Dilip Depan

Structure–process–property relationship of the polar graphene oxide-mediated cellular response and stimulated growth of osteoblasts on hybrid chitosan network structure nanocomposite scaffolds

We here describe the structure-process-property relationship of graphene oxide-mediated proliferation and growth of osteoblasts in conjunction with the physico-chemical, mechanical, and structural properties. Chitosan-graphene network structure scaffolds were synthesized by covalent linkage of the carboxyl groups of graphene oxide with the amine groups of chitosan. The negatively charged graphene oxide in chitosan scaffolds was an important physico-chemical factor influencing cell-scaffold interactions. Furthermore, it was advantageous in enhancing the biocompatibility of the scaffolds and the degradation products of the scaffolds. The high water retention ability, hydrophilic nature, and high degree of interconnectivity of the porous structure of chitosan-graphene oxide scaffolds facilitated cell attachment and proliferation and improved the stability against enzymatic degradation. The cells infiltrated and colonized the pores of the scaffolds and established cell-cell interactions. The interconnectivity of the porous structure of the scaffolds helps the flow of medium throughout the scaffold for even cell adhesion. Moreover, the seeded cells were able to infiltrate inside the pores of chitosan-graphene oxide scaffolds, suggesting that the incorporation of polar graphene oxide in scaffolds is promising for bone tissue engineering.

Cell proliferation and controlled drug release studies of nanohybrids based on chitosan-g-lactic acid and montmorillonite.

The present paper reveals the potential uses of novel hybrids of chitosan-g-lactic acid and sodium montmorillonite (MMT) in controlled drug delivery and tissue engineering applications. The drug-loaded novel nanohybrid films and porous scaffolds have been prepared by solvent casting and freeze-drying of the grafted polymer solution, respectively. Sodium Ibuprofen was loaded into nanohybrids of chitosan-g-lactic acid/sodium montmorillonite (CS-g-LA/MMT). Grafting of lactic acid and the drug loading were characterized by Fourier transform infrared spectroscopy. Formation of intercalated nanocomposites was confirmed by X-ray diffraction. Mechanical properties measurements have shown improvement in modulus and strength with expense of elongation by MMT reinforcement. The nanohybrids were found to be stable regardless of pH of the medium. The cell proliferation profile also shows that prepared nanohybrids are biocompatible. MMT reinforcement was found to control the drug (Ibuprofen) release rate in phosphate buffer saline solution (pH 7.4). MMT clay is therefore a viable additive for formulating sustained drug delivery systems based on lactic acid grafted chitosan.

Organic/inorganic hybrid network structure nanocomposite scaffolds based on grafted chitosan for tissue engineering.

We describe the first study of structure-processing-property relationship in organic/inorganic hybrid network structure nanocomposite scaffolds based on grafted chitosan for bone tissue engineering. Chitosan was first grafted with propylene oxide to form hydroxypropylated chitosan, which was subsequently linked with ethylene glycol functionalized nanohydroxyapatite to form an organic/inorganic network structure. The resulting scaffold was characterized by a highly porous structure and significantly superior physico-chemical, mechanical and biological properties compared to pure chitosan. The scaffolds exhibited high modulus, controlled swelling behavior and reduced water uptake, but the water retention ability was similar to pure chitosan scaffold. MTT assay studies confirmed the non-cytotoxic nature of the scaffolds and enabled degradation products to be analyzed. The nanocomposite scaffolds were biocompatible and supported adhesion, spreading, proliferation and viability of osteoblasts cells. Furthermore, the cells were able to infiltrate and colonize into the pores of the scaffolds and establish cell-cell interactions. The study suggests that hydroxypropylation of chitosan and forming a network structure with a nano-inorganic constituent is a promising approach for enhancing physico-chemical, functional and biological properties for utilization in bone tissue engineering applications.

The interplay between nanostructured carbon-grafted chitosan scaffolds and protein adsorption on the cellular response of osteoblasts: structure-function property relationship.

The rapid adsorption of proteins occurs during the early stages of biomedical device implantation into physiological systems. In this regard, the adsorption of proteins is a strong function of the nature of a biomedical device, which ultimately governs the biological functions. The objective of this study was to elucidate the interplay between nanostructured carbon-modified (graphene oxide and single-walled carbon nanohorn) chitosan scaffolds and consequent protein adsorption and biological function (osteoblast function). We compare and contrast the footprint of protein adsorption on unmodified chitosan and nanostructured carbon-modified chitosan. A comparative analysis of cell-substrate interactions using an osteoblast cell line (MC3T3-E1) implied that biological functions were significantly enhanced in the presence of nanostructured carbon, compared with unmodified chitosan. The difference in their respective behaviors is related to the degree and topography of protein adsorption on the scaffolds. Furthermore, there was a synergistic effect of nanostructured carbon and protein adsorption in terms of favorably modulating biological functions, including cell attachment, proliferation and viability, with the effect being greater on nanostructured carbon-modified scaffolds. The study also underscores that protein adsorption is favored in nanostructured carbon-modified scaffolds such that bioactivity and biological function are promoted.

On the determining role of network structure titania in silicone against bacterial colonization: Mechanism and disruption of biofilm

Silicone-based biomedical devices are prone to microbial adhesion, which is the primary cause of concern in the functioning of the artificial device. Silicone exhibiting long-term and effective antibacterial ability is highly desirable to prevent implant related infections. In this regard, nanophase titania was incorporated in silicone as an integral part of the silicone network structure through cross-link mechanism, with the objective to reduce bacterial adhesion to a minimum. The bacterial adhesion was studied using crystal violet assay, while the mechanism of inhibition of biofilm formation was studied via electron microscopy. The incorporation of nanophase titania in silicone dramatically reduced the viability of Staphylococcus aureus (S. aureus) and the capability to adhere on the surface of hybrid silicone by ~93% in relation to stand alone silicone. The conclusion of dramatic reduction in the viability of S. aureus is corroborated by different experimental approaches including biofilm inhibition assay, zone of inhibition, and through a novel experiment that involved incubation of biofilm with titania nanoparticles. It is proposed that the mechanism of disruption of bacterial film in the presence of titania involves puncturing of the bacterial cell membrane.

Structural and physicochemical aspects of silica encapsulated ZnO quantum dots with high quantum yield and their natural uptake in HeLa cells.

Photoluminescent semiconductor quantum dots (QDs) are of significant interest for bioimaging and fluorescence labeling. In this regard, we describe here the design of high sensitivity and high specificity non-toxic ZnO QDs (∼5 nm) with long-term stability of up to 12 months. The embedding of ZnO QDs on silica nanospheres led to significant increase in photoluminescence intensity rendering them highly bright QD-based probes. The QDs were characterized in vitro with respect to cancer cells (HeLa) and evaluated in terms of viability, fluorescence and cytoskeletal organization. The immobilization of ZnO QDs on silica nanospheres promoted the internalization and enhanced fluorescence emission of HeLa cells. The fluorescence emission from QDs was stable for 3 days, indicating excellent stability toward photobleaching. Cytoskeletal reorganization was observed after internalization of QDs such that the ZnO QDS on silica nanospheres resulted in broadening of the actin cytoskeleton. The study underscores that ZnO QDs immobilized on Si nanospheres are promising for tracking cancer cells in cell therapy.

Processing–structure–functional property relationship in organic–inorganic nanostructured scaffolds for bone‐tissue engineering: The response of preosteoblasts

We elucidate here for the first time the structure-processing-functional property relationship in chitosan (CS)-based scaffolds, where molecular machinery governing proliferation and growth of osteoblasts is mediated by nanostructured carbon. The interconnected network structure of organic-inorganic scaffolds was obtained by covalent linkage of carboxyl group of functionalized single-walled carbon nanohorn with the amine group of CS. The molecular-scale dispersibility of functionalized nanostructured carbon was an important physicochemical factor influencing cellular interactions and biological response. Furthermore, it was beneficial in promoting the biocompatibility and the degradation product of the scaffolds. The hydrophilicity, good water retention ability, and interconnected porous structure of organic-inorganic scaffolds enabled pronounced cell attachment and proliferation and enhanced the stability toward enzymatic degradation. The infiltration of cells and colonization of the pores of the scaffolds and cellular interactions were promoted due to covalent linkage of nanostructured carbon with CS. Additionally, the interconnectivity of porous scaffolds facilitated cells to infiltrate inside the pores of CS-nanostructured scaffolds, implying that nanostructured carbon merits consideration in tissue engineering.

Stability of chitosan/montmorillonite nanohybrid towards enzymatic degradation on grafting with poly(lactic acid)

Abstract Enzymatic degradation of nanohybrid based on intercalation of chitosan (CS) within the galleries of montmorillonite (MMT) clay and grafted with poly(lactic acid) (PLA) was studied using esterase enzyme in phosphate buffered solution. Chitosan was first intercalated between the galleries of natural unmodified sodium MMT clay and subsequently grafted with PLA to prepare nanohybrids of CS-g-PLA/MMT. The prepared membranes were characterised by X-ray diffraction, transmission electron microscopy and NMR spectroscopy. The specimens were then subjected to enzymatic degradation to understand the effect of copolymerisation with PLA and the effect of incorporation of MMT in the CS matrix. The presence of MMT clay provided stability towards degradation of polymer matrix because of nanoscale dispersibility, thereby acting as a barrier towards the permeation of water molecules to induce hydrolysis of PLA. Similarly, the grafting of CS with crystalline PLA stabilised the CS matrix towards degradation, rendering it suitable for tissue engineering applications.

The effect of dimensionality of nanostructured carbon on the architecture of organic–inorganic hybrid materials

The natural tendency of carbon nanotubes (CNTs) to agglomerate is an underlying reason that prevents the realization of their full potential. On the other hand, covalent functionalization of CNTs to control dispersion leads to disruption of π-conjugation in CNTs and the non-covalent functionalization leads to a weak CNT-polymer interface. To overcome these challenges, we describe the characteristics of fostering of direct nucleation of polymers on nanostructured carbon (CNTs of diameters (~2-200 nm), carbon nanofibers (~200-300 nm), and graphene), which culminates in interfacial adhesion, resulting from electrostatic and van der Waals interaction in the hybrid nanostructured carbon-polymer architecture. Furthermore, the structure is tunable through a change in undercooling. High density polyethylene and polypropylene were selected as two model polymers and two sets of experiments were carried out. The first set of experiments was carried out using CNTs of diameter ~2-5 nm to explore the effect of undercooling and polymer concentration. The second set of experiments was focused on studying the effect of dimensionality on geometrical confinements. The periodic crystallization of polyethylene on small diameter CNTs is demonstrated to be a consequence of the geometrical confinement effect, rather than epitaxy, such that petal-like disks nucleate on large diameter CNTs, carbon nanofibers, and graphene. The application of the process is illustrated in terms of fabricating a system for cellular uptake and bioimaging.

Hybrid nanostructured drug carrier with tunable and controlled drug release

We describe here a transformative approach to synthesize a hybrid nanostructured drug carrier that exhibits the characteristics of controlled drug release. The synthesis of the nanohybrid architecture involved two steps. The first step involved direct crystallization of biocompatible copolymer along the long axis of the carbon nanotubes (CNTs), followed by the second step of attachment of drug molecule to the polymer via hydrogen bonding. The extraordinary inorganic-organic hybrid architecture exhibited high drug loading ability and is physically stable even under extreme conditions of acidic media and ultrasonic irradiation. The temperature and pH sensitive characteristics of the hybrid drug carrier and high drug loading ability merit its consideration as a promising carrier and utilization of the fundamental aspects used for synthesis of other promising drug carriers. The higher drug release response during the application of ultrasonic frequency is ascribed to a cavitation-type process in which the acoustic bubbles nucleate and collapse releasing the drug. Furthermore, the study underscores the potential of uniquely combining CNTs and biopolymers for drug delivery.