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Whole Organ Engineering

Organ engineering, as opposed to tissue engineering, poses significant challenges including the requirement for an immediately functional vascular network, functional parenchymal cells, and lymphatic and innervation potential. In recent years a promising approach for functional organ replacement has emerged: the decellularization of whole organs, providing an acellular three-dimensional scaffold composed of extracellular matrix (ECM). Importantly, the scaffold has been shown to retain the native vascular network of the organ (Figure 1).

Recent studies have shown that tissue/organ specific ECMs can support site appropriate cell phenotype and lineage-directed differentiation. It is intuitive that the native 3-dimensional architecture and microenviromental niche provided by the extracellular matrix are important for cell attachment and differentiation. By decellularizing the entire organ, most of the 3D structure of the ECM can be retained to provide a native framework for organ reconstruction.

The long term goal of this work is to establish the decellularization, recellularization with autologous cells (thus avoiding the need for subsequent immunosuppression), and transplantation criteria necessary to produce functional bioengineered organs for clinical translation.

The Badylak lab specifically focuses on whole liver and heart regeneration.


Engineering a Liver

To engineer a functional whole organ liver for treatment of end stage liver disease.

Approximately 27,000 deaths occur annually in the United States alone from end-stage liver disease. We are aggressively investigating a therapeutic whole organ replacement strategy that is based upon the concept that functional hepatic tissue can be engineered by the effective delivery of autologous hepatic parenchymal and non-parenchymal cells within a xenogeneic 3-dimensional scaffold composed of liver extracellular matrix (3D L-ECM). This approach would include immediate in-situ transplantation of the cell seeded scaffold, providing the requisite perfusion by the host circulation that supplies appropriate microenvironmental cues, nutrients, and signaling factors necessary for liver regeneration.

Figure 1: Snapshots of blue dye flowing through the vasculature of a three-dimensional rat liver ECM scaffold.

Recent studies have shown that tissue/organ specific ECMs can support site appropriate cell phenotype and lineage-directed differentiation. It is intuitive that the native 3-dimensional architecture and microenviromental niche provided by the extracellular matrix are important for cell attachment and differentiation.

By decellularizing the entire organ, most of the 3D structure of the ECM can be retained to provide a native framework for organ reconstruction. The long term goal of this work is to establish the decellularization, recellularization and transplantation criteria necessary to produce a fully functional bioengineered liver for organ transplantation and drug discovery.


Engineering a Heart

The use of Cardiac ECM (C-ECM) versus ECM derived for other tissue sources may promote faster myocardial reconstruction of functional tissue due to similar structure and function.

Our laboratory has shown that an entire porcine heart can be decellularized thus providing a platform for whole organ engineering (Fig. 2) [1]. The resultant decellularized heart provides a three-dimensional scaffold and microenvironment to support site-appropriate cell differentiation and spatial organization. The decellularization protocol is completed in less than 10 hours using pulsatile retrograde aortic perfusion with serial perfusion of an enzymatic, nonionic detergent, ionic detergent, and acid solution with hypotonic and hypertonic rinses to systemically remove cellular content. The resultant c-ECM retains collagen, elastin, glycosaminoglycans, and mechanical integrity.

Figure 2: Representative images of the gross appearance of intact porcine hearts subjected to decellularization by retrograde perfusion.

Our laboratory subsequently evaluated a patch of this c-ECM in a full-thickness right ventricle outflow tract repair compared to an inert Dacron in a rat model up to 4 months [2]. The Dacron patch was encapsulated with a fibrous capsule with minimal cellular infiltration, while the c-ECM patch remodeled into a dense connective tissue with scattered islands of striated cardiomyocytes (Fig. 3) and showed superior echocardiography results. This response was consistent with a previous study by our laboratory in which a decellularized biological scaffold derived from porcine bladder tissue was compared to a synthetic material for an LV-free wall infarction in a porcine animal model up to 3 months [3]. However, the constructive remodeling responses are not fully understood and are the subject of present study.

Figure 3: Immunofluorescent staining of a Dacron and cECM right ventricle explant. The Dacron patch explant had an intact endothelium but no cellular infiltration while the cECM patch explant had cellular infiltration with striation.

While these results are promising, the mechanism by which ECM promotes a constructive remodeling response is only partially understood. Further, the term ECM is not used in a consistent manner in the literature – there are different tissue sources and protocols that may result in different structures and fractions of remnant constituent proteins. Our laboratory is currently performing an extensive in-vitro characterization of the structure and cell-ECM interaction on ECM derived from cardiac and other tissue types treated with different detergents. Both cardiac and non-cardiac derived stem cells will be used to assess if the ‘seed’ or ‘soil’ is critical to a constructive remodeling response in cardiac tissue. The findings will be used to define the optimal tissue type and detergent treatment for a cardiac site-specific constructive remodeling response.

References:

  1. Robinson KA, Li J, Mathison M, Redkar A, Cui J, Chronos NA, Matheny RG, Badylak SF. Extracellular Matrix Scaffold for Cardiac Repair. Circulation. 2005 Aug 30;112(9 Suppl):I135-43. PMID: 16256789
  2. Wainwright JM, Czajka CA, Patel UB, Freytes DO, Tobita K, Gilbert TW, Badylak SF. Preparation of Cardiac Extracellular Matrix from an Intact Porcine Heart. Tissue Engineering Part C: Methods. 2009;16(3):525-532. PMID: 19702513
  3. Wainwright JM, Hashizume R, Fujimoto KL, Remlinger NT, Pesyna C, Wagner WR, Tobita K, Gilbert TW, Badylak SF. Right Ventricular Outflow Tract Repair with a Cardiac Biologic Scaffold. Cells Tissues Organs. 2011;15219:1-12. PMID: 22025093

 

 

Updated 20-Mar-2014