Ocular biocompatibility of gelatin microcarriers functionalized with oxidized hyaluronic acid

Chemical modification of hyaluronic acid as a strategy for the development of advanced drug delivery systems

Hyaluronic acid (HA) has emerged as a promising biopolymer for various biomedical applications due to its biocompatibility, biodegradability, and intrinsic ability to interact with cell surface receptors, making it an attractive candidate for drug delivery systems and tissue engineering. Chemical modification of HA has opened up versatile possibilities to tailor its properties, enabling the development of advanced drug delivery systems and biomaterials with enhanced functionalities and targeted applications. This review analyzes the strategies and applications of chemically modified HA in the field of drug delivery and biomaterial development. The first part of the review focuses on the different methods and functional groups used for the chemical modification of HA, highlighting the impact of these modifications on its physicochemical properties, degradation behavior and interactions with drugs. The second part of the review evaluates the use of chemically modified HA in the development of advanced biomedical materials including nano- and microparticles, hydrogels and mucoadhesive materials with tailored drug release profiles, site-specific targeting and stimuli-responsive behavior. Thus, the review consolidates the current advances and future perspectives in the field of chemical modification of HA, underscoring its immense potential to drive the development of advanced drug delivery systems and biomaterials with diverse biomedical applications.

Volumetric imaging of human mesenchymal stem cells (hMSCs) for non-destructive quantification of 3D cell culture growth

The adoption of cell-based therapies into the clinic will require tremendous large-scale expansion to satisfy future demand, and bioreactor-microcarrier cultures are best suited to meet this challenge. The use of spherical microcarriers, however, precludes in-process visualization and monitoring of cell number, morphology, and culture health. The development of novel expansion methods also motivates the advancement of analytical methods used to characterize these microcarrier cultures. A robust optical imaging and image-analysis assay to non-destructively quantify cell number and cell volume was developed. This method preserves 3D cell morphology and does not require membrane lysing, cellular detachment, or exogenous labeling. Complex cellular networks formed in microcarrier aggregates were imaged and analyzed in toto. Direct cell enumeration of large aggregates was performed in toto for the first time. This assay was successfully applied to monitor cellular growth of mesenchymal stem cells attached to spherical hydrogel microcarriers over time. Elastic scattering and fluorescence lightsheet microscopy were used to quantify cell volume and cell number at varying spatial scales. The presented study motivates the development of on-line optical imaging and image analysis systems for robust, automated, and non-destructive monitoring of bioreactor-microcarrier cell cultures.

Oxidized hyaluronic acid/adipic acid dihydrazide hydrogel as cell microcarriers for tissue regeneration applications

Hyaluronic acid (HA) is a biopolymer present in various human tissues, whose degradation causes tissue damage and diseases. The oxidized hyaluronic acid/adipic acid dihydrazide (oxi-HA/ADH) hydrogels have attracted attention due to their advantages such as thermosensitivity, injectability, in situ gelation, and sterilization. However, studies are still scarce in the literature as microcarriers. In that sense, this work is a study of oxi-HA/ADH microparticles of 215.6 ± 2.7 µm obtained by high-speed shearing (18,000 rpm at pH 7) as cell microcarriers. Results showed that BALB/c 3T3 fibroblasts and adipose mesenchymal stem cells (h-AdMSC) cultured on the oxi-HA/ADH microcarriers presented a higher growth of both cells in comparison with the hydrogel. Moreover, the extrusion force of oxi-HA/ADH microparticles was reduced by 35% and 55% with the addition of 25% and 75% HA fluid, respectively, thus improving its injectability. These results showed that oxi-HA/ADH microcarriers can be a potential injectable biopolymer for tissue regeneration applications.

Photo-crosslinked hydrogels for tissue engineering of corneal epithelium

The vast majority of patients with corneal blindness cannot recover their vision due to the serious shortage of donor cornea. However, the technology to construct a feasible corneal substitute is a promising treatment method for corneal blindness. In this paper, methacrylated gelatin (GelMA)-methacrylated hyaluronic acid (HAMA) double network (GHDN) hydrogels were prepared by modifying gelatin and hyaluronic acid with methacrylate anhydride (MA). GHDN hydrogel was compared with GelMA single network and HAMA single network hydrogels through characterization experiments of mechanical properties, optical properties, hydrophilicity and in-situ degradation in vitro. At the same time, the biocompatibility of hydrogel was tested by inoculating rabbit corneal epithelial cells (CEpCs) epidermal cells on hydrogels using CCK-8 test, live/dead staining, immunofluorescence staining and qRT-PCR. It was found that the GHDN hydrogel has optical transparency in the visible region, and its mechanical properties are better than those of GelMA and HAMA hydrogels, and its hydrophilicity is similar to that of normal human corneas. The results of in vitro hydrogel culture of CEpCs showed that the proliferation of CEpCs on GHDN hydrogel was two times higher than that of HAMA hydrogel, and the expression of specific marker Cytokeratin 3 (CK3) and Cytokeratin 12 (CK12) could be better maintained on GHDN hydrogel. All the experimental results proved that GHDN hydrogel has good physical properties and biocompatibility and is a potential candidate for corneal tissue engineering scaffolds.

Hyaluronic acid targeted and pH-responsive multifunctional nanoparticles for chemo-photothermal synergistic therapy of atherosclerosis

Atherosclerosis is a global disease with an extremely high morbidity and fatality rate, so it is necessary to develop effective treatments to reduce its impact. In this work, we successfully prepared a multifunctional drug-loaded nano-delivery system with pH-responsive, CD44-targeted, and chemical-photothermal synergistic treatment. Dendritic mesoporous silica nanoparticles capped with copper sulfide (CuS) were synthesized via an oil-water biphase stratification reaction system; these served as the carrier material and encapsulated the anticoagulant drug heparin (Hep). The pH-sensitive Schiff base bond was used as a gatekeeper and targeting agent to modify hyaluronic acid (HA) on the surface of the nanocarrier. HA coating endowed the nanocomposite with the ability to respond to pH and target CD44-positive inflammatory macrophages. Based on this multifunctional nanocomposite, we achieved precise drug delivery, controlled drug release, and chemical-photothermal synergistic treatment of atherosclerosis. The in vitro drug release results showed that the nanocarriers exhibited excellent drug-controlled release properties, and could release drugs in the weakly acidic microenvironment of atherosclerotic inflammation. Cytotoxicity and cell uptake experiments indicated that nanocarriers had low cytotoxicity against RAW 264.7 cells. Modification of HA to nanocarriers can be effectively internalized by RAW 264.7 cells stimulated by lipopolysaccharide (LPS). Combining CuS photothermal treatment with anti-atherosclerosis chemotherapy showed better effects than single treatment in vitro and in vivo. In summary, our research proved that H-CuS@DMSN-NC-HA has broad application prospects in anti-atherosclerosis.

Self-sealing hyaluronic acid-coated 30-gauge intravitreal injection needles for preventing vitreous and drug reflux through needle passage

Self-sealing hyaluronic acid (HA)-coated self-sealing 30-gauge needles exhibiting instant leakage prevention of intravitreal humor and injected drug were developed in this study. Ninety New Zealand rabbits were used in this study. We assessed dye regurgitation in intravitreal ICG dye injections using HA-coated needles (HA needle group) and conventional needles (control group). Vitreous humor levels of anti-vascular endothelial growth factor (VEGF) were compared between groups one, three, and seven days after intravitreal bevacizumab (0.016 mL) injections. Expression levels of inflammatory cytokines in the aqueous humor and vitreous humor, including prostaglandin E₂ (PGE₂), interferon-γ, tumor necrosis factor-α, interleukin (IL)-1β, IL-4, IL-6, IL-17, and IL-8, were compared between HA needle, control, and normal (in which intravitreal injection was not performed) groups following 12 intravitreal injections over a period of one week. In the HA needle group, HA remained at the injection site and blocked the hole after intravitreal injection. Dye regurgitation occurred significantly less frequently in the HA needle group (16.7%) than the control group (55.6%) after intravitreal ICG dye injection. Meanwhile, vitreous anti-VEGF levels were markedly higher in the HA needle group than the control group one and three days after intravitreal bevacizumab injections. After 12 intravitreal injections, expression levels of aqueous and vitreous IL-8 significantly increased in the control group compared to the HA needle and normal groups. Conversely, there were no significant differences in the expression of the other seven cytokines among the three groups. Intravitreal injections using HA-coated self-sealing 30-gauge needles can block the outflow of vitreous humor and drugs through the needle passage.

Feasibility study of oxidized hyaluronic acid cross-linking acellular bovine pericardium with potential application for abdominal wall repair

Bovine pericardium(BP)is one of the biological membranes with extensive application in tissue engineering. To fully investigate the potential clinical applications of this natural biological material, a suitable cross-linking reagent is hopefully adopted for modification. Glutaraldehyde (GA) is a clinically most common synthetic cross-linking reagent. In the study, oxidized hyaluronic acid (AHA) was developed to substitute GA to fix acellular bovine pericardium (ABP) for lower cytotoxicity, aiming to evaluate the feasibility of AHA as a cross-linking reagent and develop AHA-fixed ABP as a biological patch for abdominal wall repair. The AHA with the feeding ratio (1.8:1.0) has an appropriate molecular weight and oxidation degree, almost no cytotoxicity and good cross-linking effect. The critical cross-linking characteristics and cytocompatibility of AHA-fixed ABP were also investigated. The results demonstrated that 2.0% AHA-fixed ABP had the most suitable mechanical properties, thermal stability, resistance to enzymatic degradation and hydrophilicity. Moreover, 2.0% AHA-fixed samples exhibited an excellent cytocompatibility with human peritoneal mesothelial cells (HPMC) and low antigenicity. It also showed a prominent anti-calcification ability required for abdominal wall repair. Our data provided experimental basis for future research on AHA as a new cross-linking reagent and AHA-fixed ABP for abdominal wall repair.

A structure-supporting, self-healing, and high permeating hydrogel bioink for establishment of diverse homogeneous tissue-like constructs

The ready-to-use, structure-supporting hydrogel bioink can shorten the time for ink preparation, ensure cell dispersion, and maintain the preset shape/microstructure without additional assistance during printing. Meanwhile, ink with high permeability might facilitate uniform cell growth in biological constructs, which is beneficial to homogeneous tissue repair. Unfortunately, current bioinks are hard to meet these requirements simultaneously in a simple way. Here, based on the fast dynamic crosslinking of aldehyde hyaluronic acid (AHA)/N-carboxymethyl chitosan (CMC) and the slow stable crosslinking of gelatin (GEL)/4-arm poly(ethylene glycol) succinimidyl glutarate (PEG-SG), we present a time-sharing structure-supporting (TSHSP) hydrogel bioink with high permeability, containing 1% AHA, 0.75% CMC, 1% GEL and 0.5% PEG-SG. The TSHSP hydrogel can facilitate printing with proper viscoelastic property and self-healing behavior. By crosslinking with 4% PEG-SG for only 3 min, the integrity of the cell-laden construct can last for 21 days due to the stable internal and external GEL/PEG-SG networks, and cells manifested long-term viability and spreading morphology. Nerve-like, muscle-like, and cartilage-like in vitro constructs exhibited homogeneous cell growth and remarkable biological specificities. This work provides not only a convenient and practical bioink for tissue engineering, targeted cell therapy, but also a new direction for hydrogel bioink development.

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A time-sharing structure-supporting (TSHSP) bioink based on gelation time difference between two gelling systems.

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The high permeability of TSHSP hydrogel is the basis for effective matter exchange.

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The TSHSP hydrogel facilitates room temperature printing with proper viscoelastic property and self-healing behavior.

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Cells manifest long-term viability and spreading morphology in bioprinted TSHSP constructs.

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In vitro tissue-like TSHSP constructs exhibit homogeneous cell growth and remarkable biological specificities.

Glycol chitosan/oxidized hyaluronic acid hydrogel film for topical ocular delivery of dexamethasone and levofloxacin

In the present study, we fabricated a glycol chitosan/oxidized hyaluronic acid hydrogel film with promising potential for the dual ophthalmic delivery of dexamethasone (Dex) and levofloxacin (Lev). Utilizing different oxidation degrees of oxidized hyaluronic acid (OHA), several blank hydrogel films and Lev-loaded hydrogel films were successfully fabricated. With an increase in the oxidation degree of OHA, the swelling ratio of the hydrogel films decreased accordingly. The hydrogel films displayed a stepwise release of Lev and Dex, with Lev rapidly released from the hydrogel film, followed by a sustained release of Dex. Lev-loaded hydrogel films revealed a potent capacity to inhibit bacterial growth in different bacterial strains. In lipopolysaccharide-activated RAW264.7 macrophages, the formulated hydrogel films displayed potent in vitro anti-inflammatory activity by significantly downregulating various inflammatory cytokines. Overall, the fabricated hydrogel film acting as a dual drug delivery system might be a promising vehicle for the treatment of postoperative endophthalmitis.

Modified hyaluronic acid hydrogels with chemical groups that facilitate adhesion to host tissues enhance cartilage regeneration

Stable integration of hydrogel implants with host tissues is of critical importance to cartilage tissue engineering. Designing and fabricating hydrogels with high adhesive strength, stability and regeneration potential are major challenges to be overcome. This study fabricated injectable adhesive hyaluronic acid (HA) hydrogel modified by aldehyde groups and methacrylate (AHAMA) on the polysaccharide backbone with multiple anchoring mechanisms (amide bond through the dynamic Schiff base reaction, hydrogen bond and physical interpenetration). AHAMA hydrogel exhibited significantly improved durability and stability within a humid environment (at least 7 days), together with higher adhesive strength (43 KPa to skin and 52 KPa to glass), as compared to commercial fibrin glue (nearly 10 KPa) and HAMA hydrogel (nearly 20 KPa). The results showed that AHAMA hydrogel was biocompatible and could be easily and rapidly prepared in situ. In vitro cell culture experiments showed that AHAMA hydrogel could enhance proliferation (1.2-folds after 3 days) and migration (1.5-folds after 12 h) of bone marrow stem cells (BMSCs), as compared to cells cultured in a culture dish. Furthermore, in a rat osteochondral defect model, implanted AHAMA hydrogel significantly promoted integration between neo-cartilage and host tissues, and significantly improved cartilage regeneration (modified O'Driscoll histological scores of 16.0 ± 4.1 and 18.3 ± 4.6 after 4 and 12-weeks of post-implantation in AHAMA groups respectively, 12.0 ± 2.7 and 12.2 ± 2.8 respectively in HAMA groups, 9.8 ± 2.4 and 11.5 ± 2.1 respectively in untreated groups). Hence, AHAMA hydrogel is a promising adhesive biomaterial for clinical cartilage regeneration and other biomedical applications.

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Adhesive hydrogel composed of single natural polymer component.

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The single component enhance stable and easy to use in surgical operation of hydrogel.

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Adhesive hydrogel exhibited strong adhesive strength through multiple anchoring mechanisms.

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Adhesive hydrogel promoted integration between neo-cartilage and host tissues, drastically improved cartilage regeneration.

Corneal Repair and Regeneration: Current Concepts and Future Directions

The cornea is a unique tissue and the most powerful focusing element of the eye, known as a window to the eye. Infectious or non-infectious diseases might cause severe visual impairments that need medical intervention to restore patients' vision. The most prominent characteristics of the cornea are its mechanical strength and transparency, which are indeed the most important criteria considerations when reconstructing the injured cornea. Corneal strength comes from about 200 collagen lamellae which criss-cross the cornea in different directions and comprise nearly 90% of the thickness of the cornea. Regarding corneal transparency, the specific characteristics of the cornea include its immune and angiogenic privilege besides its limbus zone. On the other hand, angiogenic privilege involves several active cascades in which anti-angiogenic factors are produced to compensate for the enhanced production of proangiogenic factors after wound healing. Limbus of the cornea forms a border between the corneal and conjunctival epithelium, and its limbal stem cells (LSCs) are essential in maintenance and repair of the adult cornea through its support of corneal epithelial tissue repair and regeneration. As a result, the main factors which threaten the corneal clarity are inflammatory reactions, neovascularization, and limbal deficiency. In fact, the influx of inflammatory cells causes scar formation and destruction of the limbus zone. Current studies about wound healing treatment focus on corneal characteristics such as the immune response, angiogenesis, and cell signaling. In this review, studied topics related to wound healing and new approaches in cornea regeneration, which are mostly related to the criteria mentioned above, will be discussed.

Design and Biophysical Characterization of Poly (l-Lactic) Acid Microcarriers with and without Modification of Chitosan and Nanohydroxyapatite

Nowadays, microcarriers are widely utilized in drug delivery, defect filling, and cell culture. Also, many researchers focus on the combination of synthetic and natural polymers and bioactive ceramics to prepare composite biomaterials for tissue engineering and regeneration. In this study, three kinds of microcarriers were prepared based on physical doping and surface modification, named Poly (l-lactic) acid (PLLA), PLLA/nanohydroxyapatite (PLLA/nHA), and PLLA/nHA/Chitosan (PLLA/nHA/Ch). The physicochemical properties of the microcarriers and their functional performances in MC3T3-E1 cell culture were compared. Statistical results showed that the average diameter of PLLA microcarriers was 291.9 ± 30.7 μm, and that of PLLA/nHA and PLLA/nHA/Ch microcarriers decreased to 275.7 ± 30.6 μm and 269.4 ± 26.3 μm, respectively. The surface roughness and protein adsorption of microcarriers were enhanced with the doping of nHA and coating of chitosan. The cell-carrier cultivation stated that the PLLA/nHA microcarriers had the greatest proliferation-promoting effect, while the PLLA/nHA/Ch microcarriers performed the strongest attachment with MC3T3-E1 cells. Besides, the cells on the PLLA/nHA/Ch microcarriers exhibited optimal osteogenic expression. Generally, chitosan was found to improve microcarriers with superior characteristics in cell adhesion and differentiation, and nanohydroxyapatite was beneficial for microcarriers regarding sphericity and cell proliferation. Overall, the modified microcarriers may be considered as a promising tool for bone tissue engineering.

Biomaterials for corneal bioengineering

Corneal transplantation is an important surgical treatment for many common corneal diseases. However, a worldwide shortage of tissue from suitable corneal donors has meant that many people are not able to receive sight-restoring operations. In addition, rejection is a major cause of corneal transplant failure. Bioengineering corneal tissue has recently gained widespread attention. In order to facilitate corneal regeneration, a range of materials is currently being investigated. The ideal substrate requires sufficient tectonic durability, biocompatibility with cultured cellular elements, transparency, and perhaps biodegradability and clinical compliance. This review considers the anatomy and function of the native cornea as a precursor to evaluating a variety of biomaterials for corneal regeneration including key characteristics for optimal material form and function. The integration of appropriate cells with the most appropriate biomaterials is also discussed. Taken together, the information provided offers insight into the requirements for fabricating synthetic and semisynthetic corneas for in vitro modeling of tissue development and disease, pharmaceutical screening, and in vivo application for regenerative medicine.

Development of gelatin/ascorbic acid cryogels for potential use in corneal stromal tissue engineering

To offer an ideal hospitable environment for corneal keratocyte growth, the carrier materials can be functionalized with incorporation of signaling molecules to regulate cell biological events. This study reports, for the first time, the development of gelatin/ascorbic acid (AA) cryogels for keratocyte carriers in vitro and in vivo. The cryogel samples were fabricated by blending of gelatin with varying amounts of AA (0-300 mg) and carbodiimide cross-linking via cryogelation technique. Hydrophilic AA content in the carriers was found to significantly affect cross-linking degree and pore dimension of cryogels, thereby dictating their mechanical and biological stability and AA release profile. The cryogel carriers with low-to-moderate AA loadings were well tolerated by rabbit keratocyte cultures and anterior segment eye tissues, demonstrating good ocular biocompatibility. Although higher incorporated AA level contributed to enhanced metabolic activity and biosynthetic capacity of keratocytes grown on cryogel matrices, the presence of excessive amounts of AA molecules could lead to toxic effect and limit cell proliferation and matrix production. The cytoprotective activity against oxidative stress was shown to be strongly dependent on AA release, which further determined cell culture performance and tissue reconstruction efficiency. With the optimum AA content in carrier materials, intrastromally implanted cell/cryogel constructs exhibited better capability to enhance tissue matrix regeneration and transparency maintenance as well as to mitigate corneal damage in an alkali burn-induced animal model. It is concluded that understanding of antioxidant molecule-mediated structure-property-function interrelationships in gelatin/AA cryogels is critical to designing carrier materials for potential use in corneal stromal tissue engineering.

STATEMENT OF SIGNIFICANCE

Multifunctional cryogel material can offer an ideal hospitable environment for cell-mediated tissue reconstruction. To our knowledge, this is the first report describing the use of gelatin/ascorbic acid (AA) cryogels as keratocyte carriers for corneal stromal tissue engineering. The AA loading during cryogel fabrication is found to have a significant effect on cross-linking degree and pore dimension, mechanical and biological stability, ocular biocompatibility, cell culture performance, and cytoprotective activity, giving comprehensive insight into fine-tuning the structure-property-function interrelationships of keratocyte carrier material. Using an alkali burn-induced animal model, we present evidence that with the optimum AA loading into cryogel materials, intrastromally implanted cell/carrier constructs exhibited better capability to enhance tissue matrix regeneration and transparency maintenance as well as to mitigate corneal damage.