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Biomedical subjects

Robert Langer

Publications and source records attributed to Robert Langer.

At least 127 records · Page 7Linked to original sources
PubMed2004

Poly(beta-amino ester)s promote cellular uptake of heparin and cancer cell death.

Heparin/heparan sulfate-like glycosaminoglycans (HSGAGs) are involved in diverse cellular processes in the extracellular matrix (ECM). The biological effect of HSGAGs depends on disaccharide content and physiological location within the ECM. HSGAGs are also brought into cells during membrane transcytosis and growth factor signaling while protein bound. We sought to probe the impact of free HSGAGs within the cell by using heparin as a model HSGAG. A library of poly(beta-amino ester)s, which internalize DNA, was examined for the capacity of its members to internalize heparin. Fourteen polymers enabled heparin internalization. The most efficacious polymer reduced murine melanoma cell growth by 73%. No glycosaminoglycan was as efficacious as highly sulfated, full-length heparin. Internalized heparin likely interferes with transcription factor function and subsequently induces apoptotic cell death. Therefore, internalized heparin is a novel mechanism for inducing apoptosis of cancer cells.

Animals↗
PubMed2004

FGF-2 enhances TGF-beta1-induced periosteal chondrogenesis.

The use of periosteum as a cell source for the in vitro engineering of grafts for articular cartilage repair requires the development of methods to obtain high viable cell numbers in the early stages of culture. In this study, we demonstrate that the addition of a mitogen, fibroblast growth factor-2 (FGF-2), during the early stage of the in vitro culture of periosteum in the presence of transforming growth factor-beta1 (TGF-beta1), significantly enhances cell proliferation, which results in increased neo-cartilage formation at later stages. Periosteal explants were cultured in vitro within alginate or agarose based gels in the presence of either FGF-2 for the first week, TGF-beta1 for the first 2 weeks, FGF-2 and TGF-beta1 for the first week and first 2 weeks respectively, or no added factors. Consistent with previous studies, periosteum derived neo-chondrogenesis occurred only in the presence of TGF-beta1. The neo-cartilage was found to contain cartilage specific proteoglycans and Type-II collagen as determined by safranin-O and immunohistochemical staining respectively. Further medium supplementation with FGF-2 stimulated early cell proliferation (>3 fold higher total DNA content per explant at day 10). This resulted in a marked increase in the size of the cultured explants and in the total area of the explant staining positive for safranin-O (from around 50% to 85%, (p<0.05)) after 6 weeks culture. The ability to generate significant quantities of neo-cartilage within a biocompatible and biodegradable matrix such as alginate, which lacks the immunogenicity of agarose, could open new pathways to utilizing such constructs in articular cartilage tissue engineering applications.

Alginates↗
PubMed2004

A simple soft lithographic route to fabrication of poly(ethylene glycol) microstructures for protein and cell patterning.

We present a simple, direct soft lithographic method to fabricate poly(ethylene glycol) (PEG) microstructures for protein and cell patterning. This lithographic method involves a molding process in which a uniform PEG film is molded with a patterned polydimethylsiloxane stamp by means of capillary force. The patterned surfaces created by this method provide excellent resistance towards non-specific protein and cell adsorption. The patterned substrates consist of two regions: the molded PEG surface that acts as a resistant layer and the exposed substrate surface that promotes protein or cell adsorption. A notable finding here is that the substrate surface can be directly exposed during the molding process due to the ability to control the wetting properties of the polymer on the stamp, which is a key factor to patterning proteins and cells.

Adsorption↗
PubMed2004

A preliminary report on the biocompatibility of photopolymerizable semi-interpenetrating anhydride networks.

A new family of poly(anhydrides) (PA) has been developed which can be cured photochemically to produce degradable networks. These degradable anhydride networks may be useful in orthopaedics as bone cements and as matrices for drug delivery. This system, which is a semi-interpenetrating network (semi-IPN), has been evaluated for biocompatibility in subcutaneous tissue in rats and appears to undergo degradation primarily by surface erosion. The inflammatory response to the semi-IPN implants was minimal at both short (3 and 6 weeks) and long (28 weeks) time points and the fibrotic response was largely absent throughout the duration of this study. Furthermore, the OrthoCure implant material integrated well with the surrounding tissue and was invaded with vascularized connective tissue. For reference, linear PA controls were tested and showed a foreign body response culminating in the formation of relatively avascular fibrous capsule several cell layers thick, which became thicker over time, a response similar to what is typically observed in FDA approved implantable polymeric device systems.

Absorbable Implants↗
PubMed2004

Bone tissue engineering using human mesenchymal stem cells: effects of scaffold material and medium flow.

We report studies of bone tissue engineering using human mesenchymal stem cells (MSCs), a protein substrate (film or scaffold; fast degrading unmodified collagen, or slowly degrading cross-linked collagen and silk), and a bioreactor (static culture, spinner flask, or perfused cartridge). MSCs were isolated from human bone marrow, characterized for the expression of cell surface markers and the ability to undergo chondrogenesis and osteogenesis in vitro, and cultured for 5 weeks. MSCs were positive for CD105/endoglin, and had a potential for chondrogenic and osteogenic differentiation. In static culture, calcium deposition was similar for MSC grown on collagen scaffolds and films. Under medium flow, MSC on collagen scaffolds deposited more calcium and had a higher alcaline phosphatase (AP) activity than MSC on collagen films. The amounts of DNA were markedly higher in constructs based on slowly degrading (modified collagen and silk) scaffolds than on fast degrading (unmodified collagen) scaffolds. In spinner flasks, medium flow around constructs resulted in the formation of bone rods within the peripheral region, that were interconnected and perpendicular to the construct surface, whereas in perfused constructs, individual bone rods oriented in the direction of fluid flow formed throughout the construct volume. These results suggest that osteogenesis in cultured MSC can be modulated by scaffold properties and flow environment.

Bioreactors↗
PubMed2004

Patterning and separating infected bacteria using host-parasite and virus-antibody interactions.

Bacteria were selectively deposited on substrates patterned with poly(ethylene glycol) (PEG) microstructures by using host-parasite and virus-antibody interactions. In this scheme viruses were used to attach onto a host bacterium, Escherichia coli (E. coli). The E. coli expressing the virus were selectively adhered to the regions pretreated with an antibody against the virus proteins while E. coli without the virus showed no selectivity. Single or aggregated cell arrays were fabricated depending on the initial pattern size with respect to the size of E. coli. The current approach could be a general route to spatially positioning or controlling adhesion of other biological species that are not accessible by conventional methods and as a tool for separating and isolating specific cell populations based on host-parasite interactions.

Antibodies, Viral↗
PubMed2004

Current status and future potential of transdermal drug delivery.

The past twenty five years have seen an explosion in the creation and discovery of new medicinal agents. Related innovations in drug delivery systems have not only enabled the successful implementation of many of these novel pharmaceuticals, but have also permitted the development of new medical treatments with existing drugs. The creation of transdermal delivery systems has been one of the most important of these innovations, offering a number of advantages over the oral route. In this article, we discuss the already significant impact this field has made on the administration of various pharmaceuticals; explore limitations of the current technology; and discuss methods under exploration for overcoming these limitations and the challenges ahead.

Acoustic Stimulation↗
PubMed2004

Selectin inhibitor bimosiamose prolongs survival of kidney allografts by reduction in intragraft production of cytokines and chemokines.

Binding of the P-, L-, and E-selectins to sialyl Lewis(x) (sLe(x)) retards circulating leukocytes, thereby facilitating their attachment to the blood vessels of allografts. Whether the selectin inhibitor bimosiamose (BIMO; C(46)H(54)O(16) . 0.25 H(2)O [867.4 molecular weight]) inhibits the rejection process of kidney allografts in a rat model was examined. Rat recipients acutely rejected kidney allografts at a mean survival time of 8.8 +/- 0.75 d. An intravenous 7-d infusion by osmotic pump of 2.5, 5, 10, or 20 mg/kg BIMO extended kidney allograft survival to 11.5 +/- 2.2 d (P < 0.03), 25.4 +/- 11.4 d (P < 0.006), 37.4 +/- 13.6 d (P < 0.001), and 39.8 +/- 34.5 d (P < 0.01), respectively. Combination of BIMO with cyclosporine produced synergistic interactions, as documented by the combination index (CI) values of 0.34 to 0.43 (CI <1 is synergistic; CI = 1 is additive; and CI >1 is antagonistic). Similarly, BIMO interacted synergistically with sirolimus (CI = 0.64) and FTY720 (CI = 0.22). While the mechanism of immunosuppression was being analyzed, decreased infiltration of CD4(+), CD8(+), and macrophages on day 7 after grafting was observed. Multiple cytokines were also expressed, including IL-1alpha, IL-1beta, IL-2, IL-4, IL-6, IL-10, IL-12, IL-18, TNF-alpha, and IFN-gamma in kidney allografts on days 3, 5, and 7 after grafting, as measured by a ribonuclease protection assay. Furthermore, at similar time points, BIMO treatment reduced intragraft expression of P-selectin glycoprotein ligand-1, CX(3)CL1, CCL19, CCL20, and CCL2. Thus, BIMO blocks allograft rejection by reduction of intragraft expression of cytokines and chemokines.

Animals↗
PubMed2004

In vivo inflammatory and wound healing effects of gold electrode voltammetry for MEMS micro-reservoir drug delivery device.

The in vivo biocompatibility and biofouling of gold electrodes for a microelectromechanical systems drug delivery device were investigated in a rodent model. The role of the applied voltage and gold electrolysis products in modulating the inflammatory response (biocompatibility), and the temporal adhesion of cellular populations onto macroscopic gold film electrodes (biofouling) were analyzed in reference to two controls, devices to which voltage was not applied (uncorroded) or voltage was applied to inert platinum electrodes (electrical controls). Voltammetry was applied to the gold surfaces once (day 4, 7, 14, 21, 28, 35, 42, or 49), while voltage of identical magnitude was applied to the electrical controls. An inflammatory response characterized by a rapid decrease of leukocyte concentration to control levels was observed 48 h following voltage application with no significant cell concentration difference (p > 0.05) between the corroded devices and electrical controls. The histological evaluation of the direct implant fibrous capsule showed comparable thickness of voltage applied and control specimens. The gold corrosion peak current showed no significant difference (p > 0.05) among peak values at all time points. It was concluded that gold electrode corrosion was biocompatible and its electrochemical performance was not hindered by fibrous capsule formation.

Animals↗
PubMed2004

Differential degradation rates in vivo and in vitro of biocompatible poly(lactic acid) and poly(glycolic acid) homo- and co-polymers for a polymeric drug-delivery microchip.

The biocompatibility and biodegradation rate of component materials are critical when designing a drug-delivery device. The degradation products and rate of degradation may play important roles in determining the local cellular response to the implanted material. In this study, we investigated the biocompatibility and relative biodegradation rates of PLA, PGA and two poly(lactic-co-glycolic acid) (PLGA) polymers of 50:50 mol ratio, thin-film component materials of a drug-delivery microchip developed in our laboratory. The in vivo biocompatibility and both in vivo and in vitro degradation of these materials were characterized using several techniques. Total leukocyte concentration measurements showed normal acute and chronic inflammatory responses to the PGA and low-molecular-weight PLGA that resolved by 21 days, while the normal inflammatory responses to the PLA and high-molecular-weight PLGA were resolved but at slower rates up to 21 days. These results were paralleled by thickness measurements of fibrous capsules surrounding the implants, which showed greater maturation of the capsules for the more rapidly degrading materials after 21 days, but less mature capsules of sustained thicknesses for the PLA and high-molecular-weight PLGA up to 49 days. Gel-permeation chromatography of residual polymer samples confirmed classification of the materials as rapidly or slowly degrading. These materials showed thinner fibrous capsules than have been reported for other materials by our laboratory and have suitable biocompatibility and biodegradation rates for an implantable drug-delivery device.

Biocompatible Materials↗
PubMed2003

Enhancement of a human immunodeficiency virus env DNA vaccine using a novel polycationic nanoparticle formulation.

In an effort to develop a more effective DNA immunization strategy for HIV, we synthesized an HIV-2 env DNA vaccine and delivered it in a novel polycationic adjuvant formulation that forms nanoparticles in solution and enhances protein expression. The polycationic adjuvant contained imidazole moieties to facilitate endosomal escape. Nanoparticles containing the DNA vaccine plasmid were formed by electrostatic condensation with the polycationic adjuvant. We hypothesized that this formulation would improve immune responses to the gp140 env gene from HIV-2(UC2) by increasing the level of expressed antigen. We found that the nanoparticles were superior at inducing high levels of systemic antibody responses compared to naked DNA when delivered by the intradermal route in BALB/c mice. In addition, the nanoparticles induced higher levels of IgM, IgG, and IgA antibodies. These results suggest that nanoparticles may be an important adjuvant formulation to improve the effectiveness of genetic immunization and rationalize its use in the evaluation of vaccine candidates in non-human primate models for AIDS.

AIDS Vaccines↗
PubMed2003

Differentiation of human embryonic stem cells on three-dimensional polymer scaffolds.

Human embryonic stem (hES) cells hold promise as an unlimited source of cells for transplantation therapies. However, control of their proliferation and differentiation into complex, viable 3D tissues is challenging. Here we examine the use of biodegradable polymer scaffolds for promoting hES cell growth and differentiation and formation of 3D structures. We show that complex structures with features of various committed embryonic tissues can be generated, in vitro, by using early differentiating hES cells and further inducing their differentiation in a supportive 3D environment such as poly(lactic-co-glycolic acid)/poly(L-lactic acid) polymer scaffolds. We found that hES cell differentiation and organization can be influenced by the scaffold and directed by growth factors such as retinoic acid, transforming growth factor beta, activin-A, or insulin-like growth factor. These growth factors induced differentiation into 3D structures with characteristics of developing neural tissues, cartilage, or liver, respectively. In addition, formation of a 3D vessel-like network was observed. When transplanted into severe combined immunodeficient mice, the constructs continue to express specific human proteins in defined differentiated structures and appear to recruit and anastamose with the host vasculature. This approach provides a unique culture system for addressing questions in cell and developmental biology, and provides a potential mechanism for creating viable human tissue structures for therapeutic applications.

Animals↗
PubMed2003

Medium perfusion enables engineering of compact and contractile cardiac tissue.

We hypothesized that functional constructs with physiological cell densities can be engineered in vitro by mimicking convective-diffusive oxygen transport normally present in vivo. To test this hypothesis, we designed an in vitro culture system that maintains efficient oxygen supply to the cells at all times during cell seeding and construct cultivation and characterized in detail construct metabolism, structure, and function. Neonatal rat cardiomyocytes suspended in Matrigel were cultured on collagen sponges at a high initial density (1.35 x 10(8) cells/cm(3)) for 7 days with interstitial flow of medium; constructs cultured in orbitally mixed dishes, neonatal rat ventricles, and freshly isolated cardiomyocytes served as controls. Constructs were assessed at timed intervals with respect to cell number, distribution, viability, metabolic activity, cell cycle, presence of contractile proteins (sarcomeric alpha-actin, troponin I, and tropomyosin), and contractile function in response to electrical stimulation [excitation threshold (ET), maximum capture rate (MCR), response to a gap junctional blocker]. Interstitial flow of culture medium through the central 5-mm-diameter x 1.5-mm-thick region resulted in a physiological density of viable and differentiated, aerobically metabolizing cells, whereas dish culture resulted in constructs with only a 100- to 200-microm-thick surface layer containing viable and differentiated but anaerobically metabolizing cells around an acellular interior. Perfusion resulted in significantly higher numbers of live cells, higher cell viability, and significantly more cells in the S phase compared with dish-grown constructs. In response to electrical stimulation, perfused constructs contracted synchronously, had lower ETs, and recovered their baseline function levels of ET and MCR after treatment with a gap junctional blocker; dish-grown constructs exhibited arrhythmic contractile patterns and failed to recover their baseline MCR levels.

Actins↗
PubMed2003

In vivo degradation characteristics of poly(glycerol sebacate).

We have developed a series of biodegradable elastomers, poly(glycerol sebacate) (PGS), based on glycerol and sebacic acid. The polymers are potentially useful in soft tissue regeneration and engineering. To evaluate the performance of PGS in a physiological environment, we compared their degradation profiles with poly(DL-lactide-co-glycolide) (50:50, carboxyl ended, M(w) 15,000) in vivo. Among the parameters examined are changes in weight and mechanical strength with time, implant geometry, surface characteristics, and degree of swelling. Unlike poly(DL-lactide-co-glycolide), PGS primarily degrades by surface erosion, which gives a linear degradation profile of mass, preservation of geometry and intact surface, and retention of mechanical strength.

Absorbable Implants↗
PubMed2003

[Autotransplantation of the kidney 100 years after Imre Ullmann's pioneering operation].

The authors give an overview on renal autotransplantation on occasion of Emerich (Imre) Ullmann's pioneer operation 100 years ago. Ullmann was born in 1861 in Pécs, Hungary. After finishing the Vienna Medical School, he worked on the I. Surgical Clinic of the University of Vienna. In 1902, already as the chief of surgery of a Vienna hospital he successfully performed canine kidney autotransplantation, later also technically successful allo- and xenotransplantation. Human renal autotransplantations have been performed since the early 1960's mainly because of renovascular hypertension/aneurysm or ureter injuries or tumor. Rare indications are the loin pain-hematuria syndrome, echinococcosis of the kidney, the nutcracker syndrome, ureteroarterial fistula and there are reports about allograft autotransplantations also. Lately, laparoscopy gained place and nephrectomies are done more often minimally invasive. In Hungary twenty-four cases of kidney autotransplantation were performed.

Austria↗
PubMed2003

High-density seeding of myocyte cells for cardiac tissue engineering.

Tissue engineering of 1- to 5-mm-thick, functional constructs based on cells that cannot tolerate hypoxia for prolonged time periods (e.g., cardiac myocytes) critically depends on our ability to seed the cells at a high and spatially uniform initial density and to maintain their viability and function. We hypothesized that rapid gel-cell inoculation in conjunction with direct medium perfusion through the seeded scaffold would increase the rate, yield, viability, and uniformity of cell seeding. Two cell types were studied: neonatal rat cardiomyocytes for feasibility studies of seeding and cultivation with direct medium perfusion, and C2C12 cells (a murine myoblast cell line) for detailed seeding studies. Cells were seeded at densities corresponding to those normally present in the adult rat heart ([0.5-1] x 10(8) cells/cm(3)), into collagen sponges (13 mm x 3 mm discs), using Matrigel as a vehicle for rapid cell delivery. Scaffolds inoculated with cell-gel suspension were seeded either in perfused cartridges with alternating medium flow or in orbitally mixed Petri dishes. The effects of seeding time (1.5 or 4.5 h), initial cell number (6 or 12 million cells per scaffold), and seeding set-up (medium perfusion at 0.5 and 1.5 mL/min; orbitally mixed dishes) were investigated using a randomized three-factor factorial experimental design with two or three levels and three replicates. The seeding cell yield was consistently high (over 80%), and it appeared to be determined by the rapid gel inoculation. The decrease in cell viability was markedly lower for perfused cartridges than for orbitally mixed dishes (e.g., 8.8 +/- 0.8% and 56.3 +/- 4%, respectively, for 12 million cells at 4.5 h post-seeding). Spatially uniform cell distributions were observed in perfused constructs, whereas cells were mainly located within a thin (100-200 microm) surface layer in dish seeded constructs. Over 7 days of cultivation, medium perfusion maintained the viability and differentiated function of cardiac myocytes, and the constructs contracted synchronously in response to electrical stimulation. Direct perfusion can thus enable seeding of hypoxia-sensitive cells at physiologically high and spatially uniform initial densities and maintain cell viability and function.

Animals↗