Scaffold Design To Prime Soft Tissue Regeneration and Replacement Antonio D’Amore 1,2,3 and William R. Wagner 1 1 Department of Bioengineering, Swanson School of Engineering and The McGowan Institute for Regenerative Medicine,University of Pittsburgh 2 Dipartimento di Ingegneria Chimica, Gestionale,Informatica e Meccanica, University of Palermo 3 Fondazione RiMED, Italy
Altered tissue mechanics can lead to adverse tissue remodeling and regeneration
Ventricular wall thinning, stiffening in ischemic cardiomyopathy with increased wall stress Image: Jessup M, Brozena S. Heart Failure. N Engl J Med 348: 2007 (2003).
In tissue engineering, mechanical training is often necessary to develop correctly anisotropic, mechanically robust tissue Bioreactors for cyclic loading Actuating arm Stationary Pin Media 10 mm x 19 mm bath Bioreactor well Laboratory of Dr. Michael Sacks
Temporarily altering the mechanical environment of the tissue will alter remodeling, regeneration F F
How might the ventricular wall mechanical environment be altered with localized therapy? X
Elastomeric patch placement on 2 week old infarct (rat) examined at 8 weeks Infarct control PEUU patch patch × P S 5mm 5mm Create myocardial infarction by ligating left anterior descending coronary artery 2 weeks post-infarct, implant PEUU scaffold to cover infarcted region of left ventricle Examine at 8 weeks 5mm 5mm
Ventricular wall is significantly thicker and softer than controls H&E staining Infarction alone 500um Explant at 8 weeks PEUU patch Fujimoto KL, et al. J Am Coll Cardiol 49:2292 (2007).
Echocardiography FAC (fractional area change) EDA (end-diastolic LV cavity area) † 0.70 30 Fractional Area Change (%) End-diastolic Area (cm 2 ) † 0.60 * † * 20 0.50 † † 10 0.40 Pre 4w 8w Pre 4w 8w Patch Infarction control Mean ± SEM, Two-factor repeated ANOVA: Fujimoto K, et al. J Am Coll Cardiol . 49: 2292 (2007) *; p <0.05 between groups, †; p <0.05 vs. 0w within group
Mechanical support in the vascular system Could a mechanically protective elastic matrix be deposited around a saphenous vein for arterial bypass?
Spinning a temporary, conformal, elastic jacket on a vein to protect from sudden expansion at arterial pressure In collaboration with the El-Kurdi MS, et al. Biomaterials 29:3213 laboratory of Dr. David Vorp (2008).
Tuning wrap “mechanical degradation” PEUU/elastin/collagen El-Kurdi MS, et al. Biomaterials 29:3213 (2008).
Mechanical support for developing, engineered tissue Elastomeric scaffolds for the development of tissue engineered cardiovascular structures with matching mechanics (blood vessel & pulmonary valve)
An appropriately elastic scaffold, seeded with precursor cells, will match the compliance of the native artery and exhibit higher patency Soletti L, et al. Biomaterials 27:4863 (2006). Nieponice, et al. Tissue Eng A 16:1215 (2010). Collaboration with He W, et al. Cardiovasc Eng Tech (2011). laboratory of Dr. David Nieponice A, et al. Biomaterials 29:825 (2008). Vorp Soletti L, et al. Acta Biomater 5:2901 (2010).
Critical gap: Biodegradable materials with tunable properties to meet the hypothesized needs for soft tissue mechanical protection and tissue engineering
Structure Function Design Scales Nano (molecular) Micro Meso Macro
Molecular design: biodegradable thermoplastic elastomers Poly(ester urethane) urea (PEUU) O O HO(CH 2 ) 5 C C(CH 2 ) 5 OH + OCN(CH 2 ) 4 NCO Polycaprolactone diol 1,4-diisocyanatobutane ( Mw =2000) 70 o C, Sn(OCt) 2 patch Prepolymer H 2 N(CH 2 ) 4 NH 2 Putrescine O O O O O O ...HNRNHCNH(CH 2 ) 4 NHCO(CH 2 ) 5 C C(CH 2 ) 5 OCNH(CH 2 ) 4 NHCNHRNH...
Tuning degradation to be faster with polyether blocks Poly(ether ester urethane) urea
Creating enzymatically labile elastomers O O HO(CH 2 CH 2 O) n H + (MW=600 or 1000) O O O(CH 2 CH 2 O) n C(CH 2 ) 5 O m OH HO O(CH 2 ) 5 C m + OCN(CH 2 ) 4 NCO O O O O O(CH 2 CH 2 O) n C(CH 2 ) 5 O m OCN(CH 2 ) 4 NHC O(CH 2 ) 5 C m CNH(CH 2 ) 4 NCO elastase + AAK lability O O O O O O ... ... CN(CH 2 ) 4 NHC CNH(CH 2 ) 4 NCNHAAKNH KAANH O(CH 2 ) 5 C m O(CH 2 CH 2 O) n C(CH 2 ) 5 O m
Tuning degradation to be slower with a polycarbonate blocks Hong Y, et al. Biomaterials 31:4249 (2010)
Tuning mechanics with labile segment selection and length Diethylene glycol Diethylene glycol =PCL, PTMC or PVLCL Diethylene glycol BDI Putrescine PUU Ma Z., et al. Biomacromolecules 12:3265 (2011)
Tuning mechanics with labile segment selection and length 7 PUU-PTMC1500 6 PUU-PTMC2500 Stress (Mpa) 5 PUU-PCL2000 PUU-PVLCL2246 4 3 PUU-PTMC5400 2 PUU-PVLCL6000 1 0 0 10 20 30 40 50 Strain (%) Ma Z., et al. Biomacromolecules 12:3265 (2011)
Structure Function Design Scales Nano (molecular) Micro Meso Macro
Introduction: overview on the modeling strategy Artificial Input: Output: network Mechanical Image model 1: Material Mechanical FEM response generation sample Analysis testing simulation from 1: Macro level experimental 2: SEM 2: Micro level data From the micro-structure to the mechanical response at micro and macro levels Input: Artificial Output: Optimal network model clinical FEM micro- Material application, generation architecture simulation fabrication targeted macro- in the design meso mechanical identification parameters space response From the targeted mechanical behavior at micro and macro levels to the material micro-structure
Input: 1: Material Micro-control: electrohydrodynamic processing sample 2: SEM Isotropic VSMCs int C A 1 µm 1 µm Microspheres int Anisotropic B D 1 µm 10 µm fiber intersection density can be controlled by the rastering speed fiber main angle of orientation can be controlled by the mandrel speed
Input: Methods: material fabrication 1: Material sample 2: SEM Isotropic VSMCs int C A 1 µm 1 µm 1 µm 1 µm Microspheres int Microspheres int Anisotropic Anisotropic B D 1 µm 1 µm 10 µm 10 µm fiber intersection density can be controlled by the rastering speed fiber main angle of orientation can be controlled by the mandrel speed
Input: Methods: image analysis and 1: Material material characterization sample 2: SEM ϑ 180 ----- OI ___ ϑ 140 100 60 20 [*] D’Amore Stella, Wagner Sacks Characterization of the Complete Fiber Network Topology of Planar Fibrous Tissues and Scaffolds. Biomat 2010; 31:(20) 5345-5354
Mechanical Methods: mechanical testing testing A B [*] [*] Sacks. Biaxial Mechanical Evaluation of Planar Biological Materials. Journal of Elasticity 61: 199 – 246, 2000.
Mechanical Methods: mechanical testing testing A [*] λ NAR = 1.3 NAR = 1 Nuclear Aspect Ratio from confocal microscopy [*] Stella , Wagner et al et al. Tissue-to-cellular level deformation coupling in cell micro-integrated elastomeric scaffolds. Biomaterials Volume 29, Issue 22, August 2008, Pages 3228-3236 .
Artificial Methods: mechanical modeling, network model generation from artificial fiber network generation experimental data Anisotropic model • Size=120 µm • OI = 0.65 • Diameter= 0.5 µm • Int Den=0.28 [n/ µm 2 ] [*] D’Amore et al. Micro Scale Based Mechanical Models for Electrospun Poly (Ester Urethane) Urea Scaffolds. Proceedings of the 7th European Solid Mechanics Conference (ESMC2009) September 7-11 2009, Lisbon, Portugal.
FEM Methods: mechanical modeling, finite element model simulation • Mesh Topology Fiber network cast into finite element form (from 20 x 20 µm 2 to150 x 150 µm 2 ) . • Element Fibers idealized as truss elements (2000-3000 nodes, 10000 – 11000 elements ) ABAQUS (t2d2h) • Solver Static solution, Newton -Raphson method Large deformation enabled • Boundary conditions Equi-biaxial stress conditions
Output: Mechanical response Results: MESO LEVEL RESPONSE 1: Macro level 2: Micro level Confocal Model SEM [*] ε Changes in isotropic ES-PEUU fiber micro- architecture under biaxial stretch. [*] J Stella, W R Wagner et al. Scale dependent kinematics of fibrous elastomeric scaffolds for tissue engineering. Journal of Biomedical Materials Research. 2008. In press.
Output: Mechanical Results: MESO LEVEL RESPONSE response 1: Macro level 2: Micro level ( n=50 cells for each data point, model prediction solid line) Scaffold model under strip biaxial deformation. Red dots represent the experimental data, model prediction in black
Output: Mechanical Results: MICRO LEVEL RESPONSE response 1: Macro level 2: Micro level Single fiber initial shear modulus prediction [*] Kis A. et. al. Nanomechanics of Microtubules Phys. Rev. Lett. 89, 248101 (2002)
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