Track 19. Biotransport

7357 We, 15:00-15:15 (P35) Red blood cells as carrier for nanoparticles H. B~umler, M. Br~hler, A. Lemke, J. M6schwitzer, A. MUller, J. Pinkernelle, V. Staedtke, U. Teichgr~ber. Charit6 - Universit~tsmedizin Berlin, Germany

Superparamagnetic iron oxide nanoparticles (SPION) in the size range of 3-20 nm are often used in magnetic resonance imaging (MRI). Their circulating half-life time of only two hours and their fast phagocytosis by the lymphocyte- macrophage system hindered an optimal use. Additionally, highly efficient drugs for the therapy of cancer or cerebral fungal infections are very often water insoluble. We developed a method for loading erythrocytes with nanoparticles utilizing them as a potent carrier system characterized by excellent biocompatibility, biodegradability and non-immunogenic properties. As very poorly water soluble drug served Amphotericin B. The loading procedure leads to a final concentration of 4 pg AmB per erythro- cyte. It was proven that an amount of only 750AmB-Ioaded erythrocytes per ml is sufficient to reach an antifungal effect, representing 1 ml loaded blood for the whole body. Additionally loading the erythrocytes with magnetite nanoparticles and mag- netically focussing them to the desired sites can realize targeting of organs or tissues. Loading erythrocytes simultaneously with both, AmB and magnetite, did neither reduce the AmB concentration per erythrocyte nor its bioactivity. Additionally, magnetite loaded erythrocytes can be visualized by MRI, offering the opportunity for diagnostic monitoring of the therapy. The advantages of our erythrocyte-carrier-system are not limited to AmB. Any other water insoluble drug has potential to be loaded onto erythrocytes thereby exploiting the advantages of our carrier system. Due to their unique qualities erythrocytes can be used as therapeutically drug delivery systems, which cannot just deliver a high dosage of different drugs but also protects them from inactivating effects and minimizes side reactions. The additional diagnostic capacities as MRI contrast media and the possibility to focus on certain tissues make our delivery system one of the most versatile drug carriers.

6474 We, 15:15-15:30 (P35) Computational study of chronic myelogenous leukemia culture in a 3D perfusion bioreactor C.Y.J. Ma, A. Mantalaris, X.'~ Xu. Department ef Chemical Engineering, Imperial College London, London, UK

Bone marrow (BM) is the site of blood formation which consists of the vascular network and haematopoietic compartment. The process of haematopoiesis is precisely controlled by the three dimensional (3D) microenvironment in the BM. Abnormality in this regulating process results in haematological disease such as chronic myelogenous leukaemia (CML), one of the most common types of bone marrow and blood disease. Until now, the only effective treatment is bone marrow transplantation (BMT). Because of unavailability of suitable donors and unprecedented demand for BMT, there is a continuous effort in the development of effective new drugs. Traditionally, test systems for evaluating the toxicity and efficacy of new medicines involve the use of two dimensional (2D) flask cultures. However, it has been well established that the 3D marrow microenvironment is critical in the regulation of stem cell self- renewal, proliferation, and differentiation. The ability to reproduce the process of CML pathogenesis in a fashion that mimics the natural microenvironment is of great importance. To investigate the growth characteristics of CML cells in BM, a 3D mathematical model has been developed to examine the force distribution (shear stress) and nutrient utilisation (oxygen and glucose) in a culture system. A custom- designed scaffold is embedded in the Rotating Wall Perfused Bioreactor (RWPB-Synthecon) to mimic the 3D extravascular space in the BM qual- itatively. Finally, the cellular growth model for CML of various lineages is incorporated in the study to capture the complexity of the BM functionality. The model is implemented using the commercial computational fluid dynamics (CFD) software CFX 4.4 (CFX-ANSYS). The development of a transport model for the growth of CML in a 3D envi- ronment offers be a valuable tool to illustrate and understand the regulation mechanism of haematopoiesis in pathological state.

19.5. Biothermomechanics

4517 We, 08:15-08:30 (P29) Fracture formation in vitrified thin films of cryoprotectants and its application to cryopreservation Y. Rabin, P.S. Steif, K.C. Hess, J.L. Jimenez-Rios, M.C. Palastro. Biethermal Technology Laboratory, Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

Vitrification is an alternative to conventional cwopreservation of biological materials (vitreous in Latin means glassy), first suggested by Basile Luyet

19.5. Biothermomechanics $379

in 1937, but applied successfully only in recent years. A major factor that impacts the survival and integrity of bulky biological specimens during cry- opreservation is the development of thermo-mechanical stress, with fracture formation as its most dramatic outcome. As part of an ongoing effort to study the continuum mechanics effects associated with cryopreservation, the current report focuses on fracture formation in vitrified thin films of cryoprotectants, which promote glass formation. The samples under investigation are 0.5ml droplets of cryoprotective agents, (20 mm in diameter 1.5 mm in thickness) imaged with a cryomacroscope [1]. Tested samples included DMSO, and the cryoprotectant cocktails VS55 and DP6; photos of fracture formation are available at [2]. Some samples contained small bovine muscle segments to study stress concentration effects. Experimental results show high consistency in the onset temperature of fracturing, while the fracture pattern was affected by the cooling rate. Tissue segments affected the pattern of fracturing, but not the onset temperature. From continuum mechanics analysis, a simple picture of stress development has emerged: with cooling, the stress is nearly zero until a "set" temperature is reached (a few degrees above glass transition); the stress builds up linearly thereafter, with diminishing temperature. Strains which cause fracture in DMSO were found to be in the range of 0.28% to 0.36%, typical of brittle organic materials. Acknowledgment: This study has been supported by the National Heart Lung and Blood Institute (NHLBI, USA), R01 HL069944-01A1.

References [1] Rabin Y., Taylor M.J., Walsh J.R., Baicu S., Steif ES. Cell Preservation Tech-

nology 2005; 3(3): 169-183. [2] http://www.me.cmu.edu/facultyl/rabin/CwomacroscopylmagesO2.html

4519 We, 08:30-08:45 (P29) Continuum mechanics prediction of fracture progression in vitrified DP6 and its application to cryopreservation P.S. Steif, M.C. Palastro, Y. Rabin. Biethermal Technology Laboratory, Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

Cwopreservation via vitrification has recently proven to be a promising al- ternative to conventional cwopreservation (vitreous in Latin means glassy). However, the reasonably high cooling rates necessary to facilitate vitrification, when cryoprotective agents are used in non-toxic concentrations, result in high temperature gradients in bulky biological specimens. Thermo-mechanical stresses driven by these temperature gradients frequently lead to the formation of fractures. As part of a series of investigations into continuum mechanics effects associated with cwopreservation, the current report focuses on pre- dictions of crack progression in vitrified cryoprotective agents. In a previous investigation, the process of fracture formation in 1 ml of the cryoprotectant cocktail DP6 was recorded in various thermal histories, while it was contained in a glass vial, and cooled from room temperature to a minimum temperature of -135°C (16°C below its glass transition temperature). Imaging was performed by means of cryomacroscopy [1]; selected images of fracture formation in this process are available at [2]. Based on experimental observations of tem- perature measurements and fractures, the spatial distribution of cracking was found to be dependent on the cooling rate. At lower cooling rates, cracking was initiated throughout the vial simultaneously, while higher cooling rates initiated cracks in the outer portion of the vial, inward progression of cracks occurred with further cooling. The emphasis in this presentation is on methodology for predicting crack formation during vitrification based on stress computations, and its application to the experimental observations of cracking in vials. Acknowledgment: This study has been supported by the National Heart Lung and Blood Institute (NHLBI, USA), R01 HL069944-01A1.

References [1] Rabin Y., Taylor M.J., Walsh J.R., Baicu S., Steif P.S. Cell Preservation Tech-

nology 2005; 3(3): 169-183. [2] http://www.me.cmu.edu/facultyl/rabin/CwomacroscopylmagesOl.html

4878 We, 08:45-09:00 (P29) Experimental study of viscoelasticity effects in cryopreservation of blood vessels by means of vitrif ication J.L. Jimenez-Rios, P.S. Steif, '~ Rabin. Biethermal Technology Laboratory, Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

Vitrification is a promising alternative to cwopreservation (vitreous in Latin means glassy), in which the tissue is permeated with cryoprotective agents (CPA) in order to circumvent the hazardous effects associated with ice for- mation. The viscosity of the CPA increases exponentially with decreasing temperature, an effect which suppresses crystallization at high cooling rates. However, due to the thermophysical properties of the material and the shear size of the specimen, vitrification is often associated with large temperature gradients, leading to thermo-mechanical stresses that can result in structural