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-ß/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.

Chitosan-based 3D-printed scaffolds for bone tissue engineering.

Despite the spontaneous regenerative properties of autologous bone grafts, this technique remains dilatory and restricted to fractures and injuries. Conventional grafting strategies used to treat bone tissue damage have several limitations. This highlights the need for novel approaches to overcome the persisting challenges. Tissue-like constructs that can mimic natural bone structurally and functionally represent a promising strategy. Bone tissue engineering (BTE) is an approach used to develop bioengineered bone with subtle architecture. BTE utilizes biomaterials to accommodate cells and deliver signaling molecules required for bone rejuvenation. Among the various techniques available for scaffold creation, 3D-printing technology is considered to be a superior technique as it enables the design of functional scaffolds with well-defined customizable properties. Among the biomaterials obtained from natural, synthetic, or ceramic origins, naturally derived chitosan (CS) polymers are promising candidates for fabricating reliable tissue constructs. In this review, the physicochemical-biological properties and applications of CS-based 3D-printed scaffolds and their future perspectives in BTE are summarized.

3D-poly (lactic acid) scaffolds coated with gelatin and mucic acid for bone tissue engineering.

Three-dimensional (3D) printing is a promising technology to fabricate the intricate biomimetic structure. The primary focus of this study was to develop the bioactive 3D-scaffolds to enhance bone regeneration. The 3D-poly (lactic acid) (PLA) scaffolds were extruded based on a computer-aided design (CAD) model and coated with gelatin (Gel) containing different concentrations of mucic acid (MA) and were investigated for their osteogenic potential. Coating the PLA scaffolds with Gel/MA improved their physicochemical properties, and the addition of MA did not alter these properties. The viability of mouse mesenchymal stem cells (mMSCs, C3H10T1/2) seeded onto the PLA/Gel/MA scaffolds remained unaffected both at metabolic and cell membrane integrity levels. Alkaline phosphatase and von Kossa staining indicated the promotion of osteoblast differentiation of mMSCs by MA in the PLA/Gel scaffolds. Inclusion of MA in PLA/Gel scaffolds also increased the expression of the master bone transcription factor, Runx2, and other osteoblastic differentiation marker genes in mMSCs. Thus, our results suggested that the 3D-printed PLA scaffolds coated with Gel/MA favor osteoblast differentiation and have potential applications in bone tissue engineering.

Temperature- and pH-responsive chitosan-based injectable hydrogels for bone tissue engineering.

Spontaneous bone regeneration is heavily restricted because of bone defects, and external mediation is required to enhance repair and regeneration. Bone tissue engineering (BTE) is a multidisciplinary field that offers promising substitutes to traditional methods-namely, autografts, allografts, and xenografts. Amidst the various scaffolds for BTE applications, it has been demonstrated that hydrogels are promising templates for bone regeneration owing to their similarities to the natural extracellular matrix. Regardless of the development of a variety of biomaterials, chitosan (CS) as a natural biopolymer has drawn tremendous attention in recent years for its use as a valuable graft material to form thermo/pH-responsive injectable hydrogels. Formulations of CS-based injectable hydrogels are advantageous in terms of their high-water imbibing capability, minimal invasiveness, porous networks, and ability to mold perfectly into an irregular defect. In this review, the physicochemical properties and applications of thermo/pH-responsive CS-based hydrogels and their future perspectives in BTE are briefly outlined.

Biodistribution and pharmacokinetics of thiolated chitosan nanoparticles for oral delivery of insulin in vivo.

To improve the quality of life of diabetic patients, oral delivery of insulin would be better than subcutaneous injection, and the encapsulation of insulin for its oral delivery is a promising alternative one. In this study, we prepared an oral insulin delivery system using thiolated chitosan nanoparticles (TCNPs) loaded with insulin (Ins) and tested under in vitro and in vivo systems. TCNPs prepared from CS and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) at 4:1 ratio showed 220 ± 4 nm, 2.3 ± 1 mV, and 119 ± 4 µmol g-1 in their size, charge and sulfhydryl content, respectively. There was a sustained release of insulin from the TCNPs at pH 5.3. TCNPs treatment did not alter cell viability in vitro and oral administration of TCNPs reached over the tip of the microvilli near the intestinal mucosa in vivo. There were increased and decreased the levels of insulin and glucose in the blood, respectively when Ins-TCNPs were orally administered in the diabetes induced rats. Thus, our results suggested that the insulin stays significantly for a prolonged period to make bio-distribution and bioavailability due to its interaction with the mucus of the intestine, thus offering a better oral insulin delivery system for diabetic patients.

Osteostimulatory effect of biocomposite scaffold containing phytomolecule diosmin by Integrin/FAK/ERK signaling pathway in mouse mesenchymal stem cells.

Non-availability of an ideal alternative for autografts in treating critical-size bone defects is a major challenge in orthopedics. Phytocompounds have been proven to enhance osteogenesis via various osteogenic signaling pathways, but its decreased bioavailability and increased renal clearance limit its application. In this study, we designed a biocomposite scaffold comprising gelatin (Gel) and nanohydroxyapatite (nHAp) incorporated with diosmin (DM) and we investigated its bone forming potential in vitro and in vivo. Physiochemical characterization of the scaffold showed that DM had no effect on altering the material characteristics of the scaffold. The addition of DM enhanced the osteoblast differentiation potential of the scaffold in mouse mesenchymal stem cells at both cellular and molecular levels, possibly via the integrin-mediated activation of FAK and ERK signaling components. Using the rat tibial bone defective model, we identified the effect of DM in Gel/nHAp scaffold on enhancing bone formation in vivo. Based on our results, we suggest that Gel/nHAp/DM can be a potential therapeutic agent in scaffold-mediated bone regeneration.

Osteogenic stimulatory effect of heraclenin purified from bael in mouse mesenchymal stem cells in vitro.

Osteoporosis is a major health concern occurring to the aging adult population across the globe. Currently, there is an increasing demand for treatment of osteoporosis with plant-based medicines. In the present study, we report that heraclenin was extracted and purified from unripe fruit portion of Bael (Aegle marmelos Corr.) using silica gel column chromatography. The identification and characterization of heraclenin were carried out by UV-Vis, HPLC, LC-MS, NMR, FT-IR, and XRD analyses. The standardized purification method recorded a yield efficiency of 42% heraclenin microcrystals with 99% purity from bael fruit. SEM image revealed the shape of the purified compound to be an orthorhombic-sphenoid prism. Cytotoxicity studies indicated that heraclenin-treatment did not alter cell viability in mouse mesenchymal stem cells (mMSCs, C3H10T1/2). The mRNA expression of Runx2, a bone transcription factor was found to be stimulated by heraclenin in these cells. At the cellular level, heraclenin-treatment enhanced osteoblast differentiation and mineralization in mMSCs. Thus, these results suggested that heraclenin purified from bael fruit has an osteogenic effect, indicating its potential towards bone regeneration.

Sustained release of chrysin from chitosan-based scaffolds promotes mesenchymal stem cell proliferation and osteoblast differentiation.

Numerous phytochemical compounds have recently been reported to stimulate osteogenesis. In this study, the bioavailability and osteogenic effects of chrysin, a natural flavonoid, were investigated. Chrysin was incorporated at different concentrations into biocomposite scaffolds containing carboxymethyl cellulose, chitosan, and nano-hydroxyapatite, through the freeze-drying method. The physicochemical and material characteristics of chrysin-incorporated scaffolds were investigated, and chrysin had no effect on them. These chrysin-containing scaffolds were not cytotoxic to mouse mesenchymal stem cells (mMSCs). Chrysin released from scaffolds stimulated cell proliferation and promoted osteoblast differentiation. Osteoblast differentiation enhanced by chrysin from scaffolds could be due to downregulation of co-repressors of the osteoblast differentiation transcription factor Runx2 in these cells. Thus, chrysin release from scaffolds has potential effects on proliferation and differentiation of mMSCs; hence, it has potential application in bone tissue engineering.