Size distribution and waiting times for the avalanches of the Cell Network Model of Fracture

The Cell Network Model is a fracture model recently introduced that resembles the microscopical structure and drying process of the parenchymatous tissue of the Bamboo Guadua angustifolia. The model exhibits a power-law distribution of avalanche sizes, with exponent -3.0 when the breaking thresholds are randomly distributed with uniform probability density. Hereby we show that the same exponent also holds when the breaking thresholds obey a broad set of Weibull distributions, and that the humidity decrements between successive avalanches (the equivalent to waiting times for this model) follow in all cases an exponential distribution. Moreover, the fraction of remaining junctures shows an exponential decay in time. In addition, introducing partial breakings and cumulative damages induces a crossover behavior between two power-laws in the avalanche size histograms. This results support the idea that the Cell Network Model may be in the same universality class as the Random Fuse Model

Regenerative Medicine: A New Paradigm in Bone Regeneration

Bone defects are the cause of functional disability and the restoration of skeletal function remains an important challenge on orthopedics, neurosurgery and oral and maxillofacial surgery. Because of the limitations of the currently used techniques for the reconstruction of bone defects and the difficulties for the implementation of new therapeutic strategies, a new paradigm in the field of reconstructive surgery has arisen, leading to tissue engineering and regenerative medicine. Mesenchymal stem cells (MSC) have emerged as a promising alternative for the treatment of bone lesions. It was postulated that the therapeutic action was the result of proliferation and differentiation of MSCs, replacing injured tissue. However, recent studies have shown that MSCs secrete a number of trophic factors that have a strong effect during repair and tissue regeneration. This represents a shift from a paradigm centered on MSC proliferation and differentiation to a new paradigm in which the MSCs exert their beneficial effect by the secretion of paracrine factors that induce endogenous repair mechanisms. This chapter will bring together basic and clinical aspects, focused on novel findings on MSC paracrine effect and the development of new therapeutic strategies based on growth factors, cytokines and signaling molecules involved in bone regeneration