Jos Istiyanto

PDMS Surface Modification Using Biomachining Method for Biomedical Application

Engineering a cell-friendly material in a form of lab-on-chip is the main goal of this study. The chip was made of polydimethyl siloxane (PDMS) with a surface modification to realize a groovy structure on its surface. This groovy surface was naturally and randomly designed via biomachining process. This measure was aimed to improve the cell attachment on the PDMS surface that always known as hydrophobic surface. The biomachined surface of mold and also products were characterized as surface roughness and wettability. The result shows that the biomachining process were able to be characterized in three classes of roughness on the surface of PDMS.

Visible Light Maskless Photolithography for Biomachining Application

Maskless photolithograpy is an alternative method of conventional UV photolithograpy for microfabrication since its advantages of time and cost saving. For this reason, a visible-light based maskless photolithograpy is proposed as a part of biomachining process. Modification of the method is done by replacing light source of UV light to visible light, utilizing commercial DLP projector and changing the material removal process that generally uses echant with biomachining process. The process was done by using the profile generated by computer then displayed through a commercial DLP projector shining speciment test. Focusing lens placed under the projector to draw the focal point and reduces the size of the profile. The best parameter was determined by setring exposure time, developing time, variation profiles, focusing, colors combination and optical aspect. Using a commercial projector maskless photolithography on a negative resist tone successfully performed. The best characteristic was obtained by placing the focusing lens 3X magnification within 3 cm below the projector and 14 cm above speciment test, color combination of black-light blue (R = 0, G = 176, B = 240), with the timing of prebake 1 minute, exposure 7 minutes, postbake 5 minutes, developing 5 minutes produces the smallest profile 166 μm with 13,7 μm deviation. Biomachining process with bacteria Acidithiobacillus ferrooxidans NBRC 14262 on copper was also successfully performed with the smallest profile of 180 μm with 26 μm deviation.

Delivery of Amphotericin B to Candida albicans by Using Biomachined Lab-on-a-Chip

This paper investigates the ability of biomachined lab-on-a-chip (LoC) to perform drug testing of Amphotericin B to the Candida albicans. The chip is made of polydimethyl siloxane (PDMS). Molds are patterned using CNC milling followed by biomachining. CNC milling process creates channel features on the bottom mold, while biomachining forms rough surface on the channels. After the molds are created, LoC can be manufactured using those molds. Hence, contour surface on LoC’s channels is also realized following the mold surface. Later, Candida albicans is seeded on the LoC’s channels for 24 and 48 hours with the continuous flow of Yeast Nitrogen Base (YNB) Sterile. Then, cell viability is tested using 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium (MTT).The result shows that C. albicans could adhere and grow in the LoC channels. Based on this result, drug testing is conducted in the presence and absence of Amphotericin B (Amp B) under two schemes: without (static) and with (dynamic) the continuous flow of YNB Sterile and Amp B. After 48 hour incubation period, C. albicans biofilm of 28.72 % is shown during dynamic scheme, whereas static scheme had C. albicans biofilm of 99.32 % indicating that the dynamic scheme provides a better efficacy compared to the static scheme.

Inclination Angle Effect on Surface of Copper in Biomachining

Nowadays micro fabrication technology is very varied and being continuously developed. One of them uses bacteria as tools that known as biomachining. Acidithiobacillus ferooxidans is a one of bacteria which can do metal removal as a source of energy. The previous research has proven the ability of Acidithiobacillus ferooxidans for material removal process. In this research, biomachining process was added by angle of inclination parameter to know the effect on copper surface profile and roughness. This method was used to get profile shape result of multi-axis in biomachining. Workpieces were patterned by photolithography method and put in the bacterial culture medium, which was inclined 20° and 30° on inclinator. Profile shape and the surface roughness measurement data were taken by SURFCOM machine. The results of this research showed that by inclining 20° and 30° of biomachining sample produced different profile shapes and surface roughness.

Effects of Wall Thickness and Crush Initiators Position under Experimental Drop Test on Square Tubes

Crush initiators are the weakest points to reduce initial peak load force with significant energy absorption ability. The objective of this paper is to study the effects of square tube thickness and crush initiators position for impact energy absorber (IEA) performance on thin-walled square tubes. Two square tubes having thickness about 0.6 mm (specimen code A) and 1 mm (specimen Code C) were tested under dynamic load. The crushing initiator is designed around the shape of the tube wall and has eight holes with a fixed diameter of 6.5 mm. In the experiment, the crushing initiator was determined at 5 different locations on the specimen wall. These locations are 10 mm, 20 mm. 30 mm, 40 mm, and 50 mm measured from the initial collision position of the specimen tested. The impact load mass was about 80 kg and had a drop height of about 1.5 m. Using the simulation program of the LabVIEW Professional Development System 2011 and National Instrument (NI) 9234 software equipped with data acquisition hardware NI cDAQ-9174 the signal from the load cell was sent to a computer. By controlling the thickness of the thin-walled square tube, the peak loading force can be decreased by approximately 56.75% and energy absorption ability of IEA can be increased approximately to 11.83%. By using different thin-walled square tube can produce different best crush initiators position with the lowest peak load force.

Surface characteristics of Ti6Al4V-EDM implant engineered by PVD coated-etching and Acidithiobacillus ferrooxidans based-biomachining

Presented study aims to characterize the surface implant engineered by PVD (Physical Vapor Deposition) coated-etching and biomachining. The material used is Ti6Al4V manufactured by electrical discharge machining (EDM). Copper (Cu) was used as its electrode material. The results show that acid etching and it followed by PVD coating (ΔRa 51%) were able to decrease the average of surface roughness (Ra) of original EDM to moderately rough category compared to biomachined samples (ΔRa 31%). SEM and EDS observations indicated that Acidithiobacillus ferrooxidans were not capable of removing Cu effectively in its condition as a contaminant on the Ti6Al4V surface. Moreover, significant increasing of the percentage of element weight (wt%) of Oxygen (O) generated by the biomachining can be applied as an alternative to the PVD coating (wt% O 8,9) to enhance the bioactivity of the etched implant. On the other hand, the contact angles generated by the biomachined samples prove that the surface is hydrophobic in nature that prone to increase cell attachment than the hydrophilic surface generated by PVD coated-etching.

Modification of surface roughness for a narrow path microfluidic application

Micro-fabrication is a technology that uses several methods in its application. There are 3 methods in micro-fabrication: physical process, chemical process, and biological process. The main methods used in material feeding are milling, chemical etching, and bio-machining. Each method will results surface roughness value. This research analyzes the surface roughness value by comparing each other to see the best surface roughness value in mold microfluidic application on copper. There are 2 methods to be compared, those are bio-machining and etching. Those methods are natural and random because the roughness produced doesn’t have clear pattern. Research in etching method is done by variating time between 6, 8, 10 and 12 minutes. However, in bio-machining the time variations are 12 and 24 hours based on the previous research. Based on the research done, the optimum result for each method is obtained. For etching method, the best result obtained at 8 minutes with 2.03 µm surface roughness value & 31.89 µm depth. The best result for bio-machining obtained at 24 hours with 2.02 µm surface roughness value & 43.1 µm depth. Based on those values, it can be concluded that optimum value for etching has smaller depth compared to biomachining.Micro-fabrication is a technology that uses several methods in its application. There are 3 methods in micro-fabrication: physical process, chemical process, and biological process. The main methods used in material feeding are milling, chemical etching, and bio-machining. Each method will results surface roughness value. This research analyzes the surface roughness value by comparing each other to see the best surface roughness value in mold microfluidic application on copper. There are 2 methods to be compared, those are bio-machining and etching. Those methods are natural and random because the roughness produced doesn’t have clear pattern. Research in etching method is done by variating time between 6, 8, 10 and 12 minutes. However, in bio-machining the time variations are 12 and 24 hours based on the previous research. Based on the research done, the optimum result for each method is obtained. For etching method, the best result obtained at 8 minutes with 2.03 µm surface roughness value & 31.89 µm de...

Implementation of analytical boundary simulation method for cutting force prediction model in five-axis milling

ABSTRACT A simulation system was developed that deals with cut geometry and machining forces when a toroidal cutter is used during semifinishing in five-axis milling. The cut geometry was calculated using an analytical method called analytical boundary simulation (ABS). ABS was implemented to calculate the cut geometry when the machining used an inclination angle and a screw angle. The effect of tool orientation on the cut geometry was analyzed. The accuracy of the proposed method was verified by comparing the cut lengths calculated using ABS with cuts obtained experimentally. The result indicated that the method was accurate. ABS was subsequently applied to support a cutting force prediction model. A validation test showed that there was a good agreement with the cutting force generated experimentally.

The Improvement of the Closed Bounded Volume (CBV) Evaluation Methods to Compute a Feasible Rough Machining Area Based on Faceted Models

The rough machining is aimed at shaping a workpiece towards to its final form. This process takes up a big proportion of the machining time due to the removal of the bulk material which may affect the total machining time. In certain models, the rough machining has limitations especially on certain surfaces such as turbine blade and impeller. CBV evaluation is one of the concepts which is used to detect of areas admissible in the process of machining. While in the previous research, CBV area detection used a pair of normal vectors, in this research, the writer simplified the process to detect CBV area with a slicing line for each point cloud formed. The simulation resulted in three steps used for this method and they are: 1. Triangulation from CAD design models, 2. Development of CC point from the point cloud, 3. The slicing line method which is used to evaluate each point cloud position (under CBV and outer CBV). The result of this evaluation method can be used as a tool for orientation set-up on each CC point position of feasible areas in rough machining.

Effects of welding time and welding current to weld nugget and shear load on electrical resistance spot welding of cold rolled sheet for body construction

In this study, the electric resistance spot welding process was applied to cold rolled sheet used in automotive industry for body construction. Resistance spot welding parameter such as, electrode form, electrode material, and electrode force were stayed constant. This experiment uses different welding time and welding current to identify the optimum welding parameters for maximum joint strength. By using 1, 2, and 3 kA welding current and 4, 6, and 8 cycles welding times 0.8 mm, sheets were spot welded to prepare samples. These spot-welded joints were tested with uniaxial tensile test in laboratory to identify shear strength from spot-welded joint. This experiment is not only to identify shear load from the result of uniaxial tensile test but also to observe the size of weld nugget. Weld nugget can detect the quality of spot-welded joint with its size to prevent the expulsion and get the acceptable nugget diameter in that process. This experiment shows the optimum welding parameters that can be used in the automotive application especially in body construction.