Development of composite porous scaffolds based on poly(lactide-co-glycolide)/nano-hydroxyapatite via selective laser sintering

Poly(lactide-co-glycolide) (PLGA)/nano-hydroxyapatite (nano-HAP) composite porous scaffolds with well-controlled pore architectures as well as high exposure of the bioactive ceramics to the scaffold surface were fabricated via selective laser sintering. Neat PLGA and the composite of PLGA/nano-HAP were used to obtain suitable process parameters. The effects of nano-HAP content on the microstructure and mechanical properties were investigated. The testing results showed that the compressive strength and modulus of the scaffolds were highly enhanced when the nano-HAP content reached from 0 to 20 wt%, while the mechanical properties experienced a sharp dropped with the nano-HAP content further increased. This might be due to the large reduction in polymer which decreased the interface bond strength between particles. It suggests that the introduction of nano-HAP as a reinforcing phase can improve the mechanical properties of the polymer porous scaffolds. The novel developed scaffolds may serve as a three-dimensional bone substrate in tissue engineering.     

Fabrication of macroscopic solid models of three-dimensional microscopic data by selective laser sintering

We discuss and give examples of the use of selective laser sintering to fabricate solid macroscopic models of microscopic specimens that have been imaged with a confocal microscope. The digital image processing necessary to create structurally sound models of both translucent and opaque specimens is presented. The fabricated models offer the ultimate in data visualization since they can be physically handled and manipulated to investigate the shape and features of the specimen. Such a powerful visualization tool is useful in both research and educational environments.     

Fabrication of porous bioactive structures using the selective laser sintering technique

Hydroxyapatite, a ceramic with which natural bone inherently bonds, has been incorporated into a polymer matrix to enhance the bioactivity of implant materials. In order to manufacture custom-made bioactive implants rapidly, selective laser sintering has been investigated to fabricate hydroxyapatite and polyamide composites and their properties investigated. One objective of this research was to identify the maximum hydroxyapatite content that could be incorporated into the matrix, which was sintered at various parameters. The study focused on investigating the control of porosity and pore size of the matrix by manipulating the selective laser sintering parameters of the laser power and laser scan speed. The interception method was used to analyse the internal porous morphology of the matrices which were cross-sectioned through the vertical plane. Most notably, all structures built demonstrated interconnection and penetration throughout the matrix. Liquid displacement was also used to analyse the porosity of the matrices. The laser power showed a negative relationship between porosity and variation in parameter values until a critical power value was reached. However, the same relationship for laser scan speed matrices was inconsistent. The effects of the laser power and laser scanning speed on the features of porous structures that could influence cell spreading, proliferation, and bone regeneration are presented.     

Fabrication of porous polymeric matrix drug delivery devices using the selective laser sintering technique

New techniques in solid freeform fabrication (SFF) have prompted research into methods of manufacturing and controlling porosity. The strategy of this research is to integrate computer aided design (CAD) and the SFF technique of selective laser sintering (SLS) to fabricate porous polymeric matrix drug delivery devices (DDDs). This study focuses on the control of the porosity of a matrix by manipulating the SLS process parameters of laser beam power and scan speed. Methylene blue dye is used as a drug model to infiltrate the matrices via a degassing method; visual inspection of dye penetration into the matrices is carried out. Most notably, the laser power matrices show a two-stage penetration process. The matrices are sectioned along the XZ planes and viewed under scanning electron microscope (SEM). The morphologies of the samples reveal a general increase in channel widths as laser power decreases and scan speed increases. The fractional release profiles of the matrices are determined by allowing the dye to diffuse out in vitro within a controlled environment. The results show that laser power and scan speed matrices deliver the dye for 8-9 days and have an evenly distributed profile. Mercury porosimetry is used to analyse the porosity of the matrices. Laser power matrices show a linear relationship between porosity and variation in parameter values. However, the same relationship for scan speed matrices turns out to be rather inconsistent. Relationships between the SLS parameters and the experimental results are developed using the fractional release rate equation for the infinite slab porous matrix DDD as a basis for correlation.     

Note: Thermal conductivity measurement of individual poly(ether ketone)/carbon nanotube fibers using a steady-state dc thermal bridge method

Customized engineered fibers are currently being used extensively in the aerospace and automobile industries due to the ability to "design in" specific engineering characteristics. Understanding the thermal conductivity of these new fibers is critical for thermal management and design optimization. In the current investigation, a steady-state dc thermal bridge method (DCTBM) is developed to measure the thermal conductivity of individual poly(ether ketone) (PEK)/carbon nanotube (CNT) fibers. For non-conductive fibers, a thin platinum layer was deposited on the test articles to serve as the heater and temperature sensor. The effect of the platinum layer on the thermal conductivity is presented and discussed. DCTBM is first validated using gold and platinum wires (25 μm in diameter) over a temperature ranging from room temperature to 400 K with ±11% uncertainty, and then applied to PEK/CNT fibers with diverse CNT loadings. At a 28 wt. % CNT loading, the thermal conductivity of fibers at 390 K is over 27 Wm(-1)K(-1), which is comparable to some engineering alloys.     

Tribological studies of poly(ether ether ketone) blends

A review of friction and wear studies of poly(ether ether ketone) (PEEK) blended with other polymers is presented. PEEK is a high performance thermoplastic now commonly employed in many engineering applications, but its tribological properties deteriorate in high temperature environments. One approach to improving the friction and wear properties of PEEK is to blend this plastic with appropriate polymers. In recent years, a number of investigations into the tribology of PEEK blended with poly(ether imide) (PEI), polytetrafluoroethylene (PTFE) and liquid crystalline polymers (LCPs) have been reported and these studies are discussed.     

Fabrication and mechanical properties of PLLA and CPC composite scaffolds

The brittleness and insufficient strength of biomaterials such as calcium phosphate cement (CPC) limit their applications in physiologically non-load-bearing bone lesions. These limitations stimulated the research for developing degradable polymer-ceramic composite materials that can closely match the modulus of bones. In this study, poly (L-lactic acid)/calcium phosphate cement (PLLA/CPC) composite scaffolds were fabricated via a four-step process, namely, measurement, prototyping, compounding, and dissolving. The design and mechanical properties of the PLLA/CPC composite structures were theoretically and experimentally studied. The PLLA/CPC scaffold improved the mechanical properties of the CPC. The CPC??s compressive strength and strengthening percentage increase with higher PLLA volume. Such composites may have a clinical use for load-bearing bone fixation.     

Development of an optical three-dimensional laser tracker using dual modulated laser diodes and a signal detector

Laser trackers are widely used in industry for tasks such as the assembly of airplanes and automobiles, contour measurement, and robot calibration. However, laser trackers are expensive, and the corresponding solution procedure is very complex. The influence of measurement uncertainties is also significant. This study proposes a three-dimensional space position measurement system which consists of two tracking modules, a zero tracking angle return subsystem, and a target quadrant photodiode (QPD). The target QPD is placed on the object being tracked. The origin locking method is used to keep the rays on the origin of the target QPD. The position of the target QPD is determined using triangulation since the two laser rays are projected onto one QPD. Modulation and demodulation are utilized to separate the coupled positional values. The experiment results show that measurement errors in the X, Y, and Z directions are less than ±0.05% when the measured object was moved by 300, 300, and 200 mm in the X, Y, and Z axes, respectively. The theoretical measurement error estimated from the measurement model is between ±0.02% and ±0.07% within the defined measurable range. The proposed system can be applied to the measurements of machine tools and robot arms.     

Fabrication of functional poly(thiophene) electrode for biosensors

Three-type polymer electrodes such as poly(Th), poly(Th-AP) and poly(Th-AP-TAA) were fabricated, respectively, by electro-oxidative polymerization of thiophene (Th), mixture of Th and 2-aminophenol (AP), and mixture of Th, AP and 3-thiopheneacetic acid (TAA) on the surface of indium tin oxide (ITO) glass by cyclic voltammetry (CV). The polymer electrodes were electrodeposited by cycling the potential between -1.0 and +2.5V in acetonitrile containing 50mM tetrabutylammoniumhexafluorophosphate (TBAF(6)P). The surface morphology of polymer electrodes was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The surface morphology of the poly(Th) showed typical roughness and fractal-like growth patterns, and the morphologies of poly(Th-AP) and poly(Th-AP-TAA) were dramatically changed. The water contact angle at the poly(Th-AP-TAA) (23 degrees ) is lower in comparison to poly(Th) (47 degrees ). The functional groups (-OH) and carboxylic acid (-COOH) group play an important role. Horseradish peroxidase was loaded onto poly(Th-AP-TAA) surface and used to test the sensing of H(2)O(2).     

Quality certification and control of polymer laser sintering: layerwise temperature monitoring using thermal imaging

In additive manufacturing (3D printing) of products for aerospace, medical, or other critical applications, the quality of the manufactured part must be “certified” before it can be used. New methods are needed to certify the quality during the fabrication process. The digital 3D quality certificate (3DQC) assures that process monitor values were within specification during the entire fabrication process. This paper proposes an approach for using high resolution infrared thermal imaging to monitor the temperature of individual layers before, during, and after laser scanning. Temperature data is indexed to the part geometry using a binary template created from the sliced 3D model. This data provides a record of the process conditions during the creation of each volume element of the part. Two temperatures are discussed in this paper: the peak temperature achieved during laser scanning and the residual temperature in the layer just before adding the next powder layer. Both of these monitors show a relationship to the geometry of the part, the layer cross-sectional area, and the presence or absence of an underlying solid layer. While both of these temperatures likely relate to part quality, this relationship is not yet understood. Ultimately, this monitor data can be used to control the process, e.g., modify the laser scan or the wait time before recoating, in order to provide more uniform sintering of each volume element of the part.     

Microstructural characterization and mechanical properties of functionally graded PA12/HDPE parts by selective laser sintering

The use of selective laser sintering in the production of functional gradient materials offers advantages, as freeform construction and localized control of the composition and process parameters, compared to other rapid manufacturing processes. In this work, selective laser sintering was used for manufacturing three-dimensional parts in functionally graded polymer blends based on polyamide 12 and high-density polyethylene with gradient composition in two directions (Y and Z). Test specimens were prepared in PA12/HDPE ratios of 0/100, 20/80, 50/50, 80/20 and 100/0 (w/w). These specimens were assessed in terms of density, microstructure by scanning electron microscopy and polarized light microscopy and mechanical performance by DMA. The sintered binary blend systems with composition gradient showed microstructure and properties variation as function of the blend compositions. The results demonstrated the potential of selective laser sintering to manufacture advanced polymeric functional gradient material parts.     

Fabrication of microgrooves on a curved surface by the confocal measurement system using pulse laser and continuous laser

In order to fabricate microgrooves on a curved surface, the curved surface was measured with a confocal system and then it was used for laser microprocessing. This paper proposes a new method of using a pulse laser for the confocal system to measure the curved surface. It also compares the conventional way of using a continuous laser and a new way of using the pulse laser with the confocal system. Using the data measured with the pulse laser for fabrication, microgrooves were fabricated on a curved surface. The width of the fabricated microgroove was 10 μm and the depth was 27 μm. The microgroove fabricated on a curved surface as a part of this study can be used in injection molding to manufacture a micropatterned plastic surface at a low cost. This plastic surface can be applied for a superhydrophobic surface, a self-cleaning surface, or a biochip.     

Fabrication of high quality factor lithium niobate double-disk using a femtosecond laser

We demonstrate fabrication of a high-quality factor lithium niobate double-disk whispering-gallery microcavity using femtosecond laser assisted ion beam milling. Using this method, two vertically stacked 30-µm diameter disks with a 200-nm gap are fabricated. With our device, an optical quality factor as high as 1.35?×?10⁵ is demonstrated. Our approach is scalable to fabricate multiple disks on a single chip.     

Fabrication of polycrystalline diamond microtool using a Q-switched Nd:YAG laser

A Q-switched Nd:YAG laser (1,064 nm, 100 ns) was used to machine 2?×?1.5?×?0.5-mm rhombus-shaped tool inserts from a 60?×?0.5-mm circular disk of polycrystalline diamond. A systematic experimental study was undertaken to examine the effects of pulse repetition rate, feed rate, and number of laser passes on kerf, material removal rate, recast layer, surface morphology, and surface roughness. The optimal laser parameters for generating two-dimensional tool profiles were an average power of 3 W, a pulse repetition rate of 2 kHz, a feed rate of 1 mm/s, and a total of 45 laser passes. The beneficial results were a material removal rate of 0.02 mm³/min, kerf width of 27 μm, cutting edge radius of 6 μm, and surface roughness (Ra) of 0.625 μm. Recast layer formation, undulations, and striations were observed in the laser-cut regions. These features were attributed to the presence of a molten layer of cobalt binder, and amorphous carbon and graphite transitioned from diamond. An intriguing feature is the presence of fine particulate matter ranging in size from nanometers to a few micrometers in the laser-cut regions. It is believed that phase transition of diamond and cobalt during laser machining created thermal expansion mismatch stresses sufficient to fracture the solid into fine fragments.     

毛细力辅助飞秒激光直写制备各向异性及多级结构

将飞秒激光双光子聚合加工技术和毛细力诱导自组装技术相结合实现了各向异性结构和多级结构的制备。首先,使用飞秒激光双光子加工技术加工出微柱阵列,将微柱置于显影液中显影,然后放置在空气中。在显影液蒸发的过程中,微柱结构单元受到毛细力的作用而弯曲实现自组装。通过控制微柱的高度和直径的不一致性实现了两种各向异性结构制备方法,并成功制备了底层微柱直径分别为2μm和6μm双层结构。由于毛细力的大小和微柱高度无关,且同样端部变形量下较高微柱的弹性回复力小于较低微柱的弹性回复力,更易发生弯曲;直径较大的微柱具有更强的抗弯曲能力,从而引导直径较小的微柱向较大的微柱倾斜,藉此制备了各向异性结构。使用毛细力自组装辅助飞秒激光微纳加工可以实现灵活可控的复杂3D结构的加工,并将在生物医药、化学分析、微流体等领域发挥重要作用。     

Tool damage and machined-surface quality using hot-pressed sintering Ti(C7N3)/WC/TaC cermet cutting inserts for high-speed turning stainless steels

The International Journal of Advanced Manufacturing Technology - A Ti(C7N3)/WC/TaC cermet cutting tool was developed using a hot-pressed technology. A standard orthogonal array was used to...     

选择性激光烧结激光能量密度与温度补偿规律研究

选择性激光烧结（SLS）成型预热温度从成型缸中间到缸壁呈降低趋势,由于预热温度不均匀,导致SLS成型件密度不均匀。针对这一问题,通过增加激光能量密度对预热温度不足进行了补偿。通过试验建立了激光能量密度差△E与预热温差△T的经验公式,并比较了温度补偿前后烧结件的机械强度。实验结果表明,通过增加激光能量密度对预热温度不足进行补偿,提高了产品机械强度。