TABLE 2.
Recent applications of stratification in vascular interface tissue engineering.
| Reference(s) | Stratification | Targeted interfacial tissues | Geometry and stratification direction | Material(s) used | Fabrication method(s) | Primary stratification value(s) |
|---|---|---|---|---|---|---|
| Thomas et al.63 and Zhang et al.71 | Porosity, Material | Tunicae of the vasculature | 3 layer, cylindrical (radial layering) | Gelatin, elastin, polyglyconate | Electrospinning process | Molar ratio of trilayered GE/GEM/GM: 4:1/1:2:8/1:4, Porosity: 67–82% |
| Gauvin et al.14 (Fig. 3a) | Cell type | Tunicae of the vasculature | 2 layer, cylindrical (radial layering) | Smooth muscle cells, dermal fibroblasts | Cells grown on gelatin-coated tissue culture plate cell sheets rolled on tubular shaft in various configurations | Identical density of smooth muscle cells and fibroblasts |
| Kim et al.27 | Porosity | Tunicae of the vasculature | 2 layer, cylindrical (radial layering) | PLCL and sodium chloride | Gelatin PLCL spun onto tubular rod pretreated with NaCl, salt then leached out | Fibrous layer pore size ~153 μm and porosity ~67%, dual layer construct pore size average ~80 μm and porosity ~45% |
| Ju et al.24 | Fiber diameter, Pore area | Tunicae of the vasculature | 2 layer, cylindrical (radial layering) | Inner layer fibers: 5 w/v% PCL/collagen solution, Outer layer fibers: 15 w/v% PCL/collagen solution | Electrospinning process | Inner layer: FD ~0.3 μm, PA ~2 μm2, Outer layer: FD ~4.5 μm, PA ~1200 μm2 |
| Chen et al.7 | Drug loading, Eluted drug concentration | Bulk tissue and neovasculature | 2 layer (axial layering) | VEGF on mixture of PLGA 85:15 and 75:25 microspheres encapsulated with PDGF | PDGF microspheres from double emulsion, VEGF added ectopically by lyophilization in MVM alginate | Mathematical modeling for VEGF shows gradient of concentrations: 0–250 ng/mL, magnitude proportional to loading values of each protein |
| Asakawa et al.2 (Fig. 3b) | Cell type | Bulk tissue and neovasculature | 3 layer (axial layering) | Human umbilical vein endothelial cells and human dermal fibroblasts | Cell layers pressed together with plunger and 35 mm PIPAAm dish apparatus | Endothelial cells at 333,000 cells/layer, fibroblasts at 666,000 cells/layer |
| Lee et al.33 | Cell concentration | Skin layering, potential incorporation with vasculature | 10 layer, square or plus-shaped (axial layering) | Type I collagen, fibroblasts, keratinocytes | 3D freeform fabrication: bioprinter and automated dispensing nozzles | 106 cells per layer (or 93 cells per droplet)—acellular layers |
| Hoganson et al.20 (Fig. 3c) | Vasculature diameter, length, and incidence | Bulk tissue and neovasculature | 7 level, radial layering | Sylgard 184 poly(dimethylsiloxane) | PDMS cast into stainless steel made with soft lithography | Vessel diameters: 267–727 μm, pressures: 3–9 mmHg |
| Reference(s) | Interface and characteristics | Mechanical properties | Biological model(s) | Bulk tissue regenaration | Interface regeneration or cell interaction |
|---|---|---|---|---|---|
| Thomas et al.63 and Zhang et al.71 | Layered electrospinning and prolonged exposure to desiccant | Trilayered construct tensile strength: 3 MPa, tensile modulus: 20 MPa failure strain: 140%, native femoral artery TS: 3 MPa, TM: 9 MPa | Not directly evaluated | Not directly evaluated | Delamination of inner layer with degradation studies |
| Gauvin et al.14 (Fig. 3a) | Well-integrated tissue matrix | UTS ~2 MPa, BP ~1000 mmHg, LM ~13 MPa, and FS ~35% for single step method | Cultured layered constructs in vitro for 14 days after 28-day cell sheet formation and construct rolling | Type I collagen present in all layers, while elastin present only with certain rolling methods utilizing fibroblasts | Layer integration and thickness dependent upon cell type and assembly method |
| Kim et al.27 | SEM reveals integration between inner compact layer and gel fibers | UTS ~3 MPa, BP ~900 mmHg, LM ~0.82 MPa, and FS ~604% | Blood infusion to evaluate leakage and burst pressure | Not directly evaluated | Not directly evaluated |
| Ju et al.24 | SEM shows integrated but distinct layers | Inner layer: UTS ~3 MPa, LM ~2 MPa, FE ~90%; Outer layer: UTS ~0.75 MPa LM ~0.26 MPa, FE ~734% | Smooth muscle cells and endothelial cells cultured in vitro | Endothelial cell adhesion localized to lumen, while SMCs infiltrated outer layer. Both cell types maintained native phenotypes | Layers and cell types segregated, interface had lowest cell density |
| Chen et al.7 | Layers pressed together at 1500 psi | Not directly evaluated | Mathematical modeling and in vivo: mouse hindlimb ischemia for 2 and 6 weeks | No major limitations of bulk connective tissue regeneration | Neovasculature interface with bulk tissue more mature, less dense, with sequential delivery of VEGF and PDGF from different layers |
| Asakawa et al.2 (Fig. 3b) | Layer fused with fibrin gel at 37 °C | Not directly evaluated | Multilayered sheets cultured for 3 or 7 days in vitro | Lumen area greatest in constructs with two fibroblast layers on top of a single endothelial cell layer, as opposed to single endothelial layer between two fibroblast layers | Multiple, distinct tubular formation via immunofluorescence confocal laser micrograph |
| Lee et al.33 | Layers crosslinked by nebulized aqueous sodium bicarbonate | Not directly evaluated | In vitro: primary adult human dermal fibroblasts and epidermal keratinocytes, cultured for 8 days at most | No statistical difference in tissue properties between printed cells and control | Cell types localized to intended layers |
| Hoganson et al.20 (Fig. 3c) | Not directly evaluated | Shear stress variation between 11 and 23 dyne/cm3. Other properties not evaluated | Mathematical modeling and in vitro loading with anticoagulated sheep blood | Not directly evaluated | Not directly evaluated |
PLCL, poly(L-lactide-co-e-caprolactone); PCL, polycaprolactone; VEGF, vascular endothelial growth factor; PLGA, poly(D,L-latide-co-glycolic acid); PDGF, platelet-derived growth factor; NaCl, sodium chloride; MVM, alginate gels with >50% mannuronic units; PIPPAm, poly(N-isopropylacrylimide); PDMS, poly(dimethylsiloxane), GE, gelatin-elastin; GEM, gelatin-elastin-maxon; GM, gelatin-maxon; FD, Fiber diameter; PA, pore area; SEM, scanning electron microscopy; TS, tensile strain; TM, tensile modulus; UTS ultimate tensile strength; BP, burst pressure; LM, longitudinal modulus; FS, failure strain; FE, fracture elongation; SMC, smooth muscle cell.