In this study, we describe composite scaffolds composed of synthetic and natural materials with physicochemical properties suitable for tissue engineering applications. Fibrous scaffolds were co-electrospun from a blend of a synthetic biodegradable polymer (poly(lactic-co-glycolic acid), PLGA, 10% solution) and two natural proteins, gelatin (denatured collagen, 8% solution) and alpha-elastin (20% solution) at ratios of 3:1:2 and 2:2:2 (v/v/v). The resulting PLGA-gelatin-elastin (PGE) fibers were homogeneous in appearance with an average diameter of 380 +/- 80 nm, which was considerably smaller than fibers made under identical conditions from the starting materials (PLGA, 780 +/- 200 nm; gelatin, 447 +/- 123 nm; elastin, 1060 +/- 170 nm). Upon hydration, PGE fibers swelled to an average fiber diameter of 963 +/- 132 nm, but did not disintegrate. Importantly, PGE scaffolds were stable in an aqueous environment without crosslinking and were more elastic than those made of pure elastin fibers. To investigate the cytocompatibility of PGE, we cultured H9c2 rat cardiac myoblasts and rat bone marrow stromal cells (BMSCs) on fibrous PGE scaffolds. We found that myoblasts grew equally as well or slightly better on the scaffolds than on tissue-culture plastic. Microscopic evaluation confirmed that myoblasts reached confluence on the scaffold surfaces while simultaneously growing into the scaffolds. Histological characterization of the PGE constructs indicated that BMSCs penetrated into the center of scaffolds and began proliferating shortly after seeding. Our results suggest that fibrous scaffolds made of PGE and similar biomimetic blends of natural and synthetic polymers may be useful for engineering soft tissues, such as heart, lung, and blood vessels.
Many studies on phage biology are based on isolation methods that may inadvertently select for narrow-host-range phages. Consequently, broad-host-range phages, whose ecological significance is largely unexplored, are consistently overlooked. To enhance research on such polyvalent phages, we developed two sequential multihost isolation methods and tested both culturedependent and culture-independent phage libraries for broad infectivity. Lytic phages isolated from activated sludge were capable of interspecies or even interorder infectivity without a significant reduction in the efficiency of plating (0.45 to 1.15). Two polyvalent phages (PX1 of the Podoviridae family and PEf1 of the Siphoviridae family) were characterized in terms of adsorption rate (3.54 ؋ 10 ؊10 to 8.53 ؋ 10 ؊10 ml/min), latent time (40 to 55 min), and burst size (45 to 99 PFU/cell), using different hosts. These phages were enriched with a nonpathogenic host (Pseudomonas putida F1 or Escherichia coli K-12) and subsequently used to infect model problematic bacteria. By using a multiplicity of infection of 10 in bacterial challenge tests, >60% lethality was observed for Pseudomonas aeruginosa relative to uninfected controls. The corresponding lethality for Pseudomonas syringae was ϳ50%. Overall, this work suggests that polyvalent phages may be readily isolated from the environment by using different sequential hosts, and this approach should facilitate the study of their ecological significance as well as enable novel applications.T he total bacteriophage (phage) population on Earth is estimated at 10 31 or more, making phages by far the most abundant biological entities on the planet (1, 2). As such, phages exert a significant influence over global biogeochemical cycles (3, 4) and are important drivers of bacterial diversity (5). Considering their ecological importance and value as a potential genetic resource, increasing our fundamental understanding of phage biology may facilitate the development of novel applications. However, research on phage diversity and ecology may be inadvertently limited by the use of biased isolation techniques that preferentially select for narrow-host-range phages (6, 7), while-broad hostrange phages are consistently overlooked.The classic approach to isolate and study phages is typically performed with high-density, nutrient-rich batch monocultures grown under planktonic conditions and most often results in the isolation of narrow-host-range phages (8)(9)(10).Previous studies have demonstrated the existence of polyvalent phages, among which the temperate phages P1 and Mu are the most studied (11, 12). However, their broad-host-range properties were discovered accidently, and few studies have explored methods for isolating and enriching polyvalent phages. Jensen et al. developed a multiple-host enrichment method to identify phages capable of interclass infectivity (13), and Bielke et al. used a sequential isolation method to isolate phages with intergenus infectivity (14). However, these phage isolation methods have...
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