Vascular Endothelial Growth Factor (VEGF) and Semaphorin 3A (Sema3A) signaling for vascularized bone grafts

One of the major challenges for the treatment of critical size bone defects is to ensure a rapid and efficient vascularization of tissue-engineered bone grafts upon implantation in vivo. The biological processes of osteogenesis and angiogenesis are intimately coupled, and many factors play important roles in this cross-talk. Among them, Vascular Endothelial Growth Factor (VEGF), the master regulator of vascular growth, is crucial during bone development, homeostasis and repair, and it is a key molecular target for the generation of vascularized bone grafts. However, in order to exploit its therapeutic potential, VEGF dose and spatial-temporal distribution have to be precisely controlled. Semaphorin 3A (Sema3A) regulates osteoblasts and osteoclasts to promote bone synthesis through the Neuropilin-1 receptor (NP-1) and it has important roles in angiogenesis. We previously found that VEGF dose-dependently inhibits endothelial Sema3A expression in skeletal muscle. Here we investigated the role of VEGF and Sema3A in the coupling of angiogenesis and osteogenesis in engineered bone grafts in order to provide rational bases for novel, safe and effective therapeutic strategies for the repair of bone tissue To this purpose, osteogenic constructs were prepared with human bone marrow mesenchymal cells (BMSCs) in combination with fibrin matrices decorated with recombinant VEGF or Sema3A engineered with a transglutaminase substrate sequence (TG-VEGF and TG-Sema3A) to allow cross-linking into fibrin hydrogels and controlled release. We found that VEGF-dose dependently regulates both angiogenesis and osteogenesis. Low VEGF doses accelerated vascular invasion and ensured efficient bone depositio. High VEGF doses delayed vascular ingrowth, increased osteoclast recruitment and decreased bone formation by impairing the differentiation of the implanted human osteogenic progenitor cells. Moreover, we showed that VEGF-dose dependently downregulates Sema3A expression and that Sema3A is critical for both vascularization and intramembranous bone formation in osteogenic grafts. These results confirm the importance of both VEGF and Sema3A in bone biology and provide the basis for the design of novel rational strategies to generate vascularized bone grafts with the aim to improve the healing of critical-size bone defects

On the use of SIFT features for face authentication

Several pattern recognition and classification techniques have been applied to the biometrics domain. Among them, an interesting technique is the Scale Invariant Feature Transform (SIFT), originally devised for object recognition. Even if SIFT features have emerged as a very powerful image descriptors, their employment in face analysis context has never been systematically investigated. This paper investigates the application of the SIFT approach in the context of face authentication. In order to determine the real potential and applicability of the method, different matching schemes are proposed and tested using the BANCA database and protocol, showing promising results

Understanding critical factors in gender recognition

Gender classification is a task of paramount importance in face recognition research, and it is potentially useful in a large set of applications. In this paper we investigate the gender classification problem by an extended empirical analysis on the Face Recognition Grand Challenge version 2.0 dataset (FRGC2.0). We propose challenging experimental protocols over the dimensions of FRGC2.0 – i.e., subject, face expression, race, controlled or uncontrolled environment. We evaluate our protocols with respect to several classification algorithms, and processing different types of features, like Gabor and LBP. Our results show that gender classification is independent from factors like the race of the subject, face expressions, and variations of controlled illumination conditions. We also report that Gabor features seem to be more robust than LBPs in the case of uncontrolled environment

Robust visual servoing in 3d reaching tasks

This paper describes a novel approach to the problem of reaching an object in space under visual guidance. The approach is characterized by a great robustness to calibration errors, such that virtually no calibration is required. Servoing is based on binocular vision: a continuous measure of the end-effector motion field, derived from real-time computation of the binocular optical flow over the stereo images, is compared with the actual position of the target and the relative error in the end-effector trajectory is continuously corrected. The paper outlines the general framework of the approach, shows how visual measures are obtained and discusses the synthesis of the controller along with its stability analysis. Real-time experiments are presented to show the applicability of the approach in real 3-D applications

Performance of P-P and P-U intensity probes using Scan & Paint

This paper aims to clarify the principal advantages and disadvantages of using sound intensity probes which implement different measurement principles: p-p probes versus p-u probes or Microflowns. A novel measurement technique based on scanning principles called “Scan & Paint” had been chosen to evaluate their performanc