Ernest S. Kim

A biodegradable microvessel scaffold as a framework to enable vascular support of engineered tissues.

A biodegradable microvessel scaffold comprised of distinct parenchymal and vascular compartments separated by a permeable membrane interface was conceptualized, fabricated, cellularized, and implanted. The device was designed with perfusable microfluidic channels on the order of 100 μm to mimic small blood vessels, and high interfacial area to an adjacent parenchymal space to enable transport between the compartments. Poly(glycerol sebacate) (PGS) elastomer was used to construct the microvessel framework, and various assembly methods were evaluated to ensure robust mechanical integrity. In vitro studies demonstrated the differentiation of human skeletal muscle cells cultured in the parenchymal space, a 90% reduction in muscle cell viability due to trans-membrane transport of a myotoxic drug from the perfusate, and microvessel seeding with human endothelial cells. In vivo studies of scaffolds implanted subcutaneously and intraperitoneally, without or with exogenous cells, into nude rats demonstrated biodegradation of the membrane interface and host blood cell infiltration of the microvessels. This modular, implantable scaffold could serve as a basis for building tissue constructs of increasing scale and clinical relevance.

Performance and scaling effects in a multilayer microfluidic extracorporeal lung oxygenation device

Microfluidic fabrication technologies are emerging as viable platforms for extracorporeal lung assist devices and oxygenators for cardiac surgical support and critical care medicine, based in part on their ability to more closely mimic the architecture of the human vasculature than existing technologies. In comparison with current hollow fiber oxygenator technologies, microfluidic systems have more physiologically-representative blood flow paths, smaller cross section blood conduits and thinner gas transfer membranes. These features can enable smaller device sizes and a reduced blood volume in the oxygenator, enhanced gas transfer efficiencies, and may also reduce the tendency for clotting in the system. Several critical issues need to be addressed in order to advance this technology from its current state and implement it in an organ-scale device for clinical use. Here we report on the design, fabrication and characterization of multilayer microfluidic oxygenators, investigating scaling effects associated with fluid mechanical resistance, oxygen transfer efficiencies, and other parameters in multilayer devices. Important parameters such as the fluidic resistance of interconnects are shown to become more predominant as devices are scaled towards many layers, while other effects such as membrane distensibility become less significant. The present study also probes the relationship between blood channel depth and membrane thickness on oxygen transfer, as well as the rate of oxygen transfer on the number of layers in the device. These results contribute to our understanding of the complexity involved in designing three-dimensional microfluidic oxygenators for clinical applications.

Development of a Microfluidics-Based Intracochlear Drug Delivery Device

Background: Direct delivery of drugs and other agents into the inner ear will be important for many emerging therapies, including the treatment of degenerative disorders and guiding regeneration. Methods: We have taken a microfluidics/MEMS (MicroElectroMechanical Systems) technology approach to develop a fully implantable reciprocating inner-ear drug-delivery system capable of timed and sequenced delivery of agents directly into perilymph of the cochlea. Iterations of the device were tested in guinea pigs to determine the flow characteristics required for safe and effective delivery. For these tests, we used the glutamate receptor blocker DNQX, which alters auditory nerve responses but not cochlear distortion product otoacoustic emissions. Results: We have demonstrated safe and effective delivery of agents into the scala tympani. Equilibration of the drug in the basal turn occurs rapidly (within tens of minutes) and is dependent on reciprocating flow parameters. Conclusion: We have described a prototype system for the direct delivery of drugs to the inner ear that has the potential to be a fully implantable means for safe and effective treatment of hearing loss and other diseases.

Kinetics of reciprocating drug delivery to the inner ear.

Reciprocating drug delivery is a means of delivering soluble drugs directly to closed fluid spaces in the body via a single cannula without an accompanying fluid volume change. It is ideally suited for drug delivery into small, sensitive and unique fluid spaces such as the cochlea. We characterized the pharmacokinetics of reciprocating drug delivery to the scala tympani within the cochlea by measuring the effects of changes in flow parameters on the distribution of drug throughout the length of the cochlea. Distribution was assessed by monitoring the effects of DNQX, a reversible glutamate receptor blocker, delivered directly to the inner ear of guinea pigs using reciprocating flow profiles. We then modeled the effects of those parameters on distribution using both an iterative curve-fitting approach and a computational fluid dynamic model. Our findings are consistent with the hypothesis that reciprocating delivery distributes the drug into a volume in the base of the cochlea, and suggest that the primary determinant of distribution throughout more distal regions of the cochlea is diffusion. Increases in flow rate distributed the drug into a larger volume that extended more apically. Over short time courses (less than 2h), the apical extension, though small, significantly enhanced apically directed delivery of drug. Over longer time courses (>5h) or greater distances (>3mm), maintenance of drug concentration in the basal scala tympani may prove more advantageous for extending apical delivery than increases in flow rate. These observations demonstrate that this reciprocating technology is capable of providing controlled delivery kinetics to the closed fluid space in the cochlea, and may be suitable for other applications such as localized brain and retinal delivery.

A portable and reconfigurable multi-organ platform for drug development with onboard microfluidic flow control.

The drug development pipeline is severely limited by a lack of reliable tools for prediction of human clinical safety and efficacy profiles for compounds at the pre-clinical stage. Here we present the design and implementation of a platform technology comprising multiple human cell-based tissue models in a portable and reconfigurable format that supports individual organ function and crosstalk for periods of up to several weeks. Organ perfusion and crosstalk are enabled by a precision flow control technology based on electromagnetic actuators embedded in an arrayed format on a microfluidic platform. We demonstrate two parallel circuits of connected airway and liver modules on a platform containing 62 electromagnetic microactuators, with precise and controlled flow rates as well as functional biological metrics over a two week time course. Technical advancements enabled by this platform include the use of non-sorptive construction materials, enhanced scalability, portability, flow control, and usability relative to conventional flow control modes (such as capillary action, pressure heads, or pneumatic air lines), and a reconfigurable and modular organ model format with common fluidic port architecture. We demonstrate stable biological function for multiple pairs of airway-liver models for periods of 2 weeks in the platform, with precise control over fluid levels, temperature, flow rate and oxygenation in order to support relevant use cases involving drug toxicity, efficacy testing, and organ-organ interaction.

Microfabricated infuse-withdraw micropump component for an integrated inner-ear drug-delivery platform

One of the major challenges in treatment of auditory disorders is that many therapeutic compounds are toxic when delivered systemically. Local intracochlear delivery methods are becoming critical in emerging treatments and in drug discovery. Direct infusion via cochleostomy, in particular, is attractive from a pharmacokinetics standpoint, as there is potential for the kinetics of delivery to be well-controlled. Direct infusion is compatible with a large number of drug types, including large, complex molecules such as proteins and unstable molecules such as siRNA. In addition, hair-cell regeneration therapy will likely require long-term delivery of a timed series of agents. This presents unknown risks associated with increasing the volume of fluid within the cochlea and mechanical damage caused during delivery. There are three key requirements for an intracochlear drug delivery system: (1) a high degree of miniaturization (2) a method for pumping precise and small volumes of fluid into the cochlea in a highly controlled manner, and (3) a method for removing excess fluid from the limited cochlear fluid space. To that end, our group is developing a head-mounted microfluidics-based system for long-term intracochlear drug delivery. We utilize guinea pig animal models for development and demonstration of the device. Central to the system is an infuse-withdraw micropump component that, unlike previous micropump-based systems, has fully integrated drug and fluid storage compartments. Here we characterize the infuse-withdraw capabilities of our micropump, and show experimental results that demonstrate direct drug infusion via cochleostomy in animal models. We utilized DNQX, a glutamate receptor antagonist that suppresses CAPs, as a test drug. We monitored the frequency-dependent changes in auditory nerve CAPs during drug infusion, and observed CAP suppression consistent with the expected drug transport path based on the geometry and tonotopic organization of the cochlea.

A bilayer small diameter in vitro vascular model for evaluation of drug induced vascular injury

In pre-clinical safety studies, drug-induced vascular injury (DIVI) is defined as an adverse response to a drug characterized by degenerative and hyperplastic changes of endothelial cells and vascular smooth muscle cells. Inflammation may also be seen, along with extravasation of red blood cells into the smooth muscle layer (i.e., hemorrhage). Drugs that cause DIVI are often discontinued from development after considerable cost has occurred. An in vitro vascular model has been developed using endothelial and smooth muscle cells in co-culture across a porous membrane mimicking the internal elastic lamina. Arterial flow rates of perfusion media within the endothelial chamber of the model induce physiologic endothelial cell alignment. Pilot testing with a drug known to cause DIVI induced extravasation of red blood cells into the smooth muscle layer in all devices with no extravasation seen in control devices. This engineered vascular model offers the potential to evaluate candidate drugs for DIVI early in the discovery process. The physiologic flow within the co-culture model also makes it candidate for a wide variety of vascular biology investigations.

An inner-ear drug delivery platform with fully integrated control, actuation, and fluidics hardware

Here we report on advances toward a miniaturized, fully-integrated intracochlear drug-delivery micropump and controller. Our device is designed to be worn as a head mount for guinea-pig animal models (with the ultimate goal of generating an implantable device for humans) that delivers liquid-solubilized drug through a cannula to the inner ear. Our completed platform will have infuse-withdraw capabilities, and an integrated drug reservoir. Here we present experimental data demonstrating the performance of a simplified version of the device, which has no drug reservoir and is operated only in infusion mode (though it is capable of withdrawing fluid as well). We show that our device successfully delivers the desired infusion profile in a guinea pig model.

Contents Vol. 14, 2009

Maurizio Barbara, Rome Olivier Bertrand, Bron F. Owen Black, Portland Th omas Brandt, München Barbara Canlon, Stockholm John P. Carey, Baltimore Douglas A. Cotanche, Boston Cor W.R.J. Cremers, Nijmegen Norbert Dillier, Zürich Robert Dobie, Sacramento Manuel Don, Los Angeles Jill B. Firszt, St. Louis Andrew Forge, London Bernard Fraysse, Toulouse Rick Friedman, Los Angeles Bruce J. Gantz, Iowa City Pablo Gil-Loyzaga, Madrid Anthony W. Gummer, Tübingen James W. Hall III, Gainesville Joseph W. Hall III, Chapel Hill Michael Halmagyi, Camperdown Rudolf Häusler, Bern Vicente Honrubia, Los Angeles Gary D. Housley, Auckland Karl-Bernd Hüttenbrink, Köln Pawel J. Jastreboff , Atlanta Margaret A. Kenna, Boston Philippe P. Lefebvre, Liège Bernd Lütkenhöner, Münster Linda L. Luxon, London Geoff rey A. Manley, Freising Alessandro Martini, Ferrara Jennifer R. Melcher, Boston Saumil N. Merchant, Boston Brian C.J. Moore, Cambridge David R. Moore, Nottingham Cynthia C. Morton, Boston Donata Oertel, Madison Kaoru Ogawa, Tokyo Stephen J. O’Leary, Parkville Alan R. Palmer, Nottingham Lorne S. Parnes, London, Ont. Jean-Luc Puel, Montpellier Ramesh Rajan, Monash Yehoash Raphael, Ann Arbor J. Th omas Roland, New York John J. Rosowski, Boston Rudolf Rübsamen, Leipzig Mario A. Ruggero, Evanston Leonard P. Rybak, Springfi eld Richard J. Salvi, Buff alo Robert V. Shannon, Los Angeles Guido F. Smoorenburg, Besse sur Issole Haim Sohmer, Jerusalem Olivier Sterkers, Clichy Istvan Sziklai, Debrecen Peter R. Th orne, Auckland Shin-ichi Usami, Matsumoto P. Ashley Wackym, Milwaukee Tatsuya Yamasoba, Tokyo Fan-Gang Zeng, Irvine Basic Science and Clinical Research in the Auditory and Vestibular Systems and Diseases of the Ear

Design of a single capillary-parenchymal co-culture bioreactor using a self-assembling peptide membrane

Publisher Summary A bio-reactor is designed and fabricated for the co-culture of endothelial and hepatic parenchymal cells. The device provides a structured environment mimicking the in vivo characteristics of a single capillary and the adjacent tissue. The bio-reactor consists of two cell-scale fluid channels separated by a bio-compatible thin porous membrane made of self-assembling oligopeptide gel. Analytic and computational modeling techniques were used to investigate the fluid flow and mass transfer characteristics and aid in design of the bioreactor. The device concept was to form a peptide gel membrane between two cell-sized channels by first flowing peptide solution between the two channels, then flowing saline in the two side channels to cause the peptide solution to gel. Channel dimensions were chosen based on the material properties of the peptide gel and on typical dimensions of hepatocytes and capillaries. When forming the peptide membrane in the bioreactor, the composition and flow rates of the peptide and saline solutions are closely regulated.