Direct reciprocity in spatial populations enhances R-reciprocity as well as ST-reciprocity.

As is well-known, spatial reciprocity plays an important role in facilitating the emergence of cooperative traits, and the effect of direct reciprocity is also obvious for explaining the cooperation dynamics. However, how the combination of these two scenarios influences cooperation is still unclear. In the present work, we study the evolution of cooperation in 2 × 2 games via considering both spatial structured populations and direct reciprocity driven by the strategy with 1-memory length. Our results show that cooperation can be significantly facilitated on the whole parameter plane. For prisoner's dilemma game, cooperation dominates the system even at strong dilemma, where maximal social payoff is still realized. In this sense, R-reciprocity forms and it is robust to the extremely strong dilemma. Interestingly, when turning to chicken game, we find that ST-reciprocity is also guaranteed, through which social average payoff and cooperation is greatly enhanced. This reciprocity mechanism is supported by mean-field analysis and different interaction topologies. Thus, our study indicates that direct reciprocity in structured populations can be regarded as a more powerful factor for the sustainability of cooperation

Characterization and evaluation of graphene oxide scaffold for periodontal wound healing of class II furcation defects in dog

Introduction: The 3-dimensional scaffold plays a key role in volume and quality of repair tissue in periodontal tissue engineering therapy. We fabricated a novel 3D collagen scaffold containing carbon-based 2-dimensional layered material, named graphene oxide (GO). The aim of this study was to characterize and assess GO scaffold for periodontal tissue healing of class II furcation defects in dog. Materials and methods: GO scaffolds were prepared by coating the surface of a 3D collagen sponge scaffold with GO dispersion. Scaffolds were characterized using cytotoxicity and tissue reactivity tests. In addition, GO scaffold was implanted into dog class II furcation defects and periodontal healing was investigated at 4 weeks postsurgery. Results: GO scaffold exhibited low cytotoxicity and enhanced cellular ingrowth behavior and rat bone forming ability. In addition, GO scaffold stimulated healing of dog class II furcation defects. Periodontal attachment formation, including alveolar bone, periodontal ligament-like tissue, and cementum-like tissue, was significantly increased by GO scaffold implantation, compared with untreated scaffold. Conclusion: The results suggest that GO scaffold is biocompatible and possesses excellent bone and periodontal tissue formation ability. Therefore, GO scaffold would be beneficial for periodontal tissue engineering therapy

Bone Induction by α-tricalcium Phosphate Microparticle Emulsion Containing Simvastatin

To improve the degradability and operability of conventional bone graft materials, we fabricated a water-oil emulsion based on α-tricalcium phosphate (α-TCP) bone paste. Simvastatin, a lipophilic hyperlipidemia treatment agent, reportedly enhances the expression of bone morphogenetic protein-2 and subsequent bone formation. Accordingly, we assessed the bone forming effects of α-TCP bone-paste containing simvastatin in rat cranial bone defects. Bone paste exhibited porous structure and generation of hydroxyapatite after solidification. X-ray image analysis and histological examination were carried out after implantation of bone paste into rat skull defect. The results showed that new bone was formed after implantation of bone paste containing simvastatin. In particular, bone volume in the 0.1 mg simvastatin group was significantly promoted when compared to controls (no implantation). No bone paste residue was observed in the bone defect at 4 weeks after surgery. Therefore, α-TCP bone paste containing simvastatin is degradable and beneficial for bone tissue engineering

Dose effects of beta-tricalcium phosphate nanoparticles on biocompatibility and bone conductive ability of three-dimensional collagen scaffolds

Three-dimensional collagen scaffolds coated with beta-tricalcium phosphate (β-TCP) nanoparticles reportedly exhibit good bioactivity and biodegradability. Dose effects of β-TCP nanoparticles on biocompatibility and bone forming ability were then examined. Collagen scaffold was applied with 1, 5, 10, and 25 wt% β-TCP nanoparticle dispersion and designated TCP1, TCP5, TCP10, and TCP25, respectively. Compressive strength, calcium ion release and enzyme resistance of scaffolds with β-TCP nanoparticles applied increased with β-TCP dose. TCP5 showed excellent cell-ingrowth behavior in rat subcutaneous tissue. When TCP10 was applied, osteoblastic cell proliferation and rat cranial bone augmentation were greater than for any other scaffold. The bone area of TCP10 was 7.7-fold greater than that of non-treated scaffold. In contrast, TCP25 consistently exhibited adverse biological effects. These results suggest that the application dose of β-TCP nanoparticles affects the scaffold bioproperties; consequently, the bone conductive ability of TCP10 was remarkable

Fraction of cooperation and strategy parameters, <i>p</i> and <i>q</i> in dependence on dilemma strength.

<p>Obviously, cooperative behavior can be remained even under extremely strong dilemma structure when both memory length and the network are assumed.</p

(a) Time courses for the evolution of cooperation and strategy profile <i>p, q</i> at <i>Dg</i> = <i>Dr</i> = 1.

<p>(b) The corresponding snapshots for the corresponding evolution course. (b)-A shows parameter <i>p</i>; (b)-B shows parameter <i>q</i> and the behaviors of cooperators (C, white) or defectors (D, black) are presented in the panel of (b)-C. For these snapshots, the time steps from left to right are 0, 20, 60, 100, 300 and 700, respectively.</p

Schematic presentation for fraction of cooperators in well-mixed populations derived by replicator dynamics.

<p>(a) is illustrated by <i>T</i>-<i>S</i> parameter plane, and (b) is illustrated by <i>D_g</i>-<i>D_r</i> parameter plane, where PD, CH, SH and H denote prisoner's dilemma game, chicken game, stag-hunt game and harmony game, respectively.</p