Scaffold development using 3D printing with a starch-based polymer

Rapid prototyping (RP) techniques have been utilised by tissue engineers to produce three-dimensional (3D) porous scaffolds. RP technologies allow the design and fabrication of complex scaffold geometries with a fully interconnected pore network. Three-dimensional printing (3DP) technique was used to fabricate scaffolds with a novel micro- and macro-architecture. In this study, a unique blend of starch-based polymer powders (cornstarch, dextran and gelatin) was developed for the 3DP process. Cylindrical scaffolds of five different designs were fabricated and post-processed to enhance the mechanical and chemical properties. The scaffold properties were characterised by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), porosity analysis and compression tests

Measuring the mechanical properties of ground ophthalmic polymer surfaces using nanoindentation

This work is motivated by the need to efficiently machine the edges of ophthalmic polymer lenses for mounting in spectacle or instrument frames. The polymer materials used are required to have suitable optical characteristics such high refractive index and Abbe number, combined with low density and high scratch and impact resistance. Edge surface finish is an important aesthetic consideration; its quality is governed by the material removal operation and the physical properties of the material being processed. The wear behaviour of polymer materials is not as straightforward as for other materials due to their molecular and structural complexity, not to mention their time-dependent properties. Four commercial ophthalmic polymers have been studied in this work using nanoindentation techniques which are evaluated as tools for probing surface mechanical properties in order to better understand the grinding response of polymer materials.

Measuring the mechanical properties of ground ophthalmic polymer surfaces using nanoindentation

This work is motivated by the need to efficiently machine the edges of ophthalmic polymer lenses for mounting in spectacle or instrument frames. The polymer materials used are required to have suitable optical characteristics such high refractive index and Abbe number, combined with low density and high scratch and impact resistance. Edge surface finish is an important aesthetic consideration; its quality is governed by the material removal operation and the physical properties of the material being processed. The wear behaviour of polymer materials is not as straightforward as for other materials due to their molecular and structural complexity, not to mention their time-dependent properties. Four commercial ophthalmic polymers have been studied in this work using nanoindentation techniques which are evaluated as tools for probing surface mechanical properties in order to better understand the grinding response of polymer materials.

Fabrication and characterization of plasma polymer thin films from monoterpene alcohols for applications in organic electronics and biotechnology

After more than twenty years of basic and applied research, the use of nanotechnology in the design and manufacture of nanoscale materials is rapidly increasing, particularly in commercial applications that span from electronics across renewable energy areas, and biomedical devices. Novel polymers are attracting significant attention for they promise to provide a low−cost high−performance alternative to existing materials. Furthermore, these polymers have the potential to overcome limitations imposed by currently available materials thus enabling the development of new technologies and applications that are currently beyond our reach. This work focuses on the development of a range of new low−cost environmentally−friendly polymer materials for applications in areas of organic (flexible) electronics, optics, and biomaterials. The choice of the monomer reflects the environmentally−conscious focus of this project. Terpinen−4−ol is a major constituent of Australian grown Melaleuca alternifolia (tea tree) oil, attributed with the oil's antimicrobial and anti−inflammatory properties. Plasma polymerisation was chosen as a deposition technique for it requires minimal use of harmful chemicals and produces no hazardous by−products. Polymer thin films were fabricated under varied process conditions to attain materials with distinct physico−chemical, optoelectrical, biological and degradation characteristics. The resultant materials, named polyterpenol, were extensively characterised using a number of well−accepted and novel techniques, and their fundamental properties were defined. Polyterpenol films were demonstrated to be hydrocarbon rich, with variable content of oxygen moieties, primarily in the form of hydroxyl and carboxyl functionalities. The level of preservation of original monomer functionality was shown to be strongly dependent on the deposition energy, with higher applied power increasing the molecular fragmentation and substrate temperature. Polyterpenol water contact angle contact angle increased from 62.7° for the 10 W samples to 76.3° for the films deposited at 100 W. Polymers were determined to resist solubilisation by water, due to the extensive intermolecular and intramolecular hydrogen bonds present, and other solvents commonly employed in electronics and biomedical processing. Independent of deposition power, the surface topography of the polymers was shown to be smooth (Rq <0.5 nm), uniform and defect free. Hardness of polyterpenol coatings increased from 0.33 GPa for 10 W to 0.51 GPa for 100 W (at 500 μN load). Coatings deposited at higher input RF powers showed less mechanical deformation during nanoscratch testing, with no considerable damage, cracking or delamination observed. Independent of the substrate, the quality of film adhesion improved with RF power, suggesting these coatings are likely to be more stable and less susceptible to wear. Independent of fabrication conditions, polyterpenol thin films were optically transparent, with refractive index approximating that of glass. Refractive index increased slightly with deposition power, from 1.54 (10 W) to 1.56 (100 W) at 500 nm. The optical band gap values declined with increasing power, from 2.95 eV to 2.64 eV, placing the material within the range for semiconductors. Introduction of iodine impurity reduced the band gap of polyterpenol, from 2.8 eV to 1.64 eV, by extending the density of states more into the visible region of the electromagnetic spectrum. Doping decreased the transparency and increased the refractive index from 1.54 to 1.70 (at 500 nm). At optical frequencies, the real part of permittivity (k) was determined to be between 2.34 and 2.65, indicating a potential low-k material. These permittivity values were confirmed at microwave frequencies, where permittivity increased with input RF energy – from 2.32 to 2.53 (at 10 GHz ) and from 2.65 to 2.83 (at 20 GHz). At low frequencies, the dielectric constant was determined from current−voltage characteristics of Al−polyterpenol−Al devices. At frequencies below 100 kHz, the dielectric constant varied with RF power, from 3.86 to 4.42 at 1 kHz. For all samples, the resistivity was in order of 10⁸−10⁹ _m (at 6 V), confirming the insulating nature of polyterpenol material. In situ iodine doping was demonstrated to increase the conductivity of polyterpenol, from 5.05 × 10⁻⁸ S/cm to 1.20 × 10⁻⁶ S/cm (at 20 V). Exposed to ambient conditions over extended period of time, polyterpenol thin films were demonstrated to be optically, physically and chemically stable. The bulk of ageing occurred within first 150 h after deposition and was attributed to oxidation and volumetric relaxation. Thermal ageing studies indicated thermal stability increased for the films manufactured at higher RF powers, with degradation onset temperature associated with weight loss shifting from 150 ºC to 205 ºC for 10 W and 100 W polyterpenol, respectively. Annealing the films to 405 °C resulted in full dissociation of the polymer, with minimal residue. Given the outcomes of the fundamental characterisation, a number of potential applications for polyterpenol have been identified. Flexibility, tunable permittivity and loss tangent properties of polyterpenol suggest the material can be used as an insulating layer in plastic electronics. Implementation of polyterpenol as a surface modification of the gate insulator in pentacene-based Field Effect Transistor resulted in significant improvements, shifting the threshold voltage from + 20 V to –3 V, enhancing the effective mobility from 0.012 to 0.021 cm²/Vs, and improving the switching property of the device from 10⁷ to 10⁴. Polyterpenol was demonstrated to have a hole transport electron blocking property, with potential applications in many organic devices, such as organic light emitting diodes. Encapsulation of biomedical devices is also proposed, given that under favourable conditions, the original chemical and biological functionality of terpinen−4−ol molecule can be preserved. Films deposited at low RF power were shown to successfully prevent adhesion and retention of several important human pathogens, including P. aeruginosa, S. aureus, and S. epidermidis, whereas films deposited at higher RF power promoted bacterial cell adhesion and biofilm formation. Preliminary investigations into in vitro biocompatibility of polyterpenol demonstrated the coating to be non−toxic for several types of eukaryotic cells, including Balb/c mice macrophage and human monocyte type (HTP−1 non-adherent) cells. Applied to magnesium substrates, polyterpenol encapsulating layer significantly slowed down in vitro biodegradation of the metal, thus increasing the viability and growth of HTP−1 cells. Recently, applied to varied nanostructured titanium surfaces, polyterpenol thin films successfully reduced attachment, growth, and viability of P. aeruginosa and S. aureus.

Electro-magnetically Actuated Minute Polymer Pump Fabricated using Packaging Technology

Design, fabrication and preliminary testing of a flat pump with millimetre thickness are described in this paper. The pump is entirely made of polymer materials barring the magnet and copper coils used for electromagnetic actuation. The fabrication is carried out using widely available microelectronic packaging machinery and techniques. Therefore, the fabrication of the pump is straightforward and inexpensive. Two types of prototypes are designed and built. One consists of copper coils that are etched on an epoxy plate and the other has wound insulated wire of 90 mu m diameter to serve as a coil. The overall size of the first pump is 25 mm x 25 mm x 3.6 mm including the 3.1 mm-thick NdFeB magnet of diameter 12 mm. It consists of a pump chamber of 20 mm x 20 mm x 0.8 mm with copper coils etched from a copper-clad epoxy plate using dry-film lithography and milled using a CNC milling machine, two passive valves and the pump-diaphragm made of Kapton film of 0.089 mm thickness. The second pump has an overall size of 35 mm x 35 mm x 4.4 mm including the magnet and the windings. A breadboard circuit and DC power supply are used to test the pump by applying an alternating square-wave voltage pulse. A water slug in a tube attached to the inlet is used to observe and measure the air-flow induced by the pump against atmospheric pressure. The maximum flow rate was found to be 15 ml/min for a voltage of 2.5 V and a current of 19 mA at 68 Hz.

Polymer-based board-level optical interconnects

This paper provides an overview of the rationale behind the significant interest in polymer-based on-board optical links together with a brief review of recently reported work addressing certain challenges in this field. Polymer-based optical links have garnered considerable research attention due to their important functional attributes and compelling cost-benefit advantages in on-board optoelectronic systems as they can be cost-effectively integrated on conventional printed circuit boards. To date, significant work on the polymer materials, their fabrication process and their integration on standard board substrates have enabled the demonstration of numerous high-speed on-board optical links. However, to be deployed in real-world systems, these optoelectronic printed circuit boards (OE PCBs) must also be cost-effective. Here, recent advances in the integration process focusing on simple direct end-fire coupling schemes and the use of low-cost FR4 PCB substrates are presented. Performance of two proof-of-principle 10 Gb/s systems based on this integration method are summarised while work in realising more complex yet compact planar optical components is outlined. © 2011 IEEE.

Polymer waveguide-based backplanes for board-level optical interconnects

Optical interconnects are increasingly considered for use in high-performance electronic systems. Multimode polymer waveguides are a promising technology for the formation of optical backplane as they enable cost-effective integration of optical links onto standard printed circuit boards. In this paper, two different types of polymer waveguide-based optical backplanes are presented. The first one implements a passive shuffle architecture enabling non-blocking on-board optical interconnection between different cards/modules, while the second one deploys a regenerative bus architecture allowing the interconnection of an arbitrary number of electrical cards over a common optical bus. The polymer materials and the multimode waveguide components used to form the optical backplanes are presented, while details of the interconnection architectures and design of the backplanes are described. Proof-of-principle demonstrators fabricated onto low-cost FR4 substrates, including a 10-card 1 Tb/s-capacity passive shuffle router and 4-channel 3-card polymeric bus modules, are reported and their optical performance characteristics are presented. Low-loss, low-crosstalk on-board interconnection is achieved and error-free (BER10 12) 10 Gb/s communication between different card/module interfaces is demonstrated in both polymeric backplane systems. © 2012 IEEE.

Application of particle swarm optimisation to evaluation of polymer cure kinetics models

A particle swarm optimisation approach is used to determine the accuracy and experimental relevance of six disparate cure kinetics models. The cure processes of two commercially available thermosetting polymer materials utilised in microelectronics manufacturing applications have been studied using a differential scanning calorimetry system. Numerical models have been fitted to the experimental data using a particle swarm optimisation algorithm which enables the ultimate accuracy of each of the models to be determined. The particle swarm optimisation approach to model fitting proves to be relatively rapid and effective in determining the optimal coefficient set for the cure kinetics models. Results indicate that the singlestep autocatalytic model is able to represent the curing process more accurately than more complex model, with ultimate accuracy likely to be limited by inaccuracies in the processing of the experimental data.

Biaxial Characterisation of Materials for Thermoforming and Blow Moulding

During free surface moulding processes such as thermoforming and blow moulding heated polymer materials are subjected to rapid biaxial deformation as they are drawn into the shape of a mould. In the development of process simulations it is therefore essential to be able to accurately measure and model this behaviour. Conventional uniaxial test methods are generally inadequate for this purpose and this has led to the development of specialised biaxial test rigs. In this paper the results of several programmes of biaxial tests conducted at Queen’s University are presented and discussed. These have included tests on high impact polystyrene (HIPS), polypropylene (PP) and aPET, and the work has involved a wide variety of experimental conditions. In all cases the results clearly demonstrate the unique characteristics of materials when subjected to biaxial deformation. PP draws the highest stresses and it is the most temperature sensitive of the materials. aPET is initially easier to form but exhibits strain hardening at higher strains. This behaviour is increased with increasing strain rate but at very high strain rates these effects are increasingly mollified by adiabatic heating. Both aPET and PP (to a lesser degree) draw much higher stresses in sequential stretching showing that this behaviour must be considered in process simulations. HIPS showed none of these effects and it is the easiest material to deform.

Measurement of Polymer-to-Polymer Contact Friction in Thermoforming

Contact friction plays a critical role in all the major thermoforming processes for polymers. However, these effects are very difficult to measure in practice and, as a result, have received little scientific investigation. In this work, two independently developed test methods for the measurement of elevated temperature polymer-to-polymer contact friction are presented, and their results are compared in detail for the first time. One is based on a modified moving sled friction test, whereas the other uses a rotational rheometer. In each case, friction tests were conducted between two plug and two sheet materials. The results show that broadly similar coefficients of friction were obtained from the two test methods. The measured values were quite low (<0.3) at lower temperatures and typically were higher for polypropylene (PP) sheet than for polystyrene (PS). On approaching the glass transition temperature for PS (95°C) and the crystalline melting point for PP (165°C), the friction coefficients rose very sharply, and both test techniques became increasingly unreliable. It was concluded that despite their physical differences, both test techniques were able to capture the highly temperature sensitive nature of friction between polymer materials used in thermoforming.

The inferential monitoring of the screw disturbance torque to predict process fluctuations in polymer extrusion

Polymer extrusion is one of the major methods of processing polymer materials and advanced process monitoring is important to ensure good product quality. However, commonly used process monitoring devices, e.g. temperature and pressure sensors, are limited in providing information on process dynamics inside an extruder barrel. Screw load torque dynamics, which may occur due to changes in solids conveying, melting, mixing, melt conveying, etc., are believed to be a useful indicator of process fluctuations inside the extruder barrel. However, practical measurement of the screw load torque is difficult to achieve. In this work, inferential monitoring of the screw load torque signal in an extruder was shown to be possible by monitoring the motor current (armature and/or field) and simulation studies were used to check the accuracy of the proposed method. The ability of this signal to aid identification and diagnosis of process issues was explored through an experimental investigation. Power spectral density and wavelet frequency analysis were implemented together with a covariance analysis. It was shown that the torque signal is dominated by the solid friction in the extruder and hence it did not correlate well with melting fluctuations. However, it is useful for online identification of solids conveying issues.

Development and microwave characterization of selected biocompatible materials and conducting polymers

The 20th century witnessed the extensive use of microwaves in industrial, scientific and medical fields. The major hindrance to many developments in the ISM field is the lack of knowledge about the effect of microwaves on materials used in various applications. The study of the interaction of microwaves with materials demanded the knowledge of the dielectric properties of these materials. However, the dielectric properties of many of these materials are still unknown or less studied. This thesis is an effort to shed light into the dielectric properties of some materials which are used in medical, scientific and industrial fields. Microwave phantoms are those materials used in microwave simulation applications. Effort has been taken to develop and characterize low cost, eco-friendly phantoms from Biomaterials and Bioceramics. The interaction of microwaves with living tissues paved way to the development of materials for electromagnetic shielding. Materials with good conductivity/absorption properties could be used for EMI shielding applications. Conducting polymer materials are developed and characterized in this context. The materials which are developed and analyzed in this thesis are Biomaterials, Bioceramics and Conducting polymers. The use of materials of biological origin in scientific and medical applications provides an eco-friendly pathway. The microwave characterization of the materials were done using cavity material perturbation method. Low cost and ecofriendly biomaterial films were developed from Arrowroot and Chitosan. The developed films could be used in applications such as microwave phantom material, capsule material in pharmaceutical applications, trans-dermal patch material and eco-friendly Band-Aids. Bioceramics with better bioresorption and biocompatibility were synthesized. Bioceramics such as Hydroxyapatite, Beta tricalcium phosphate and Biphasic Calcium Phosphate were studied. The prepared bioceramics could be used as phantom material representing Collagen, Bone marrow, Human abdominal wall fat and Human chest fat. Conducting polymers- based on Polyaniline, are developed and characterized. The developed materials can be used in electromagnetic shielding applications such as in anechoic chambers, transmission cables etc

A complete atomistic model of molten polyethylene from neutron scattering data: a new methodology for polymer structure

A new approach to the study of the local organization in amorphous polymer materials is presented. The method couples neutron diffraction experiments that explore the structure on the spatial scale 1–20 Å with the reverse Monte Carlo fitting procedure to predict structures that accurately represent the experimental scattering results over the whole momentum transfer range explored. Molecular mechanics and molecular dynamics techniques are also used to produce atomistic models independently from any experimental input, thereby providing a test of the viability of the reverse Monte Carlo method in generating realistic models for amorphous polymeric systems. An analysis of the obtained models in terms of single chain properties and of orientational correlations between chain segments is presented. We show the viability of the method with data from molten polyethylene. The analysis derives a model with average C-C and C-H bond lengths of 1.55 Å and 1.1 Å respectively, average backbone valence angle of 112, a torsional angle distribution characterized by a fraction of trans conformers of 0.67 and, finally, a weak interchain orientational correlation at around 4 Å.

Preparation and photoluminescence properties of functionalized silica materials incorporating europium complexes

In the present work, the surface of the Eu-BTC = [Eu(EMA)(H(2)O)(2)], [Eu(TLA)(H(2)O)(4)] and [Eu(TMA)(H(2)O)(6)] complexes (EMA = 1,2,3-benzenetricarboxylate, TLA = 1,2,4-benzenetricarboxylate and TMA = 1,3,5-benzenetricarboxylate) was modified using 3-aminopropyltriethoxysilane (APTES) by a new microwave assisted method that proved to be simple and efficient. According to our observations, the most efficient luminescence is the material based on APTES incorporating [Eu(TMA)(H(2)O)(6)] complexes, denoted as Eu-TMA-Si, shows the highest emission efficiency. Therefore, it is proposed as a promising material for molecular conjugation in clinical diagnosis. (C) 2011 Elsevier B.V. All rights reserved.

FEA simulation of contact and wear between non-metallic materials for accelerated new product development

The conventional approach ie laboratory life testing to examine the reliability of products takes long time and involves tremendous cost as samples are tested till failures. The accelerated life test (ALT) has recently been used as an alternative method. Although ALT reduces the cost of reliability testing through applying more severe environmental conditions than the normal ones, it is no longer sufficient as it does not describe the process of products’ failure explicitly and it is still highly dependent on physical testing. Consequently, novel practices need to be developed for better understanding of the products’ reliability. A novel Finite Element Analysis (FEA) model incorporating mathematical wear equations is developed in the current work and applied to polymer materials. Wear rate, a key parameter, is calculated by using a combinatorial formula that combines a conventional linear equation with a recently published exponential equation. The local wear is firstly calculated and then integrated over the sliding distance. The FEA simulation works in a loop and performs a series of simulation with updated surface geometries. The simulation is in good agreement with the physical testing result.