One step creation of multifunctional 3D architectured hydrogels inducing bone regeneration

Structured hydrogels showing form stability and elastic properties individually tailorable on different length scales are accessible in a one-step process. They support cell adhesion and differentiation and display growing pore size during degradation. In vivo experiments demonstrate their efficacy in biomaterial-induced bone regeneration, not requiring addition of cells or growth factors

Evidence, Content and Corroboration and the Tree of Life

We examine three critical aspects of Popper’s formulation of the ‘Logic of Scientific Discovery’—evidence, content and degree of corroboration—and place these concepts in the context of the Tree of Life (ToL) problem with particular reference to molecular systematics. Content, in the sense discussed by Popper, refers to the breadth and scope of existence that a hypothesis purports to explain. Content, in conjunction with the amount of available and relevant evidence, determines the testability, or potential degree of corroboration, of a statement; content distinguishes scientific hypotheses from metaphysical assertions. Degree of corroboration refers to the relative and tentative confidence assigned to one hypothesis over another, based upon the performance of each under critical tests. Here we suggest that systematists attempt to maximize content and evidence to increase the potential degree of corroboration in all phylogenetic endeavors. Discussion of this “total evidence” approach leads to several interesting conclusions about generating ToL hypotheses

Local optical spectroscopy of semiconductor nanostructures in the linear regime

We present a theoretical approach to calculate the local absorption spectrum of excitons confined in a semiconductor nanostructure. Using the density-matrix formalism, we derive a microscopic expression for the nonlocal susceptibility, both in the linear and nonlinear regimes, which includes a three-dimensional description of electronic quantum states and their Coulomb interaction. The knowledge of the nonlocal susceptibility allows us to calculate a properly defined local absorbed power, which depends on the electromagnetic field distribution. We report on explicit calculations of the local linear response of excitons confined in single and coupled T-shaped quantum wires with realistic geometry and composition. We show that significant interference effects in the interacting electron-hole wave function induce new features in the space-resolved optical spectra, particularly in coupled nanostructures. When the spatial extension of the electromagnetic field is comparable to the exciton Bohr radius, Coulomb effects on the local spectra must be taken into account for a correct assignment of the observed features

Characterization of a rat osteotomy model with impaired healing

<p>Abstract</p> <p>Background</p> <p>Delayed union or nonunion are frequent and feared complications in fracture treatment. Animal models of impaired bone healing are rare. Moreover, specific descriptions are limited although understanding of the biological course of pathogenesis of fracture nonunion is essential for therapeutic approaches.</p> <p>Methods</p> <p>A rat tibial osteotomy model with subsequent intramedullary stabilization was performed. The healing progress of the osteotomy model was compared to a previously described closed fracture model. Histological analyses, biomechanical testing and radiological screening were undertaken during the observation period of 84 days (d) to verify the status of the healing process. In this context, particular attention was paid to a comparison of bone slices by histological and immunohistological (IHC) methods at early points in time, <it>i.e</it>. at 5 and 10 d post bone defect.</p> <p>Results</p> <p>In contrast to the closed fracture technique osteotomy led to delayed union or nonunion until 84 d post intervention. The dimensions of whole reactive callus and the amounts of vessels in defined regions of the callus differed significantly between osteotomized and fractured animals at 10 d post surgery. A lower fraction of newly formed bone and cartilaginous tissue was obvious during this period in osteotomized animals and more inflammatory cells were observed in the callus. Newly formed bone tissue accumulated slowly on the anterior tibial side with both techniques. New formation of reparative cartilage was obviously inhibited on the anterior side, the surgical approach side, in osteotomized animals only.</p> <p>Conclusion</p> <p>Tibial osteotomy with intramedullary stabilisation in rats leads to pronounced delayed union and nonunion until 84 d post intervention. The early onset of this delay can already be detected histologically within 10 d post surgery. Moreover, the osteotomy technique is associated with cellular and vascular signs of persistent inflammation within the first 10 d after bone defect and may be a contributory factor to impaired healing. The model would be excellent to test agents to promote fracture healing.</p

Characterising neovascularisation in fracture healing with laser Doppler and micro-CT scanning

Vascularity of the soft tissues around a bone fracture is critical for successful healing, particularly when the vessels in the medullary canal are ruptured. The objective of this work was to use laser Doppler and micro-computer tomography (micro-CT) scanning to characterise neovascularisation of the soft tissues surrounding the fracture during healing. Thirty-two Sprague–Dawley rats underwent mid-shaft osteotomy of the left femur, stabilised with a custom-designed external fixator. Five animals were killed at each of 2, 4 days, 1, 2, 4 and 6 weeks post-operatively. Femoral blood perfusion in the fractured and intact contralateral limbs was measured using laser Doppler scanning pre- and post-operatively and throughout the healing period. At sacrifice, the common iliac artery was cannulated and infused with silicone contrast agent. Micro-CT scans of the femur and adjacent soft tissues revealed vessel characteristics and distribution in relation to the fracture zone. Blood perfusion dropped immediately after surgery and then recovered to greater than the pre-operative level by proliferation of small vessels around the fracture zone. Multi-modal imaging allowed both longitudinal functional and detailed structural analysis of the neovascularisation process

Hydrogels: one step creation of multifunctional 3D architectured hydrogels inducing bone regeneration.

The back cover highlights the unique degradation behavior of hydrogels with 3D architectures (ArcGels). Hydrolytic cleavage of bonds results in a merging of pores, comparable to soap bubbles. This mechanism, described by A. Lendlein and co-workers on page 1738, results in pore growth during degradation, which putatively leads to mechanical stimulation of cells during the in vivo regeneration of bone