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Sodium alginate (SA) is a non-toxic, biocompatible and biodegradable natural polymer. It has good printability, which is why it is often used in inks for three-dimensional (3D) printing in tissue engineering fields. However, pure SA hydrogel has unstable mechanical properties. In this study, we fabricated a structurally stable 3D scaffold by blending SA with poly(vinyl alcohol) (PVA) to enhance the mechanical properties of the scaffold. Moreover, we characterized the surface morphology and various mechanical properties of the scaffolds using scanning electron microscopy, Fourier transform-infrared spectroscopy, thermogravimetric analysis and several mechanical tests. The SA/PVA scaffolds were mechanically more stable than the pure SA scaffold and are good candidate as implantable biodegradable scaffolds for tissue engineering and medical applications.

To adapt biomaterials for solid freeform fabrication (SFF), methoxy polyethylene glycol (MPEG)-(PLLA-co-PCL) (LxCy) block copolymers were prepared using MPEG as the initiator to precisely control the molecular weight of PLLA and PCL. The LxCy block copolymers were designed such that the PLLA and PCL content varied and their molecular weights were within 200–1000 kDa. The cylindrical LxCy scaffolds were prepared by using LxCy block copolymers in SFF. The feasibility of using LxCy block copolymers was examined in terms of flowability from the micronozzle and solidification at room temperature after scaffold printing. The flowability and solidification of LxCy block copolymers mainly depend on the proportions of PLLA and PCL. Fabrication of the cylindrical LxCy scaffolds by using SFF was rapid and showed high reproducibility. In in vivo implantation, the cylindrical LxCy scaffolds exhibited biocompatibility and gradual biodegradation on a 16 week timescale. Immunohistochemical characterization showed that the in vivo LxCy scaffolds elicit only a modest inflammatory response. Taken together, these results show that LxCy block copolymers may serve as suitable biomaterials for the fabrication of well-defined three-dimensional scaffolds by using SFF.

Although three-dimensional (3D) bioprinting technology is rapidly developing, the design strategies for biocompatible 3D-printable bioinks remain a challenge. In this study, we developed a machine learning-based method to design 3D-printable bioink using a model system with naturally derived biomaterials. First, we demonstrated that atelocollagen (AC) has desirable physical properties for printing compared to native collagen (NC). AC gel exhibited weakly elastic and temperature-responsive reversible behavior forming a soft cream-like structure with low yield stress, whereas NC gel showed highly crosslinked and temperature-responsive irreversible behavior resulting in brittleness and high yield stress. Next, we discovered a universal relationship between the mechanical properties of ink and printability that is supported by machine learning: a high elastic modulus improves shape fidelity and extrusion is possible below the critical yield stress; this is supported by machine learning. Based on this relationship, we derived various formulations of naturally derived bioinks that provide high shape fidelity using multiple regression analysis. Finally, we produced a 3D construct of a cell-laden hydrogel with a framework of high shape fidelity bioink, confirming that cells are highly viable and proliferative in the 3D constructs.

Three-dimensional (3D) printing is a novel process used to manufacture bone tissue engineered scaffolds. This process allows for easy control of the architecture at the micro structure. However, the scaffold properties are typically limited in terms of cellular activity at the scaffold surface due to the printed materials properties. In this study, we developed a polycaprolactone (PCL) blended with polyethylene glycol (PEG) 3D printed scaffold using a rapid prototyping system. The manufactured scaffolds were then washed out to form small pores on the surface in order to improve the scaffolds hydrophilicity. We analyzed the resultant material by using Scanning Electron Microscopy (SEM), water absorption, water contact angle, in vitro WST-1, and the Bradford assay. Additionally, cells incubated on the fabricated scaffolds were visualized by Confocal Laser Scanning Microscopy (CLSM). The developed scaffolds exhibited small pores on the strand surface which served to increase hydrophilicity as well as improve cellular proliferation and increase total protein content. Our findings suggest that the presence of small pores on the scaffolds can be used as an effective tool for improving implant cellular interaction. This research indicates that these modified scaffolds can be considered useful for bone tissue engineering applications to improve human health.

In this study, we designed scaffolds coated with gold nanoparticles (GNPs) grown on a polydopamine (PDA) coating of a three-dimensional (3D) printed polycaprolactone (PCL) scaffold. Our results demonstrated that the scaffolds developed here may represent an innovative paradigm in bone tissue engineering by inducing osteogenesis as a means of remodeling and healing bone defects.

Cell-printing techniques that can construct three-dimensional (3D) structures with biocompatible materials and cells are of great interest for various biomedical applications, such as tissue engineering and drug-screening studies. For successful cell-printing with cells, bioinks are critical for both the processability of printing and the viability of printed cells. However, the influence of composition on 3D bio-printing with cells has not been well explored. In this study, we investigated different compositions of alginate bioinks by varying the concentrations of high molecular weight alginate (High Alg) and low molecular weight alginate (Low Alg). Bioinks of 3wt% alginate containing High Alg alone or a 1:2 (Low Alg:High Alg) composite allowed for the construction of 3D scaffolds with good processability and shapes. Cell-printing with fibroblasts and in vitro culture studies revealed good viability and growth of the printed cells after up to 7days of culture. Bioinks prepared with High and Low Alg at a 2:1 ratio exhibited better cell growth compared with those of other compositions. This study progresses the design and applications of alginate-based bioinks for cell-printing platforms in soft tissue engineering.

β-tricalcium phosphate (β-TCP) and polycaprolactone (PCL) composites were manufactured using the lab-made 3D bioprinting system to produce 50TCP50PCL (50% β-TCP with 50% PCL) and 70TCP30PCL (70% β-TCP with 30% PCL) composite scaffolds for bone tissue engineering. The 70TCP30PCL scaffold containing the highest β-TCP content exhibited rougher morphologies and more porous than the other scaffolds ( i.e. , PCL and 50TCP50PCL). In vitro studies revealed that cell proliferation and alkaline phosphate activity were improved on the β-TCP-based composite scaffolds. Our results suggest that our 3-D printed β-TCP-containing PCL scaffolds would benefit new dental applications or regeneration therapies.

This paper demonstrates a simple and cost-effective method to maintain superhydrophilicity of three-dimensional shaped aluminum fins' surface of dehumidifier over long period of time in order to improve water collection and energy efficiency. Wire-metallization, commercially available method in the ...

Sang Jin Lee1,2, Ha Hyeon Jo1, Seong Keun Kwon3, Jin Ho Lee4, Wan Doo Kim1, Jun Hee Lee1, Il Keun Kwon*2, and Su A Park,*,1 Department of Nature-Inspired Nanoconvergence Systems, Korea Institute of Machinery and Materials, 156 Gajeongbuk-ro, Yuseong-gu, Daejeon 34103, Korea Department of Dental Materials, School of Dentistry, Kyung Hee University, 26 Kyunghee-daero, Dongdaemun-gu, Seoul 02447, Korea Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea Department of Advanced Materials, Hannam University, 1646 Yuseong-daero, Yuseong-gu, Daejeon 34054, Korea

In this study, we prepared a helical, biocompatible, and biodegradable stent by 3D rapid prototyping. The fabricated polycaprolactone (PCL) stent was coated with sirolimus mixed with poly-(lactide-co-glycolide) (PLGA), and polyethylene glycol (PEG), via a spraying method for slow drug release. The engineered, drug-eluting, bio-absorbable vascular stent (BVS) was analyzed and tested in vivo, and proving effective in animal experiments. These findings suggest that our new approach is useful for treating coronary thrombosis, and it may provide a promising scaffold for developing biological stent technology.

For patients who suffer from sensorineural hearing loss by damaged or loss of hair cells in the cochlea, biomimetic artificial cochleas to remedy the dis­advantages of existing implant systems have been intensively studied. Here, a new concept of an inorganic-based piezoelectric acoustic nanosensor (iPANS) for the purpose of a biomimetic artificial hair cell to mimic the functions of the original human hair cells is introduced. A trapezoidal silicone-based membrane (SM) mimics the function of the natural basilar membrane for frequency selectivity, and a flexible iPANS is fabricated on the SM utilizing a laser lift-off technology to overcome the brittle characteristics of inorganic piezoelectric materials. The vibration amplitude vs piezoelectric sensing signals are theoretically examined based on the experimental conditions by finite element analysis. The SM is successful at separating the audible frequency range of incoming sound, vibrating distinctively according to varying locations of different sound frequencies, thus allowing iPANS to convert tiny vibration displacement of ≈15 nm into an electrical sensing output of ≈55 μV, which is close to the simulation results presented. This conceptual iPANS of flexible inorganic piezoelectric materials sheds light on the new fields of nature-inspired biomimetic systems using inherently high piezoelectric charge constants.

In this research, we have developed a multi-channel piezoelectric acoustic sensor (McPAS) that mimics the function of the natural basilar membrane capable of separating incoming acoustic signals mechanically by their frequency and generating corresponding electrical signals. The McPAS operates without an external energy source and signal processing unit with a vibrating piezoelectric thin film membrane. The shape of the vibrating membrane was chosen to be trapezoidal such that different locations of membrane have different local resonance frequencies. The length of the membrane is 28 mm and the width of the membrane varies from 1 mm to 8 mm. Multiphysics finite element analysis (FEA) was carried out to predict and design the mechanical behaviors and piezoelectric response of the McPAS model. The designed McPAS was fabricated with a MEMS fabrication process based on the simulated results. The fabricated device was tested with a mouth simulator to measure its mechanical and piezoelectrical frequency response with a laser Doppler vibrometer and acoustic signal analyzer. The experimental results show that the as fabricated McPAS can successfully separate incoming acoustic signals within the 2.5 kHz–13.5 kHz range and the maximum electrical signal output upon acoustic signal input of 94 dBSPL was 6.33 mVpp. The performance of the fabricated McPAS coincided well with the designed parameters.

In this paper, a simple and low-cost fabrication method is demonstrated to make superhydrophobic and superoleophobic Aluminum (Al) surfaces. The Al surfaces have hierarchical structures mimicking the lotus leaf. The manufacturing process is easily performed via grinding, acid etching, and low surface tension chemical coating, in sequence. The wettability of the fabricated Al surfaces is characterized with several liquids having different surface tension energy such as water, diiodomethane, and hexadecane. The effects of grinding and acid etching on wettability are also investigated to enhance the superhydrophobicity and superoleophobicity of the Al surface. The grinding process makes the surface rough effectively and improves the wetting behavior. Especially, the ground sample prepared with a sandpaper of P1000 grade shows the highest static contact angle and lowest sliding angle among the fabricated samples. Even though the wetting properties are generally improved by increasing the acid etching time, the repellency of the liquids on the surface is saturated at 10min of acid etching time. The morphology difference of Al surfaces is characterized by measurement of field-emission scanning electron microscope (FE-SEM). The hierarchical micro/nanostructures combined with chemical coating enable the Al surface to be superhydrophobic and superoleophobic.

Totally implantable middle-ear prosthetic devices, such as the Esteem system (Envoy Medical Corporation), detect vibrational motion of the middle-ear ossicles rather than acoustic stimulation to the eardrum. This eliminates the need for a subcutaneous microphone, which is susceptible to interference by ambient noises. Study of the vibrational characteristics of the human ossicles provides valuable information for determining the site of maximum ossicular motion that would be optimal for attachment of the sensor portion of the prosthesis. In this study, vibrational responses at seven locations on the middle-ear ossicles (i.e., the malleus head, 4 different points on the incus body, middle of the incus long process, tip of the incus long process) in human temporal bones (n = 6) were measured using a laser Doppler vibrometer. The measurements were repeated after separating the incudostapedial joint (ISJ). Measured displacement at each location was normalized with the sound pressure level near the tympanic membrane (TM) for representation in the form of a displacement transfer function (DTF). The normalized squared sum of the DTFs (NSSDTF) was then calculated as a measure of vibration motion through a specific frequency range at the considered sites. The relatively large NSSDTF was observed at the sites on the superior part of the malleus head (MH), on the lateral part of the incus body (IBL), and on the superior part of the incus body near the incudomalleal joint (IBS1) for the frequency ranges of 1-4 kHz and 1-9 kHz, regardless of the condition of the ISJ. This indicates that maximum vibrational motion of the middle-ear is deliverable to the piezoelectric transducer of totally implantable devices through these sites. This article is part of a special issue entitled "MEMRO 2012".

Graphical abstractDisplay Omitted Highlights? Single conducting polymer nanowire is fabricated directly on the device platform. ? Facile method provids the controlled position, width, and length of nanowire. ? Nanowire is electrochemically deposited on the nanopatterned area of electrode. ? Polypyrrole nanowire based field effect transistor is successfully established. In this paper, a facile method by which conducting polymer nanowire can be fabricated directly on the device platform in controlled position, width, and length is proposed. Conducting polymer was electrochemically deposited on the nanopatterned area of a working electrode. The shape and position of the nanowire, in particular the length of the nanowire can be easily controlled by modulation of the nanopatterned area via lithography method. Through the proposed fabrication method, a polypyrrole nanowire based field effect transistor was successfully established. This fabrication design provides an easy way to manufacture the conducting polymer nanowire based devices in controlled manner, and the devices are suitable for application in chemical and biological sensors as well as organic electronics.

Rubber components have been widely used in automotive industry as anti-vibration components for many years. These subjected to fluctuating loads, often fail due to the nucleation and growth of defects or cracks. To prevent such failures, it is necessary to understand the fatigue failure mechanism for rubber materials and to evaluate the fatigue life for rubber components. The objective of this study is to develop the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue life at initial product design step. The determination method of nonlinear material constants for FE analysis was proposed. In order to investigate the applicability of the commonly used damage parameters, fatigue tests and corresponding finite element analyses were carried out and strain energy density was proposed as the fatigue damage parameter for rubber components. The fatigue analysis for automotive rubber components was performed and the durability analysis process was reviewed.

The basilar membrane (BM), one of organs of cochlea, has the specific positions of the maximum amplitude at each of related frequencies. This phenomenon is due to the geometry of BM. In this study, as the part of the research for the development of fully implantable artificial cochlea which is based on polymer membrane, parametric studies are performed to suggest the desirable artificial basilar membrane model which can detect wider range of frequency separation. The vibro-acoustic characteristics of the artificial basilar membrane are predicted through finite element analysis using commercial software Abaqus. Simulation results are verified by comparing with experimental results. Various geometric shapes of the BM and residual stress effects on the BM are investigated through the parametric study to enable a wider detectable frequency separation range.

We demonstrate the desert beetle back mimicking hybrid superhydrophilic/superhydrophobic patterned surface by using the combination method of colloidal lithography and gravure offset printing for nano and micro patterning, respectively. The two methods are cost-effective and industrially available techniques compared to the other nano/micro patterning methods. To verify the water collecting function of the hybrid surface, the water condensation behavior is investigated on the chilled surface in ambient temperature and high humidity. Due to the synergetic effect of drop and film wise condensation, the hybrid superhydrophobic/superhydrophilic surface shows the higher efficiency than one of single wettability surfaces. The work is underway to get the good patterns of hybrid surfaces for water collecting from the dew or fog.

For tissue engineering and regeneration, a porous scaffold with interconnected networks is needed to guide cell attachment and growth/ingrowth in three-dimensional (3D) structure. Using a rapid prototyping (RP) technique, we designed and fabricated 3D plotting system and three types of scaffolds: those from polycaprolactone (PCL), those from PCL and hydroxyapatite (HA), and those from PCL/HA and with a shifted pattern structure (PCL/HA/SP scaffold). Shifted pattern structure was fabricated to increase the cell attachment/adhesion. The PCL/HA/SP scaffold had a lower compressive modulus than PCL and PCL/HA scaffold. However, it has a better cell attachment than the scaffolds without a shifted pattern. MTT assay and alkaline phosphatase activity results for the PCL/HA/SP scaffolds were significantly enhanced compared to the results for the PCL and PCL/HA scaffolds. According to their degree of cell proliferation/differentiation, the scaffolds were in the following order: PCL/HA/SP > PCL/HA > PCL. These 3D scaffolds will be applicable for tissue engineering based on unique plotting system.

This paper reports on a web of superamphiphobic fluoro-compound fibers that forms as a result of a typical electrospinning method without any additional treatment. An electrospun web of poly(2,2,2-trifluoroethyl methacrylate) fibers exhibits superamphiphobicity when the water and hexadecane contact angles both exceed 150°. The morphology of a web is modulated by changing the polymer solution concentration from 24 to 30 wt.-% with other fixed processing conditions. The fiber diameter length depends mainly on the polymer concentration. A web formed from a 26 wt.-% solution has the smallest and most uniform fiber diameter; it also has the highest robustness parameter on wetting, thus the highest water and hexadecane contact angles. This result offers the possibility of simple industrial production of an amphiphobic surface.

Nanoscale patterning of gold layers on GaAs substrate is demonstrated using a combination of soft lithographic molding and galvanic displacement deposition. First, an electroless deposition method has been developed to plate gold on GaAs with ease and cost-effectiveness. The electroless metallization process is performed by dipping the GaAs substrates into a gold salt solution without any reducing agents or additives. The deposition proceeds via galvanic displacement in which gold ions in the aqueous solution are reduced by electrons arising from the GaAs substrate itself. The deposition rate, surface morphology and adhesion property can be modulated by the plating parameters such as the choice of acids and the immersion time. Second, soft lithographic patterning of nanodots, nanorings, and nanolines are demonstrated on GaAs substrates with hard-polydimethylsiloxane (h-PDMS) mold and plasma etching. This method can be easily applied to the metallization and nanopatterning of gold on GaAs surfaces.

In this paper, we design and fabricate a 3D scaffold using rapid prototyping (RP) technology for tissue engineering. The scaffold should have a three-dimensional interconnected pore network. We fabricate a polycaprolactone (PCL) scaffold with interconnecting pores and uniform porosity for cell ingrowth using a 3D plotting system. In order to keep the three dimensional shape under mechanical loading while implanted, we design an oscillating nozzle system to increase elastic modulus and yield strength of PCL strand. We characterize the influence of pore geometry, compressive modulus of the scaffold, elastic modulus and yield strength of the strand using SEM, dynamical mechanical analysis (DMA) and Nano-UTM. Finally the cell responses on scaffolds are observed.

This paper describes a simple fabrication method for creating superhydrophobic and transparent glass surfaces that mimic natural surfaces such as lotus leaves, moth eyes or cicada wings. Nanostructured glass surfaces were created by a combination of colloidal lithography and plasma etching. A colloidal mask was formed simply by the spin coating of the polystyrene beads and with modification of the interparticle distance between the beads. The etching of the glasses was conducted by CF4 plasma. Tower-shaped nanostructures at an aspect ratio of 1:4 were treated using fluoroalkylsilane self-assembled monolayers (SAMs) to obtain the hydrophobic surfaces. The treated glass surfaces showed superhydrophobicity with a water contact angle of around 150° and a hexadecane contact angle of around 110°. Furthermore, the nanostructured glass was transparent to visible light.

Fatigue life prediction and evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Fatigue lifetime prediction methodology of the rubber component was proposed by incorporating the finite element analysis and fatigue damage parameter from fatigue test. Finite element analysis of rubber component was performed based on a hyper-elastic material model determined from material test. The Green–Lagrange strain at the critical location determined from the finite element method was used to evaluate the fatigue damage parameter of the natural rubber. Fatigue life of rubber components was predicted by using the fatigue damage parameter at the critical location. Predicted fatigue life of the rubber component agreed fairly well with the experimental fatigue lives.

Super-hydrophobic surfaces showed that contact angle of water was higher than 140 degrees. That surface could be made several methods such as Carbon nano tubes grown vertically, PDMS asperities arrays, hydrophobic fractal surfaces, and self assembled monolayers coated by CVD and so on. However, we fabricated super-hydrophobic surfaces with plasma treatments which were very cost efficient processes. Their surfaces were characterized by static contact angles, advancing, receding, and stability against UV irradiation. Optimal surfaces showed static contact angles were higher than 150 degrees. Super-hydrophobic property was remained after UV irradiation for one week. 1. 서 론 초소수성은 여러 산업 분야에서 관심을 끄는 표면특성이다. 이는 연꽃잎에서 보이는 자정효과를 분석하여 응용하려는 연구에서 시도 되었으며, 그 응용사례는 페인트, (1) 자동차용 유리, (2) 의류 3) , 오염되지 않는 표면 4) 등 다양하다. 이러한 초소수성 표면을 얻기 위하여 여러 가지 방법으로 제조되어 왔으며 5)~9) 최근에는 단분자막 코팅을 통해서도 얻을 수 있는 것으로 알려지고 있다. (10) 이에 대한 이론적인 연구는 1932년 Wenzel (11) 등이 주축이 되어 왁스의 표면 형상에 따른 물의 접촉각 거동을 연구한 것이 시초가 된다.

Soluble eggshell proteins were used as a reinforcing material of electrospun micro/nanofibers for tissue engineering. A biocomposite composed of poly(epsilon-caprolactone) (PCL) micro/nanofibers and soluble eggshell protein was fabricated with a two-step fabrication method, which is an electrospinning process followed by an air-spraying process. To achieve a stable electrospinning process, we used an auxiliary cylindrical electrode connected with a spinning nozzle. PCL biocomposite was characterized in water contact angle and mechanical properties as well as cell proliferation for its application as a tissue engineering material. It showed an improved hydrophilic characteristic compared with that of a micro/nanofiber web generated from a pure PCL solution using a typical electrospinning process. Moreover, the fabricated biocomposite had good mechanical properties compared to a typical electrospun micro/nanofiber mat. The fabricated biocomposite made human dermal fibroblasts grow better than pure PCL. From the results, the reinforced polymeric micro/nanofiber scaffold can be easily achieved with these modified processes.

We have developed a novel atomic force microscope (AFM) probe as a highly sensitive sensor and an application of the probe into various mechanical tests for characterizing micro/nanostructures. Using MEMS fabrication technique, we have designed and fabricated rhombus-shaped symmetric AFM probe. Adhesion forces between silicon tip and artificial nano-hair structures of cyclic olefin copolymer (COC) and polypropylene (PP) were measured using the probe with a flat tip. The results exhibited the usual characteristics of force-displacement curves of COC and PP nano-hair structures, in which a pull-off force was detected at the point of unloading. The average adhesion forces of the COC and PP hair structures are about 9.48 μN and 10.67 μN, respectively.

Flexible printed circuit board (PCB), which is used for folder and slide type cellular phones, consists of flexible copper clad laminate (FCCL) and cover layer. Through it an electric current is applied to liquid crystal display (LCD) from the main board of cellular phone. In thin Cu foils of flexible PCB fatigue cracks due to repeated bending motion generate and propagate, and they cause a short circuit. Fatigue behavior of thin Cu foils being used for flexible PCB must be evaluated and confirmed to resolve this problem. It is based on findings by several researches that the mechanical properties of thin film materials differ from those of their bulk counterparts. Thin film properties have been investigated over the last years; however fatigue behavior of thin films has not yet been studied as thoroughly as monotonic behavior. In this study fatigue properties of thin Cu foils for the application in flexible PCB are obtained. Fatigue testing was performed for two kinds of Cu foils that were made by rolling and electrochemical procedures respectively. Differences of fabrications in fatigue behavior of thin foils were distinguished. Especially for rolled Cu foils, effects of rolling directions in fatigue properties were evaluated.

The material properties of rubber were determined by the experiments of simple tension, simple compression tension, pure shear, equi‐biaxial tension test. In simple tension test, dumbbell specimen is generally used to obtain a state of pure tensile strain. It is shown that a narrow strip specimen for length is over 10 times of the width can be also used in. In simple compression test, the effect of the friction force between the specimen and the platen is investigated. The test device with the tapered platen is proposed to overcome the effect of friction. It is verified by experimental and finite element analysis results. In pure shear tests, it is shown that the width of specimen must be at least 10 times of the height. Specimen and equipment of equi‐biaxial tension was development a state of strain equivalent to pure compression.

Engineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape-ability to form a variety of shapes and sizes. In this study, we produced design-based poly (e-carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x-y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric-field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x-y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.

For tissue engineering, a bio-porous scaffold which is applied to bone-tissue regeneration should provide the hydrophilicity for cell attachment as well as provide for the capability to bind a bioactive molecule such as a growth factor in order to improve cell differentiation. In this work, we prepared a three-dimensional (3D) printed polycaprolactone scaffold (PCLS) grafted with recombinant human bone morphogenic protein-2 (rhBMP2) attached via polydopamine (DOPA) chemistry. The DOPA coated PCL scaffold was characterized by contact angle, water uptake, and X-ray photoelectron spectroscopy (XPS) in order to certify that the surface was successfully coated with DOPA. In order to test the loading and release of rhBMP2, we examined the release rate for 28 days. For the In vitro cell study, pre-osteoblast MC3T3-E1 cells were seeded onto PCL scaffolds (PCLSs), DOPA coated PCL scaffold (PCLSD), and scaffolds with varying concentrations of rhBMP2 grafted onto the PCLSD 100 and PCLSD 500 (100 and 500 ng/ml loaded), respectively. These scaffolds were evaluated by cell proliferation, alkaline phosphatase activity, and real time polymerase chain reaction with immunochemistry in order to verify their osteogenic activity. Through these studies, we demonstrated that our fabricated scaffolds were well coated with DOPA as well as grafted with rhBMP2 at a quantity of 22.7 ± 5 ng when treatment with 100 ng/ml rhBMP2 and 153.3 ± 2.4 ng when treated with 500 ng/ml rhBMP2. This grafting enables rhBMP2 to be released in a sustained pattern. In the in vitro results, the cell proliferation and an osteoconductivity of PCLSD 500 groups was greater than any other group. All of these results suggest that our manufactured 3D printed porous scaffold would be a useful construct for application to the bone tissue engineering field. Statement of Significance Tissue-engineered scaffolds are not only extremely complex and cumbersome, but also use organic solvents which can negatively influence cellular function. Thus, a rapid, solvent-free method is necessary to improve scaffold generation. Recently, 3D printing such as a rapid prototyping technique has several benefits in that manufacturing is a simple process using computer aided design and scaffolds can be generated without using solvents. In this study, we designed a bio-active scaffold using a very simple and direct method to manufacture DOPA coated 3D PCL porous scaffold grafted with rhBMP2 as a means to create bone-tissue regenerative scaffolds. To our knowledge, our approach can allow for the generation of scaffolds which possessed good properties for use as bone-tissue scaffolds.

The last decade has seen artificial blood vessels composed of natural polymer nanofibers grafted into human bodies to facilitate the recovery of damaged blood vessels. However, electrospun nanofibers (ENs) of biocompatible materials such as chitosan (CTS) suffer from poor mechanical properties. This study describes the design and fabrication of artificial blood vessels composed of a blend of CTS and PCL ENs and coated with PCL strands using rapid prototyping technology. The resulting tubular vessels exhibited excellent mechanical properties and showed that this process may be useful for vascular reconstruction.

Miniaturized artificial hearing organ with excellent sensitivity and wide dynamic frequency range over human hearing range, while requiring small amount of energy, is important step to develop artificial systems interacting in human living space. This paper presents the development of piezoelectric artificial cochlea PAC capable of analyzing incoming vibratory signals over human hearing range without external power source. The design, component and function of PAC were inspired by those of human cochlea. The PAC was made of corona-poled piezoelectric thin film with vibrating membrane part of unique shape. The vibration displacement of membrane was measured using laser Doppler vibrometer and analyzed to show the frequency separation of the developed PAC. The experimental results of mechanical vibratory behavior demonstrated successful separation of incoming signals into 13 different frequency bands depending on their frequency over 300 Hz ~ 6,000 Hz.

The structure and morphology of the electrospun nanofiber depend on the parameters such as the physical properties of polymer, the applied voltages, tip to collector distance and ambient condition. Until now, most of studies have been focused on the effects of the above mentioned parameters for electrospinning process. But the study on vacuum conditions in electrospinning process almost not exists. The goal of this study is to investigate the effects of vacuum conditions in electrospinning process. The setup of electrospinning device is installed within homemade vacuum chamber. The polymer jets are ejected from a multi-spinneret connected with a microsyringe pump towards the collector located at fixed distance from the needle tip under a vacuum condition. The nanofiber mats are fabricated using a rotating collector. The visualization and imaging system of electrospinning process are consisted of a green laser devices, microscope, CCD camera and image recording device. During the electrospinning process, the behaviors of nanofiber are visualized and analyzed by this system. The morphologies and dimensions of electrospun fiber mat are measured with SEM. As a final result, the vacuum conditions of electrospinning process influence the behaviors of nanofiber.

The interest of the fatigue life for rubber components was increasing according to the extension of warranty period of the automotive components. In this study, the fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue tests. Finite element analysis of 3D dumbbell specimen and rubber component was performed based on a hyper-elastic material model determined from the mechanical tests. The Green-Lagrange strain at the critical location determined from the finite element analysis was used for evaluating the fatigue damage parameter of the natural rubber. Fatigue tests were performed using the 3D dumbbell specimens and rubber component with different levels of maximum strain and various load. Fatigue life curves can be effectively represented by a following single function using the maximum Green-Lagrange strain. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the rubber component for automobile vehicle agreed fairly with the experimental fatigue lives.

Nanosize fibers were fabricated using an extra-cylindrical electrode connected with single and multiple nozzles of an electrospinning process to stabilize the initial spun jets. To predict stability of spun jets, an electric field concentration factor (EFCF), which could be defined as a degree of a convergence of jets to a spinning axis, was introduced. The proposed parameter EFCF is utilized for the comparison of the experimental results for single and multi-nozzles electrospinning process. To consider the mass productivity of the multi-nozzles electrospinning supported by an auxiliary electrode, the weight of nanofibers that were spun to a rectangular shape target plate during 40 min was measured. The result indicates that the modified electrospinning technique shows a possibility as a useful method for increasing the production rate of nanofiber manufacturing.

The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Heat-aging process affects not only the material properties but also the fatigue life of vulcanized natural rubber. In this paper, the heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The stress-strain curves were obtained from the results of tensile test. The rubber specimens were heat-aged in an oven at the temperature ranging from 50°C to 100°C for a period ranging from 1 day to 90 days. Fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Fatigue life tests were performed using the 3-dimensional dumbbell specimen, which were aged in different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain.

Fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Finite element analysis of 3D dumbbell specimen of natural rubber was performed based on a hyper-elastic material model determined from the tension, compression and shear tests. Stroke controlled fatigue tests were conducted using fatigue specimens at different levels of mean strain. The Green-Lagrange strain at the critical location determined from the FEM was used for evaluating the fatigue damaged parameter of the natural rubber. It was shown that the maximum Green-Lagrange strain was proper damage parameter, taking the mean strain effects into account. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the natural rubber agreed fairly well the experimental fatigue lives a factor of two.

This paper discusses experimental test methods for the purpose of defining the nonlinear properties of rubbery materials used for finite element analysis. The typical tests are simple tension, simple compression and pure shear tests. It has been found in the simple tension test that a narrow strip specimen whose length is 10 times longer than the width can be used more appropriately than a dumbbell type specimen. In order to eliminate the effect of friction between the specimen and the platens in the compression test, a tapered platen is suggested. The effect of the tapered platens is verified by experimental and finite element analysis. In a shear test, it has been shown that the specimen width must be at least 10 times larger than the height of the specimen. The mechanical preconditioning has significant effects on the prediction of the behaviours of rubbery materials and components. The static stiffness of an automotive engine mount is calculated by nonlinear finite element analysis using the experimentally determined material properties and is compared with experimental results that take into account the mechanical preconditioning effect, resulting in a good correlation. Copyright © 2004 Society of Chemical Industry

Mechanical testing methods to determine the material constants for large deformation nonlinear finite element analysis were demonstrated for natural rubber. Uniaxial tension, uniaxial compression, equi-biaxial tension and pure shear tests of rubber specimens are performed to achieve the stress-strain curves. The stress-strain curves are obtained after between 5 and 10 cycles to consider the Mullins effect. Mooney and Ogden strain-energy density functions, which are typical form of the hyperelastic material, are determined and compared with each other. The material constants using only uniaxial tension data are about 20% higher than those obtained by any other test data set. The experimental equations of shear elastic modulus on the hardness and maximum strain are presented using multiple regression method. Large deformation finite element analysis of automotive transmission mount using different material constants is performed and the load-displacement curves are compared with experiments. The selection of material constant in large deformation finite element analysis depend on the strain level of component in service.

Acrylonitrile–butadiene rubber (NBR) hybrid nanocomposites with organoclays were prepared by melt mixing, and their properties were compared with those of conventional rubber compounds filled with carbon black and silica. Based on X-ray diffraction and transmission electron microscopy, the NBR nanocomposites obtained were found to form generally an intercalated structure, although they formed an exfoliated structure when the organoclay content was low enough

The resistance to air permeation was investigated for ­an intercalated clay/acrylonitrile-butadiene copolymer ­nanocomposite. The nanocomposite is prepared by melt mixing the organo-treated montmorillonite into a rubber matrix, together with peroxide curative, and crosslinked by conventional compression molding for typical rubbers. In the case of intercalated nanocomposite, the air permeability decreases considerably with increasing clay content, and the decreasing trend agrees reasonably with the Neilson's tortuous model. No considerable improvement is found when the pure montmorillonite is added. Copyright © 2002 John Wiley & Sons, Ltd.

Rubber components have been widely used in automotive industry as anti-vibration components for many years. These subjected to fluctuating loads, often fail due to the nucleation and growth of defects or cracks. To prevent such failures, it is necessary to understand the fatigue failure mechanism for rubber materials and evaluate the fatigue life for rubber components. Fatigue lifetime prediction and evaluation are the key technologies to assure the safety and reliability of automotive rubber components. The objective of this study is to develop the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue lifetime at initial product design step. Fatigue lifetime prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter of maximum Green-Lagrange strains appearing at the critical location determined from fatigue test. In order to develop an appropriate fatigue damage parameter of the rubber material, a series of displacement controlled fatigue tests was conducted using 3-dimensional dumbbell specimens with different levels of mean displacement. It was shown that the maximum Green-Lagrange strain was a proper damage parameter, taking the mean displacement effects into account. Nonlinear finite element analyses of the engine mount insulator and 3-dimensional dumbbell specimens were performed based on a hyper-elastic material model determined from the simple tension, equi-biaxial tension and planar test. Fatigue lifetime prediction of engine mount insulator was made by incorporating the maximum Green-Lagrange strain values, which was evaluated from the finite element analysis and fatigue tests, respectively. Predicted fatigue lives of the rubber component showed a fairly good agreement with the experimental fatigue lives. Fatigue analysis procedure employed in this study could be used approximately for the fatigue design.