Modulation of osteogenic and haemostatic activities by tuning cationicity of genipin-crosslinked chitosan hydrogels

The Diamond Concept Enigma: Recent Trends of Its Implementation in Cross-linked Chitosan-Based Scaffolds for Bone Tissue Engineering

An increasing number of publications over the past ten years have focused on the development of chitosan-based cross-linked scaffolds to regenerate bone tissue. The design of biomaterials for bone tissue engineering applications relies heavily on the ideals set forth by a polytherapy approach called the "Diamond Concept". This methodology takes into consideration the mechanical environment, scaffold properties, osteogenic and angiogenic potential of cells, and benefits of osteoinductive mediator encapsulation. The following review presents a comprehensive summarization of recent trends in chitosan-based cross-linked scaffold development within the scope of the Diamond Concept, particularly for nonload-bearing bone repair. A standardized methodology for material characterization, along with assessment of in vitro and in vivo potential for bone regeneration, is presented based on approaches in the literature, and future directions of the field are discussed.

Tannic acid-crosslinked O-carboxymethyl chitosan hydrogels for enhanced antibacterial activity and rapid hemostasis

Bacterial infection and massive blood loss are major challenges for global public health. Herein, a series of tannic acid encapsulated O-carboxymethyl chitosan (CMC) based hydrogels were prepared using a facile approach for both hemorrhage control and effective anti-bacterium. The results indicated that the tannic acid-cosslinked CMC hydrogels had excellent mechanical property, swelling ability as well as great cytocompatibility. Comparably, with increasing tannic acid loading, the bleeding control and antibacterial performance against both E. coli and S. aureus were improved simultaneously, especially for the 5% tannic acid-cosslinked CMC hydrogel. Moreover, the prepared CMC hydrogel loading with tannic acid could induce hemocytes and platelets aggregation, promote the blood clotting and achieve bleeding control in vivo due to the interconnected fibrous web structure and the chemical activation (the phenol group of tannic acid). Thus, the resultant CMC hydrogel enabled the maintenance of high bioavailability of tannic acid and synchronization with the interconnected fibrous structure of CMC hydrogels, which was expected to be a promising candidate for robust and safe hemostatic dressings.

Recent advances of 3D hydrogel culture systems for mesenchymal stem cell-based therapy and cell behavior regulation

Mesenchymal stem cells (MSCs) have been increasingly recognized as resources for disease treatments and regenerative medicine. Meanwhile, the unique chemical and physical properties of hydrogels provide innate advantages to achieve...

Controlled domain gels with a biomimetic gradient environment for osteochondral tissue regeneration

In order to repair an osteochondral defect, it is critical to advance a bi-lineage constructive scaffold with gradient transition. In this study, we developed a simple and straightforward approach for fabricating a multi-domain gel scaffold through the assembly/disassembly of low-molecular-weight gels (LMWGs) inside a stable PEGDA network by photopolymerization. The versatility of this technology enabled to vary biological, topological, and mechanical properties through material selection and to generate a chondrogenic-osteogenic gradient transition. The multi-domain gel exhibited an increasing stiffness gradient along the longitudinal direction from the cartilage layer at approximately 20 kPa to the bone layer at approximately 300 kPa as well as spatial variation at the gradient interface. Moreover, the transitional layer with a condensed structure and intermediate stiffness prevented delamination of the contrasting layers and maintained microenvironmental differences in the upper and lower layers. The in vitro results indicated that each domain had an individual capacity to spatially control the differentiation of MSCs toward osteoblastic lineage and chondrocytic lineage. This was mainly because the mechanical and topographical cues from the respective domains played an important role in modulating the Rho-ROCK signaling pathway, whereas the blockage of ROCK signals significantly impaired domain-modulated osteogenesis and enhanced chondrogenesis. Additionally, the quantity and quality of osteochondral repair were evaluated at 4 and 8 weeks through histological analysis and micro-computed tomography (micro-CT). The results indicated that the multi-domain gels distinctly improved the regeneration of subchondral bone and cartilage tissues. Overall, the outcomes of this study can motivate future bioinspired gradient and heterogeneity strategies for osteochondral tissue regeneration. STATEMENT OF SIGNIFICANCE: The regeneration of osteochondral defects remains a major challenge due to the complexity of osteochondral structure and the limited self-repair capacity of cartilage. The gradient design to mimic the transition between the calcified cartilage and the subchondral bone plate as well as the zones of cartilage is an effective strategy. In this study, controlled multi-domain gels were fabricated through the assembly/disassembly of low-molecular-weight gels inside a stable PEGDA network by photopolymerization. The prepared multi-domain gels showed a chondrogenic-osteogenic gradient transition, which decreased the possibility of delamination and stimulated osteochondral tissue regeneration in vivo. Overall, our study promotes new strategies of bioinspired gradients and heterogeneities for more challenging applications.

Covalent immobilization of DJK-5 peptide on porous titanium for enhanced antibacterial effects and restrained inflammatory osteoclastogenesis

Currently, implant-related bone infection characterized by aggravated infection-induced inflammatory responses and osteolysis, remains a severe challenge in orthopedic surgery, especially in patients with osteoporosis. Attempts to control such responses using biomaterials with combined immunomodulatory and anti-bacterial properties may provide novel strategies. Herein, DJK-5, a class of host defense peptides (HDPs) with established antimicrobial and immunomodulatory functions, was introduced into porous Ti alloy. Our results indicated that the DJK-5 immobilized surfaces showed intrinsically multifunctional properties, including antibacterial ability, anti-inflammation, biocompatibility and osteolysis-inhibiting properties. The results demonstrated that the antibacterial efficiency of DJK-5 functionalized surfaces was over 90 % for both Gram-positive and Gram-negative bacteria. Specifically, DJK-5 functionalized samples also possessed the excellent anti-bacterial activity against a mixture of bacterial strains, including S. aureus, S. epidermidis and P. aeruginosa, with an antibacterial rate against mixed bacteria reaching 91.36 %, as well as reduced biofilm formation. The remarkable anti-bacterial efficacy was likely based on the direct anti-bacterial effect of DJK-5, which destroyed the integrity of bacteria membranes, leading to the leakage of intracellular materials. Additionally, the immobilized DJK-5 surfaces could indirectly kill bacteria through promoted macrophage capacity to bacteria uptake. Furthermore, DJK-5 functionalized surfaces suppressed inflammatory reaction by decreasing the release of pro-inflammatory factors and increasing the secretions of anti-inflammatory factors, and thereby impeded the activation of NF-κB signal pathway, which resulted in the disruption of the actin rings and decreased Tracp5b expressions. Based on these promising findings, the multi-functional DJK-5 immobilized titanium represents an efficient alternative to realize better osseointegration in sever implant-associated bacterial infections.

Genipin-cross-linked hydrogels based on biomaterials for drug delivery: a review

Genipin is a naturally occurring nontoxic cross-linker, which has been widely used for drug delivery due to its excellent biocompatibility, admirable biodegradability and stable cross-linked attributes. These advantages led to its extensive application in the fabrication of hydrogels for drug delivery. This review describes the physicochemical characteristics and pharmacological activities of genipin and attempts to elucidate the detailed mechanisms of the cross-linking reaction between genipin and biomaterials. The current article entails a general review of the different biomaterials cross-linked by genipin: chitosan and its derivatives, collagen, gelatin, etc. The genipin-cross-linked hydrogels for various pharmaceutical applications, including ocular drug delivery, buccal drug delivery, oral drug delivery, anti-inflammatory drug delivery, and antibiotic and antifungal drug delivery, are reported. Finally, the future research directions and challenges of genipin-cross-linked hydrogels for pharmaceutical applications are also discussed in this review.

Development of chitosan nanocapsules containing essential oil of Matricaria chamomilla L. for the treatment of cutaneous leishmaniasis

Matricaria chamomilla L. has been used for centuries in many applications, including antiparasitic activity. Leishmaniasis is a parasitic disease, with limited treatments, due to high cost and toxicity. Thus, there is a need to develop new treatments, and in this context, natural products are targets of these researches. We report the development of chitosan nanocapsules containing essential oil of M. chamomilla (CEO) from oil-in-water emulsions using chitosan modified with tetradecyl chains as biocompatible shell material. The nanocapsules of CEO (NCEO) were analyzed by optical microscopy and dynamic light scattering, which revealed spherical shape and an average size of 800 nm. Successful encapsulation of CEO was further confirmed by fluorescence microscopy observations taking advantage of the autofluorescence properties of CEO. The encapsulation efficiency was around 90%. The entrapment of CEO reduced its cytotoxicity towards normal cells. On the other hand, the CEO was active against promastigotes and intracellular amastigotes, exhibiting IC₅₀ of 3.33 μg/mL and 14.56 μg/mL, respectively, while NCEO showed IC₅₀ for promastigotes of 7.18 μg/mL and for intracellular amastigotes of 14.29 μg/mL. These results demonstrate that encapsulation of CEO in nanocapsules using an alkylated chitosan biosurfactant as a "green" stabilizer is a promising therapeutic strategy to treat leishmaniasis.

Uncommon Sorption Mechanism of Aromatic Compounds onto Poly(Vinyl Alcohol)/Chitosan/Maleic Anhydride-β-Cyclodextrin Hydrogels

Aromatic hydrocarbons are extensive environmental pollutants occurring in both water and air media, and their removal is a priority effort for a healthy environment. The use of adsorbents is among the several strategies used for the remediation of these compounds. In this paper, we aim the synthesis of an amphiphilic hydrogel with the potential for the simultaneous sorption of a set of monocyclic and polycyclic aromatic hydrocarbons associated with toxicity effects in humans. Thus, we start by the synthesis of a copolymer-based in chitosan and β-cyclodextrin previously functionalized with the maleic anhydride. The presence of β-cyclodextrin will confer the ability to interact with hydrophobic compounds. The resulting material is posteriorly incorporated in a cryogel of poly(vinyl alcohol) matrix. We aim to improve the amphiphilic ability of the hydrogel matrix. The obtained hydrogel was characterized by swelling water kinetics, thermogravimetric analysis, rheological measurements, and scanning electron microscopy. The sorption of aromatic hydrocarbons onto the gel is characterized by pseudo-first-order kinetics and Henry isotherm, suggesting a physisorption mechanism. The results show that the presence of maleic anhydride-β-cyclodextrin and chitosan into hydrogels leads to an increase in the removal efficiency of the aromatic compounds. Additionally, the capacity of this hydrogel for removing these pollutants from a fossil fuel sample has also been tested.

Modulating cationicity of chitosan hydrogel to prevent hypertrophic scar formation during wound healing

It is of great clinical significance to design wound dressing materials with combined excellent wound healing properties and superior capability to suppress hypertrophic scar formation. This study aimed to examine if and how the cationicity of chitosan would affect the hypertrophic scar-related outcomes, through preparing carboxymethyl chitosan hydrogels with different genipin concentrations (2.5%, 5%, 10% and 15%, respectively). An optimum window of chitosan cationicity (5% in our case) demonstrated potential to mitigate hypertrophic scar in wound healing by suppressing the expression of a-smooth muscle actin (a-SMA) and promoting secretion of type I matrix metalloproteinases (MMP-1). In vivo, the CMCS-5% hydrogel again showed smaller, thinner and smoother wound appearance. Moreover, the CMCS-5% sample with additional incorporation of 2% (V/V) Aloe vera gel exhibited further improved performance in scar inhibition. Overall, such findings might have important implications in chitosan-based wound dressing design for high-quality wound repair and effective scar inhibition.

Regeneration of skeletal system with genipin crosslinked biomaterials

Natural biomaterials, such as collagen, gelatin, and chitosan, are considered as promising candidates for use in tissue regeneration treatment, given their similarity to natural tissues regarding components and structure. Nevertheless, only receiving a crosslinking process can these biomaterials exhibit sufficient strength to bear high tensile loads for use in skeletal system regeneration. Recently, genipin, a natural chemical compound extracted from gardenia fruits, has shown great potential as a reliable crosslinking reagent, which can reconcile the crosslinking effect and biosafety profile simultaneously. In this review, we briefly summarize the genipin extraction process, biosafety, and crosslinking mechanism. Subsequently, the applications of genipin regarding aiding skeletal system regeneration are discussed in detail, including the advances and technological strategies for reconstructing cartilage, bone, intervertebral disc, tendon, and skeletal muscle tissues. Finally, based on the specific pharmacological functions of genipin, its potential applications, such as its use in bioprinting and serving as an antioxidant and anti-tumor agent, and the challenges of genipin in the clinical applications in skeletal system regeneration are also presented.

Biocompatibility and paclitaxel/cisplatin dual-loading of nanotubes prepared from poly(ethylene glycol)-polylactide-poly(ethylene glycol) triblock copolymers for combination cancer therapy

Nanotubes were prepared by self-assembly of the copolymer using co-solvent evaporation method. The biocompatibility of the nanotubes was assessed in comparison with spherical micelles and filomicelles prepared from poly(ethylene glycol)-poly(L-lactide-co-glycolide) (PEG-PLGA) and poly(ethylene glycol)-poly(L-lactide) (PEG-PLA), respectively. Several aspects of biocompatibility of the aggregates were considered, including agar diffusion and MTT assay, release of cytokines, hemolysis, protein adsorption, dynamic clotting in vitro, and Zebrafish embryonic compatibility in vivo. The nanotubes present good cell compatibility and blood compatibility in vitro, and almost no toxicity towards Zebrafish embryos development in vivo. Furthermore, dual-loading of hydrophilic cisplatin and hydrophobic paclitaxel was achieved in the nanotubes with high loading content and loading efficiency. The release of both drugs was slower from dual-loaded nanotubes than from single-loaded ones, but the total amount of released drugs in higher for dual-loaded nanotubes than from single-loaded ones. Cellular uptake and inhibition tests showed that the nanotubes were successfully taken up by tumor cells and effectively inhibited cell growth. It is thus concluded that PEG-PLA-PEG nanotubes with outstanding biocompatibility could be promising for co-delivery of hydrophilic and hydrophobic agents in combination cancer therapy.

Iron oxide nanoparticles in liquid or powder form enhanced osteogenesis via stem cells on injectable calcium phosphate scaffold

The objectives of this study were to incorporate iron oxide nanoparticles (IONPs) into calcium phosphate cement (CPC) to enhance bone engineering, and to investigate the effects of IONPs as a liquid or powder on stem cells using IONP-CPC scaffold for the first time. IONP-CPCs were prepared by adding 1% IONPs as liquid or powder. Human dental pulp stem cells (hDPSCs) were seeded. Subcutaneous implantation in mice was investigated. IONP-CPCs had better cell spreading, and greater ALP activity and bone mineral synthesis, than CPC control. Subcutaneous implantation for 6 weeks showed good biocompatibility for all groups. In conclusion, incorporating IONPs in liquid or powder form both substantially enhanced hDPSCs on IONP-CPC scaffold and exhibited excellent biocompatibility. IONP incorporation as a liquid was better than IONP powder in promoting osteogenic differentiation of hDPSCs. Incorporating IONPs and chitosan lactate together in CPC enhanced osteogenesis of hDPSCs more than using either alone.