Rupak Dua

Graphene nanoplatelet-induced strengthening of ultrahigh molecular weight polyethylene and biocompatibility in vitro.

Graphene nanoplatelets (GNPs) are added as reinforcement to ultrahigh molecular weight polyethylene (UHMWPE) with an intended application for orthopedic implants. Electrostatic spraying is established as a potential fabrication method for synthesizing large-scale UHMWPE-GNP composite films. At a low concentration of 0.1 wt % GNP, the composite film shows highest improvement in fracture toughness (54%) and tensile strength (71%) as compared to UHMWPE. Increased GNP content of 1 wt % leads to improvement in elastic modulus and yield strength but fracture toughness and tensile strength are reduced significantly at higher GNP content. The strengthening mechanisms of the UHMWPE-GNP system are highly influenced by the GNP concentration, which dictates its degree of dispersion and extent of polymer wrapping. The fraction of GNPs oriented along the tensile axis influences the elastic deformation, whereas the wrapping of polymer and GNP-polymer interfacial strength determines the deformation behavior in the plastic regime. The cytotoxicity of GNP to osteoblast is dependent on its concentration and is also influenced by agglomeration of particles. Lowering the concentration of GNPs in UHMWPE improves the biocompatibility of the composite surface to bone cells. The survivability of osteoblasts deteriorates up to 86% on 1 wt % GNP containing surface, whereas much smaller (6-16%) reduction is observed for 0.1 wt % GNP over 5 days of incubation.

Surface modification of Ni–Ti alloys for stent application after magnetoelectropolishing

The constant demand for new implant materials and the multidisciplinary design approaches for stent applications have expanded vastly over the past decade. The biocompatibility of these implant materials is a function of their surface characteristics such as morphology, surface chemistry, roughness, surface charge and wettability. These surface characteristics can directly influence the materials corrosion resistance and biological processes such as endothelialization. Surface morphology affects the thermodynamic stability of passivating oxides, which renders corrosion resistance to passivating alloys. Magnetoelectropolishing (MEP) is known to alter the morphology and composition of surface films, which assist in improving corrosion resistance of Nitinol alloys. This work aims at analyzing the surface characteristics of MEP Nitinol alloys by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the alloys was determined by contact angle measurements and the mechanical properties were assessed by Nanoindentation. Improved mechanical properties were observed with the addition of alloying elements. Cyclic potentiodynamic polarization tests were performed to determine the corrosion susceptibility. Further, the alloys were tested for their cytotoxicity and cellular growth with endothelial cells. Improved corrosion resistance and cellular viability were observed with MEP surface treated alloys.

Augmentation of engineered cartilage to bone integration using hydroxyapatite

Articular cartilage injuries occur frequently in the knee joint. Photopolymerizable cartilage tissue engineering approaches appear promising; however, fundamentally, forming a stable interface between the subchondral bone and tissue engineered cartilage components remains a major challenge. We investigated the utility of hydroxyapatite (HA) nanoparticles to promote controlled bone-growth across the bone-cartilage interface in an in vitro engineered tissue model system using bone marrow derived stem cells. Samples incorporated with HA demonstrated significantly higher interfacial shear strength (at the junction between engineered cartilage and engineered bone) compared with the constructs without HA (p < 0.05), after 28 days of culture. Interestingly, this increased interfacial shear strength due to the presence of HA was observed as early as 7 days and appeared to have sustained itself for an additional three weeks without interacting with strength increases attributable to subsequent secretion of engineered tissue matrix. Histological evidence showed that there was ∼7.5% bone in-growth into the cartilage region from the bone side. The mechanism of enhanced engineered cartilage to bone integration with HA incorporation appeared to be facilitated by the deposition of calcium phosphate in the transition zone. These findings indicate that controlled bone in-growth using HA incorporation permits more stable anchorage of the injectable hydrogel-based engineered cartilage construct via augmented integration between bone and cartilage.

The effect of uranium on bacterial viability and cell surface morphology using atomic force microscopy in the presence of bicarbonate ions.

Past disposal practices at nuclear production facilities have led to the release of liquid waste into the environment creating multiple radionuclide plumes. Microorganisms are known for the ability to interact with radionuclides and impact their mobility in soils and sediments. Gram-positive Arthrobacter sp. are one of the most common bacterial groups in soils and are found in large numbers in subsurface environments contaminated with radionuclides. This study experimentally analyzed changes on the bacteria surface at the nanoscale level after uranium exposure and evaluated the effect of aqueous bicarbonate ions on U(VI) toxicity of a low uranium-tolerant Arthrobacter oxydans strain G968 by investigating changes in adhesion forces and cell dimensions via atomic force microscopy (AFM). Experiments were extended to assess cell viability by the Live/Dead BacLight Bacterial Viability Kit (Molecular Probes) and quantitatively illustrate the effect of uranium exposure in the presence of varying concentrations of bicarbonate ions. AFM and viability studies showed that samples containing bicarbonate were able to withstand uranium toxicity and remained viable. Samples containing no bicarbonate exhibited deformed surfaces and a low height profile, which, in conjunction with viability studies, indicated that the cells were not viable.

Integration of Stem Cell to Chondrocyte-Derived Cartilage Matrix in Healthy and Osteoarthritic States in the Presence of Hydroxyapatite Nanoparticles

We investigated the effectiveness of integrating tissue engineered cartilage derived from human bone marrow derived stem cells (HBMSCs) to healthy as well as osteoarthritic cartilage mimics using hydroxyapatite (HA) nanoparticles immersed within a hydrogel substrate. Healthy and diseased engineered cartilage from human chondrocytes (cultured in agar gels) were integrated with human bone marrow stem cell (HBMSC)-derived cartilaginous engineered matrix with and without HA, and evaluated after 28 days of growth. HBMSCs were seeded within photopolymerizable poly (ethylene glycol) diacrylate (PEGDA) hydrogels. In addition, we also conducted a preliminary in vivo evaluation of cartilage repair in rabbit knee chondral defects treated with subchondral bone microfracture and cell-free PEGDA with and without HA. Under in vitro conditions, the interfacial shear strength between tissue engineered cartilage derived from HBMSCs and osteoarthritic chondrocytes was significantly higher (p < 0.05) when HA nanoparticles were incorporated within the HBMSC culture system. Histological evidence confirmed a distinct spatial transition zone, rich in calcium phosphate deposits. Assessment of explanted rabbit knees by histology demonstrated that cellularity within the repair tissues that had filled the defects were of significantly higher number (p < 0.05) when HA was used. HA nanoparticles play an important role in treating chondral defects when osteoarthritis is a co-morbidity. We speculate that the calcified layer formation at the interface in the osteoarthritic environment in the presence of HA is likely to have attributed to higher interfacial strength found in vitro. From an in vivo standpoint, the presence of HA promoted cellularity in the tissues that subsequently filled the chondral defects. This higher presence of cells can be considered important in the context of accelerating long-term cartilage remodeling. We conclude that HA nanoparticles play an important role in engineered to native cartilage integration and cellular processes.

SERS Biosensor for Label Free Monitoring of Environmental Stress

The increasing threat of environmental contamination with toxins has led to substantial advances in biosensor techniques. So far, there is no label free portable dynamic sensor, which can replace standard ELISA to monitor the levels of toxins intracellular in living cells or organisms. Our group has developed a silver nanoparticle (AgNPs) based Surface Enhanced Raman Spectroscopy (SERS) sensor to detect levels of stress protein (RAD54) expressed by a human surrogate (yeast) in response to environmental toxins (H2O2 and U.V.). The fabricated SERS sensor allowed label-free and rapid detection over the ELISA and showed good correlation in extracellular detection of RAD54. In our progress towards intracellular detection, we tested three possible techniques (active, passive and peptide facilitated) for efficient delivery of AgNPs. TAT-HA2 facilitated delivery resulted in increased and rapid uptake of AgNPs as compared to passive diffusion. Dynamic monitoring of RAD54 marker expressed by living cells in response to environmental stress using multiplex SERS sensor with targeting and delivery moieties is in progress.

Novel design to integrate tissue engineered cartilage to native bone using hydroxyapatite nanoparticles

Nanomaterial layer plays a vital role in forming the biological interface between the host and tissue engineered constructs. Size may change the potential interfacial strength of the construct. For the potential treatment of osteoarthritis in the knee, cartilage has been engineered using photopolymerizable, hydrogel-based scaffolding approaches; however there remains a need for enhanced anchorage of the engineered tissue to the underlying subchondral bone. Previous studies have taken approaches based on the principles of mechanical fixation, protein biochemistry and polymer science in order to form novel strategies of integration but have demonstrated limited success in terms of hydrogel retention within the defect space. In this paper, we have demonstrated the integration of a tissue engineered model with the native tissue with the help of a thin layer of bio ceramic hydroxyapatite nanoparticles between the host tissue and the tissue engineered construct.