Genetic bistable systems are a large class of important biological systems. Bistability, the capacity to achieve two distinct stable steady states in response to a set of external stimuli, arises within biological systems ranging from the ? phage switch in bacteria to cellular signal transduction pathways in mammalian cells. On the other hand, the increasing experimental evidence in the form of bimodal population distribution has indicated that noise plays a very key role in the switching of bistable systems. However, the physiological mechanism underling noise-induced switching behaviors has not been well explored yet. In the previous work, it has been showed that noise can induce coherent switch for a single genetic Toggle switch system. Here the influence of several kinds of noises (including intracellular and extracellular noises) on synchronized switch was investigated for a multicell gene toggle switch network system. It has been found that multiplicative noises resulting from fluctuations of either synthesis or degradation rates and the additive noise within each cell (they altogether are called as intracellular noises) all can induce the synchronized switch, and that there exists an optimal noise intensity such that the synchronized switch is optimally achieved and the amplification factor has the maximal value. On the other hand, the extracellular noises arising from the stochastic fluctuation of the cellular environment, not only brings about the synchronized switch, but also enhances it by suppressing intracellular fluctuations when the intracellular noises are not enough to induce the synchronized switch. Finally, the influence of the diffusive rate of signal molecules affected by noise on the dynamics of the multicellular system was also investigated, showing that the larger the diffusive rate, the better the synchronized switch and the larger the amplification factor.

BACKGROUND:Poly(butylene succinate) (PBS) and polypropylenecarbonate (PPC) are new medical materials developed in recent years, characterized as good biocompatibility, biodegradability and the low price. OBJECTIVE:To prepare the PBS/PPC biofilm by electrostatic spinning method and evaluate its physical and chemical properties, degradation performance and effect on cel proliferationin vitro. METHODS:The PBS/PPC biofilm was prepared using electrostatic spinning method: 0.9 g PBS and 0.9 g PPC were dissolved in 10 mL of trichloromethane at room temperature and stirred magneticaly until they were fulydissolved. Then, the spinning solution was added into a spinning tube with a distance of about 15 cm and at a voltage of 18 kV. The surface morphology was observed by scanning electron microscopy. The intensity, contact angle and water absorption, pH value and weight loss in the process ofin vitro degradation were measured. MG63 cels were co-cultured with the biofilm for 7 days and cel proliferation was detected by cel counting kit-8. RESULTS AND CONCLUSION: The PBS/PPC biofilm showed a porous structure with interconnected pores. The fiber diameter was about 0.88 μm, the average aperture was about 5.68 μm, the porosity was 78.3%, the fracture intensity was 2.31 MPa, the elongation rate at break was 23.48%, the average value of contact angle was 87°, and the water absorption rate was 68.54%. During the biofilm degradation, the pH value decreased gradualy andreduced to 6.76 at 12 weeks; meanwhile, the biofilm degraded equaly and gradualy, and the weight loss rate was 6.04% at the end of the 12th week. The results of cel counting kit-8 showed that the PBS/PPC biofilm could promote cel proliferation. Overal, the PBS/PPC biofilm has good physical and chemical properties, good space-making feature, wettability and degradability, which can provide sufficient time for bone tissue regeneration.

There are different degrees of bone defect in immediate implantation for anterior dentition. During conventional guided bone regeneration, the wound was difficultly closed in operation,and there was more inflammatory response and infection risk. In this paper,a case of immediate implantation for anterior dentition combined with platelet rich-fibrin(PRF) was reported,the clinical effects of guiding bone regeneration and alleviating the inflammatory response.