Biomedical subjects

Tejal A Desai

Publications and source records attributed to Tejal A Desai.

At least 19 recordsLinked to original sources

PubMed2007

Osteogenic differentiation of marrow stromal cells cultured on nanoporous alumina surfaces.

A major goal in orthopedic biomaterials research is to design implant surfaces, which will enhance osseointegration in vivo. Several microscale as well as nanoscale architectures have been shown to significantly affect the functionality of bone cells i.e., osteoblasts. In this work, nanoporous alumina surfaces fabricated by a two-step anodization process were used. The nanostructure of these surfaces can be controlled by varying the voltage used for anodization process. Marrow stromal cells were isolated from mice and seeded on nanoporous and amorphous (control) alumina surfaces. Cell adhesion, proliferation, and viability were investigated for up to 7 days of culture. Furthermore, the cell functionality was investigated by calcein staining. The cells were provided with differentiation media after 7 days of culture. The alkaline phosphatase (ALP) activity and matrix production were quantified using a colorimetric assay and X-ray photoelectron spectroscopy (XPS) for up to 3 weeks of culture (2 weeks after providing differentiation media). Further, scanning electron microscopy (SEM) was used to investigate osteoblast morphology on these nanoporous surfaces. Over the 3-week study, the nanoporous alumina surfaces demonstrated approximately 45% increase in cell adhesion, proliferation, and viability, 35% increase in ALP activity, and 50% increase in matrix production when compared with the control surfaces.

Alkaline Phosphatase↗

PubMed2006

Development and characterization of a porous micro-patterned scaffold for vascular tissue engineering applications.

The fabrication of functional small diameter blood vessel analogs has implications in vascular disease treatment. Current 3D models of the medial vessel layer lack micron-scale topographical cues that have shown promise in vitro by recapitulating native vascular smooth muscle cell (VSMC) behavior. A major obstacle to fabricating 3D scaffolds is maintaining adequate nutrient diffusion to cells. We have developed and characterized porous micro-patterned poly-caprolactone (PCL) scaffolds using a novel technique that integrates soft lithography, melt molding and particulate leaching of polylactic-co-glycolic acid (PLGA) micro/nanoparticles. Scanning electron microscopy showed that PLGA-leached scaffolds have circular pores significantly smaller than the size scale of the grooved surface pattern (48 microm grooves; 5 microm deep; 12 microm spacing). Diffusion of media through PLGA-leached scaffolds was six-fold greater than through non-porous scaffolds, indicating successful introduction of through-pores into PCL by the PLGA leaching technique. VSMC alignment on micro-patterned PLGA-leached scaffolds was similar to that on micro-patterned non-porous scaffolds, indicating no loss in cellular organization on PLGA-leached scaffolds. In contrast, cells seeded on micro-patterned sodium bicarbonate-leached scaffolds remained un-aligned. The ability to micro-pattern cells on porous scaffolds may facilitate the transfer of micro-technology from simple 2D substrates to complex 3D architectures, allowing for tight control over cellular organization in fabricated tissues.

Animals↗

PubMed2006

Methods for fabrication of nanoscale topography for tissue engineering scaffolds.

Observations of how controlling the microenvironment of cell cultures can lead to changes in a variety of parameters has lead investigators to begin studying how the nano-environment of a culture can affects cells. Cells have many structures at the nanoscale such as filipodia and cytoskeletal and membrane proteins that interact with the environment surrounding them. By using techniques that can control the nano-environment presented to a cell, investigators are beginning to be able to mimic the nanoscale topographical features presented to cells by extracellular matrix proteins such as collagen, which has precise and repeating nano-topography. The belief is that these nanoscale surface features are important to creating more natural cell growth and function. A number of techniques are currently being used to create nanoscale topographies for cell scaffolding. These techniques fall into two main categories: techniques that create ordered topographies and those that create unordered topographies. Electron Beam lithography and photo-lithography are two standard techniques for creating ordered features. Polymer demixing, phase separation, colloidal lithography and chemical etching are most typically used for creating unordered surface patterns. This review will give an overview of these techniques and cite observations from experiments carried out using them.

Animals↗

PubMed2006

Evaluation of silicon nanoporous membranes and ECM-based microenvironments on neurosecretory cells.

Understanding the interactions between microfabricated synthetic interfaces and cultured cells expressing a neuronal phenotype are critical for advancing research in the field of neural engineering such as neural recording and stimulation and neural microdevice interactions with the human brain. Here we explore the integration of these two components for therapeutic applications of neural prostheses. Microfabricated silicon nanoporous membranes were investigated for their effects on survival, proliferation, and differentiation of the well-known PC12 clonal line. Specifically, cell morphology, examined through fluorescence staining, were comparable in many respects on both silicon membrane and widely-used polystyrene culture surfaces. The attachment and differentiation of PC12 cells cultured on collagen and laminin-modified membranes and standard tissue culture surfaces were similar. Lastly, the differentiation response and tyrosine hydroxylase activity of PC12 cells embedded in a type I collagen matrix on experimental membrane substrates while exposed to NGF were significant and indistinguishable from tissue-culture polystyrene (TC-PS) surfaces. Results from this research suggest that microfabricated silicon nanoporous membranes may be useful, biocompatible permselective structures for neuroprosthetic applications and that collagen may be a useful immobilizing matrix for PC12 cells loaded in implantable macroencapsulation devices designed for the treatment of neurodegenerative disorders.

Animals↗

PubMed2006

Expression, localization and hormonal control of angiopoietin-1 in the rhesus macaque endometrium: potential role in spiral artery growth.

Angiopoietin-1 (Ang-1) is an important angiogenic factor that has not been thoroughly studied in the primate endometrium. We evaluated the endometrial expression of Ang-1 and its receptor, Tie2, during induced menstrual cycles in rhesus macaques. Tie2 expression was confined to the vascular endothelium without marked change during the cycle. However, Ang-1 expression varied considerably during the cycle. In the proliferative phase, Ang-1 was only expressed in the basal zone glands, and this expression was estradiol (E2) dependent. In the early- to mid-secretory phase, Ang-1 expression spread to the upper glands, luminal epithelium and the vascular smooth muscle cells (VSMC) of spiral arteries. In the late secretory phase, the signal disappeared from the glands but remained elevated in the VSMC of spiral arteries. Notably, there was a significant correlation between VSMC proliferation and Ang-1 expression in the VSMC of the spiral arteries. Progesterone (P) withdrawal in the early secretory phase induced a decline in Ang-1 expression in the glands and VSMC of spiral arteries along with a complete suppression of VSMC proliferation. These data suggest, for the first time, that Ang-1 may play a key role in the P-dependent growth of the unique spiral arteries in the primate endometrium.

Angiopoietin-1↗

PubMed2006

Nanostructured surfaces for bone biotemplating applications.

A major goal of orthopedic biomaterials research is to design better surface chemistries and configurations to control behavior of bone cells such as osteoblasts. Nanostructured architecture significantly affects the response of several cell lines. In this work, nanostructured surfaces were prepared by vapor liquid solid growth of silicon nanowires from size-controlled gold colloid catalysts deposited on fused silica substrates. The lengths and surface densities of the nanowires were varied to assess the effect of these parameters on bone cell response. Osteoblasts were seeded on nanowire surfaces to investigate both short-term adhesion and proliferation and long-term functionality and matrix production. Cell adhesion and proliferation were characterized using a standard 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay and cell counting for up to 4 days of culture. The total protein content, alkaline phosphatase activity, and matrix production were quantified using standard colorimetric assays for up to 4 weeks of culture. Matrix production was also characterized by measuring surface concentrations of calcium and phosphorus using X-ray photoelectron spectroscopy. Further, scanning electron microscopy was used to investigate osteoblast morphology on nanostructured surfaces. Over the 4-week study, the nanostructured surfaces demonstrated improved osteoblast adhesion and proliferation and increased alkaline phosphatase activity and matrix production compared to non-nanostructured control surfaces.

Alkaline Phosphatase↗

PubMed2005

Stoichiometry-dependent formation of quantum dot-antibody bioconjugates: a complementary atomic force microscopy and agarose gel electrophoresis study.

The unique advantages of quantum dot (QD) bioconjugates have motivated their application in biological assays. However, physical characterization of bioconjugated QDs after surface modification has often been overlooked. Here, biotinylated antibodies (biotin-IgG) were attached to commercial streptavidin-conjugated quantum dots (strep-QDs) at different stoichiometric ratios, and these QD bioconjugates were characterized with atomic force microscopy and discontinuous sodium dodecyl sulfate agarose gel electrophoresis (SDS-AGE). The results from these complementary analytical techniques showed that the molar ratio determined the relative sizes, molecular weights and morphologies of the QD bioconjugates. Additionally, the novel discontinuous SDS-AGE analysis confirmed specific binding between biotin-IgG and strep-QDs. Researchers who design QD bioconjugates for cell-based assays should consider stoichiometry-dependent differences in the physical properties of their QD bioconjugates.

Antibodies↗

PubMed2005

Micromachined devices: the impact of controlled geometry from cell-targeting to bioavailability.

Advances in microelectomechanical systems (MEMS) have allowed the microfabrication of polymeric substrates and the development of a novel class of controlled delivery devices. These vehicles have specifically tailored three-dimensional physical and chemical features which, together, provide the capacity to target cells, promote unidirectional controlled release, and enhance permeation across the intestinal epithelial barrier. Examining the biological response at the microdevice biointerface may provide insight into the benefits of customized surface chemistry and structure in terms of complex drug delivery vehicle design. Therefore, the aim of this work was to determine the interfacial effects of selective surface chemistry and architecture of tomato lectin (TL)-modified poly(methyl methacrylate) (PMMA) drug delivery microdevices on the Caco-2 cell line, a model of the gastrointestinal tract.

Biological Availability↗

PubMed2005

Modeling of RGDC film parameters using X-ray photoelectron spectroscopy.

Immobilization of peptides on surfaces is a common method to investigate biological response to biomaterials for the development of improved tissue engineering constructs. Peptide immobilization can be achieved by either physical adsorption or covalent attachment on the surface. In this work, the RGDC peptide was covalently immobilized to alumina substrate for investigation of bone cell response. An understanding of RGDC film formation is necessary for further biological characterization. Thus, X-ray photoelectron spectroscopy was used to chemically characterize these films. These data were further utilized to calculate RGDC film thickness, density, and coverage, which are essential for understanding bone cell interactions with the underlying films and substrate.

Adsorption↗

PubMed2005

Gastrointestinal patch systems for oral drug delivery.

Gastrointestinal patch systems with integrated multifunctions could surmount the challenges associated with conventional drug delivery. Several gastrointestinal patch systems provide bioadhesion, drug protection and unidirectional release. This combination of function could improve the overall oral bioavailability of large molecules that can currently be delivered only by injection, for example, epoetin-alpha and granulocyte-colony-stimulating factor, which are commonly used to treat chemotherapy-associated anemia and leukopenia, respectively. Furthermore, self-regulated release and cell-specific targeting provide additional 'smart' characteristics to this innovative therapeutic platform.

Administration, Oral↗

PubMed2005

Fabrication and evaluation of nanoporous alumina membranes for osteoblast culture.

An understanding of osteoblast response to surface topography is essential for successful bone tissue engineering applications. Alumina has been extensively used as a substrate for bone tissue constructs. However, current techniques do not allow precise surface topography and orientation of the material. In this research, a two-step anodization process was optimized for the fabrication of nanoporous alumina membranes with uniform pore dimension and distribution. The anodization voltage can be varied to create nanoporous alumina membranes with pore sizes ranging from 30 to 80 nm in diameter. The impact of the nanoscale pores on osteoblast response was studied by evaluating cell adhesion, morphology, and matrix production. Scanning electron microscopy and atomic force microscopy were used to characterize the nanoporous alumina membranes. Osteoblast adhesion and morphology were investigated using scanning electron microscopy images and matrix production was characterized using energy dispersive spectroscopy. This research combined the advantages of using alumina, a material with proven biocompatibility and current orthopedic clinical applications, and incorporated porous features on the nanoscale which have been reported to improve osteoblast response.

Aluminum Oxide↗

PubMed2005

Microscale multilayer cocultures for biomimetic blood vessels.

Living tissues have complex and well-organized microstructures. Although microtechnology has been used to create in vivo-like cell microstructures in vitro, most available microscale systems are two-dimensional, and few three-dimensional (3D) systems have been explored. This article demonstrates a 3D hierarchical biomimetic multilayer microsystem created by a generally applicable technique. The technique employs layer-by-layer microfluidics to build layers of cells and biopolymers in microchannels, allowing controlled patterning of cells and their microenvironments in the x, y, and z-dimension. As a prototype, a multilayer system was created using three vascular cell types within heterogeneous types of biopolymers to mimic the structure and composition of a blood vessel wall. The effects of matrix composition and multilayer configurations on 3D cell-cell interactions and cell biology were revealed. Cell migration in the z-dimension, matrix remodeling, intercellular adhesion molecule expression and actin organization were examined under different 3D coculture conditions. A more biomimetic coculture was found to reproduce a more stable structure and in vivo-like function. This approach provides a method to fabricate microscale hierarchical "neotissues" with 3D configurations of matrix materials and multiple cell types, and an in vitro cell coculture model to understand 3D processes of cell-cell and cell-matrix interactions.

Actin Cytoskeleton↗

PubMed2005

Vascular tissue engineering: microtextured scaffold templates to control organization of vascular smooth muscle cells and extracellular matrix.

The in vitro construction of tissue-engineered small diameter (<6mm) blood vessels with sufficient strength and mechanical compliance has evaded researchers. We hypothesize that the high spatial organization of the medial layer of vascular smooth muscle cells (VSMCs) and their surrounding matrix provides high burst strength, compliance, and stability. We investigated the effect of microfabricated polydimethylsiloxane (PDMS) scaffolds with various groove widths on VSMC organization. We found that the presence of these grooved topographical cues significantly enhanced VSMC aspect ratio, alignment, and oriented remodeling of the underlying extracellular matrix. This study suggests that topographical patterning of tissue scaffolds can influence cellular and matrix spatial organization and could provide a framework for achieving the required organization and physical properties for blood vessels.

Actins↗

PubMed2005

Peptide-immobilized nanoporous alumina membranes for enhanced osteoblast adhesion.

Bone tissue engineering requires the ability to regulate cell behavior through precise control over substrate topography and surface chemistry. Understanding of the cellular response to micro-environment is essential for biomaterials and tissue engineering research. This research employed alumina with porous features on the nanoscale. These nanoporous alumina surfaces were modified by physically adsorbing vitronectin and covalently immobilizing RGDC peptide to enhance adhesion of osteoblasts, bone-forming cells. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize the modified nanoporous alumina surface. Survey and high-resolution C1s scans suggested the presence of RGDC and vitronectin on the surface and SEM images confirmed the pores were not clogged after modification. Cell adhesion on both unmodified and modified nanoporous alumina was compared using fluorescence microscopy and SEM. RGDC was found to enhance osteoblast adhesion after 1 day of culture and matrix production was visible after 2 days. Cell secreted matrix was absent on unmodified membranes for the same duration. Vitronectin-adsorbed surfaces did not show significant improvement in adhesion over unmodified membranes.

Adsorption↗

PubMed2005

Peptide-conjugated quantum dots activate neuronal receptors and initiate downstream signaling of neurite growth.

Quantum dots (QDs) could serve as fluorescent scaffolds for effecting specific physiological and pharmacological responses in cells. Here, we conjugate the peptide ligand betaNGF to QD surfaces, and confirm surface modification and single QD nanostructure using AFM. We show that betaNGF-QDs retain bioactivity, activate TrkA receptors, and initiate neuronal differentiation in PC12 cells. Receptor-evoked activity of QD-immobilized ligands has wide-ranging implications for the development of molecular tools and therapeutics targeted at understanding and regulating cell function.

Animals↗

PubMed2005

Nanoporous alumina capsules for cellular macroencapsulation: transport and biocompatibility.

BACKGROUND: Currently, the most widely used treatment for diabetes is the daily subcutaneous injection of recombinant human insulin. Daily injections, however, cannot match the physiological biphasic behavior of normal insulin release, nor can they precisely meet the demands of food intake, exercise, and stress. Cellular encapsulation, or immunoisolation, is a possible solution to this problem. This cell-based therapy allows patients to receive the benefits of more physiological insulin and blood glucose regulation, without the need for immunosuppressants that are associated with organ or cell transplantation. METHODS: Immunoisolation capsules were fabricated out of aluminum and aluminum oxide using a two-step anodization procedure. The diffusion behavior of glucose, immunoglobulin G (IgG), and insulin were measured. Furthermore, the functionality and viability of encapsulated MIN6 cells were tested. Finally, live cells were stained and imaged using confocal microscopy. RESULTS: Data indicated that this device is effective in allowing the transport of relevant molecules such as glucose and insulin, while at the same time significantly impeding the transport of IgG, suggesting that it would be efficacious in protecting cell grafts in vivo. Furthermore, encapsulated cells were able to respond dynamically to glucose input signals. Finally, cell staining showed that the viability of encapsulated cells is maintained after 24 h, although the cells appear to be more heavily concentrated at the area that is closest to the membrane. CONCLUSIONS: This study has shown that nanoporous alumina membranes, with well-controlled pore sizes, can be used for the encapsulation of therapeutic cells and may provide an alternative encapsulation strategy for the treatment of diabetes.

Aluminum Oxide↗

PubMed2005

Nanostructured antifouling poly(ethylene glycol) films for silicon-based microsystems.

The creation of antifouling surfaces is one of the major prerequisites for silicon-based micro-electrical-mechanical systems for biomedical and analytical applications (known as BioMEMS). Poly(ethylene glycol) (PEG), a water-soluble, nontoxic, and nonimmunogenic polymer has the unique ability to reduce nonspecific protein adsorption and cell adhesion and, therefore, is generally coupled with a wide variety of surfaces to improve their biocompatibility. To this end, we have analyzed PEG thin films of various grafting densities (i.e., number of PEG chains per unit area) coupled to silicon using a single-step PEG-silane coupling reaction scheme using variable-angle ellipsometry. Initial PEG concentration and coupling time were varied to attain different grafting densities. These data were theoretically analyzed to understand the phenomenon of PEG film formation. Furthermore, all the PEG films were evaluated for their ability to control biofouling using albumin and fibrinogen as the model proteins. PEG thin films formed by using higher PEG concentrations ( > or = 10 mM PEG) or coupling time ( > or = 1 h) demonstrated enhanced protein fouling resistance behavior. This analysis is expected to be useful to form PEG films of desired grafting density on silicon substrates for appropriate application.

Adsorption↗

PubMed2004

Influence of nanoporous alumina membranes on long-term osteoblast response.

A major goal of bone tissue engineering is to design better scaffold configuration and materials to better control osteoblast behavior. Nanoporous architecture has been shown to significantly affect cellular response. In this work, nanoporous alumina membranes were fabricated by a two-step anodization method to investigate bone cell response. Osteoblasts were seeded on nanoporous alumina membranes to investigate both short-term adhesion and proliferation and long-term functionality and matrix production. Cell adhesion and proliferation were characterized using a standard MTT assay and cell counting. The total protein content was measured after cell lysis using the BCA assay. Matrix production was characterized in terms of surface concentrations of calcium and phosphorous, components of bone matrix, using X-ray photoelectron spectroscopy (XPS). The results from nanoporous alumina membranes were compared with those of amorphous alumina, aluminum, commercially available ANOPORE and glass. Results indicate improved osteoblast adhesion and proliferation and increased matrix production after 4 weeks of study.

Aluminum↗