Chitosan-coated and thymol-loaded polymeric semi-interpenetrating hydrogels: An effective platform for bioactive molecule delivery and bone regeneration in vivo

Thymol (2-isopropyl-5-methylphenol; Thy) is a monoterpene phenolic phytocompound with medicinal properties; however, its impact on osteogenesis is yet to be thoroughly investigated. Its distribution is often hampered because of its intricate hydrophobic structure, which reduces its bioavailability. In this study, we synthesized a drug delivery vehicle using semi-interpenetrating polymer network (SIPN) hydrogels containing sodium alginate and poly(2-ethyl-2-oxazoline) (SA/Pox) loaded with Thy at varying concentrations (100, 150, and 200 μM). Subsequently, they were coated with chitosan (CS) to increase bioactivity and for sustained and prolonged release of Thy. Thy-loaded CS-coated SIPN hydrogels (SA/Pox/CS-Thy) were developed using ionic gelation and polyelectrolyte-complexation techniques. The addition of CS to hydrogels enhanced their physicochemical and material properties. These hydrogels were cytofriendly toward mouse mesenchymal stem cells (mMSCs). When mMSCs were cultured on hydrogels, Thy stimulated osteoblastic differentiation, as evidenced by calcium deposits at the cellular level. The expression of RUNX2, a key bone transcriptional factor, and other differentiation biomarkers was significantly enhanced in mMSCs cultured on SA/Pox/CS-Thy hydrogels. Notably, Thy in the SA/Pox/CS hydrogels significantly activated the TGF-β/BMP signaling pathway, which is involved in osteogenesis. A rat tibial bone defect model system revealed that the incorporation of Thy into SA/Pox/CS hydrogels augmented bone regeneration. Thus, sustained and prolonged release of Thy from the SA/Pox/CS hydrogels promoted osteoblast differentiation in vitro and bone formation in vivo. These findings shed light on the effect of Thy bioavailability in fostering osteoblast differentiation and its prospective application in bone rejuvenation.

Angiogenic and Osteogenic Effects of Flavonoids in Bone Regeneration

Bone is a highly vascularised tissue that relies on a close spatial and temporal interaction between blood vessels and bone cells. As a result, angiogenesis is critical for bone formation and healing. The vascular system supports bone regeneration by delivering oxygen, nutrients, and growth factors, as well as facilitating efficient cell-cell contact. Most clinical applications of engineered bone grafts are hampered by insufficient vascularization after implantation. Over the last decade, a number of flavonoids have been reported to have osteogenic-angiogenic potential in bone regeneration because of their excellent bioactivity, low cost, availability, and minimal in vivo toxicity. During new bone formation, the osteoinductive nature of certain flavonoids is involved in regulating multiple signaling pathways contributing toward the osteogenic-angiogenic coupling. This review briefly outlines the osteogenic-angiogenic potential of those flavonoids and the mechanisms of their action in promoting bone regeneration. However, further studies are needed to investigate their delivery strategies and establish their clinical efficacy. This article is protected by copyright. All rights reserved.

Orsellinic acid-loaded chitosan nanoparticles in gelatin/nanohydroxyapatite scaffolds for bone formation in vitro

AIM

Orsellinic acid (2,4-Dimethoxy-6-methylbenzoic acid) (OA) is a hydrophobic polyphenolic compound with therapeutic potential, but its impact on actuating osteogenesis remains unknown. The bioavailability of OA is hampered by its hydrophobic nature. This study aimed to fabricate nano-drug delivery system-based scaffolds for OA and test its potential for osteogenesis in vitro.

MATERIALS AND METHODS

OA was loaded into chitosan nanoparticles (nCS + OA) using the ionic gelation technique at different concentrations. nCS + OA were incorporated onto the scaffolds containing gelatin (Gel) and nanohydroxyapatite (nHAp) by the lyophilization method. Biocomposite scaffolds were examined for their physicochemical and material characteristic properties. The effect of OA in the scaffolds for osteoblast differentiation was determined by alizarin red and von Kossa staining at the cellular level and by reverse transcriptase-qPCR and western blot analysis at the molecular level.

KEY FINDINGS

The scaffolds showed excellent physiochemical and material characteristics and remained cyto-friendly to mouse mesenchymal stem cells (mMSCs, C3H10T1/2). The release of OA from Gel/nHAp/nCS scaffolds enhanced the differentiation of mMSCs towards osteoblasts, as observed through cellular and molecular studies. Moreover, the osteogenic potential of OA was mediated by the activation of FAK and ERK signaling pathways through integrins.

SIGNIFICANCE

The inclusion of OA into Gel/nHAp/nCS biocomposite scaffolds at 80 μM concentration promoted osteoblast differentiation via cell adhesion mediated signaling, compared with that shown by Gel/nHAp/nCS alone. Overall, this study identified the potential therapeutic OA containing Gel/nHAp/nCS scaffolds, accelerating its potential for clinical application towards bone regeneration.

Bioactive Molecules-incorporated Polymeric Electrospun Fibers in Bone Tissue Engineering

Bone tissue engineering (BTE) enforces the concerted participation and combination of different biomaterials, cells, and bioactive molecules to make biosynthetic grafts for bone regeneration. Electrospinning has been used to fabricate fibrous scaffolds, which provide nanoscale architecture comprising interconnecting pores, resembling the natural hierarchy of tissues, and enabling the formation of artificial functional tissues. Electrospun fibers for BTE applications have been mostly made from polymers (chitosan, alginate, polycaprolactone, polylactic acid) and bioceramics (hydroxyapatite). Stem cells are among the most prolific members employed in regenerative medicine due to their self-renewal and differentiation capacity. Most importantly, the bioactive molecules such as synthetic drugs, growth factors, phytocompounds consistently regulate cell behavior inducing differentiation towards osteoblast lineage. A growing literature now evidenced these electrospun fibers loaded with bioactive molecules supporting the differentiation of stem cells towards osteoblasts. Thus, this review briefly describes the current development of polymers and bioceramics-based electrospun fibers and the influence of bioactive molecules in these electrospun fibers for bone tissue regeneration.

Preparation and characterization of chitosan/carboxymethyl pullulan/bioglass composite films for wound healing

Wound dressings play a vital role in the wound healing process. Although a variety of wound dressings have been developed so far, most of them still have many drawbacks such as rigidity, non-porosity, low mechanical strength, an affinity to stick onto the injury surface and less antimicrobial activity. To overcome these issues, a novel type of porous three-dimensional (3D) film was fabricated using chitosan/carboxymethyl pullulan polyelectrolyte complex (PEC) loaded with 45S5 bioglass (CCMPBG) by the freeze-drying method for wound healing application. The developed films were analysed by FTIR, XRD, EDS and SEM to confirm their chemical nature, microstructure and surface morphologies. The CCMPBG films exhibited rough surface morphology and well-interconnected micropores with an average size range of 101-74 μm. Compared to the control chitosan/carboxymethyl pullulan (CCMP) film, the CCMPBG films showed an enhanced mechanical strength and controlled rate of swelling and biodegradation behaviours due to the interaction of polymer matrix and 45S5 bioglass (BG). Furthermore, CCMPBG films presented the improved biocompatibility, antimicrobial activity and wound closure ability because of the synergistic effects of chitosan, carboxymethyl pullulan (CMP) and BG. The results demonstrated that CCMPBG films can be an effective dressing material for wound therapy.

Synthesis and characterization of magnesium diboride nanosheets in alginate/polyvinyl alcohol scaffolds for bone tissue engineering

Boride, which belongs to the distinct category of ceramic materials, has attracted significant attention in tissue engineering applications. Magnesium diboride (MgB2) consists of a plane of magnesium atoms sandwiched between the layers of boron. Even though MgB2 showed its role in various applications, its effect on osteogenesis has not yet been investigated. In this study, we synthesized MgB2 nanosheets (MgB2NS), a new class of 2D-nanoscale structures, by the ultrasonication exfoliation method and incorporated them into a polymeric mixture of alginate (Alg) and polyvinyl alcohol (PVA) by the freeze-drying procedure. The synthesized scaffolds (Alg/PVA/MgB2NS) were characterized by SEM, XRD, FT-IR, protein adsorption, swelling, degradation, and biomineralization studies. These scaffolds were non-toxic to mouse mesenchymal stem cells (mMSCs). MgB2NS in the scaffolds enhanced osteoblast differentiation of mMSCs at the molecular level by the expression of Runx2 and osteoblast differentiation marker genes and at the cellular level by alkaline phosphatase, alizarin Red and von Kossa staining. Overall, our results showed that MgB2NS in Alg/PVA scaffolds have osteogenic potential, suggesting their possible use in bone tissue engineering applications.

Polycaprolactone/polyvinylpyrrolidone coaxial electrospun fibers containing veratric acid-loaded chitosan nanoparticles for bone regeneration

Veratric acid (3,4-dimethoxy benzoic acid) (VA) is a hydrophobic phenolic phytocompound possessing therapeutic potential, but it has not been reported as actuating bone regeneration to date. Furthermore, delivery of hydrophobic compounds is often impeded in the body, thus depreciating their bioavailability. In this study, VA was found to have osteogenic potential and its sustained delivery was facilitated through a nanoparticle-embedded coaxial electrospinning technique. Polycaprolactone/polyvinylpyrrolidone (PCL/PVP) coaxial fibers were electrospun, encasing VA-loaded chitosan nanoparticles (CHS-NP). The fibers showed commendable physiochemical and material properties and were biocompatible with mouse mesenchymal stem cells (mMSCs). When mMSCs were grown on coaxial fibers, VA promoted these cells towards osteoblast differentiation as was reflected by calcium deposits. The mRNA expression of Runx2, an important bone transcriptional regulator, and other differentiation markers such as alkaline phosphatase, collagen type I, and osteocalcin were found to be upregulated in mMSCs grown on the PCL/PVP/CHS-NP-VA fibers. Overall, the study portrays the delivery of the phytocompound, VA, in a sustained manner to promote bone regeneration.

An osteoinductive effect of phytol on mouse mesenchymal stem cells (C3H10T1/2) towards osteoblasts

In recent years, phytochemicals have been widely researched and utilized for the treatment of various medical conditions such as cancer, cardiovascular diseases, age-related problems and are also said to have bone regenerative effects. In this study, phytol (3,7,11,15-tetramethylhexadec-2-en-1-ol), an acyclic unsaturated diterpene alcohol and a secondary metabolite derived from aromatic plants was investigated for its effect on osteogenesis. Phytol was found to be nontoxic in mouse mesenchymal stem cells (C3H10T1/2). At the cellular level, phytol-treatment promoted osteoblast differentiation, as seen by the increased calcium deposits. At the molecular level, phytol-treatment stimulated the expression of Runx2 (a bone-related transcription factor) and other osteogenic marker genes. MicroRNAs (miRNAs) play an essential role in controlling bone metabolism by targeting genes at the post-transcriptional level. Upon phytol-treatment in C3H10T1/2 cells, mir-21a and Smad7 levels were increased and decreased, respectively. It was previously reported that mir-21a targets Smad7 (an antagonist of TGF-beta1 signaling) and thus, protects Runx2 from its degradation. Thus, based on our results, we suggest that phytol-treatment promoted osteoblast differentiation in C3H10T1/2 cells via Runx2 due to downregulation of Smad7 by mir-21a. Henceforth, phytol was identified to bolster osteoblast differentiation, which in turn may be used for bone regeneration.

Syringic acid, a phenolic acid, promotes osteoblast differentiation by stimulation of Runx2 expression and targeting of Smad7 by miR-21 in mouse mesenchymal stem cells

Syringic acid (SA), a phenolic acid, has been used in Chinese and Indian medicine for treating diabetes but its role in osteogenesis has not yet been investigated. In the present study, at the molecular and cellular levels, we evaluated the effects of SA on osteoblast differentiation. At the cellular level, there was increased alkaline phosphatase (ALP) activity and calcium deposition by SA treatment in mouse mesenchymal stem cells (mMSCs). At the molecular level, SA treatment of these cells stimulated expression of Runx2, a bone transcription factor, and of osteoblast differentiation marker genes such as ALP, type I collagen, and osteocalcin. It is known that Smad7 is an antagonist of TGF-β/Smad signaling and is a negative regulator of Runx2. microRNAs (miRNAs) play a key role in the regulation of osteogenesis genes at the post-transcriptional level and studies have reported that Smad7 is one of the target genes of miR-21. We found that there was down regulation of Smad7 and up regulation of miR-21 in SA-treated mMSCs. We further identified that the 3'-untranslated region (UTR) of Smad7 was directly targeted by miR-21 in these cells. Thus, our results suggested that SA promotes osteoblast differentiation via increased expression of Runx2 by miR-21-mediated down regulation of Smad7. Hence, SA may have potential in orthopedic applications.

Chitosan/nano-hydroxyapatite/nano-zirconium dioxide scaffolds with miR-590-5p for bone regeneration

Bone tissue engineering (BTE) relies on biocomposite scaffolds and bioactive molecules for bone regeneration. The present study was aimed to synthesize and characterize biocomposite scaffolds containing chitosan (CS), nano-hydroxyapatite (nHAp) and nano‑zirconium dioxide (nZrO₂) along with microRNA (miRNA) for BTE applications. miRNAs act as post-transcriptional regulator of gene expression. The fabricated biocomposite scaffolds were characterized using SEM, FT-IR and XRD analyses. The effect of a bioactive molecule (miR-590-5p) with scaffolds was tested for osteoblast differentiation at the cellular and molecular levels using mouse mesenchymal stem cells (C3H10T1/2). The results showed that CS/nHAp/nZrO₂ scaffolds promoted osteoblast differentiation, and this effect was further increased in the presence of miR-590-5p in C3H10T1/2 cells. Thus, we suggested that CS/nHAp/nZrO₂ scaffolds with miR-590-5p would have potential towards the treatment of bone defects.

Chitosan based nanofibers in bone tissue engineering

Bone tissue engineering involves biomaterials, cells and regulatory factors to make biosynthetic bone grafts with efficient mineralization for regeneration of fractured or damaged bones. Out of all the techniques available for scaffold preparation, electrospinning is given priority as it can fabricate nanostructures. Also, electrospun nanofibers possess unique properties such as the high surface area to volume ratio, porosity, stability, permeability and morphological similarity to that of extra cellular matrix. Chitosan (CS) has a significant edge over other materials and as a graft material, CS can be used alone or in combination with other materials in the form of nanofibers to provide the structural and biochemical cues for acceleration of bone regeneration. Hence, this review was aimed to provide a detailed study available on CS and its composites prepared as nanofibers, and their associated properties found suitable for bone tissue engineering.

An investigation on the diversity of mosquitocidal bacteria and its relationship with incidence of vector borne diseases

Control of mosquitoes is the most important aspect of public health, as mosquitoes transmit many human diseases, including the fatal infection, Japanese encephalitis. This paper addresses the isolation of new mosquitocidal bacteria from soil samples in the Union Territory of Pondicherry, India, where, no clinical cases of vector borne infections have been reported. Bacterial isolates from soil samples were screened for potential mosquitocidal strains and bioassays against mosquito vectors (Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti) were carried out. Genomic DNA of potential mosquitocidal isolates was amplified and species identification was carried out using BLASTn program (NCBI). Phylogenetic analysis of 16S rRNA sequences of mosquitocidal bacteria revealed seven potential isolates. SDS-PAGE results have shown that there was considerable difference in the protein profiles. Numerical analysis revealed 4 distinct groups at similarity level 25%. The relationship between VBDs and prevalence of soil mosquitocidal bacteria in the study sites has elicited considerable interest in the diversity of mosquitocidal bacteria and their application for mosquito borne diseases control.