Interpenetrating porous networks in HA-based

hydrogels

S. Vanessa Aguilar2/2/2011

Techniques Gas Foaming Porogen Leaching Solid 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, 2006 King 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. 2005

Tosihma et al, Arch Histol Cytol, 2004

Simple hydrogel porous network applied to spinal cord injury model

Willenberg et al. JBMR part A, 2006 Prang et al. Biomaterials, 2006

• Micro and macro analysis properties

• Mechanical testing• Handling properties• Self Adhesiveness• Swelling ratios• Degradation rate

Plan of WorkGoal: 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 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-CHAPS Alginate - kdp GMHA – kdp

Alginate – βcd GMHA - urea GMHA - urea

Courtesy of Scott Zawko

Parameters Techniques

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

• Vtotal = V2 – V3

• The porosity is determined using• X = (V1 –V3)/Vtotal *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

http://news.thomasnet.com/news/sensors-monitors-transducers/sensors-detectors/force-load-strain-sensors/compression-tension-sensors/20

Parameters Techniques

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 templatingGoal: 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 ThomasJohn Fonner