Paulomi Ghosh

Dextrin cross linked with poly(HEMA): a novel hydrogel for colon specific delivery of ornidazole

We report on the synthesis and characterization of a novel hydrogel based on dextrin grafted with poly(2-hydroxyethyl methacrylate) by embedding N,N′-methylene bis acrylamide (MBA) as cross linker, into a polymeric network in the presence of potassium persulphate (KPS) initiator for colon specific delivery of ornidazole. Various grades of hydrogels [Dxt-g-p(HEMA)] have been synthesized by altering the reaction parameters and the best one optimized. The developed hydrogel has been characterized using FTIR spectra, 13C NMR spectra, elemental analysis, XRD study, SEM analysis, TGA analysis, swelling study and cell viability study. The equilibrium swelling ratio of the hydrogels has been recorded in different media and found to be at a maximum at pH 7.4. A cell viability study indicates that the hydrogel is non-cytotoxic in nature. The drug delivery results demonstrate that Dxt-g-p(HEMA) delivers ornidazole successfully in the colonic region in a controlled way and is a good candidate for an orally administered drug delivery system. The release mechanism and kinetics of ornidazole from various hydrogels have been determined using different linear and nonlinear mathematical models, which confirm that ornidazole release from hydrogel follows first order kinetics and a non-Fickian diffusion mechanism.

Development and application of a nanocomposite derived from crosslinked HPMC and Au nanoparticles for colon targeted drug delivery

Herein, we report a novel route for the synthesis of a poly(acrylamide) (PAAm) crosslinked hydroxypropyl methyl cellulose/Au nanocomposite where chemically crosslinked HPMC (c-HPMC) works as a reducing agent. At first, the crosslinked polymer was developed by grafting PAAm chains onto the HPMC backbone using ethylene glycol dimethacrylate (EGDMA) crosslinker and potassium persulfate (K2S2O8) initiator. Afterwards, AuNPs have been incorporated in situ on the surface of the crosslinked hydrogel, where the hydrogel itself reduces the tetrachloroauric acid (HAuCl4) in the reaction medium to form the nanocomposite. Different grades of nanocomposites (c-HPMC/Au) have been synthesized by altering the reaction parameters and the best one was optimized with the help of UV-visible spectroscopy. The nanocomposites synthesized, have been characterized by FTIR spectroscopy, 13C NMR spectroscopy, XRD studies, FESEM/EDAX/elemental mapping analyses, HR-TEM analysis and TGA analysis. HR-TEM analysis reveals the uniform distribution of spherical AuNPs on the surface of c-HPMC. Rheological characteristics disclose that the nanocomposite demonstrates higher gel strength than that of the crosslinked polymer, mainly because of the enhanced interactions between the organic matrix and inorganic fillers. The pH responsive behaviour of crosslinked hydrogel/composites has been confirmed by measuring the equilibrium swelling ratio in various buffer solutions (pH 1.2 and 7.4) at 37 °C. Biodegradability of the hydrogel/nanocomposite has been verified using hen egg lysozyme. The synthesized nanocomposite also demonstrates non-cytotoxic behaviour towards human mesenchymal stem cells (hMSCs). The in vitro drug release profiles indicate that both ornidazole and 5-amino salicylic acid (5-ASA) are released from the nanocomposite matrix in a controlled fashion. This confirms that the c-HPMC/Au nanocomposite is likely be an excellent alternative for the controlled release of colonic drugs. The release kinetics and mechanism of ornidazole and 5-ASA from the nanocomposite material has been explained using various linear and non-linear mathematical models.

Covalent cross-links in polyampholytic chitosan fibers enhances bone regeneration in a rabbit model

Chitosan fibers were prepared in citric acid bath, pH 7.4 and NaOH solution at pH 13, to form ionotropically cross-linked and uncross-linked fibers, respectively. The fibers formed in citric acid bath were further cross-linked via carbodiimide chemistry; wherein the pendant carboxyl moieties of citric acid were used for new amide bond formation. Moreover, upon covalent cross-linking in the ionically gelled citrate-chitosan fibers, incomplete conversion of the ion pairs to amide linkages took place resulting in the formation of a dual network structure. The dual cross-linked fibers displayed improved mechanical property, higher stability against enzymatic degradation, hydrophobicity and superior bio-mineralization compared to the uncross-linked and native citrate cross-linked fibers. Additionally, upon cyclic loading, the ion pairs in the dual cross-linked fibers dissociated by dissipating energy and reformed during the relaxation period. The twin property of elasticity and energy dissipation mechanism makes the dual cross-linked fiber unique under dynamic mechanical conditions. The differences in the physico-chemical characteristics were reflected in protein adsorption, which in turn influenced the cellular activities on the fibers. Compared to the uncross-linked and ionotropically cross-linked fibers, the dual cross-linked fibers demonstrated higher proliferation and osteogenic differentiation of the MSCs in vitro as well as better osseous tissue regeneration in a rabbit model.

Dextrin and poly(lactide)-based biocompatible and biodegradable nanogel for cancer targeted delivery of doxorubicin hydrochloride

Herein, we report the development and application of a novel biocompatible, chemically crosslinked nanogel for use in anticancer drug delivery. The nanogel [n-Dxt-p(lactide)] has been synthesized from dextrin and poly (lactide) by in situ crosslinking with a homobifunctional crosslinker through a conventional radical polymerization technique. The properties of the nanogel have been investigated using FTIR spectroscopy, 1H NMR spectroscopy, TGA, FESEM, TEM and DLS. The stimuli responsiveness of the nanogel has been detected by measuring its pH dependent swelling in different buffer solutions at 37 ± 0.5 °C. It was found that the size of nanogel was less than 10 nm. Degradation experiments using hen egg lysozyme revealed that the nanogel is biodegradable. In vitro cytocompatibility studies against human mesenchymal stem cell (hMSCs) suggested that the nanogel is non-toxic. The nanogel can efficiently load and encapsulate doxorubicin hydrochloride (Dox) within the matrix with 28.26 ± 0.20% loading efficiency and 91.16 ± 0.64% encapsulation efficiency. Additionally, the native nanogel showed non-toxic effects on MG 63 cancer cells, while Dox-loaded nanogel demonstrated high toxicity towards cancer cells. Because of its very small size, the nanogel can effortlessly enter into the cell cytoplasm and destroy cancer cells. The n-Dxt-p(lactide) nanogel released doxorubicin in a sustained manner and appears to be a high-quality option for doxorubicin hydrochloride delivery.

2,5-Dimethoxy 2,5-dihydrofuran crosslinked chitosan fibers enhance bone regeneration in rabbit femur defects

Chitosan fibers were fabricated via pH induced neutralization and precipitation in a 5 w/v% NaOH bath. Intermolecular covalent crosslinking of these fibers were performed through imine linkages between the glucosamine units of polymers and the dialdehyde groups of 2,5-dimethoxy-2,5-dihydrofuran at 60 °C, pH 2.2. The covalently crosslinked fibers demonstrated improved tensile strength, stiffness, hydrophobicity and higher stability against enzymatic degradation compared to uncrosslinked ones under wet conditions. The differences in the physico-chemical characteristics were reflected in protein adsorption which in turn facilitated higher cellular proliferation and adhesion to the crosslinked fibers. Osteogenesis of human bone marrow derived mesenchymal stem cells (hMSCs) was significantly higher on crosslinked fibers compared to the uncrosslinked ones as evidenced by higher alkaline phosphatase expression, calcium deposition and osteocalcin secretion. In vivo study performed subcutaneously in a rabbit model with crosslinked fibers revealed its ability to integrate with host tissues and showed differential extent of cellular infiltration and extracellular matrix production after specified periods of implantation. Further bone regeneration ability at the defect site filled with crosslinked fibers was evident by histological analysis. Thus, the study suggests that the imine crosslinked fibers could be used for bone tissue engineering applications.

Citrate cross-linked gels with strain reversibility and viscoelastic behavior accelerate healing of osteochondral defects in a rabbit model.

Most living tissues are viscoelastic in nature. Self-repair due to the dissipation of energy by reversible bonds prevents the rupture of the molecular backbone in these tissues. Recent studies, therefore, have aimed to synthesize biomaterials that approximate the mechanical performance of biological materials with self-recovery properties. We report an environmentally friendly method for the development of ionotropically cross-linked viscoelastic chitosan gels with a modulus comparable to that of living tissues. The strain recovery property was found to be highest for the gels with the lowest cross-linking density. The force-displacement curve showed significant hysteresis due to the presence of reversible bonds in the cross-linked gels. Nanoindentation studies demonstrated the creep phenomenon for the cross-linked chitosan gels. Creep, hysteresis, and plasticity index confirmed the viscoelastic behavior of the cross-linked gels. The viscoelastic gels were implanted at osteochondral defect sites to assess the tissue regeneration ability. In vivo results demonstrated early cartilage formation and woven bone deposition for defects filled with the gels compared to nontreated defects.

Novel pH-responsive graft copolymer based on HPMC and poly(acrylamide) synthesised by microwave irradiation: application in controlled release of ornidazole

Herein, the microwave-assisted grafting method was employed for the development of a novel pH-responsive graft copolymer derived from polyacrylamide-modified hydroxypropyl methyl cellulose [g-HPMC (M)]. The synthesised copolymer has been used for in vitro sustained release of ornidazole. Various characterizations confirm the formation of graft copolymer. Swelling studies indicate the pH-dependent swelling behaviour, while deswelling studies suggest that g-HPMC (M) shows faster deswelling in response to change in pH and/temperature. The cell viability study signifies that g-HPMC (M) is cytocompatible. The in-vitro release study demonstrates that g-HPMC (M) delivers ornidazole specifically in the colon pH, without release of the drug in the acidic environment, ensuring g-HPMC (M) as an ideal candidate for orally administered colonic drug carriers. The kinetics and mechanism of drug release suggest that it follows a non-Fickian release mechanism.

Investigating the potential of human placenta-derived extracellular matrix sponges coupled with amniotic membrane-derived stem cells for osteochondral tissue engineering

Osteochondral injuries are challenging to repair due to their complex tissue anatomy and restricted self-repairing ability associated with a limited blood supply. Osteochondral tissue engineering is an important clinical aspect of the management and treatment of cartilage and underlying bone. In the present study, we fabricated human placenta-derived extracellular matrix sponges (PEMS) for repair of osteochondral tissue through a decellularization process. There were no significant cellular components present in the PEMS; hematoxylin & eosin/DAPI staining, DNA quantification and agarose gel electrophoresis were used to evaluate the extent of decellularization. Moreover, no significant alteration to the collagen and glycosaminoglycan (native extracellular matrix) content of the PEMS was observed. PEMS in vitro provided a non-cytotoxic environment rich in bioactive cues for human amniotic membrane-derived stem cells (HAMSCs) to proliferate in and differentiate into chondrogenic and osteogenic lineages under induction. Histological analysis at 28 days after the PEMS were subcutaneously implanted demonstrated no severe immune response in the host and supported the formation of blood vessels. To assess the osteochondral tissue repair ability of PEMS, cell-free PEMS (CFP) and cell-seeded PEMS (CSP) were implanted at osteochondral defect sites in a rabbit model. Histological scores indicated that osteochondral regeneration was more successful in the defects filled with CSP compared to those filled with CFP and empty defects (ED) after 60 days of implantation. In summary, a naturally derived biocompatible scaffold composed of extracellular matrix from human placenta has been successfully developed for osteochondral tissue engineering.

Chitosan Derivatives Cross-Linked with Iodinated 2,5-Dimethoxy-2,5- dihydrofuran for Non-Invasive Imaging

Radiopaque polymer derivatives were successfully prepared through surface diffusion mediated cross-linking of chitosan with iodinated 2,5-dimethoxy-2,5-dihydrofuran. The incorporation of iodine in 2,5-dimethoxy-2,5-dihydrofuran was validated by (1)H NMR and mass spectroscopy. The cross-linking of the glucosamine moieties of chitosan with the iodinated product was confirmed by (13)C NMR and energy-dispersive X-ray spectroscopy. Radiography analysis proved inherent opacity of the iodinated fibrous sheets and microspheres that were comparable to the X-ray visibility of aluminum hollow rings of equivalent thickness and commercially available radiopaque tape, respectively. Microscopic studies evidenced retention of the fiber/microsphere morphology after the iodination/cross-linking reactions. The effects of iodination/cross-linking on the mechanical and biodegradation properties of fibers were studied by nanoindentation and enzymatic assay, respectively. In vitro and in vivo studies established the nontoxic, biodegradable nature of radiopaque derivatives. Iodinated fiber mesh implanted in a rabbit model was significantly X-ray opaque compared to the uncross-linked fiber mesh and medical grade surgical swabs. Further, opacity of the iodinated mesh was evident even after 60 days, though the intensity was reduced, which indicates the biodegradable nature of the iodinated polymer. The opacity of the iodinated sutures was also established in the computed tomography images. Finally, the sufficient in vivo contrast property of the radiopaque microspheres in the gastrointestinal tract indicates its possible role in clinical diagnostics.

Silk Sponges Ornamented with a Placenta-Derived Extracellular Matrix Augment Full-Thickness Cutaneous Wound Healing by Stimulating Neovascularization and Cellular Migration

Regeneration of full-thickness wounds without scar formation is a multifaceted process, which depends on in situ dynamic interactions between the tissue-engineered skin substitutes and a newly formed reparative tissue. However, the majority of the tissue-engineered skin substitutes used so far in full-thickness wound healing cannot mimic the natural extracellular matrix (ECM) complexity and thus are incapable of providing a suitable niche for endogenous tissue repair. Herein, we demonstrated a simple approach to fabricate porous hybrid ECM sponges (HEMS) using a placental ECM and silk fibroin for full-thickness wound healing. HEMS with retained cytokines/growth factors provided a noncytotoxic environment in vitro for human foreskin fibroblasts (HFFs), human epidermal keratinocytes (HEKs), and human amniotic membrane-derived stem cells to adhere, infiltrate, and proliferate. Interestingly, HEMS-conditioned media accelerated the migration of HFFs and HEKs owing to the presence of cytokines/growth factors. Also, the ex vivo chick chorioallantoic membrane assay of HEMS demonstrated its excellent vascularization potential by inducing and supporting blood vessels. Additionally, HEMS when subcutaneously implanted demonstrated no severe immune response to the host. Furthermore, HEMS implanted in full-thickness wounds in a rat model showed augmented healing progression with well-organized epidermal-dermal junctions via pronounced angiogenesis, accelerated migration of HFFs/HEKs, enhanced granulation tissue formation, and early re-epithelialization. Taken together, these findings show that porous HEMS ornamented with cytokines/growth factors having superior physicomechanical properties may be an appropriate skin substitute for full-thickness cutaneous wounds.