Fabrication of Biomimetic Scaffolds With Well-Defined Pore Geometry by Fused Deposition Modeling

It is well established that the pore size and distribution affect the rate of cell migration and the extent of extracellular matrix formation. The objective of this work was to develop a process for fabrication of biodegradable and shape-specific polymeric scaffolds with well-defined pore geometry, functionalized with covalently attached bioactive peptides, for applications in tissue regeneration. We have used the Fused Deposition Modeling (FDM) RP technology to fabricate degradable and functional scaffolds with well-defined pore geometry. Computer aided design (CAD) using SolidWorks was used to create models of the cubic orthogonal geometry. The models were used to create the machine codes necessary to build the scaffolds with FDM with wax as the build material. A novel biodegradable in-situ crosslinkable macromer, poly(lactide-co-glycolide fumarate) or PLGF, mixed with reactive functional peptides was infused in the scaffold and allowed to crosslink. The scaffold was then immersed in a hydrocarbon solvent to remove the wax, leaving just the PLGF behind as the support material dissolved. The pore morphology of the PLGF scaffold was imaged with micro-computed tomography and scanning electron microscopy. Cellular function in the PLFG scaffolds with well-defined pore geometry was studied with bone marrow stromal cells isolated from rats. Results demonstrate that the scaffolds support homogeneous formation of mineralized tissue.

Thermal-Electric Finite Element Analysis of Electrosurgical Cautery Process

Cautery is a process to coagulate tissues and seal blood vessels using the heat. In this study, finite element modeling (FEM) was performed to analyze temperature distribution in biological tissue subject to cautery electrosurgical technique. FEM can provide detailed insight into the heat transfer in biological tissue to reduce the collateral thermal damage and improve the safety of cautery surgical procedure. A coupled thermal-electric FEM module was applied with temperature-dependent electrical and thermal properties for the tissue. Tissue temperature was measured at different locations during the electrosurgical experiments and compared to FEM results with good agreement. The temperature-dependent electrical conductivity has demonstrated to be critical. In comparison, the temperature-dependent thermal conductivity does not impact heat transfer as much as the electrical conductivity. FEM results show that the thermal effects can be varied with the electrode geometry that focuses the current density at the midline of the instrument profile.

A Review on Thermally Assisted Machining

Thermally assisted machining (TAM) involves the use of a heating source to elevate the workpiece temperature at the cutting zone to facilitate the material removal process. TAM has evolved over the years with the emergence of new heating sources and the need to machine newly developed hard and brittle materials. In recent years, the main activities in this research area have been focused on laser assisted machining (LAM) at both the macro and micro scale, largely because of focused and controlled delivery of energy that can be achieved with a laser. This paper attempts to provide an overview of research in the general area of TAM, with an emphasis on LAM at the macro scale. Both experimental and theoretical/numerical work will be presented in this review. The challenges and progresses made so far will be detailed. And finally, future research directions in this area will be discussed.

Effect of Micro-Manufacturing Processes on Surface Behavior

Surface texturing has become a valuable technique for reducing friction and wear in contacting parts; laser surface texturing is one such method used to create micro-dimples on the interface surface. This work investigates the surface material property variation caused by laser surface texturing. The hardness and modulus of elasticity of a steel laser surface texture sample were evaluated near the dimples and away from the dimpled zone through nano-indentation. Resulting data shows that no significant difference exists between the material properties from the two positions. An alternate technique for surface texture generation was also explored, involving the use of micro-punches to create surface features in a metal sample. Computational simulations were performed using a second material underneath a thin copper sheet. The second material was present to serve as a support and to allow extensive deformation of the top material. The choice of the support material and ratio of material thicknesses was optimized to minimize pile up. Trials were conducted for three base supporting materials: PTFE, PMMA, and aluminum. Results show that PMMA performed better than the other materials. Positive deflection was minimized when the PMMA thickness was at least fifteen times that of the copper sheet. Physical experiments were completed with a thin copper sheet to verify the results. An array of micro-indentations was also created in a bulk steel sample. In order to assess the effect of dimpling via micro-forming, nano-indentation was performed near and far from the deformed material of the dimples. Similar to the laser textured sample, no significant differences were found between the two locations.

Part Repairing Using a Hybrid Manufacturing System

At present, part remanufacturing technology is gaining more interest from the military and industries due to the benefits of cost reduction as well as time and energy savings. This paper presents the research on one main component of part remanufacturing technology, which is part repairing. Traditionally, part repairing is done in the repair department using welding processes. However, the limitations of the traditional welding process are becoming more and more noticeable when accuracy and reliability are required. Part repairing strategies have been developed utilizing a hybrid manufacturing system in which the laser-aided deposition and CNC cutting processes are integrated. Part repairing software is developed in order to facilitate the users. The system and the software elevate the repairing process to the next level, in which accuracy, reliability, and efficiency can be achieved. The concept of the repairing process is presented in this paper, and verification and experimental results are also discussed.

Application of Simulation Technology to Hollow Die Extrusion

In recent years, the application of various simulations in hot extrusion of aluminum alloys has proven useful. However, the most of them are generally applied in the field of steady metal flow conditions with solid die extrusion. In this paper, the simulation technology is applied to hollow die extrusion. Especially, the effects of the taper port-hole shapes on the extrusion pressure-stroke diagrams and the metal flows are investigated experimentally and theoretically. Taper port-hole shapes are useful for the reduction of the extrusion pressure in comparison with straight port-hole shape, because the extrusion pressure in the port-hole filling process is decreased by the reduction of the sliding friction, and the extrusion pressure in the welding chamber filling process is decreased by the reduction of equivalent strain rate in the port-hole and the welding chamber. FEM results by FEM analysis code added with special know-how show a close match with the experimental results. Therefore, we are able to predict the extrusion pressure and the metal flow through the port-hole and the welding chamber by this simulation technology.

Extension-Based Clustering Method: An Approach to Support Adaptable Design of the Product

Design for product adaptability is one of the techniques used to provide customers with products that exactly meet their requirements. Clustering methods have been used extensively in the study of product adaptability design. Of the clustering methods, the fuzzy clustering method is the most widely in the design field. The three main kinds of fuzzy clustering methods are the transitive closure method, the dynamic direct method and the maximum tree method. The dynamic direct clustering method has been found to produce design solutions with the lowest cost. In this paper, a new approach for obtaining adaptable product designs using the clustering method is proposed. The method consists of three steps. Firstly, the extension distance formula is used to determine the distance between two products in a product database. The product design space and the distances between individuals are used as grouping criteria in this step. Secondly, the minimal distance between products is used to obtain the clustering index. Thirdly, the threshold value is used to divide the products in the database into groups. Customer demands and the results obtained from the adaptable function (based on the extension distance formula) are used to evaluate the fitness of the groups and their corresponding products. The product with the largest adaptable function value to demand ratio is selected product. In order to the show the advantage of using the extension-clustering method, both the extension-clustering method and the dynamic direct method are presented and compared. The comparison indicates that the extension-clustering method leads to quicker evaluations of design alternatives and results that more closely match customers’ demands. An example of the adaptable design of circular saws tools is used to demonstrate that with the extension-clustering design method a high variety of intelligent configurations can be obtained with significant rapidity.

Micro-Feature Replication via Polymer Molding at Ambient Pressure

The study focuses on the ability of a polymer to replicate micro-features when processed at an elevated mold temperature without externally applied pressure. Replication is performed using four different polymers—High Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Poly (Methyl Methacrylate) (PMMA) on a silicon mold containing surface features as small as 500nm. Feature replication is assessed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to compare feature dimensions of the mold to those of the replicated parts. Shrinkage in dimensions is observed to be anisotropic in the molded parts and its extent of varies among the different polymers. Crystalline HDPE shows a higher degree of shrinkage relative to amorphous polymers such as PS and PMMA. These results verify the theoretical value of shrinkage calculated from the coefficient of volumetric shrinkage values and density. By increasing the mold temperature well above the melting point of the polymer, a depth ratio of 70–80% can be achieved in parts having aspect ratios of around 0.5. The result is comparable to the values achieved by similar studies. Varying aspect ratios are fully replicated by all four polymers at elevated mold temperature. This clearly shows that increasing mold temperature results in significant improvement in depth ratios for micro-featured parts. The amorphous materials provide better feature replication and lower surface roughness than the semi-crystalline polymer.

Internal Model Control Using EWMA for a Wedge-Type Piezoelectric Motor

Wedge-type piezoelectric motor is easily subject to disturbance such as friction, preload and temperature change, which influences the performance significantly and reduces the positioning accuracy and reliability. In this study, Exponentially Weighted Moving Average (EWMA) method is considered to use for the velocity-feedback loop, which is included in an Internal Model Control (IMC) to achieve a Run-to-Run IMC (RtR-IMC) control structure. Such control scheme is able to adapt the control command following a changing system dynamics so that it can improve the tracking accuracy and robustness. Friction is also a problem of generating dead-zone area and causes serious nonlinear phenomenon especially while moving direction is changed. A feedforward controller is designed based on the friction model. Moreover, temperature increase appears in long-time operation, which is another factor influential to piezoelectric motor’ performance. Instead of using the Single EWMA method, which cannot efficiently deal with such environmental drift problem, a Double EWMA algorithm is developed. Practical experiment is carried out to verify the performance by using these proposed methods. It concludes that the Double EWMA associated with the friction-model-based feedforward controller is superior to the other methods.

Constant-Temperature Embossing of Amorphous Poly(Ethylene Terephthalate) Films

In the standard hot embossing process for thermoplastic polymers, thermal cycling is needed in order to soften and subsequently cool and solidify the polymer. This thermal cycling, however, not only results in long cycle times but also deteriorates the quality of embossed features. A new embossing method based on slowly crystallizing polymers was investigated to eliminate thermal cycling. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by casting a PET melt onto a chill roll. The amorphous PET film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than PET’s half-time of crystallization. During constant-temperature embossing, the film first liquefies, caused by rubber softening of the amorphous phase, and then solidifies, resulting from the crystallization of the amorphous phase. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio rectangular microchannels, were successfully embossed using a total cycle time about 40 s.