Gunawan Setia Prihandana

Fabrication of Polymer Microneedle Electrodes Coated with Nanoporous Parylene

In this study, we demonstrate the fabrication of polymer microneedle electrodes covered with a nanoporous parylene film that can serve as flexible electrodes for a brain–machine interface. In brain wave measurement, the electric impedance of electrodes should be below 10 kΩ at 15 Hz, and the conductive layer needs to be protected to survive its insertion into the stratum corneum. Polymer microneedles can be used as substrates for flexible electrodes, which can compensate for the movement of the skin; however, the adhesion between a conductive metal film, such as a silver film, and a polymer, such as poly(dimethylsiloxane) (PDMS), is weak. Therefore, we coated the electrode surface with a nanoporous parylene film, following the vapor deposition of a silver film. When the porosity of the parylene film is appropriate, it protects the silver film while allowing the electrode to have sufficient conductivity. The porosity can be controlled by adjusting the amount of the parylene dimer used for the deposition or the parylene film thickness. We experimentally verified that a conductive membrane was successfully protected while maintaining a conductivity below 10 kΩ when the thickness of the parylene film was between 25 and 38 nm.

Antithrombogenicity of Fluorinated Diamond-Like Carbon Films Coated Nano Porous Polyethersulfone (PES) Membrane

A nano porous polyethersulfone (PES) membrane is widely used for aspects of nanofiltration, such as purification, fractionation and dialysis. However, the low-blood-compatibility characteristic of PES membrane causes platelets and blood cells to stick to the surface of the membrane and degrades ions diffusion through membrane, which further limits its application for dialysis systems. In this study, we deposited the fluorinated-diamond-like-carbon (F-DLC) onto the finger like structure layer of the PES membrane. By doing this, we have the F-DLC films coating the membrane surface without sacrificing the membrane permeability. In addition, we examined antithrombogenicity of the F-DLC/PES membranes using a microfluidic device, and experimentally found that F-DLC drastically reduced the amount of blood cells attached to the surface. We have also conducted long-term experiments for 24 days and the diffusion characteristics were found to be deteriorated due to fouling without any surface modification. On the other hand, the membranes coated by F-DLC film gave a consistent diffusion coefficient of ions transfer through a membrane porous. Therefore, F-DLC films can be a great candidate to improve the antithrombogenic characteristics of the membrane surfaces in hemodialysis systems.

Polyethersulfone Membrane Coated With Nanoporous Parylene for Ultrafiltration

In this letter, we describe the surface modification of a polyethersulfone (PES) membrane by deposition of a nanoporous parylene film. The glycerin vapor during parylene deposition prevented parylene from forming over the pores. Water contact angle measurements and diffusion measurements revealed that parylene could be coated onto the PES membrane while keeping some pores open when the amount of dimer was properly controlled. The parylene-coated membrane prepared by our modified deposition process gave higher diffusion values than that prepared conventionally. Moreover, the platelet activation and adhesion were suppressed after coating parylene; this result indicated that the parylene-coated PES membranes showed improved biocompatibility. This advancement has a potential benefit for ultrafiltration applications.

Solute diffusion through fibrotic tissue formed around protective cage system for implantable devices

This article presents the concept of an implantable cage system that can house and protect implanted biomedical sensing and therapeutic devices in the body. Cylinder-shaped cages made of porous polyvinyl alcohol (PVA) sheets with an 80-µm pore size and/or stainless steel meshes with 0.54-mm openings were implanted subcutaneously in the dorsal region of rats for 5 weeks. Analysis of the explanted cages showed the formation of fibrosis tissue around the cages. PVA cages had fibrotic tissue growing mostly along the outer surface of cages, while stainless steel cages had fibrotic tissue growing into the inside surface of the cage structure, due to the larger porosity of the stainless steel meshes. As the detection of target molecules with short time lags for biosensors and mass transport with low diffusion resistance into and out of certain therapeutic devices are critical for the success of such devices, we examined whether the fibrous tissue formed around the cages were permeable to molecules of our interest. For that purpose, bath diffusion and microfluidic chamber diffusion experiments using solutions containing the target molecules were performed. Diffusion of sodium, potassium and urea through the fibrosis tissue was confirmed, thus suggesting the potential of these cylindrical cages surrounded by fibrosis tissue to successfully encase implantable sensors and therapeutic apparatus.

Water-Permeable Dialysis Membranes for Multi-Layered Microdialysis System.

This paper presents the development of water-permeable dialysis membranes that are suitable for an implantable microdialysis system that does not use dialysis fluid. We developed a microdialysis system integrating microfluidic channels and nanoporous filtering membranes made of polyethersulfone (PES), aiming at a fully implantable system that drastically improves the quality of life of patients. Simplicity of the total system is crucial for the implantable dialysis system, where the pumps and storage tanks for the dialysis fluid pose problems. Hence, we focus on hemofiltration, which does not require the dialysis fluid but water-permeable membranes. We investigated the water permeability of the PES membrane with respect to the concentrations of the PES, the additives, and the solvents in the casting solution. Sufficiently, water-permeable membranes were found through in vitro experiments using whole bovine blood. The filtrate was verified to have the concentrations of low-molecular-weight molecules, such as sodium, potassium, urea, and creatinine, while proteins, such as albumin, were successfully blocked by the membrane. We conducted in vivo experiments using rats, where the system was connected to the femoral artery and jugular vein. The filtrate was successfully collected without any leakage of blood inside the system and it did not contain albumin but low-molecular-weight molecules whose concentrations were identical to those of the blood. The rat model with renal failure showed 100% increase of creatinine in 5 h, while rats connected to the system showed only a 7.4% increase, which verified the effectiveness of the proposed microdialysis system.

Design and Fabrication of Multi-Layered Microfilter by Electropolishing Technique

In this paper, we present electropolishing method to fabricate a thin-structural layer of microfilter which is used for filtering blood in hemodialysis system. The electropolishing method removes material based on electrolysis process, in which material removal is done through electrical current which trigger material removal by chemical reactions. The preliminary experiment shows that the SS 316L structural layer was able to be fabricated in less than 7 minutes, under machining parameter of 7 V of DC voltage, 2 cm gap between tool electrode and workpiece, and utilizing 15% of NaCl in pure water. This promising result has indicated that electropolishing could further be used as a method to make thin-structural layer of microfilter for hemodialysis system.

Material Removal and Fracture Detection in Micro-EDM Processes

The important thing in micro-machining is its accuracy. The Micro-Electrical Discharge Machining (micro-EDM) is a promising method in micro-machining, because (1) the process is independent on the hardness of the workpiece but only depends on its thermal conductivity and melting point and (2) it can be used to machine materials with highly complex geometrical shapes using a simple-shaped tool electrode. However, the process in micro-EDM is not totally well-known, especially related to the formation of discharge pulse energy and the fracture phenomena. In the micro-EDM processes, the formation of discharge pulse energy is a complex phenomenon, since it is related to many parameters such as discharge gap, charge voltage, capacitance, and tool electrode wear. In this paper, the Acoustic Emission (AE) sensor is used to detect the changes of discharge pulse energy during machining of brass using micro-EDM. The results shows that the AE signals can detect and explain the fracture phenomena during the micro-EDM processes.

Study on the Effect of Nano and Micro MoS2 Powder in Micro-Electrical Discharge Machining

The application of powder mixed dielectric to improve the efficiency of electrical discharge machining (EDM) has been acknowledged extensively. However, the study of micro-size powder suspension in micro-EDM field is still limited. In this research, nano and micro size powder of MoS2 were used as catalyst agent. Powder suspension in different size was able to provide significant improvement in material removal rate and surface quality to increase the efficiency in μ- EDM processes.

Portable Desalination Chamber Utilizing Water Permeable Polyethersulfone (PES) Membrane

This paper presents design and fabrication of portable desalination chamber utilizing water permeable polyethersulfone (PES) membrane. The chamber has four stages of desalination process. Each stage has a membrane clamped by filter plate to desalinate sea water and an outlet to qualify the desalinated water from each stage. The chamber works without electrical power, hence desalination process can be carried out in remote areas where electricity source is difficult to find. The water stream is used to test the pumping system of the chamber to pump the water from the water container. The test shows that the pumping system of the chamber is working properly in delivering water to each stage of the chamber without any leakage. The membrane used in each chamber is a modified PES membrane which has high water permeability. Water permeability of the membrane will guarantee that the salt water will permeate easily through the membrane porous during desalination process, hence results in producing fresh water at the final outlet.

Effect of Time Variation on Shot Peening Process to the Surface Properties of SS-316L Osteosynthesis Plate

Shot-peening is one of the surface modification methods to increase material hardness and smoothen its surface at the same time. SS-316L, one type of biocompatible material, is commonly used in medical field particularly for joining fractured bones. However, the surface-crack-prone characteristic of SS-316L has limited its application to be used for such application. In this research, steel balls with diameter 0.4 mm is subjected to the surface of SS-316L Osteosynthesis Plate with variation of time; 9, 10, 11 and 12 minutes holding at constant pressure of 6 bar. The nozzle-to-plate distance is fixed at 100 mm. The impact of the shot balls is a deformed surface and produces a flat-like structure on osteosynthesis plate shot in 12 minutes time. The result shows that shot peening of SS 316L gives its best microstructure after 12 minutes of treatment.