Interpenetrating porous networks in HA-based hydrogels S. Vanessa Aguilar 2/2/2011

TechniquesGas FoamingPorogen LeachingSolid free Form Fabrication Soft Lithography Model Description Monomer is mixed with sodium bicarbonate as a foaming agent which react with acid to form carbon dioxide gas bubbles. Polymer is dissolved in a solvent containing disperse porogen. Solvent is evaporated and porogen is leached out. Layer-by-layer microstereolythography system that allow 3D microfabrication from images created by CAD programs Master mold is first created in silicon wafers. PDMS is then cast, cured, and peeled from the silicon master. Polymer is then place in the PDMS mold. Properties Interconnected pores Pore size depend on amount of salt and acidity Pores diameter >100 um Interconnected pores Pore diameter < 100 um Pores similar to the structure of salt matrix. Define pores structures Pore diameter > 100 um Smallest feature is 20 um Define pores structures Resolution limit ~ 0.1 um Advantages Creates very high porosity superporous hydrogels Compatible with biopolymers ( Room Temp) Complex micro- architectures Entrapping multiple biochemical factors High precision features Disadvantages Random porosity Timing of crosslink and gas foaming is critical Not compatible with biopolymers (high Temp) Little control over connectivity of the pores Lead to Random porosity (longer time exposure) No interconnecting pores Very expensive 2D Very expensive Reference Chen and Park, JBMR, 1998 Murphy et al, Tissue Eng, 2002 Lu et al, JBMR, 2006King et al, Adv Mater, 2004

Mimicking Human Tissue  Nature of human tissue  Vasculature and bronchi Brisken et al, J Mammary Gland Biol, 2006 Tawhai, et al. J. Appl. Phisiol Tosihma et al, Arch Histol Cytol, 2004

Simple hydrogel porous network applied to spinal cord injury model Willenberg et al. JBMR part A, 2006Prang et al. Biomaterials, 2006

Micro and macro analysis properties Mechanical testing Handling properties Self Adhesiveness Swelling ratios Degradation rate Plan of Work Goal: We aim to mimic tissues that contain two or more networks of pores by creating entwined porous networks within the same hydrogel, allowing for defined cellular control. Porosity Diameter of pores Degree of branching Aim 1: Characterize the micro-scale physical parameters of GMHA-based films using 4 different crystallites Aim 2: Characterize the macro-scale properties of GMHA-based films using 4 different crystallites Aim 3: Construct multiple crystalline networks within a single hydrogel construct Aim 3: Construct multiple crystalline networks within a single hydrogel construct

Aim 1: Experimental Set Up urea β-Cyclodextrin Potassium dihydrogen phosphate CHAPS Keep the hydrogel material constant and change processing Courtesy of Scott Zawko

Aim 1: Different crystallites GMHA-CHAPSAlginate - kdp GMHA – kdp Alginate – βcdGMHA - urea Courtesy of Scott Zawko

ParametersTechniques Mean pore diameter Polarized and phase microscopy Cryo SEM Mercury Intrusion Porosimetry Degree of Branching Image analysis using Imaris Fractal analysis Total volume of pores and pores density V total = V 2 – V 3 The porosity is determined using X = (V 1 –V 3 )/V total *100 [1] Aim 1: Micro Structure Characterization Imaris Filament Tracer Wang and Chau, Soft Matter, 2009 Fractal Analysis Jha, A.K, et al, Macromolecules, 2009 [1] Kim and Chu, JBMR, 2000

Aim 2: Macroscopic characterization transducers/sensors-detectors/force-load-strain- sensors/compression-tension-sensors/20 ParametersTechniques Young’s Modulus Ultimate Tensile Strength Elongation (elasticity) ASTM D 638 V – Tensile test for plastics / hydrogel films Swelling Ratio (Wd – Ws) /Wd = SR Degradation Rate Enzymatic degradation Chelating degradation Hydrolysis degradation % wt loss per hour

Aim 3: Dual crystal templating Goal: Create hydrogel construct with two independent but interwoven porous networks. Shown below: Variety of cell seeding for each network

Acknowledgments PI: Dr. Christine Schmidt Post-Doc: Dr. Zin Khaing Dr. John Hardy Graduate Students: Sarah Mayes Richelle Thomas John Fonner