The role of pore size on vascularization and tissue remodeling in PEG hydrogels

Obtaining functional capillaries through the bulk has been identified as a major challenge in tissue engineering, particularly for critical-sized defects. In the present study, a multilayered scaffold system was developed for bone tissue regeneration, designed for through-the-thickness vascularization of the construct. The basic principle of this approach was to alternately layer mesenchymal stem cell-seeded nanofibers (osteogenic layer) with microfibers or porous ceramics (osteoconductive layer), with an intercalating angiogenic zone between the two and with each individual layer in the microscale dimension (100-400 mm). Such a design can create a scaffold system potentially capable of spatially distributed vascularization in the overall bulk tissue. In the cellular approach, the angiogenic zone consisted of collagen/fibronectin gel with endothelial cells and pericytes, while in the acellular approach, cells were omitted from the zone without altering the gel composition. The cells incorporated into the construct were analyzed for viability, distribution, and organization of cells on the layers and vessel development in vitro. Furthermore, the layered constructs were implanted in the subcutaneous space of nude mice and the processes of vascularization and bone tissue regeneration were followed by histological and energy-dispersive X-ray spectroscopy (EDS) analysis. The results indicated that the microenvironment in the angiogenic zone, microscale size of the layers, and the continuously channeled architecture at the interface were adequate for infiltrating host vessels through the bulk and vascularizing the construct. Through-thethickness vascularization and mineralization were accomplished in the construct, suggesting that a suitably bioengineered layered construct may be a useful design for regeneration of large bone defects.

mentioning

confidence: 99%

Bone Tissue Engineering with Multilayered Scaffolds—Part I: An Approach for Vascularizing Engineered Constructs In Vivo

Sathy

Mony

Menon

et al. 2015

“…[26][27][28][29] Co-culture cell spheroids were prepared with 2500 HUVECs and 2500 HUASMCs in endothelial basal media supplemented with 2% fetal bovine serum, bovine brain extract, EGF, hydrocortisone, ascorbic acid, and gentamicin containing 0.24% (w/v) carboxymethylcellulose (Sigma). Spheroids were seeded into a nonadherent 96-well round bottom plate at 37°C and 5% CO 2 for 24 h. The resulting spheroids were encapsulated in the hydrogels by placing the spheroid in the prepolymer solution and polymerizing into the hydrogel network.…”

Section: Neovascularization Model In Vitromentioning

confidence: 99%

Controlled Proteolytic Cleavage Site Presentation in Biomimetic PEGDA Hydrogels Enhances Neovascularization In Vitro

Sokic

Papavasiliou

2012

The volume of tissue that can be engineered is limited by the extent to which vascularization can be stimulated within the scaffold. The ability of a scaffold to induce vascularization is highly dependent on its rate of degradation. We present a novel approach for engineering poly (ethylene glycol) diacrylate (PEGDA) hydrogels with controlled protease-mediated degradation independent of alterations in hydrogel mechanical and physical properties. Matrix metalloproteinase (MMP)-sensitive peptides containing one (SSite) or three (TriSite) proteolytic cleavage sites were engineered and conjugated to PEGDA macromers followed by photopolymerization to form PEGDA hydrogels with tethered cell adhesion ligands of YRGDS and with either single or multiple MMPsensitive peptide domains between cross links. These hydrogels were investigated as provisional matrices for inducing neovascularization, while maintaining the structural integrity of the hydrogel network. We show that hydrogels made from SSite and TriSite peptide-containing PEGDA macromers polymerized under the same conditions do not result in alterations in hydrogel swelling, mesh size, or compressive modulus, but result in statistically different hydrogel degradation times with TriSite gels degrading in 1-3 h compared to 2-4 days in SSite gels. In both polymer types, increases in the PEGDA concentration result in decreases in hydrogel swelling and mesh size, and increases in the compressive modulus and degradation time. Furthermore, TriSite gels support vessel invasion over a 0.3-3.6 kPa range of compressive modulus, while SSite gels do not support invasion in hydrogels above compressive modulus values of 0.4 kPa. In vitro data demonstrate that TriSite gels result in enhanced vessel invasion areas by sevenfold and depth of invasion by twofold compared to SSite gels by 3 weeks. This approach allows for controlled, localized, and cell-mediated matrix remodeling and can be tailored to tissues that may require more rapid regeneration and neovascularization.

“…[11][12][13] A number of reports have highlighted the importance of porosity within skinmimetic materials in facilitating fibroblast, endothelial, and stem cell infiltration; nutrient transport for better graft survival; and neovascularization. [14][15][16] On the other hand, if pores are too large, cells may have a difficult time filling the void with ECM. Excessive porosity or large pore diameters may also compromise scaffold mechanical properties.…”

mentioning

confidence: 99%

Microporous Dermal-Like Electrospun Scaffolds Promote Accelerated Skin Regeneration

Bonvallet

Culpepper

Bain

et al. 2014

The goal of this study was to synthesize skin substitutes that blend native extracellular matrix (ECM) molecules with synthetic polymers which have favorable mechanical properties. To this end, scaffolds were electrospun from collagen I (col) and poly(e-caprolactone) (PCL), and then pores were introduced mechanically to promote fibroblast infiltration, and subsequent filling of the pores with ECM. A 70:30 col/PCL ratio was determined to provide optimal support for dermal fibroblast growth, and a pore diameter, 160 mm, was identified that enabled fibroblasts to infiltrate and fill pores with native matrix molecules, including fibronectin and collagen I. Mechanical testing of 70:30 col/PCL scaffolds with 160 mm pores revealed a tensile strength of 1.4 MPa, and the scaffolds also exhibited a low rate of contraction ( < 19%). Upon implantation, scaffolds should support epidermal regeneration; we, therefore, evaluated keratinocyte growth on fibroblast-embedded scaffolds with matrix-filled pores. Keratinocytes formed a stratified layer on the surface of fibroblast-remodeled scaffolds, and staining for cytokeratin 10 revealed terminally differentiated keratinocytes at the apical surface. When implanted, 70:30 col/PCL scaffolds degraded within 3-4 weeks, an optimal time frame for degradation in vivo. Finally, 70:30 col/PCL scaffolds with or without 160 mm pores were implanted into full-thickness critical-sized skin defects. Relative to nonporous scaffolds or sham wounds, scaffolds with 160 mm pores induced accelerated wound closure, and stimulated regeneration of healthy dermal tissue, evidenced by a more normal-appearing matrix architecture, blood vessel in-growth, and hair follicle development. Collectively, these results suggest that microporous electrospun scaffolds are effective substrates for skin regeneration.