Supramolecular assemblies of alkane functionalized poly ethylene glycol copolymer for drug delivery

The therapeutic effects of many modern drugs were limited owing to their physical properties and half-life in the blood stream. The purpose of this research is to study the relationship between drug delivery performances and chemical properties of the polymer micelle drug carriers. Polyethylene glycol (PEG) based alternating copolymer poly[(polyoxyethylene)-oxy-5-hydroxyisophthalic] (Ppeg) with PEG molecular weights of 600 and 1000 were synthesized and modified with different alkanes to study the effects of altering the hydrophobic and hydrophilic chain lengths. The nuclear magnetic resonance (NMR) spectrum, critical micelle concentration (CMC), micelle size, and micelle zeta potential of the synthesized polymers were measured. The resulting polymer particles were able to form micelles in aqueous solution with CMCs lower than 0.04 wt%. Drug delivery studies were performed with a model hydrophobic drug, pyrene. Drug loading data showed the polymer particles were able to encapsulate pyrene and has a loading capacity up to 8 wt%. The sustain release ability was measured and the pyrene release was extended over 5 days. Both loading capacity and sustain release ability were found to be highly dependent on CMC. Cell culture study was implemented with RAW 264.7 cells in order to determine the polymer micelle’s cytocompatibility, Most Ppeg polymer micelles showed more than 85% cell viability with and without pyrene loading. Cell internalization of the micelles encapsulated drug was measured both quantitatively and qualitatively and was enhanced comparing to unencapsulated drug. The results indicated that the internalization enhancement effect of polymer micelle was mainly affected by hydrophilic chain length; neither hydrophobic chain length nor loading capacity has significant influence on internalization

pH responsive gels that deliver anti-inflammatory drugs

Anti-inflammatory drugs can suppress or prevent chronic inflammation. However, uncontrolled application of anti-inflammatory drugs often impair the wound healing process. This can be overcome by combining hydrogel wound dressings with drug delivery systems to achieve stage-dependent drug release. The pH of cutaneous wounds is dynamic and correlates with the stage of the wound healing process, with inflammation being acidic, granulation being progressively alkali, and remodeling returning skin to its pre-injury pH. By taking the advantage of this pH difference, stage-specific wound treatments can be developed to respond to these environmental cues using a pH sensitive hydrogel. In the first part of this study, pH sensitive methacrylated chitosan (MAC) hydrogels were synthesized and characterized through 1H NMR. Chitosan was first methacrylated and then crosslinked through three polymerization methods: step growth by thiol-ene photoclick reaction, chain growth by UV polymerization, and mixed model in which both step growth and chain growth mechanism were used. The resulting hydrogels exhibited adjustable mechanical properties, swelling ratios, and pH sensitivities without affecting degradation behavior and in vitro cell response. Cytocompatibility studies were performed using NIH/3T3 fibroblasts. Cell proliferation was suppressed when seeding on the hydrogel surfaces comparing to tissue culture plastic (TCP), yet no measurable cell death was observed. With appropriate drug delivery systems, the responsivity of these gels to different pH environments may prove useful as stage-responsive wound dressings. However, the therapeutic effects of many modern drugs are limited owing to their low solubility and low half-life in circulation. Furthermore, there is a lack of design principles which adds the difficulty in synthesize efficacious drug carriers. The purpose of the second part of this study is to examine the relationship between drug delivery to cells and the chemical properties of the polymer micelle drug carriers. Polyethylene glycol (PEG) based alternating copolymer poly[(polyoxyethylene)-oxy-5-hydroxyisophthalic] (Ppeg) with PEG molecular weights of 600 and 1000 were synthesized and modified with different alkanes to study the effects of altering the hydrophobic and hydrophilic chain lengths. NMR, critical micelle concentration (CMC), micelle size, and micelle zeta potential of the synthesized polymers were measured. The resulting polymer particles were able to form micelles in aqueous solution with CMCs lower than 0.04 wt%. Drug delivery studies were performed with a model hydrophobic drug, pyrene. Drug loading data showed the polymer particles were able to encapsulate pyrene and has a loading capacity up to 8 wt%. The sustain release ability was measured and the pyrene release was extended over 5 days. Both loading capacity and sustain release ability were found to be highly dependent on CMC. The micelles were exposed to RAW 264.7 cells to determine their cytocompatibility, Most Ppeg polymer micelles showed more than 85% cell viability with and without pyrene loading. Cell internalization of the micelles encapsulated drug was measured both quantitatively and qualitatively and was enhanced compared to unencapsulated drug. Predictive equations of drug loading, releasing, and internalization were obtained by factorial analysis as a function of PEG and alkane chain length. The results indicated that the internalization enhancement of polymer micelle was mainly affected by hydrophilic chain length; neither hydrophobic chain length nor loading capacity has significant influence on internalization

Research on 3D chatter stability of blade by high-speed turn-milling

High speed turn-milling is regarded as the milling of a curved surface while rotating the workpiece around its centre point, which combines effectively the advantages of both turning and milling, wherein allows for good metal removal with the difficult-to-cut thin-walled workpieces in aviation. The objective of the present work is to study chatter stability of thin-walled blade by high-speed turn-milling in cutting condition. The dynamic model and the stability critical condition determined by the relative dynamic characteristics between cutter subsystem and blade subsystem are put forward. Aiming at the small-stiffness frequency response characteristics of thin walled structures, the stability critical domain is predicted based on the high-order dynamic behavior of the multi-DOF system. It can be shown that the chatter condition in turn-milling is closely related to both cutter speed and depth of cut, besides cutter geometry, engagement conditions, frequency response function, material property of workpiece and so on. Based on chatter stability simulation model to access 3D chatter stability lobes of high-speed turn-milling machining blades. This conclusion provides a theoretical foundation and reference for the orthogonal turn-milling mechanism research

Gate current modeling of tunneling real-space transfer transistor with negative differential resistance

In this project, the modeling of gate current is introduced to obtain a negative differential resistance (NDR) on a dual-channel tunneling real-space transfer transistor (TRSTT). The device was fabricated on a GaAs (100) substrate with a GaAs/InGaAs/GaAs straddling heterostructure. According to the experimental data reported by Yu et al. in 2010 [1], they demonstrate an InGaAs and \delta-doped GaAs dual-channel TRSTT device with an \lambda-type NDR in a low drain-source voltage (VDS), which reaches a peak-to-valley current ratio of 3.3. Meanwhile, the gate-source current sharply increases at the same applied VDS. The thesis aims to build current models to reproduce these I-V characteristics, and to investigate the mechanism of current-controllable NDR effects. The drain-source I-V relation without leakage has been first derived and simulated to fit the experimental data and set down constants for later modeling processes. Then an analytic model of the gate current IG is introduced. The simulated results obtained a sharp drop similar to experimental data. The gate current model involves intermediate modeling processes such as tunnel probability (\theta_y), velocity of charges (\upsilon_y) approach to quantum well (QW), charge distribution function (f(E)), and potential difference along the channel (V (x)). These models are discussed in a progressive path step by step, which includes numerical derivation and simulations. The current flow direction will be analyzed as a core point. The complementary drain-source I-V characteristic relation is produced by considering the gate current derived before and generating a family of curves in a \lambda-shaped NDR in the same VDS region with a sharp drop of IG. All the simulations are done by mathematical iterating in Matlab with the Illinois Taub Cluster as simulator source. The simulated results will be compared with experimental data to verify the high reliability of the model. In the last section of the project, the limitation of the uncomplementary derivation of V (x) after device saturation will be discussed, accompanied by suggestions for future improvements

Research on Cutting Force of Turn-Milling Based on Thin-Walled Blade

Turn-milling is regarded as the milling of a curved surface while rotating the workpiece around its center point, which combines effectively the advantages of both turning and milling, wherein it allows for good metal removal with the difficult-to-cut thin-walled workpieces in aviation. The objective of the present work is to study cutting force by turn-milling in cutting condition. Aiming at the deformation properties of thin-walled blade, the predicted models of rigid cutting force and flexible cutting force with ball cutter are provided, respectively, in turn-milling process. The deformation values of blade and cutter are calculated, respectively, based on the engaged trajectory by using the iterative algorithm. The rigid and flexible cutting forces are compared and the influence degrees of cutting parameters on cutting forces are analyzed. These conclusions provide theoretical foundation and reference for turn-milling mechanism research

Research on dynamic performance and motion control of robot manipulator

Amongst the robotics and autonomous systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. In this paper, the purpose is to research on dynamic performance and motion control of robot manipulator for the more precise, crucial and critical tasks in industry. Firstly, the forward and inverse kinematics was accurately described by obtaining the link transformation matrices from each joint in robot manipulator. To find admissible solutions along the path, the workspace of the manipulator was determined by joint limit condition and validated by actual measurement. And then, the dynamic performance of robot manipulator is researched by using the forming flexible multi-body system. Furthermore, the frequency response curves are obtained by exciting vibration simulation based on vibration model, which the predicted method was validated by comparing simulation and experimental results. Finally, the control system architecture was given and the grasping process was conducted by gripper based on motion trajectory control in the workspace

Polarization-artifact reduction and accuracy improvement of Jones-matrix polarization-sensitive optical coherence tomography by multi-focus averaging

Polarization-sensitive optical coherence tomography (PS-OCT) is a promising biomedical imaging tool for differentiation of various tissue properties. However, the presence of multiple-scattering (MS) signals can degrade the quantitative polarization measurement accuracy. We demonstrate a method to reduce MS signals and increase the measurement accuracy of Jones matrix PS-OCT. This method suppresses MS signals by averaging of multiple Jones matrix volumes measured using different focal positions. The MS signals are decorrelated among the volumes by focus position modulation and are thus reduced by averaging. However, the single scattering signals are kept consistent among the focus-modulated volumes by computational refocusing. We validated the proposed method using a scattering phantom and a postmortem medaka fish. The results showed reduced artifacts in birefringence and degree-of-polarization uniformity measurements, particularly in deeper regions in the samples. This method offers a practical solution to mitigate MS-induced artifacts in PS-OCT imaging and improves quantitative polarization measurement accuracy

Prediction of Three-Dimensional Milling Forces Based on Finite Element

The model of milling force is mainly proposed to predict and analyze the cutting process based on finite element method in this paper. Firstly, milling finite element model is given based on orthogonal cutting principle, and then the influence laws of cutting parameters on chip formation are analyzed by using different simulation parameters. In addition, the three-dimensional milling forces are obtained from finite element models. Finally, the values of milling force by the milling experiment are also compared and analyzed with the simulation values to verify the feasibility and reasonability. It can be shown that milling forces match well between simulation and experiment results, which can provide many good basic data and analysis methods to optimize the machining parameters, reduce tool wear, and improve the workpiece surface roughness and adapt to the programming strategy of high speed machining