Bioengineered functional humanized livers: An emerging supportive modality to bridge the gap of organ transplantation for management of end-stage liver diseases

Table 1 Method adopted for whole complex organ acellularization techniques for different organisms

Organ	Acellularization agent	Perfusion method	Animal model	Reference
Heart	SDS, PEG, Triton X-100, and enzyme-based protocols deoxycholic acid	Antegrade coronary perfusion	Rat	[98]
	Trypsin, EDTA, NaN3, Triton X-100, and deoxycholic acid	Retrograde aortic perfusion	Pig	[65]
Lung	0.1% and 0.5% SDS	Antegrade pulmonary arterial perfusion	Rat	[63]
	CHAPS	Pulmonary artery and tracheal perfusion	Rat	[66]
	Triton X-100 and sodium deoxycholate	Right ventricle and tracheal perfusion	Mouse	[99]
Liver	Triton X-100 plus 0.1% SDS	Portal vein perfusion	Rat	[100]
	SDS		Rat	[70]
	1% Triton X-100 and 0.1% ammonium hydroxide		Mouse, rat, ferret, rabbit and pig	[69]
	0.25% and 0.5% SDS		Pig	[101]
	Sodium citrate + SDS + Triton-X-100	Hepatic artery perfusion	Rat	[74]
Kidney	0.5, 3, 6, 10% Triton X-100, 5 mM	Renal artery perfusion	Rat	[71]
	calcium chloride, 5 mM magnesium sulfate, 1 M sodium chloride, DNase, and 4% sodium deoxycholate		Rat	[72]
	3% Triton X-100, DNase, and 4% SDS
	1% SDS and 1% Triton X-100
	1% Triton X-100 and 0.1% ammonium hydroxide		Pig	[68]
	Heparin and antibiotic-containing physiological saline, 0.1-1.0% SDS, 0.1% Triton-X-100 and 0.0025% deoxyribonuclease 1		Goat	[75]

Table 2 Study outcome and major limitations of different types of acellularization techniques adopted for different types of whole organ scaffold development

Organ	Acellularization	Study out come	Limitation	References
	Method
Rat liver	Perfusion with detergents (SDS, Triton X-100)	Perfusion with SDS removes most of cells, damages the ECM when treated with Triton X-100 and removes 97 % of DNA	SDS damages the ECM	[69,74]
Porcine liver	Mechanical perfusion (electroporation)	Most of the cells are removed, preserves the blood vessels	Disruption of microfilament and microtubule	[102]
Mouse heart	Enzymatic, detergents, Acids	Cells are removed	Damages the ECM proteins, poorly maintains the 3D architecture	[103]
Porcine trachea	Enzymatic (trypsin) non-enzymatic (EDTA), detergent (Triton X-100) and deionized Water	Cells are removed, clear the cell debris	Disruption of glycosaminoglycan, reduce the laminin and fibronectin	[104]
Rat kidney	Perfuse with SDS, deionized water, dTriton X-100 and PBS along with antibiotics	Twice filtration is observed	Loss of cell-mediated functions like transport of solutes	[105]
Rat heart	Perfused with detergents		Long-term cell survival, oxygen tension and continuous rhythmic beating	[63,98]
Goat kidney	Perfused with Trypsin- EDTA in PBS, perfuse antibiotics and then with SDS in PBS	Cells are removed, pore to pore interconnection in the scaffold		[75,106]

ECM: Extra cellular matrix.

Table 3 List of recent studies reporting use of omentum as transplantation site to support the lost organ function from ectopic transplantation of engineered tissues or grafts

Animal model	Site of transplantation	Mode of graft used	Results	Reference
Femoral bone of New Zealand rabbit was	Greater omentum on the left side	Free transplant of the greater omentum	Process of the callus formation and its mineralisation are much quicker and thicker on the defect that was covered with the free transplant of the greater omentum.	[107]
Pancreatectomized dogs	Spleen or Omentum	Islet auto-transplantation	Beta cell response to mild non-insulin induced hypoglycemia was normal, whereas the alpha cell response was not.	[108]
Murine carotid artery injury model	Omentum was applied to the injured vessel	Omentum + Omental progenitor cells	Omentum can directly contribute reparative progenitor cells to injured tissues upon treatment with Tβ4.	[109]
Nondiabetic nude rats	Omentum/kidney capsule	Perinatal porcine islet cell grafts	In both sites, the A-cell volume increased fourfold between weeks 1 and 10 reflecting a rise in A-cell number. In the omental implants, however, the cellular insulin reserves and the percent of proliferating cells were twofold higher than in kidney implants. In parallel, the blood vessel density in omental implants increased twofold, reaching a density comparable with islets in adult pig pancreas.	[110]
Diabetic rat and nonhuman primate (NHP) models	Intra-omental	In situ-generated adherent, resorbable plasma thrombin biologic scaffold	Improved metabolic function and preservation of islet cytoarchitecture, with reconstitution of rich intrainsular vascular networks in both species.	[21]
Adult male Spraguee Dawley rats	Omental transposition	Hepatic tissue sutured into the omentum mobilization of the omentum and transposition onto the left hepatic lobe	Omental transposition provided adequate microcirculation for proliferation of ectopic hepatic cells after liver resection.	[111]