Soft Mold Research Articles

An adaptable soft-mold embossing process for fabricating optically-accessible, microfeature-based culture systems and application toward liver stage antimalarial compound testing.

Advanced cell culture methods for modeling organ-level structure have been demonstrated to replicate in vivo conditions more accurately than traditional in vitro cell culture. Given that the liver is particularly important to human health, several advanced culture methods have been developed to experiment with liver disease states, including infection with Plasmodium parasites, the causative agent of malaria. These models have demonstrated that intrahepatic parasites require functionally stable hepatocytes to thrive and robust characterization of the parasite populations' response to investigational therapies is dependent on high-content and high-resolution imaging (HC/RI). We previously reported abiotic confinement extends the functional longevity of primary hepatocytes in a microfluidic platform and set out to instill confinement in a microtiter plate platform while maintaining optical accessibility for HC/RI; with an end-goal of producing an improved P. vivax liver stage culture model. We developed a novel fabrication process in which a PDMS soft mold embosses hepatocyte-confining microfeatures into polystyrene, resulting in microfeature-based hepatocyte confinement (μHEP) slides and plates. Our process was optimized to form both microfeatures and culture wells in a single embossing step, resulting in a 100 μm-thick bottom ideal for HC/RI, and was found inexpensively amendable to microfeature design changes. Microfeatures improved intrahepatic parasite infection rates and μHEP systems were used to reconfirm the activity of reference antimalarials in phenotypic dose-response assays. RNAseq of hepatocytes in μHEP systems demonstrated microfeatures sustain hepatic differentiation and function, suggesting broader utility for preclinical hepatic assays; while our tailorable embossing process could be repurposed for developing additional organ models.

Soft mold of microlens arrays fabricated by surface self-assembly

As a micro-optical element, microlens arrays (MLAs) play an important role in imaging, optical communication, lithography, and sensing. This paper reports a new method of fabricating a soft mold of MLAs by surface self-assembly. First, a hexagonal hole array mask is placed on a polydimethylsiloxane (PDMS) film in a radially pre-stretched state, and the masked PDMS film is irradiated using a scanning UV lamp in air, to form a hexagonal array of a silica-like hard film. Because of the surface self-assembly effect, this array bends inward, yielding a soft mold of concave MLAs after the pre-strain is spontaneously released. The focal length of the MLAs could be controlled in the range of 140–330 μm with a 37-μm-diameter hexagonal hole array by varying the exposure time of the ultraviolet ozone. Moreover, the diameter of the hexagonal hole array and the wrinkle wavelength, which are key influencing factors, were systematically studied. The soft mold of MLAs was applied to fabricate replica positive MLAs on planar and curved surfaces, which may have potential applications in image sensing and artificial compound eyes.

Chitosan coatings to control soft mold on fresh blackberries (Rubus glaucus Benth.) during postharvest period

Blackberry (Rubus glaucus Benth.) is perishable fruit with high susceptibility to soft mold which reduces its marketability. The antifungal chitosan action has been studied to maintain blackberry quality during postharvest. However, this biopolymer needs to be dissolved in organic acid to be able to perform correctly as a coating. In this work, the effectiveness of different chitosan concentrations prepared with either lactic or acetic acid was evaluated, for controlling Mucor racemosus in blackberries stored at 4 °C for 14 d. Fruit decay treated with chitosan was compared with the one obtained in blackberries treated with the chemical fungicide imazalil (0.4 g L−1) and with that one obtained in untreated fruit. The treatment with chitosan 17.5 mg mL−1 - lactic acid (LA-17.5) was the most effective (p < 0.05) in the control of soft mold. Blackberry physicochemical properties and its sensory quality were not negatively affected by the treatment with chitosan 17.5 mg mL−1- lactic acid (LA-17.5). The results obtained suggested that the coating with chitosan could be used for the control of soft rot in blackberry during postharvest period.

Development of copper powder paste for direct printing and soft mold casting

Recently, additive manufacturing (AM) of metals has enjoyed significant advancement. While the mainstream AM methods utilize high-energy power beams to melt metal powders, other low-cost alternatives are also being developed (e.g., direct ink printing). In this study, a copper powder-binder paste is developed, which is not only capable to be used for direct printing, but also to be cast using soft molds. Dense three-dimensional parts can be obtained by sintering green bodies. The electrical and mechanical properties of the sintered samples are evaluated by conductivity, hardness measurements and tensile tests, respectively. The results are comparable to other powder processed copper materials.

Numerical modeling method for UV imprint process simulation using thermoviscoelastic constitutive equations

A novel numerical modeling method for UV imprint process simulation using thermoviscoelastic constitutive equations is proposed. The purpose of the process simulation is to predict transfer errors caused by UV shrinkage when a soft mold such as polydimethylsiloxane (PDMS) is used. The proposed method introduces an imaginary physical quantity, “virtual temperature,” as a measure of UV reaction progress and then replaces the UV curing/shrinkage phenomenon with the thermoviscoelastic cooling solidification/contraction phenomenon. A series of rheometry experiments are conducted for a general UV resin to identify the material properties of the UV resin as a thermoviscoelastic material. For the purpose of verification, the proposed method with the identified material properties is applied to the simulation of the rheometry experiments. Moreover, for the sake of validation, it is also applied to an actual UV imprinting process for a micromirror array molding with a PDMS mold. These analysis results prove the effectiveness of the present method in predicting transfer errors caused by UV shrinkage.

Development of Micropatterns on Curved Surfaces Using Two-Step Ultrasonic Forming.

Nanoimprint lithography (NIL) is a micro/nanoscale patterning technology on thermoplastic polymer films, and has been widely used to fabricate functional micro/nanoscale patterns. NIL was also used to develop micro/nanoscale patterns on curved surfaces by employing flexible polymer stamps or micropatterned metal molds with macroscopic curvatures. In this study, two-step ultrasonic forming was used to develop micropatterns on a curved surface out of a flat metal stamp, by connecting ultrasonic imprinting and stretching processes. Ultrasonic imprinting was used to replicate functional micropatterns on a flat polymer film, using a flat ultrasonic horn and micropatterned metal stamps with prism and dot micropatterns. An ultrasonic stretching process was then used to form a curvature on the patterned film using a curved ultrasonic horn and a soft mold insert, to avoid damage to the pre-developed micropatterns. The ultrasonic horn was designed to have three different tip radii, and the resulting forming depth and curvature formation were investigated experimentally. As a result, three different curved surfaces containing two different micropatterns were obtained. The developed curved films containing micropatterns were then evaluated optically, and showed different optical diffusion and illumination characteristics according to the film curvature and micropattern type. These results indicate that the proposed technology can extend the functionality of conventional micropatterned products by imposing appropriate curvatures.

The development of a dynamic rubber balloon spring-based asymmetric photocurable imprint system

This study aims to develop a dynamic rubber balloon spring-based asymmetric photocurable imprint system. The elastic plate used in this study combined the rubber balloon supporting force and asymmetric spring to control the asymmetric imprinting, in order to achieve photocurable micro-structural asymmetric imprinting. Firs of all, designed and developed the imprinting system, and procedure for preparation of the PDMS soft mold, and an elastic plate controlled by asymmetric spring force was used to manipulate the imprinting direction, then regulating the angle of imprinting of the direction force. The experimental results showed that, after filling the rubber balloon and the air-supporting pressure, the system used the estimated spring forced from the asymmetric spring constants to control the elastic plate to imprint and replicate the asymmetric micro structure. The results are expected to provide an alternative in the process of micro-system components.

Thermal analysis based method development for novel rapid tooling applications

The use of soft molds manufactured by additive manufacturing is gaining popularity in small-series production, thanks to the development of additive technologies and their materials. The thermal properties of soft molds, however, differ considerably from those of conventional, metal molds, and this greatly affects the conditions in the mold during manufacturing. We investigated the thermal properties and cooling conditions of epoxy acrylate-based, directly manufactured soft prototype molds. We used four different mold inserts, two with conformal cooling, one with conventional cooling and one without cooling. We found that due to the poor thermal properties of the mold material, the thermal conditions in the insert with conventional cooling and the insert without cooling were almost identical, this proves that in this case, conventional cooling cannot remove heat effectively. The use of conformal cooling, however, can reduce the cyclic heat load of mold inserts by about 70%, which increases the lifetime of the mold.

Polymer-Based Microring Resonator with the Multimode Interference Coupler Operating at Very-Near-Infrared Wavelengths

A microring resonator with the multimode interference coupler is fabricated on the polymer platform by using UV-based soft nanoimprint technique. A unique class of fluorinated polymer, perfluoropolyether (PFPE), is employed for the fabrication of the flexible soft mold. By optimizing the proportion between Ormocore and the thinner maT, the microring resonator is fabricated almost without residual layer. The fabricated device with a Q-factor up to 2.3 × 104 is demonstrated for very-near-infrared wavelengths, which shows high potential for sensing applications.

Development of 40-MHz Ultrasonic Transducers via Soft Mold Process.

This paper reports on the fabrication of 1-3 piezocomposites for ultrasonic transducers with operating frequencies up to 40 MHz based on recent developments of the soft mold technique. Compared to the established dice-and-fill technique, the soft mold process allows for the manufacturing of 1-3 piezocomposites with higher variability of pillar design and distribution as well as smaller structural size. Consequently, spurious modes generated by the lateral composite layout can be pushed to higher frequencies, which allows for increased operating frequency. Different designs of circular piezoceramic pillars in hexagonal arrangement with decreasing diameters and spacings have been developed and characterized in order to shift spurious modes to frequencies approximately twice the desired working frequency. The influence of the lateral composite layout on resonance modes is investigated by analyzing the produced transducers with respect to their electrical impedance spectra. Experimental results are explained in detail and compared to modeled data. Results show that by downsizing pillar diameter from 30 to [Formula: see text] and pitch from 40 to [Formula: see text], the first spurious mode could be shifted from ~42 to ~78 MHz. Thereby, the soft mold process proves to be suitable for the fabrication of 40-MHz ultrasonic transducers based on 1-3 piezocomposites.

Fabrication of polymeric lenses using magnetic liquid molds

Traditional molding and casting processes in optical manufacturing require sophisticated and expensive molds and molding equipment. In this work, magnetic liquid droplets were used as soft and deformable molds. The magnetic drop within an immiscible polymeric resin forms a conical shape at the interface due to the equilibrium of magnetostatic force and surface tension, which results in a plano–concave lens after curing. An apparatus was assembled to control the amplitude and gradient of the magnetic field. A Shack-Hartmann sensor was employed to measure the focal length of the formed polydimethylsiloxane lenses. The effects of magnetic field intensity, gradient of the magnetic field, and magnetic susceptibility were investigated. This technique is low cost, rapid, and straightforward and can be used for forming lenses with different sizes and shapes.

Scalable Nanoshaping of Hierarchical Metallic Patterns with Multiplex Laser Shock Imprinting Using Soft Optical Disks.

Large-area patterning of metals in nanoscale has always been a challenge. Traditional microfabrication processes involve many high-cost steps, including etching and high-vacuum deposit, which limit the development of functional nanostructures, especially multiscale metallic patterns. Here, multiplex laser shock imprinting (MLSI) process is introduced to directly manufacture hierarchical micro/nanopatterns at a high strain rate on metallic surfaces using soft optical disks with 1D periodic trenches as molds. The unique metal/polymer layered structures in inexpensive soft optical disks make them strong candidates of molds for MLSI processes. The feasibility of MLSI on hard metals toward soft molds is studied using theoretical simulation. In addition, various types of hierarchical structures are fabricated via MLSI, and their optical reflectance can be modulated via a combination of depth (laser power density), width (types of molds), and angles (rotation between molds). The optical properties have been studied with surface plasmon polariton modes theory. This work opens a new way of manufacturing hierarchical micro/nanopatterns on metals, which is promising for future applications in fields of plasmonics and metasurfaces.

Facile and precise fabrication of 10-nm nanostructures on soft and hard substrates

One of the major challenges in the field of nanotechnology is the facile and inexpensive fabrication of <10-nm nanostructures with a defect-free and precise pattern over a large area. Nanoimprint lithography (NIL) is a nanopatterning method that allows low-cost, fast production, and large-scale fabrication, but it needs improvement with regard to achieving a high resolution over a large area, processing on soft substrates, and nanomaterial patterning. Herein, it is demonstrated 10-nm patterning on soft and hard substrates via an advanced nanoimprint process. With a 100-nm master mold, both soft and hard molds with reduced pattern sizes (50, 20, 10, and 5 nm) are first fabricated using atomic layer deposition (ALD) of Al2O3. After surface functionalization of the mold, nanoscale patterns are imprinted on both hard (Si) and soft polyethylene terephthalate substrates, which result in structures with a pattern size of 10 nm. Using a hybrid supporting layer poly(methyl methacrylate) (PMMA)/poly(vinyl alcohol) (PVA) and ion sputter etching, a well-defined and clean sub-10 nm nanostructure is achieved for the nanomaterial on the substrate after lift-off and thermal annealing processes. Using this method, a graphene nanoribbon 10 nm wide is fabricated. Our approach is suitable for the fabrication of devices and structures with a 10-nm-scale pattern over a large area.

Research and development of the replication process of dynamic tilting magnetic colloid soft mold deforming imprint

This study aims to develop the replication process technology of the dynamic tilting magnetic colloid soft mold deforming imprint. It first designed and simulated a cross bi-axial soft mold. At the upper central area, it used a square tilting magnetic colloid to design a model of composite base. In the experiment, the unequal angle tilting magnetic colloid, dynamic unequal tensile deforming, and unequal magnetic pressure, were used for soft mold replication imprint. The unequal angle microstructure array element was obtained. The experimental results showed that satisfactory imprint conditions could be unequal angle tilting magnetic colloid soft mold, dynamic unequal tensile deforming, and unequal magnetic pressure. The proposed technology could rapidly acquire many case mold characteristics, produce the multi-change tilting microstructure array component, and effectively provide a rapid and effective technical method in the technological industry for fabricating the tilting array microstructure elements.

Tunable soft lithography molds enable rapid-prototyping of multi-height channels for microfluidic large-scale integration

The micromechanical valves that are used in microfluidic large-scale integration (mLSI) technology enable automated control of (bio)chemical and cell-based assays as they can perform crucial functions such as metering, mixing, pumping, and compartmentalization. The mLSI requires flow channels with a rounded profile for leak-free valve operation (i.e. ON/OFF flow control) to execute these functions. Here, we have used the deflection of an elastomeric membrane (DEM) in two configurations; free and constrained deflection, to fabricate reusable and tunable multi-height molds that in turn lead to fabrication of valvable flow channels in an unprecedented height range (up to 220 (130) µm for free (constrained) deflection) for mLSI. The constrained deflection configuration enabled the fabrication of channels that are directly in contact with a substrate, which combines the advantages of push-down and push-up valves that are commonly used in mLSI. Compared to the use of rigid master molds, fabricated either by photolithography on silicon wafers or via other processes such as 3D printing, milling etc, the tunability advantage of the multi-height DEM molds, eliminates the requirement of a different mold for each channel height, thus increases the prototyping and device optimization efficiency. We have developed functional devices to demonstrate that our enhanced soft lithography technique is high-throughput, scalable, and reproducible. The flow of large particles (110 µm diameter) were controlled that shows the suitability of the technique for organ- or spheroid-on-a-chip applications. The electrical resistance of liquid metal in microfluidic channels is modulated with a frequency of 1 kHz, showing the potential for re-configurable electronic circuits.

Mass-producible structural design and fabrication method for a slim light-guide plate having inverse-trapezoidal light out-couplers

An inverse-trapezoidal micropattern (ITM) has been considered as an optimal light out-coupler for a light-guide plate (LGP) in display devices thanks to its superiority in re-directing the light to the vertical direction. However, the ITM is not suitable for mass-production because of its over-hanging shape. Therefore, mass-production of the LGP having ITMs still remains challenging and has not been demonstrated before. In this paper, we propose and demonstrate a new structural design and mass-producible fabrication method for the LGP having ITMs as a light out-coupler. Whereas the conventional method directly fabricates the ITM using soft molds, an approach which is not mass-producible, the proposed method reverses the idea. We first fabricate trapezoidal micropattern using a rigid metallic mold and then bond it to the flat LGP substrate without optical glue. Using the proposed method, we fabricated a slim (~0.6 mm) 5.5 inch LGP having ITMs and confirmed that there was no difference in optical performance between LGPs fabricated by the proposed mass-producible method and the previous soft-molding method. This method can be a model approach for mass-producing other overhang-shaped micropatterns as well.

Soft thermal nanoimprint with a 10 nm feature size.

Nanoimprinting with rigid molds offers almost unlimited pattern resolution, but it suffers from high sensitivity to defects, and is limited to pattering flat surfaces. These limitations can be addressed by nanoimprinting with soft molds. However, soft molds have been used so far with UV resists, and could not achieve a resolution and minimal feature size comparable to those of rigid molds. Here, we explore the miniaturization edge of soft nanoimprint molds, and demonstrate their compatibility with thermal imprint resists. To that end, we produced a pattern with 10 nm critical dimensions, using electron beam lithography, and used it to replicate nanoimprint molds by direct casting of an elastomer onto the patterned resist. We showed that the produced pattern can be faithfully transferred from the mold by thermal nanoimprinting. In addition, we showed that similar nanoimprint molds can also be produced by double replication, which includes nanoimprinting of a thermal resist with an ultrahigh resolution rigid mold, and replication of a soft mold from the imprint pattern. We also demonstrated our novel nanoimprinting approach in two unconventional applications: nanopatterning of a thermal resist on a lens surface, and direct nanoimprinting of chalcogenide glass. Our novel nanoimprint approach pushes the envelope of standard nanofabrication, and demonstrates its potential for numerous applications impossible up to now.

Our Experience in the Management of Vaginal Agenesis: Its Psychosocial Impact and Role of Contrast Magnetic Resonance Imaging Scan with Vaginal Mold in the Interpretation of High Transverse Vaginal Septum.

Background:Mullerian anomalies are of many types, and it is very difficult to classify them in a simple method and plan reconstructive surgery. The aims, objective and the reconstructive surgical approach varies according to the level of vaginal agenesis as seen in our experience of management of 11 cases. The difficulties in the perception and interpretation of the surgical anatomy on magnetic resonance imaging can be minimized by placing a soft vaginal mold inside the lower developed vaginal segment in cases with transverse vaginal septum.Methods:Retrospective observational study.Results:All the operated 10 adult patients showed good created vaginal space which helped in creating good bonding in between the couples to maintain the integrity of marriage. Better successful reconstructive surgical planning by placing a soft vaginal mould in the vagina during MRI scan helps in understanding the level of septum in our single operated case of transverse vaginal septum and given excellent postoperative result.Conclusion:The impact of surgery on family life and sexual profile of the patient postsurgery on long-term has been mentioned on rare occasion. The preoperative counseling of the couples helps in better postoperative outcome in terms of psychological and sexual satisfaction of the partners and in the treatment of primary amenorrhea and infertility.

Use of amnion graft and surgicel in vaginoplasty for secondary vaginal atresia: A case report

Vaginal atresia can be congenital or acquired. The tissue is virgin in primary vaginal atresia or agenesis, so various methods have been used with successful outcomes. On the other hand, one can expect a lot of fibrosed tissue in secondary atresia. There is no elaborate literature on secondary vaginal atresia. There is also no standard treatment for both the types of vaginal atresia. The use of amnion graft and surgicel in vaginoplasty for secondary atresia is one of our experiences with best results. We report a case of a 22-year-old primipara who presented with dyspareunia and cyclical lower abdominal pain for the past 4 months. She had a history of traumatic vaginal delivery 3 months prior to presentation. On examination, she was diagnosed with secondary vaginal atresia. We managed her by vaginoplasty with amnion grafting and surgicel, followed by regular dilatation with soft vaginal mould for the next 6 weeks. Our patient is doing well with normal coital function on follow-up.

Fabrication of large scale PS monolayer colloidal crystal film by using a novel secondary self-assembly method for nanoimprint technique

PS microspheres emulsions with different PS diameters of 207 and 378 nm were prepared by using an emulsifier-free polymerization method. A novel secondary self-assembly method which combined the spin coating and the lifting-up method was used to prepare the close-packed PS MCC films. During the process, the PS MCC film was firstly assembled on a glass substrate by a spin coating technique. Secondly, the obtained PS MCC film was transferred on the air-water interface by immersing the PS glass substrate in water using a dip-coater. Thirdly, the floating close-packed PS MCC films on the air-water interface was transferred to a new glass substrate by using a lifting-up method. During the spin-coating and the self-assembly process, some SDS solution was added in the PS films to improve the uniformity of the PS layer. Effects of the spin-coating speeds, the SDS solution concentration and the lifting-up rates on the morphology of PS MCC films have been discussed. Scanning electron microscopy was used to observe the morphological properties of the PS colloidal crystal films. Results indicate that a relatively close-packed and large scale PS MCC films can be obtained when the spinning speed is 2000 rpm for 60 s, the SDS solution concentration is 2 wt% and the lifting-up rate is 2 mm/min. Furthermore, the polydimethylsiloxane soft mold was replicated from the-fabricated PS MCC films and was then imprinted onto the photosensitive hybrid film under UV-irradiation and thus the micro-lens arrays built in the photosensitive hybrid sol–gel film were obtained.