David A Edwards

University of North Carolina at Chapel Hill, North Carolina, United States

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Publications (33)108.4 Total impact

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    ABSTRACT: Injectable biomaterials are increasingly being explored to minimize risks and complications associated with surgical implantation. We describe a strategy for delivery via conventional needle-syringe injection of large preformed macroporous scaffolds with well-defined properties. Injectable 3D scaffolds, in the form of elastic sponge-like matrices, were prepared by environmentally friendly cryotropic gelation of a naturally sourced polymer. Cryogels with shape-memory properties may be molded to a variety of shapes and sizes, and may be optionally loaded with therapeutic agents or cells. These scaffolds have the capability to withstand reversible deformations at over 90% strain level, and a rapid volumetric recovery allows the structurally defined scaffolds to be injected through a small-bore needle with nearly complete geometric restoration once delivered. These gels demonstrated long-term release of biomolecules in vivo. Furthermore, cryogels impregnated with bioluminescent reporter cells provided enhanced survival, higher local retention, and extended engraftment of transplanted cells at the injection site compared with a standard injection technique. These injectable scaffolds show great promise for various biomedical applications, including cell therapies.
    Proceedings of the National Academy of Sciences 11/2012; · 9.81 Impact Factor
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    Medecine sciences: M/S 02/2011; 27(1):19-21. · 0.56 Impact Factor
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    ABSTRACT: This study establishes the immune response elicited in guinea pigs after pulmonary and parenteral immunizations with diphtheria CRM-197 antigen (CrmAg). Several spray-dried powders of formalin-treated/untreated CrmAg nanoaggregates with L-leucine were delivered to the lungs of guinea pigs. A control group consisting of alum with adsorbed CrmAg in saline was administered by intramuscular injection. Animals received three doses of powder vaccines containing 20 or 40 μg of CrmAg. The serum IgG titers were measured for 16 weeks after the initial immunization; IgA titers were measured at the time of sacrifice in the broncho-alveolar lavage fluid. Further, toxin neutralization tests in naïve guinea pigs were performed for a few select serum samples. Histopathology of the lung tissues was conducted to evaluate inflammation or injury to the lung tissues. While the highest titer of serum IgG antibody was observed in guinea pigs immunized by the intramuscular route, those animals immunized with dry powder formulation by the pulmonary route, and without the adjuvant alum, exhibited high IgA titers. A pulmonary administered dry powder, compared to parenteral immunization, conferred complete protection in the toxin neutralization test. Mild inflammation was observed in lung tissues of animals receiving dry powder vaccines by the pulmonary route. Thus, administering novel CrmAg as dry powders to the lungs may be able to overcome some of the disadvantages observed with the existing diphtheria vaccine which is administered by the parenteral route. In addition, these powders will have the advantage of eliciting a high mucosal immune response in the lungs without using traditional adjuvants.
    The AAPS Journal 09/2010; 12(4):699-707. · 4.39 Impact Factor
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    ABSTRACT: To extend the retention time of aerosol-delivered growth factors in the lung for stem cell homing/activation purposes, we examined a formulation of vascular endothelial growth factor (VEGF) complexed to dextran sulfate (DS) and chitosan (CS) polyelectrolytes. Optimal incorporation of VEGF was found at a VEGF/DS/CS ratio of 0.12:1:0.33, which resulted in nanoparticle complexes with diameters of 612+/-79 nm and zeta potentials of -31+/-1 mV. The complexes collapsed in physiological solution, and released VEGF in a biphasic time course in vitro. In rat lungs, however, VEGF delivered in the complex was cleared at a constant exponential decay rate, 8-fold slower than that delivered in free form. The extended VEGF retention was likely due to equilibrium binding of VEGF to DS and to endogenous glycosaminoglycans. A similar retention effect is expected with other glycosaminoglycans-binding proteins (including many growth factors) when complexed with these glycans. Owing to its unique application, this type of complex is, perhaps, better described as a nanoglycan complex.
    Biomacromolecules 07/2010; 11(7):1863-72. · 5.37 Impact Factor
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    ABSTRACT: Novel treatments for multidrug-resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB), or latent TB are needed urgently. Recently, we reported the formulation and characterization of the nitroimidazo-oxazine PA-824 for efficient aerosol delivery as dry powder porous particles and the subsequent disposition in guinea pigs after pulmonary administration. The objective of the present study was to evaluate the effects of these PA-824 therapeutic aerosols on the extent of TB infection in the low-inoculum aerosol infection guinea pig model. Four weeks after infection by the pulmonary route, animals received daily treatment for 4 weeks of either a high or a low dose of PA-824 dry powder aerosol. Animals received PA-824 cyclodextrin/lecithin suspensions orally as positive controls, and those receiving placebo particles or no treatment were negative controls. The lungs and spleens of animals receiving the high dose of inhaled PA-824 particles exhibited a lower degree of inflammation (indicated by wet tissue weights), bacterial burden, and tissue damage (indicated by histopathology) than those of untreated or placebo animals. Treatment with oral PA-824 cyclodextrin/lecithin suspension resulted in a more significant reduction in the bacterial burden of lungs and spleen, consistent with a dose that was larger than inhaled doses (eight times the inhaled low dose and four times the inhaled high dose). However, histopathological analysis revealed that the extent of tissue damage was comparable in groups receiving the oral or either inhaled dose. The present studies indicate the potential use of PA-824 dry powder aerosols in the treatment of TB.
    Antimicrobial Agents and Chemotherapy 04/2010; 54(4):1436-42. · 4.57 Impact Factor
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    ABSTRACT: We find that Mycobacterium smegmatis survives spray drying and retains cell viability in accelerated temperature stress (40 °C) conditions with a success rate that increases with increasing thermal, osmotic, and nutrient-restriction stresses applied to the mycobacterium prior to spray drying. M.smegmatis that are spray dried during log growth phase, where they suffer little or no nutrient-reduction stress, survive for less than 7 days in the dry powder state at accelerated temperature stress conditions, whereas M. smegmatis that are spray dried during stationary phase, where cells do suffer nutrient reduction, survive for up to 14 days. M. smegmatis that are spray dried from stationary phase, subjected to accelerated temperature stress conditions, regrown to stationary phase, spray dried again, and resubmitted to this same process four consecutive times, display, on the fourth spray drying iteration, an approximate ten-fold increase in stability during accelerated temperature stress testing, surviving up to 105 days. Microarray tests revealed significant differences in genetic expression of M. smegmatis between log phase and stationary phase conditions, between naïve (non spray-dried) and multiply cycled dried M. smegmatis (in log and stationary phase), and between M. smegmatis in the dry powder state following a single spray drying operation and after four consecutive spray drying operations. These differences, and other phenotypical differences, point to the carotenoid biosynthetic pathway as a probable pathway contributing to bacteria survival in the spray-dried state and suggests strategies for spray drying that may lead to significantly greater room-temperature stability of mycobacteria, including mycobacterium bovis bacille Calmette-Guerin (BCG), the current TB vaccine.
    Materials. 01/2010;
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    ABSTRACT: To formulate rifampicin, an anti-tuberculosis antibiotic, for aerosol delivery in a dry powder 'porous nanoparticle-aggregate particle' (PNAP) form suited for shelf stability, effective dispersibility and extended release with local lung and systemic drug delivery. Rifampicin was encapsulated in PLGA nanoparticles by a solvent evaporation process, spray dried into PNAPs containing varying amounts of nanoparticles, and characterized for physical and aerosol properties. Pharmacokinetic studies were performed with formulations delivered to guinea pigs by intratracheal insufflation and compared to oral and intravenous delivery of rifampicin. The PNAP formulations possessed properties suitable for efficient deposition in the lungs. In vitro release showed an initial burst of rifampicin, with the remainder available for release beyond eight hours. PNAPs delivered to guinea pigs by insufflation achieved systemic levels of rifampicin detected for six to eight hours. Moreover, rifampicin concentrations remained detectable in lung tissue and cells up to and beyond eight hours. Conversely, after pulmonary delivery of an aerosol without nanoparticles, rifampicin could not be detected in the lungs at eight hours. Our results indicate that rifampicin can be formulated into an aggregated nanoparticle form that, once delivered to animals, achieves systemic exposure and extends levels of drug in the lungs.
    Pharmaceutical Research 05/2009; 26(8):1847-55. · 4.74 Impact Factor
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    ABSTRACT: We formulated PA-824, a nitroimidazopyran with promise for the treatment of tuberculosis, for efficient aerosol delivery to the lungs in a dry powder porous particle form. The objectives of this study were to prepare and characterize a particulate form of PA-824, assess the stability of this aerosol formulation under different environmental conditions, and determine the pharmacokinetic parameters for the powder after pulmonary administration. The drug was spray dried into porous particles containing a high drug load and possessing desirable aerosol properties for efficient deposition in the lungs. The physical, aerodynamic, and chemical properties of the dry powder were stable at room temperature for 6 months and under refrigerated conditions for at least 1 year. Pharmacokinetic parameters were determined in guinea pigs after the pulmonary administration of the PA-824 powder formulation at three doses (20, 40, and 60 mg/kg of body weight) and compared to those after the intravenous (20 mg/kg) and oral (40 mg/kg) delivery of the drug. Oral and inhaled delivery of PA-824 achieved equivalent systemic delivery at the same body dose within the first 12 h of dosing. However, animals dosed by the pulmonary route showed drug loads that remained locally in the lungs for 32 h postexposure, whereas those given the drug orally cleared the drug more rapidly. Therefore, we expect from these pharmacokinetic data that pulmonary delivery may achieve the same efficacy as oral delivery at the same body dose, with a potential improvement in efficacy related to pulmonary infection. This may translate into the ability to deliver lower body doses of this drug for the treatment of tuberculosis by aerosol.
    Antimicrobial Agents and Chemotherapy 02/2009; 53(4):1338-43. · 4.57 Impact Factor
  • Jean C Sung, Brian L Pulliam, David A Edwards
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    ABSTRACT: The lungs are an attractive route for non-invasive drug delivery with advantages for both systemic and local applications. Incorporating therapeutics with polymeric nanoparticles offers additional degrees of manipulation for delivery systems, providing sustained release and the ability to target specific cells and organs. However, nanoparticle delivery to the lungs has many challenges including formulation instability due to particle-particle interactions and poor delivery efficiency due to exhalation of low-inertia nanoparticles. Thus, novel methods formulating nanoparticles into the form of micron-scale dry powders have been developed. These carrier particles exhibit improved handling and delivery, while releasing nanoparticles upon deposition in the lungs. This review covers the development of nanoparticle formulations for pulmonary delivery as both individual nanoparticles and encapsulated within carrier particles.
    Trends in Biotechnology 01/2008; 25(12):563-70. · 9.66 Impact Factor
  • Brian Pulliam, Jean C Sung, David A Edwards
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    ABSTRACT: The development of needle-less vaccination for pulmonary delivery may require dry forms of vaccines whose powder properties allow for a low cost, heat and freeze tolerance, efficient aerosolization, and the ability to target cells of the immune system. For each of these reasons, nanoparticles can play a critical role in the formulation, development and delivery of needle-less vaccination. This review aims to communicate present biomaterial design issues surrounding the incorporation of nanoparticles into pulmonary vaccines.
    Expert Opinion on Drug Delivery 12/2007; 4(6):651-63. · 4.87 Impact Factor
  • Jennifer Fiegel, Robert Clarke, David A Edwards
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    ABSTRACT: The current understanding of airborne pathogen spread in relation to the new methods of suppressing exhaled bioaerosols using safe surface-active materials, such as isotonic saline, is reviewed here. We discuss the physics of bioaerosol generation in the lungs, what is currently known about the relationship between expired bioaerosols and airborne infectious disease and current methods of airborne infectious disease containment. We conclude by reviewing recent experiments that suggest the delivery of isotonic saline can significantly diminish exhaled aerosol--generated from airway lining fluid in the course of natural breathing. We also discuss these implications in relation to airborne infectious disease control.
    Drug Discovery Today 02/2006; 11(1-2):51-7. · 6.55 Impact Factor
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    ABSTRACT: Humans commonly exhale aerosols comprised of small droplets of airway-lining fluid during normal breathing. These "exhaled bioaerosols" may carry airborne pathogens and thereby magnify the spread of certain infectious diseases, such as influenza, tuberculosis, and severe acute respiratory syndrome. We hypothesize that, by altering lung airway surface properties through an inhaled nontoxic aerosol, we might substantially diminish the number of exhaled bioaerosol droplets and thereby provide a simple means to potentially mitigate the spread of airborne infectious disease independently of the identity of the airborne pathogen or the nature of any specific therapy. We find that some normal human subjects expire many more bioaerosol particles than other individuals during quiet breathing and therefore bear the burden of production of exhaled bioaerosols. Administering nebulized isotonic saline to these "high-producer" individuals diminishes the number of exhaled bioaerosol particles expired by 72.10 +/- 8.19% for up to 6 h. In vitro and in vivo experiments with saline and surfactants suggest that the mechanism of action of the nebulized saline relates to modification of the physical properties of the airway-lining fluid, notably surface tension.
    Proceedings of the National Academy of Sciences 01/2005; 101(50):17383-8. · 9.81 Impact Factor
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    ABSTRACT: We demonstrate that a primary source of elimination of inhaled macromolecules after delivery to the lungs and before absorption into the systemic circulation owes to clearance by alveolar macrophages (AM). Depletion of AM by liposome-encapsulated dichloromethylene diphosphonate is shown to cause severalfold enhancement in systemic absorption of IgG and human chorionic gonadotropin after intratracheal instillation in rats. Lowering the doses of IgG delivered to the lungs alleviates local degradation and results in a dramatic increase in systemic absorption of the protein as well. Chemical and physical means of minimizing uptake of macromolecules by AM are proposed as novel methods for enhancing protein absorption from the lungs. Such strategies may have important ramifications on the development of inhalation as an attractive mode of administration of therapeutic proteins to the bloodstream.
    AJP Lung Cellular and Molecular Physiology 06/2004; 286(5):L1002-8. · 3.52 Impact Factor
  • David A. Edwards
    AIChE Journal 04/2004; 48(1):2 - 6. · 2.58 Impact Factor
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    ABSTRACT: Inhaled insulin first entered clinical human testing in the mid 1990s. Since then, the commercial potential and technical challenges of an inhaled insulin product have grown increasingly clear, with several pharmaceutical partnerships now targeting treatment of diabetes mellitus through inhalation products in clinical development. While clinical results to date show the therapy to be generally promising, recent data have raised questions related to human safety and slowed progress toward a commercial product. Answering these questions positively in the coming years will be critical to making inhalation therapy a practical diabetes-care reality.
    BioDrugs 02/2003; 17(1):9-17. · 2.12 Impact Factor
  • David A Edwards, Craig Dunbar
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    ABSTRACT: The new field of therapeutic aerosol bioengineering (TAB), driven primarily by the medical need for inhaled insulin, is now expanding to address medical needs ranging from respiratory to systemic diseases, including asthma, growth deficiency, and pain. Bioengineering of therapeutic aerosols involves a level of aerosol particle design absent in traditional therapeutic aerosols, which are created by conventionally spraying a liquid solution or suspension of drug or milling and mixing a dry drug form into respirable particles. Bioengineered particles may be created in liquid form from devices specially designed to create an unusually fine size distribution, possibly with special purity properties, or solid particles that possess a mixture of drug and excipient, with designed shape, size, porosity, and drug release characteristics. Such aerosols have enabled several high-visibility clinical programs of inhaled insulin, as well as earlier-stage programs involving inhaled morphine, growth hormone, beta-interferon, alpha-1-antitrypsin, and several asthma drugs. The design of these aerosols, limited by partial knowledge of the lungs' physiological environment, and driven largely at this stage by market forces, relies on a mixture of new and old science, pharmaceutical science intuition, and a degree of biological-impact empiricism that speaks to the importance of an increased level of academic involvement.
    Annual Review of Biomedical Engineering 02/2002; 4:93-107. · 10.95 Impact Factor
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    ABSTRACT: Conventional slow-acting insulin preparations for subcutaneous injection, e.g., suspensions of the complex with protamine and/or zinc, were reformulated as dry powders for inhalation and the insoluble aerosol tested for providing sustained insulin plasma levels. Large porous particles made of lactose, albumin, and dipalmitoylphosphatidylcholine, and incorporating insulin, protamine, and/or zinc chloride were prepared using spray-drying. Integrity of insulin after spray-drying and insulin insolubilization in spray-dried particles was verified in vitro. The pharmacokinetic profile of the formulation delivered by inhalation and subcutaneous injection was assessed in vivo in the rat. The formulation process of insulin as dry powders did not alter insulin integrity and did not impede, in most cases, insulin insolubilization by protamine and/or zinc. Large porous insulin particles presented 7 μm mass mean geometric particle diameters, 0.1 g/cm3 bulk powder tap densities and theoretical aerodynamic diameters suitable for deep lung deposition (in the range of 2.2–2.5 μm). The dry powders exhibited 40% respirable fractions in the Andersen cascade impactor and 58–75% in the Aero-Breather™. Insoluble inhaled insulin provided sustained insulin plasma levels for half a day, similar to injected insulin, and exhibited a bioavailability of 80.5% relative to subcutaneous injection of the same formulation. Drug Dev. Res. 48:178–185, 1999. ©1999 Wiley-Liss, Inc.
    Drug Development Research 02/2000; 48(4):178 - 185. · 0.87 Impact Factor
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    ABSTRACT: The pulmonary system is an attractive noninvasive route for effective delivery of drugs for both local and systemic therapies. In this study, an inhalation system was developed to effectively aerosolize and deliver small amounts (typically 1-5 mg) of dry powder polymeric and nonpolymeric particles to the lungs of anesthetized rodents over a very short period of time using a ventilator while the animals breathed spontaneously. The new aerosols were designed for size, porosity, and lightness and were characterized by particles of low mass density (rho less than or equal to 0.1 g/cm3) and large size (d approximately 10 mum). The inhalation system was tested in vivo to determine 1) whether the relatively efficient in vitro aerosolization of these large porous particles translated into a substantial respirable fraction in vivo; 2) whether the bioavailability of an encapsulated drug for systemic therapy could be increased and the drug release in the systemic circulation could be sustained; and 3) whether an encapsulated drug for local asthma therapy could sustain bronchodilation over a prolonged time period. Unlike the conventional (small non-porous) particles which deposit primarily in the tubing and trachea (80% of all particle mass delivered), 55% of the large porous particle mass deposited in the deep lung. The total systemic bioavailabilities of inhaled porous estradiol, insulin, and testosterone relative to subcutaneous injections were 86%, 88%, and 177%, respectively. The inhaled dry powder albuterol sulfate aerosol was capable of preventing sustained bronchoconstriction (in response to carbachol challenge) for approximately one day. Our data indicate that the experimental inhalation system we developed will be an excellent device for further testing of new therapeutics available in particulate form.
    Aerosol Science and Technology 01/2000; 32(5). · 2.78 Impact Factor
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    ABSTRACT: A theory of molecular absorption from the small intestine is outlined on the basis of macrotransport analysis. Certain features of the transport process that have not been previously considered in the literature are quantitatively described. These include complex interrelationships between lumen and membrane diffusion, convection, degradation and absorption mechanisms — and overall axial convection, dispersion, degradation and absorption rates. Therapeutic molecules are assumed to be introduced in the form of a bolus into the duodenum. They subsequently convect and diffuse through the duodenum, jejunum, and ileum. Absorption into the systemic circulation across the epithelial barrier, as well as possible degradation or aggregation in the lumen or at the apical epithelial membrane, contribute to the disappearance of the therapeutic as the bolus travels through the lumen in an oral to caudal direction. Space- and time-varying lumen concentrations are predicted, as are time-varying systemic concentrations following introduction of the bolus. The inputs to the model are primarily anatomical or physicochemical characteristics that are either known or can be measured for a given therapeutic and animal model. A detailed parametric study is made, elucidating the individual roles of permeability and degradation rates. This leads to a simple paradigm for determining the two unknowns of the model (the membrane permeability and degradation rate constant) from systemic absorption data; it is shown that the membrane permeability constant can alternatively be estimated by independent in vitro measurements. Comparisons with published experimental systemic concentrations are made for molecules ranging from small lipophilic substances, such as ibuprofen, to polypeptides, such as calcitonin, and proteins, such as insulin. The deduced epithelial permeability values show reasonable agreement with values determined using alveolar epithelia and Caco-2 cell monolayers. By contrast, the membrane permeability values deduced from a simplified model of absorption from the small intestine show relatively poor agreement with experimental values. The model may be useful as a numerical simulation tool for predicting (estimates of) oral dose–response relationships in animals and humans given relatively limited in vivo data.
    Chemical Engineering Science 01/2000; 55(3):473-489. · 2.61 Impact Factor
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    ABSTRACT: A method is described for evaluating the mean velocity, dispersion coefficient and deposition rate constant characterizing aerosol transport in a finite, computationally tractable, three-dimensional domain of the human lungs. The methodology is applied specifically to deduce (mesoscale) transport coefficients in an anatomically realistic human mouth and throat. In this method aerosol particles are introduced into a numerically simulated airflow in the vicinity of the entrance region of the airway unit (e.g. the mouth); the aerosol bolus is inspired such that it travels through the airway unit before being expired. The exhaled concentration of nondeposited aerosols is determined numerically, and used to deduce the three aerosol transport coefficients. The deduced transport coefficients, representing “mesoscale” averages of the microscale simulated flow, are determined as functions of air flow rate, particle size, bolus parameters, and dimensionality; these values are then incorporated into a mesoscale lung model and used to simulate macroscale aerosol transport behavior in the lungs. Special attention is given to the numerical simulation of an aerosol bolus inspired into the lungs. The calculated half-width, mode and deposition fraction agree favorably with recent macrotransport simulations, minus the upper airway generation. In these comparisons, the major influence of the upper airways is to increase aerosol deposition. Half-width and deposition fraction are also significantly affected by lung size.
    Journal of Aerosol Science. 09/1998;

Publication Stats

948 Citations
108.40 Total Impact Points

Institutions

  • 2009–2010
    • University of North Carolina at Chapel Hill
      • Division of Molecular Pharmaceutics
      North Carolina, United States
  • 2002–2010
    • Harvard University
      • • School of Engineering and Applied Sciences
      • • Faculty of Arts and Sciences
      Cambridge, Massachusetts, United States
  • 2008–2009
    • Harvard School of Engineering and Applied Sciences
      Londinium, England, United Kingdom
  • 2000
    • Pennsylvania State University
      • Department of Chemical Engineering
      University Park, MD, United States
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
  • 1993–1995
    • Massachusetts Institute of Technology
      • • Division of Health Sciences and Technology
      • • Department of Chemical Engineering
      Cambridge, Massachusetts, United States