and mechanical properties of native nucleus pulposus tissue when decellularized Wharton's jelly extracellular matrix content was 0.5 % (w/v) in the base silk hydrogel. Finally, the hydrogels were found to support cell viability, proliferation, and tissue maturation offering great potential for future applications related to nucleus pulposus tissue engineering.

Kartogenin-loaded hydrogel promotes intervertebral disc repair via protecting MSCs against reactive oxygen species microenvironment by Nrf2/TXNIP/NLRP3 axis

Intervertebral disc (IVD) degeneration (IDD) and the consequent low back pain present a major medical challenge. Stem cell-based tissue engineering is promising for the treatment of IDD. However, stem cell-based treatment is severely impaired by the increased generation of reactive oxygen species (ROS) in degenerative disc, which can lead to a high level of cell dysfunction and even death. In this study, a kartogenin (KGN)@PLGA-GelMA/PRP composite hydrogel was designed and used as a carrier of ADSCs-based therapies in disc repair. Injectable composite hydrogel act as a carrier for controlled release of KGN and deliver ADSCs to the degenerative disc. The released KGN can stimulate the differentiation of ADSCs into a nucleus pulposus (NP) -like phenotype and boost antioxidant capacity of ADSCs via activating Nrf2/TXNIP/NLRP3 axis. Furthermore, the composite hydrogel combined with ADSCs attenuated the in vivo degeneration of rat IVDs, maintained IVD tissue integrity and accelerated the synthesis of NP-like extracellular matrix. Therefore, the KGN@PLGA-GelMA/PRP composite hydrogel is a promising strategy for stem cell-based therapies of IDD.

Hyaluronic Acid as Bioink and Hydrogel Scaffolds for Tissue Engineering Applications

Bioprinting is an additive manufacturing technique that focuses on developing living tissue constructs using bioinks. Bioink is crucial in determining the stability of printed patterns, which remains a major challenge in bioprinting. Thus, the choices of bioink composition, modifications, and cross-linking methods are being continuously researched to augment the clinical translation of bioprinted constructs. Hyaluronic acid (HA) is a naturally occurring polysaccharide with the repeating unit of N-acetyl-glucosamine and d-glucuronic acid disaccharides. It is present in the extracellular matrix (ECM) of tissues (skin, cartilage, nerve, muscle, etc.) with a wide range of molecular weights. Due to the nature of its chemical structure, HA could be easily subjected to chemical modifications and cross-linking that would enable better printability and stability. These interesting properties have made HA an ideal choice of bioinks for developing tissue constructs for regenerative medicine applications. In this Review, the physicochemical properties, reaction chemistry involved in various cross-linking strategies, and biomedical applications of HA have been elaborately discussed. Further, the features of HA bioinks, emerging strategies in HA bioink preparations, and their applications in 3D bioprinting have been highlighted. Finally, the current challenges and future perspectives in the clinical translation of HA-based bioinks are outlined.

Textile Design of an Intervertebral Disc Replacement Device from Silk Yarn

Low back pain is often due to degeneration of the intervertebral discs (IVD). It is one of the most common age- and work-related problems in today's society. Current treatments are not able to efficiently restore the full function of the IVD. Therefore, the aim of the present work was to reconstruct the two parts of the intervertebral disc-the annulus fibrosus (AF) and the nucleus pulposus (NP)-in such a way that the natural structural features were mimicked by a textile design. Silk was selected as the biomaterial for realization of a textile IVD because of its cytocompatibility, biodegradability, high strength, stiffness, and toughness, both in tension and compression. Therefore, an embroidered structure made of silk yarn was developed that reproduces the alternating fiber structure of +30° and -30° fiber orientation found in the AF and mimics its lamellar structure. The developed embroidered ribbons showed a tensile strength that corresponded to that of the natural AF. Fiber additive manufacturing with 1 mm silk staple fibers was used to replicate the fiber network of the NP and generate an open porous textile 3D structure that may serve as a reinforcement structure for the gel-like NP.

Silk fibroin-based biomaterials for disc tissue engineering

Low back pain is the major cause of disability worldwide, and intervertebral disc degeneration (IVDD) is one of the most important causes of low back pain. Currently, there is no method to treat IVDD that can reverse or regenerate intervertebral disc (IVD) tissue, but the recent development of disc tissue engineering (DTE) offers a new means of addressing these disadvantages. Among numerous biomaterials for tissue engineering, silk fibroin (SF) is widely used due to its easy availability and excellent physical/chemical properties. SF is usually used in combination with other materials to construct biological scaffolds or bioactive substance delivery systems, or it can be used alone. The present article first briefly outlines the anatomical and physiological features of IVD, the associated etiology and current treatment modalities of IVDD, and the current status of DTE. Then, it highlights the characteristics of SF biomaterials and their latest research advances in DTE and discusses the prospects and challenges in the application of SF in DTE, with a view to facilitating the clinical process of developing interventions related to IVD-derived low back pain caused by IVDD.

Biomedical applications of silk and its role for intervertebral disc repair

Intervertebral disc (IVD) degeneration (IDD) is the main contributor to chronic low back pain. To date, the present therapies mainly focus on treating the symptoms caused by IDD rather than addressing the problem itself. For this reason, researchers have searched for a suitable biomaterial to repair and/or regenerate the IVD. A promising candidate to fill this gap is silk, which has already been used as a biomaterial for many years. Therefore, this review aims first to elaborate on the different origins from which silk is harvested, the individual composition, and the characteristics of each silk type. Another goal is to enlighten why silk is so suitable as a biomaterial, discuss its functionalization, and how it could be used for tissue engineering purposes. The second part of this review aims to provide an overview of preclinical studies using silk-based biomaterials to repair the inner region of the IVD, the nucleus pulposus (NP), and the IVD's outer area, the annulus fibrosus (AF). Since the NP and the AF differ fundamentally in their structure, different therapeutic approaches are required. Consequently, silk-containing hydrogels have been used mainly to repair the NP, and silk-based scaffolds have been used for the AF. Although most preclinical studies have shown promising results in IVD-related repair and regeneration, their clinical transition is yet to come.

Upregulation of biochemical and biophysical properties of cell-laden microfiber, silk-hyaluronic acid composite

Cell-laden filament-like hydrogels are advantageous for many applications including drug screening, tissue engineering, and regenerative medicine. However, most of the designed filament vehicles hold weak mechanical properties, which hinder their applications in specific tissue engineering. We present a binary hybrid silk and hyaluronic acid hydrogel microfiber generated through a microfluidic system to encapsulate cells with superior mechanical properties and biocompatibility. Cell-laden hydrogel microfibers were continuously produced through coaxial double orifice microfluidic device and horseradish peroxidase mediated crosslinking, which conjugated introduce phenolic moieties in the backbone of silk fibroin and HA derivatives (Silk-Ph and HA-Ph, respectively). The iterative hybrid Silk-Ph + HA-Ph fibers were fabricated in tunable size distribution between 195 and 680 μm through control of outer flow velocity. Tensile strength and maximum stain of prepared Silk-Ph + HA-Ph sample upregulated more than three times higher than the single HA-Ph sample, which demonstrated significant impacts of synthesized silk derivative in hydrogel fiber composition. The proteolytic degradation of microfibers manipulated by hyaluronidase and collagenase treatment. Encapsulation process and crosslinking did not insert any harmful effect on cell viability (> 90%) and the cells maintained their growth ability after encapsulation process. Cellular filament-like tissue fabricated from proliferation of cells in Silk-Ph + HA-Ph microfiber.

Antioxidative NAC-Loaded Silk Nanoparticles with Opening Mucosal Tight Junctions for Nasal Drug Delivery: An In Vitro and In Vivo Study

Using nasal routes to deliver drugs to the brain using multifunctional nanoparticles (NPs) to bypass the blood–brain barrier (BBB) might enhance the delivery efficacy. Anti-oxidative N-Acetyl-L-cysteine (NAC)-loaded silk fibroin (SF/NAC) NPs are produced, characterized and studied as a potential delivery vehicle for NAC delivered to the brain via nasal for both in vitro and in vivo studies. The NPs are not cytotoxic to RPMI 2650 cells, mucosal model cells, at a concentration of 6000 μg/mL. The anti-oxidative activities of SF/NAC NPs are demonstrated by high H₂O₂ scavenge capacities of the NPs and shown by mitochondrial superoxide (MitoSOX) immunostaining of human mesenchymal stem cells. Tight junctions in RPMI 2650 cells are opened after 30 min of incubation with SF/NAC NPs, which are demonstrated by measuring the decrease in trans-epithelial electrical resistance (TEER) values and discreteness in ZO-1 stains. The cellular uptake of SF/NAC NPs by RPMI 2650 cells is significantly greater than that for SF NPs and increased with increasing incubation time. In an in vivo imaging study (IVIS) using rats shows that the amount of NAC that is delivered to the brain by SF/NAC NPs increased by 1.40–2.60 times and NAC is retained longer in the nasal cavity than NAC solutions in a 2-h study.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Developing photothermal-responsive and anti-oxidative silk/dopamine nanoparticles decorated with drugs which were incorporated into silk films as a depot-based drug delivery

Photothermal-responsive (PTR) and anti-oxidative silk fibroin/dopamine nanoparticles (SD NPs) mediated by tyrosinase were produced, and decorated either by curcumin or albumin (BSA) to produce SD/curcumin or SD/BSA NPs as drug delivery vehicles, respectively. Both drug loaded NPs were further blended into SF solutions to produce SD films, as a depot-based drug delivery. The reaction mechanisms for producing new SD NPs were proposed. Anti-oxidative activities for SD NPs were examined by H₂O₂ scavenge capacities of NPs. NPs were not cytotoxic at concentration of 1000μg/mL. Moreover, heparin was coated to SD films to produce SDH films for temporary implants. Cumulative release profiles for drugs loaded SDH films showed fast releases and then sustained releases stages. Furthermore, the releases of curcumin in sustained stages for varying SD/curcumin NPs loaded into SDH films were dependent on amounts of NPs. BSA releases profiles for SD/BSA NPs loaded into SDH films were similar to those profiles for the films carried with SD/curcumin NPs but release periods of BSA were short. Degrees of PTR effects with irradiation of near infrared on the releases of two drugs loaded films were different. Blood clot at wound areas of rats with SDH films implantations was not found for 24 h study.

Water-based carbodiimide mediated synthesis of polysaccharide-amino acid conjugates: Deprotection, charge and structural analysis

We report here a one-step aqueous method for the synthesis of isolated and purified polysaccharide-amino acid conjugates. Two different types of amino acid esters: glycine methyl ester and L-tryptophan methyl ester, as model compounds for peptides, were conjugated to the polysaccharide carboxymethylcellulose (CMC) in water using carbodiimide at ambient conditions. Detailed and systematic pH-dependent charge titration and spectroscopy (infrared, nuclear magnetic resonance: ¹H, ¹³C- DEPT 135, ¹H- ¹³C HMBC/HSQC correlation), UV-vis, elemental and ninhydrin analysis provided solid and direct evidence for the successful conjugation of the amino acid esters to the CMC backbone via an amide bond. As the concentration of amino acid esters increased, a conjugation efficiency of 20-80% was achieved. Activated charcoal aided base-catalyzed deprotection of the methyl esters improved the solubility of the conjugates in water. The approach proposed in this work should have the potential to tailor the backbone of polysaccharides containing di- or tri-peptides.

Stretchable silk fibroin hydrogels

Hydrogels derived from silk fibroin (SF) are attractive soft materials in biomedical applications such as drug delivery and tissue engineering. However, SF hydrogels reported so far are generally brittle in tension limiting their load-bearing applications. We present here a novel strategy for preparing stretchable SF hydrogels by incorporating flexible polymer chains into the brittle SF network, which strengthen the interconnections between SF globules. We included N, N-dimethylacrylamide (DMAA) monomer and ammonium persulfate initiator into an aqueous SF solution containing a diepoxide cross-linker to in situ generate flexible poly (N,N-dimethylacrylamide) (PDMAA) chains. Moreover, instead of SF, methacrylated SF was used for the gel preparation to create an interconnected SF/PDMAA network. The free-radical polymerization of DMAA leads to the formation of PDMAA chains interconnecting globular SF molecules via their pendant vinyl groups. Incorporation of 2 w/v% DMAA into the SF network turns the brittle hydrogel into a stretchable one sustaining up to 370% elongation ratio. The mechanical properties of SF hydrogels could be adjusted by the amount of PDMAA incorporated into the SF network. The stretchable and tough SF hydrogels thus developed are suitable as a scaffold in tissue engineering and offer an advantage as a biomaterial over other SF-based biomaterials.

Physicochemical Investigations of Chitosan-Based Hydrogels Containing Aloe Vera Designed for Biomedical Use

In this work, synthesis and investigations on chitosan-based hydrogels modified with Aloe vera juice are presented. These materials were synthesized by UV radiation. Investigations involved analysis of chemical structure by FTIR spectroscopy, sorption properties in physiological liquids, strength properties by texture analyzer, surface topography by Atomic Force Microscopy (AFM technique), and in vitro cytotoxicity by MTT test using L929 murine fibroblasts. Particular attention was focused both on determining the impact of the amount and the molecular weight of the crosslinker used for the synthesis as well as on the introduced additive on the properties of hydrogels. It was proven that modified hydrogels exhibited higher swelling ability. Introduced additive affected the tensile strength of hydrogels—modified materials showed 23% higher elongation. The greater amount of the crosslinker used in the synthesis, the more compact the structure, leading to the lower elasticity and lower sorption of hydrogels was reported. Above 95%, murine fibroblasts remained viable after 24 h incubation with hydrogels. It indicates that tested materials did not exhibit cytotoxicity toward these lines. Additionally, materials with Aloe vera juice were characterized by lower surface roughness. Conducted investigations allowed us to state that such modified hydrogels may be considered as useful for biomedical purposes.