Creation of Porous, Perfusable Microtubular Networks for Improved Cell Viability in Volumetric Hydrogels.

The creation of large, volumetric tissue-engineered constructs has long been hindered due to the lack of effective vascularization strategies. Recently, 3D printing has emerged as a viable approach to creating vascular structures; however, its application is limited. Here, we present a simple and controllable technique to produce porous, free-standing, perfusable tubular networks from sacrificial templates of polyelectrolyte complex and coatings of salt-containing citrate-based elastomer poly(1,8-octanediol-co-citrate) (POC). As demonstrated, fully perfusable and interconnected POC tubular networks with channel diameters ranging from 100 to 400 µm were created. Incorporating NaCl particulates into the POC coating enabled the formation of micropores (∼19 µm in diameter) in the tubular wall upon particulate leaching to increase the cross-wall fluid transport. Casting and cross-linking gelatin methacrylate (GelMA) suspended with human osteoblasts over the free-standing porous POC tubular networks led to the fabrication of 3D cell-encapsulated constructs. Compared to the constructs without POC tubular networks, those with either solid or porous wall tubular networks exhibited a significant increase in cell viability and proliferation along with healthy cell morphology, particularly those with porous networks. Taken together, the sacrificial template-assisted approach is effective to fabricate tubular networks with controllable channel diameter and patency, which can be easily incorporated into cell-encapsulated hydrogels or used as tissue-engineering scaffolds to improve cell viability.

4-Methylumbelliferone-Functionalized Polyphosphazene and Its Assembly into Biocompatible Fluorinated Nanocoatings with Selective Antiproliferative Activity.

Advanced multifunctional biomaterials are increasingly relying on clinically dictated patterns of selectivity against various biological targets. Integration of these frequently conflicting features into a single material surface may be best achieved by combining various complementary methodologies. Herein, a drug with a broad spectrum of activity, i.e., 4-methylumbelliferone (4-MU), is synthetically multimerized into water-soluble anionic macromolecules with the polyphosphazene backbone. The polymer structure, composition, and solution behavior are studied by 1H and 31P NMR spectroscopy, size-exclusion chromatography, dynamic light scattering, and UV and fluorescence spectrophotometry. To take advantage of the clinically proven hemocompatibility of fluorophosphazene surfaces, the drug-bearing macromolecule was then nanoassembled onto the surface of selected substrates in an aqueous solution with fluorinated polyphosphazene of the opposite charge using the layer-by-layer (LbL) technique. Nanostructured 4-MU-functionalized fluoro-coatings exhibited a strong antiproliferative effect on vascular smooth muscle cells (VSMCs) and fibroblasts with no cytotoxicity against endothelial cells. This selectivity pattern potentially provides the opportunity for highly desirable fast tissue healing while preventing the overgrowth of VSMCs and fibrosis. Taken together with the established in vitro hemocompatibility and anticoagulant activity, 4-MU-functionalized fluoro-coatings demonstrate potential for applications as restenosis-resistant coronary stents and artificial joints.

Characterization of a prevascularized biomimetic tissue engineered scaffold for bone regeneration.

Significant bone loss due to disease or severe injury can result in the need for a bone graft, with over 500,000 procedures occurring each year in the United States. However, the current standards for grafting, autografts and allografts, can result in increased patient morbidity or a high rate of failure respectively. An ideal alternative would be a biodegradable tissue engineered graft that fulfills the function of bone while promoting the growth of new bone tissue. We developed a prevascularized tissue engineered scaffold of electrospun biodegradable polymers PLLA and PDLA reinforced with hydroxyapatite, a mineral similar to that found in bone. A composite design was utilized to mimic the structure and function of human trabecular and cortical bone. These scaffolds were characterized mechanically and in vitro to determine osteoinductive and angioinductive properties. It was observed that further reinforcement is necessary for the scaffolds to mechanically match bone, but the scaffolds are successful at inducing the differentiation of mesenchymal stem cells into mature bone cells and vascular endothelial cells. Prevascularization was seen to have a positive effect on angiogenesis and cellular metabolic activity, critical factors for the integration of a graft.

Mechanical and biological evaluation of a hydroxyapatite-reinforced scaffold for bone regeneration.

With over 500,000 bone grafting procedures performed annually in the United States, the advancement of bone regeneration technology is at the forefront of medical research. Many tissue-engineered approaches have been explored to develop a viable synthetic bone graft substitute, but a major challenge is achieving a load-bearing graft that appropriately mimics the mechanical properties of native bone. In this study, sintered hydroxyapatite (HAp) was used to structurally reinforce a scaffold and yield mechanical properties comparable to native bone. HAp was packed into a cylindrical framework and processed under varying conditions to maximize its mechanical properties. The resulting HAp columns were further tested in a 6-week degradation study to determine their physical and mechanical response. The cellular response of sintered HAp was determined using a murine preosteoblast cell line, MC3T3-E1. Cell viability and morphology were studied over a one-week period and MC3T3-E1 differentiation was determined by measuring the alkaline phosphatase levels. Finite element analysis was used to determine the columns' geometric configuration and arrangement within our previously developed composite bone scaffold. It was determined that incorporating four cylindrical HAp columns, fabricated under 44 MPa of pressure and sintered at 1200°C for 5 hr, led to load-bearing properties that match the yield strength of native whole bone. These preliminary results indicate that the incorporation of a mechanically enhanced HAp structural support system is a promising step toward developing one of the first load-bearing bone scaffolds that can also support cell proliferation and osteogenic differentiation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 732-741, 2019.