Unseeded Group Research Articles

The limit of targeting in networks

This paper studies the value of network-based targeting within a class of network games with strategic complements, where the designer can target a group of seed players as first movers. We define an effectiveness index, called the relative network synergy equivalent (RNSE), to quantify the effect of a network-based targeting intervention relative to across-the-board peer effect enhancement. We show that, regardless of the targeting policies and network structures, a universal and tight upper bound for this index is 2≈1.414. This upper bound is robust to considerations of revenue maximization, costly seeding, random seeding as the alternative benchmark, and multiple stages of moves. Compared with network-based targeting, peer effect enhancing policy has the advantage of being agnostic to the network structure. In the case of small synergy, we provide comparative statics of the RNSE index concerning the network structures: fixing the targeting policy, increasing network links within the seeded group or the unseeded group will decrease the index; meanwhile, adding links across these two groups will increase the index. Our analysis sheds light on policy choices between network-based targeting and peer effect enhancing policies.

Magnetic Resonance Imaging of Shear Stress and Wall Thickness in Tissue-Engineered Vascular Grafts.

Tissue-engineered vascular grafts (TEVGs) have demonstrated potential for treating congenital heart disease (CHD); however, quantitative imaging for tracking functional and structural remodeling of TEVGs has not been applied. Therefore, we evaluated the potential of magnetic resonance (MR) imaging for assessing TEVG wall shear stress (WSS) and wall thickness in a large animal model. Cell-seeded (n = 3) or unseeded (n = 3) TEVGs were implanted as inferior vena cava interposition grafts in juvenile lambs. Six months following implantation, two-dimensional phase-contrast MR imaging was performed at 3 slice locations (proximal, middle, and distal) to assess normalized WSS (i.e., WSS-to-cross sectional area). T2-weighted MR imaging was performed to assess TEVG wall thickness. Histology was qualitatively assessed, whereas immunohistochemistry was semiquantitatively assessed for smooth muscle cells (αSMA), macrophage lineage cells (CD11b), and matrix metalloproteinase activity (MMP-2 and MMP-9). Picrosirius Red staining was performed to quantify collagen content. TEVG wall thickness was significantly higher for proximal, middle, and distal slices in unseeded versus cell-seeded grafts. Significantly higher WSS values existed for proximal versus distal slice locations for cell-seeded TEVGs, whereas no differences in WSS existed between slices for unseeded TEVGs. Additionally, no differences in WSS existed between cell-seeded and unseeded groups. Both groups demonstrated elastin formation, without vascular calcification. Unseeded TEVGs possessed greater content of smooth muscle cells when compared with cell-seeded TEVGs. No differences in macrophage, MMP activity, or collagen content existed between groups. MR imaging allows for in vivo assessment of functional and anatomical characteristics of TEVGs and may provide a nonionizing approach that is clinically translatable to children undergoing treatment for CHD.

Tissue-engineered cardiac patch seeded with human induced pluripotent stem cell derived cardiomyocytes promoted the regeneration of host cardiomyocytes in a rat model.

BackgroundThousands of babies are born with congenital heart defects that require surgical repair involving a prosthetic implant. Lack of growth in prosthetic grafts is especially detrimental in pediatric surgery. Cell seeded biodegradable tissue engineered grafts are a novel solution to this problem. The purpose of the present study is to evaluate the feasibility of seeding human induced pluripotent stem cell derived cardiomyocytes (hiPS-CMs) onto a biodegradable cardiac patch.MethodsThe hiPS-CMs were cultured on a biodegradable patch composed of a polyglycolic acid (PGA) and a 50:50 poly (l-lactic-co-ε-caprolactone) copolymer (PLCL) for 1 week. Male athymic rats were randomly divided into 2 groups of 10 animals each: 1. hiPS-CM seeded group, and 2. Unseeded group. After culture, the cardiac patch was implanted to repair a defect with a diameter of 2 mm created in the right ventricular outflow tract (RVOT) wall. Hearts were explanted at 4 (n = 2), 8 (n = 2), and 16 (n = 6) weeks after patch implantation. Explanted patches were assessed immunohistochemically.ResultsSeeded patch explants did not stain positive for α-actinin (marker of cardiomyocytes) at the 4 week time point, suggesting that the cultured hiPS-CMs evacuated the patch in the early phase of tissue remodeling. However, after 16 weeks implantation, the area fraction of positively stained α-actinin cells was significantly higher in the seeded group than in the unseeded group (Seeded group: 6.1 ± 2.8% vs. Unseeded group: 0.95 ± 0.50%, p = 0.004), suggesting cell seeding promoted regenerative proliferation of host cardiomyocytes.ConclusionsSeeded hiPS-CMs were not present in the patch after 4 weeks. However, we surmise that they influenced the regeneration of host cardiomyocytes via a paracrine mechanism. Tissue-engineered hiPS-CMs seeded cardiac patches warrant further investigation for use in the repair of congenital heart diseases.

Abstract 11205: Tropoelastin Inhibits Intimal Hyperplasia of Mouse Bioresorbable Arterial Vascular Grafts

Introduction: Neointimal hyperplasia, which results from the activation, proliferation and migration of vascular smooth muscle cells (SMCs), is a detrimental condition for vascular stents or vascular grafts that leads to stenosis. Preventing neointimal hyperplasia is critically important for the success of arterial vascular grafts. Hypothesis: We assessed the hypothesis that tropoelastin seeding will prevent SMC proliferation and neointimal hyperplasia in bioresorbable arterial vascular grafts. Methods: Poly (glycolic acid) (PGA) fiber mesh coated with poly (l-lactic-co- ε -caprolactone) (PLCL) scaffolds reinforced by poly (l-lactic acid) (PLA) nano-fibers were prepared as bioresorbable arterial grafts. Tropoelastin was then seeded onto the luminal surfaces of the grafts. Female C57BL/6 mice were randomly divided into 2 groups: 1. Tropoelastin seeded group (n=10), and 2. Unseeded group (n=10). The grafts were implanted as infra-renal aortic interposition conduits. Animals were followed for 8 weeks then sacrificed to evaluate neotissue formation. Results: Tropoelastin treatment substantially reduced the number of cells that stained positive for SMC (α-SMA) and Proliferating cell nuclear antigen (PCNA) in the vessel walls (Unseeded group: 60 ± 36/HPF vs. Tropoelastin seeded group: 21 ± 13/HPF, P =0.048, Unseeded group: 11.0 ± 5.6 /HPF vs. Tropoelastin seeded group: 4.8 ± 1.7/HPF, P =0.043, SMC and PCNA, respectively, HPF; high power field) (Fig. A, B). Tropoelastin significantly reduced the thickness of the intimal layer (Unseeded group: 91 ± 22 μm vs. Tropoelastin seeded group: 50 ± 11 μm, P =0.004) (Fig. C). Conclusions: Tropoelastin seeding is beneficial in preventing SMC proliferation and neointimal hyperplasia in bioresorbable arterial vascular grafts.

Functional Effects of Delivering Human Mesenchymal Stem Cell-Seeded Biological Sutures to an Infarcted Heart.

Stem cell therapy has the potential to improve cardiac function after myocardial infarction (MI); however, existing methods to deliver cells to the myocardium, including intramyocardial injection, suffer from low engraftment rates. In this study, we used a rat model of acute MI to assess the effects of human mesenchymal stem cell (hMSC)-seeded fibrin biological sutures on cardiac function at 1 week after implant. Biological sutures were seeded with quantum dot (Qdot)-loaded hMSCs for 24 h before implantation. At 1 week postinfarct, the heart was imaged to assess mechanical function in the infarct region. Regional parameters assessed were regional stroke work (RSW) and systolic area of contraction (SAC) and global parameters derived from the pressure waveform. MI (n = 6) significantly decreased RSW (0.026 ± 0.011) and SAC (0.022 ± 0.015) when compared with sham operation (RSW: 0.141 ± 0.009; SAC: 0.166 ± 0.005, n = 6) (p < 0.05). The delivery of unseeded biological sutures to the infarcted hearts did not change regional mechanical function compared with the infarcted hearts (RSW: 0.032 ± 0.004, SAC: 0.037 ± 0.008, n = 6). The delivery of hMSC-seeded sutures exerted a trend toward increase of regional mechanical function compared with the infarcted heart (RSW: 0.057 ± 0.011; SAC: 0.051 ± 0.014, n = 6). Global function showed no significant differences between any group (p > 0.05); however, there was a trend toward improved function with the addition of either unseeded or seeded biological suture. Histology demonstrated that Qdot-loaded hMSCs remained present in the infarcted myocardium after 1 week. Analysis of serial sections of Masson's trichrome staining revealed that the greatest infarct size was in the infarct group (7.0% ± 2.2%), where unseeded (3.8% ± 0.6%) and hMSC-seeded (3.7% ± 0.8%) suture groups maintained similar infarct sizes. Furthermore, the remaining suture area was significantly decreased in the unseeded group compared with that in the hMSC-seeded group (p < 0.05). This study demonstrated that hMSC-seeded biological sutures are a method to deliver cells to the infarcted myocardium and have treatment potential.

Is There a Need for Smooth Muscle Cell Transplantation in Urethral Reconstruction?

Hypospadias and urethral strictures are conditions requiring additional tissue for reconstruction. Due to a limited source of tissue, autologous skin and oral mucosa are frequently used. However, long-term follow-up studies demonstrated significant complications and diminished quality of life. Recently, a variety of tubular biodegradable biomaterials have been used. Cell seeding seems to be important to improve the host acceptance and neovascularization. To compare in vivo performance of smooth muscle cell (SMC)-seeded and unseeded tubular collagen-based scaffolds in a rabbit urethral reconstruction model. Sixteen New Zealand rabbits underwent an open-bladder biopsy for SMC harvesting. The SMCs were cultured for 3 weeks and labeled with ethynyldeoxyuridine (EdU). A 1-cm-length tubular collagen-based 0.5 wt% scaffold was seeded and cultured with SMCs and implantation in a rabbit model. Eight rabbits received SMC-seeded scaffolds for a 1-cm-length circumferential urethral repair, situated 1.5 cm from the meatus. After 1 and 3 months, four rabbits underwent a urethrography and were sacrificed. The penises underwent hematoxylin and eosin, immunohistochemistry, and EdU fluorescence staining. In the control group eight rabbits received acellular scaffolds. The SMC-seeded group presented one stricture at 1 month and one fistula at 3 months. Three strictures were present in the unseeded group at 1 month and one at 3 months. In the seeded group, more SMC expression and neovascularization was observed, and less mononuclear and giant cells could be found. All scaffolds showed luminal urothelial cell revetment. The detection of EdU-labeled SMCs revealed SMC transplantation survival. SMC-seeded tubular collagen scaffolds improved urethral regeneration in this rabbit model. Such constructs may be valuable for repair of severe urethral diseases.

Tumor self-seeding by circulating tumor cells in nude mouse models of human osteosarcoma and a preliminary study of its mechanisms

The purpose of this study is to determine whether and how tumor self-seeding by circulating tumor cells (CTCs) plays a role in the initiation and progression of osteosarcoma. Two different nude mouse models of human osteosarcoma were established for detecting tumor self-seeding by fluorescently labeled CTCs. Various tumor growth indicators were quantitated for seeded and unseeded groups. Growth mechanisms were characterized using cell proliferation assays and immunohistochemical staining. Conditioned media of primary osteosarcoma cells was characterized in a Transwell migration assay and enzyme-linked immunosorbent assay. The effect of cytokines secreted by primary tumor cells was verified by small interfering RNA and recombinant human cytokine experiments. Red fluorescent protein-labeled CTCs seeded primary tumors in both models. Seeded primary tumors groups grew faster than control groups (P < 0.05), which was partially attributed to the CTCs having a higher proliferation rate and higher vascular endothelial growth factor expression after self-seeding. Conditioned media of primary osteosarcoma cells attracted CTCs, through an IL-6-dependent mechanism. CTC tumor self-seeding occurs in osteosarcoma and promotes the growth of primary osteosarcoma. CTCs appear to be recruited by cytokines secreted by primary osteosarcoma cells, particularly IL-6.

Gene delivery of bone morphogenetic protein-2 plasmid DNA promotes bone formation in a large animal model

In the field of bone regeneration, BMP-2 is considered one of the most important growth factors because of its strong osteogenic activity, and is therefore extensively used in clinical practice. However, the short half-life of BMP-2 protein necessitates the use of supraphysiological doses, leading to severe side-effects. This study investigated the efficiency of bone formation at ectopic and orthotopic sites as a result of a low-cost, prolonged presence of BMP-2 in a large animal model. Constructs consisting of alginate hydrogel and BMP-2 cDNA, together acting as a non-viral gene-activated matrix, were combined with goat multipotent stromal cells (gMSCs) and implanted in spinal cassettes or, together with ceramic granules, intramuscularly in goats, both for 16 weeks. Bone formation occurred in all cell-seeded ectopic constructs, but the constructs containing both gMSCs and BMP-2 plasmid DNA showed higher collagen I and bone levels, indicating an osteogenic effect of the BMP-2 plasmid DNA. This was not seen in unseeded constructs, even though transfected, BMP-2-producing cells were detected in all constructs containing plasmid DNA. Orthotopic constructs showed mainly bone formation in the unseeded groups. Besides bone, calcified alginate was present in these groups, acting as a surface for new bone formation. In conclusion, transfection of seeded or resident cells from this DNA delivery system led to stable expression of BMP-2 during 16 weeks, and promoted osteogenic differentiation and subsequent bone formation in cell-seeded constructs at an ectopic location and in cell-free constructs at an orthotopic location in a large animal model.

Recovery of endothelial cells and prostanoid production in endothelial cell-seeded grafts

To investigate the function and morphology of endothelial cell (EC) seeded grafts. Experimental, open study. Endoluminal release of prostacyclin (6-Keto-PGF1 alpha) and thromboxane B2 (TxB2), patency, EC coverage and cell identity. In 12 sheep, segments of both carotid arteries were excised. On one side a seeded and on the other an unseeded dacron graft were inserted. After 3 months the grafts were excised. In grafts and arteries, the endoluminal release of 6-keto-PGF1 alpha and TxB2 was determined in a perfusion system. Scanning electron microscopy (SEM) and light microscopy were used to determine the EC coverage and cell identity. Eight animals survived. Three seeded and two unseeded grafts were occluded. Prostacyclin release did not differ significantly between seeded and unseeded grafts and arteries, when the arteries were looked upon as one group. When the graft was compared with its corresponding artery, i.e. the artery it replaced, a significantly lower release was found in the unseeded group. Thromboxane release was undetectable in arteries but significantly higher in both graft groups. SEM revealed a cellular coverage of 75% in the seeded grafts and 50% in the unseeded (not significant). Light microscopy showed a patchy staining for Factor VIII-related antigen in some grafts in both groups. Prostacyclin release in unseeded and seeded dacron grafts did not differ 3 months after implantation in sheep, except when the graft was compared with its corresponding artery. The significance of this remains to be settled. Seeded grafts did not have a higher proportion of endothelial coverage than unseeded grafts.

Metabolic and thermoregulatory responses to burn wound colonization.

This study was designed to determine whether there is a relationship between bacterial colonization of the burn wound and resting oxygen consumption (VO2) and colonic temperature (Tc) in burned rats. Resting VO2, Tc, and blood, spleen, and wound cultures were monitored for 2 weeks after 30% total body surface full-thickness burns. The wounds of 53 animals were seeded with 10(8) nonvirulent P. aeruginosa (NVP) at the time of injury, while the wounds of 33 rats were allowed to colonize spontaneously. The seeded wounds contained 10(6) colony forming units/gm (CFU/gm) by the fourth postburn day (PBD), while the unseeded wounds did not reach this level of colonization until after the first week postinjury. Wound seeding accelerated the metabolic and thermoregulatory responses to injury. Average VO2 and Tc of the seeded group were above the unseeded group on PBD's 3-4 and 7-8, but there were no significant differences between groups on PBD's 14-15. Although the unseeded animals were hypermetabolic during the first week, they remained afebrile. There was a significant correlation between wound bacterial counts and the increase in resting VO2 of 44 nonbacteremic animals, but variations in the data suggest that factors other than number of viable wound bacteria affect this relationship. Changes in Tc were unrelated to wound bacterial count but were correlated with changes in VO2. Taken together, the data suggest that bacteria in the burn wound contribute to the rise in energy expenditure following thermal injury.