Optimizing the osteogenic potential of electrospun PVDF matrixes

With an ageing population, the ability to easily regenerate bone defects in a manner that lessens patient site morbidity takes an even more important toll. As such the development of a biomaterial that is capable of successfully mimicking the native environment encountered in the human body is necessary in order to facilitate the regenerative process. Since traditional orthopedic materials lack some of the necessary ability to mimic the native environment, new approaches must be taken, in this regard polyvinylidene difluoride (PVDF) presents a novel alternative. Since it can be produced via electrospinning in the form of a non-woven fiber matrix that mimics the morphology of the native extracellular matrix (EMC) as well as being able to simulate electrical signals, due to the appearance of a piezoelectric phase due to the electrospinning process, that act as cues for several cellular and molecular processes, including tissue regeneration. The work developed in this thesis aims to optimize the piezoelectric response under electrical stimulation of the electrospun matrixes by adjusting the spinning parameters in order to device an optimal scaffold for bone tissue growth and regeneration. Structural analysis of the material, shows that the electrospinning process give origin to a new structural organization. When compared to the original PVDF powder, after processing the polymer presents higher crystallinity and also higher content of the piezoelectric phase. However no significant differences were found in crystalline phases, porosity and overall crystallinity for samples spun under different conditions. Cytotoxicity tests shown that PVDF mats present a non-cytotoxic behavior. Cellular tests under electric stimulus showed no statistical difference between samples with higher and lower piezoelectric response. However regardless of the sample type, the cells demonstrate a much higher metabolic activity when had received an external stimulus

Internship at Be One Solutions

Included in this document is the report of my internship undertaken in the fulfilment of my Master of Cybersecurity and Informatic Forensics degree from the Polytechnic Institute of Leiria, at Be One Solutions. During the internship, I identified several issues regarding security protocols and procedures at the company, more specifically in regards to credential management. After identifying the issues, I started researching enterprise level solutions for credential management, for which the requirements had been established beforehand with the IT manager. After comparing a set of solutions based on the features they provided and the price quoted, it was possible to conclude that all solutions were unsuitable due to either unreasonable pricing or previous security issues. Since the solutions analysed were deemed unsuitable, I started working on a Proof of Concept (PoC) for a custom solution that would be able to integrate with the project structure already present in the company’s in house project management solution. It started with defining the concept of the solutions in regards to how the encryption process would be performed, then the designing of the data structure in order to integrate with the project management solution, an afterwards came the development process of said solution

The k-labeled spanning forest problem : complexity, approximability, formulations and algorithms

In this work, we study the k-labeled spanning forest problem (KLSF). The input of the KLSF is an undirected graph with labeled edges and a positive integer k. The goal is to find a spanning forest of the graph with at most k different labels associated with the edges, that minimizes the number of components. KLSF finds practical applications in different scenarios related to networks design and telecommunications. Its solutions may help to reduce the negative impact of electromagnetic fields exposure on the population health or to increase profits of internet management companies, among others. The in terest in the KLSF problem is not only practical but also theoretical since the problem generalizes the best-known NP-hard minimum labeling spanning tree problem (MLST). This work reinforces the NP-hardness of the KLSF and ensures that, even for the simple instances where the components of the original graph are only triangles and edges, the problem is NP-hard. Also as a theoretical result, an inapproximability proof is presented for it, ensuring that unless P = NP there is no polynomial time algorithm with approxi mation factor polynomial in the number of the labels. To complete the theoretical results a trivial 3-approximation result is presented for the particular case where the input graph components are edges or triangles. From the application side, to approach KLSF, we propose a fix-and-optimize matheuristic that was tested over several instances, achieving high-quality solutions in reasonable computational time. When compared to the best known algorithms in the literature, our matheuristic outperformed the other proposals in most cases, finding better solutions in less computational time for the most challenging instances

Interactions Between Ultrashort Pulses and Laser-Produced Tin Plasmas

Inside commercial EUV nanolithography sources, micrometer-sized droplets of liquid tin are irradiated by a high-power CO2 laser, creating a plasma which emits the desired 13.5 nm light. However, small dense liquid spheres are an inefficient target shape for EUV production. To solve this, each droplet is irradiated by two laser pulses. Firstly, a low-energy pre-pulse irradiates the initially-spherical droplet, deforming it via hydrodynamic expansion into a shape more favourable for EUV production. Afterwards, a time-delayed high-energy main pulse irradiates this deformed droplet. Typically, pre-pulses with nanosecond durations are used to deform the target from a sphere into a thin disk. An alternative approach involves using pre-pulses with picosecond or femtosecond durations. These shorter pulses create an intense shock wave on the droplet surface, which propagates through the droplet focusing at its center, where a bubble is formed through a process called cavitation. This bubble rapidly expands, rupturing the droplet, which then breaks up into fine particles. These “cloud” targets have in some cases shown higher conversion efficiencies than disk targets, with the drawback of additional debris created by the violent transformation process. To study the dynamics of cloud targets, we designed and built a laser system capable of producing laser pulses with durations ranging from 220 fs to 100 ps. The system includes a 1064 nm source based on Nd:YVO4 and Nd:YAG, producing pulses with durations between 15 and 100 ps and energies of up to 180 mJ. This system can be used as a standalone source or as a pump for a 1.55 μm KTA-based optical parametric chirped pulse amplifier, producing pulses with durations from 220 fs to 10 ps, with energies up to 10.5 mJ. Ultrashort mJ-level pulses from the OPCPA were used to study the effects of pulse energy and duration on microdroplet deformation. The velocities of the cavitation expansion and of the ablated material are found to decrease for longer pulses, indicating shorter pulses lead to faster, more violent dynamics. Using linearly-polarized pulses, cylindrically-asymmetric shock waves were produced, leading to novel asymmetric target shapes which show good qualitative agreement with smoothed-particle hydrodynamics simulations, highlighting the role of shock waves in the laser-driven deformation dynamics. Charge-state-resolved ion energy spectra were recorded using an electrostatic analyzer to study the processes that shape the energy of the ions emitted by the plasma. For lower laser energies we observe a linear relation between the mean ion energy of each charge state and its ionization number, a trend consistent with the typical electrostatic-driven ion acceleration model. For higher laser energies this relation becomes nonlinear, hinting at effects beyond the simple electrostatic acceleration model. Using the 1064 nm amplifier to irradiate droplet targets with a pair of 50-ps laser pulses, comprising a weaker first pulse with variable energy in the μJ range followed by a more energetic 5 mJ pulse, we produced novel target shapes which were keenly dependent on the energy of the first pulse and the time delay between the pulses. Furthermore, the addition of a small first pulse led to a significant reduction in the kinetic energy of the ions emitted by the plasma, with a 30-fold reduction in the most extreme case. Charge-state-resolved measurements show a reduction of ion kinetic energy for every charge state and a pronounced reduction in the yield of higher-charge-state ions, which are the most energetic. In certain pulse-pair configurations, it becomes possible to completely suppress higher charge states above Sn2+. This suppression of faster ions holds practical significance in extending the lifetime of optical components inside EUV sources when paired with ion mitigation techniques which are most effective for lower-energy ions