فهرست مطالب کیومرث جلیلی

In recent times, there has been significant interest in the field of biomedical applications, particularly in the realm of targeted drug delivery and medical implants, where injectable biomaterials possessing 3D printing capabilities have garnered considerable attention. While numerous biomaterials have been developed to replicate the mechanical behavior of human tissue, the quest for an ideal biocompatible material with adjustable mechanical properties that can accommodate a wide range of characteristics remains unfulfilled. Within the scope of this research, a printable and injectable elastomeric hydrogel was formulated utilizing polyurethane as the elastomer component and hydroxyethyl methacrylate as the hydrogel component. By varying the percentage composition of these constituents, a diverse array of mechanical properties was achieved. Fourier Transform Infrared Spectroscopy was employed to verify the successful synthesis of EPUH. The synthetic materials displayed modifiable mechanical properties in their dry states, encompassing a range of Young's modulus values from 20 MPa to 1.2 GPa, as well as elongation at break values ranging from 20% to 140%. Additionally, this study also encompassed an evaluation of water uptake and printability of the samples.

Hypothesis: 

Hydrophobic silicone rubber is used as coatings that create hydrophobic properties for different surfaces. Silicone rubbers have high chemical and physical stability. Hydrophobic properties and resistance to creeping flow are unique features of silicone rubber coatings. The purpose of this research is to synthesize and assess silicone rubber and alter its surface wettability by roughening and modifying the surface using materials with low surface energies.

Silicone rubber was first synthesized by hydrosilylation method in presence of a platinum catalyst, and subsequently coated onto polytetrafluoroethylene (PTFE) sheet as an example of a low surface energy substrate. In order to create roughness on the surface, industrial sandpapers were used of having grit sizes of 120, 220, and 400. In the next step, low surface energy silicon nanofilaments (SNF) were used to modify the desired surface, which were decorated on the surface of the sample through vapor deposition method. 

The SEM images show that the roughness density on the surface of the samples created by a 400-grit sandpaper is higher than that of a 220-grit sandpaper, and this sandpaper is also higher than that of a 120-grit sandpaper. Increasing the roughness density increases the static water contact angle (WCA) because in this case the Wenzel model is no longer dominant, and the hydrophobic mechanism follows Cassie Baxter theory. Due to the highest degree of roughness density created on the surface, the PTFE substrate treated with a 400 grit sandpaper was used for the next stage of silicone rubber coating and finally for the growth of SNF on top of the silicone layer. Applying SNF coating on the sample surface leads to a significant increase in the WCA (~159°). This hydrophobicity enhancement after SNF coating can be attributed to the low surface energy of the coating and the increase in roughness caused by the random growth of nanofilaments.

Research Subject:

 Poly(dimethylsiloxane) (PDMS) is a silicone polymer that nowadays despite unique characteristics and high application potential of its microparticles, their preparation via bulk emulsification methods is a main challenge due to the limitations in mixing process, high viscosity and low surface energy of PDMS that make impossible accurate  control of final obtained particles. In the present work, size-controlled PDMS microparticles were prepared from a high-viscosity material.

Research Approach: 

PDMS microparticles were obtained by using glass capillary co-flow microfluidic device. The designed microfluidic device is facile, inexpensive and reusable and facilitated preparation of the high-viscosity PDMS microdroplets. Stabilizing the oil-in-water emulsion was obtained by optimizing the bath components and curing process that resulted in monodisperse and spherical PDMS microparicles. Effect of the some important adjustable parameters such as microchannel diameter and flow rate on the flow regimes and microparticles polydispersity were investigated by means of optical microscopy and scanning electron microscopy.

Results showed a dripping regime for producing monodisperse microparticles at low flow rates of the continuous phase and monodisperse microparticles from it. On the contrary, microparticles obtained from jetting regime are more polydisperse and smaller in comparison with dripping regime. By reducing the diameter of inner microchannel, microparticles with a diameter of 1.83 µm were obtained. Using the designed technology, uniform nanocomposite PDMS/ZnO microparticles 318 µm in diameter containing 15% ZnO were obtained from an oil phase viscosity of 7550 mPa.s. Therefore by an optimized and facile method, size-controllable uniform microparticles can be prepared that are proposed for various applications including drug delivery, bioengineering and electronic industry.

 Recent advances in micro- and nanotechnology have led to possible design of functional micro/nanostructured surfaces with micro/nanotopography features that can exhibit low adhesion properties. An important example of such structures is superhydrophobic surface, which is extremely water repellent. In the present work, the effects of surface microtopography on the wetting of poly(dimethylsiloxane) (PDMS) rubber film with the goal of producing superhydrophobic surface are investigated.

Micropillar arrays inspired by biological structures found in nature are produced on PDMS surface using a soft microlithography technique with different pitch/width ratios. To this end, the masters are fabricated using conventional microfabrication techniques and photolithography. Master designs tested are inverted pillar shape fabricated by anisotropic etching of silicon (reactive-ion etching, DRIE), a high aspect ratio master and a low aspect ratio photoresist master.

Our fabricated pillars have nano-scale ripples that arise from the series of alternating, independent silicon etching and sidewall passivation steps used in the DRIE process. The elastomeric stamps are negative replicas of the masters and they are fabricated by PDMS. The stamps have a regular array of protruding features, in order to make a pattern transfer to the target substrate during m-contact printing. Several pitch/width ratios are configured to optimize the relationship between surface topography and wetting behavior of PDMS film using static water contact angle measurements. We have correlated these structures with PDMS rubber hydrophobicity and have also characterized the transition from the composite (Cassie-Baxter) to wetted (Wenzel) states for different types of surface structures. The surface topography-dependent contact angle of water underwent a transition from Cassie-Baxter to Wenzel states at pitch size ~60 mm.

Environmental and economical advantages of bulk or mass polymerization processes have made this process attractive for ABS producers. When an ABS resin with better optical properties is needed, because of small additive and no use of water and solvent, mass polymerization is the first choice. Processing problems of this method such as lower heat transfer, higher viscosity of reaction mass, and hardness of composition and morphology control in final copolymer make it to play a small role in polymerization of grafted ABS polymers. On the other hand, most of the SAN sales in the world markets are produced by this method. In this study, the bulk processes and different aspects including economical, environmental, and easiness or hardness of process control will be studied. In addition, the effects of polymerization process on the physical- mechanical properties like impact resistance and brightness will be discussed.

It is well known that the toughness of the brittle polymers can be significantly enhanced by incorporation of rubber particles or grafted-rubber particles. One of these materials is acrylonitrile-butadiene-styrene (ABS) which contains dispersed rubber particles with grafted SAN chains on it and styrene-acrylonitrile (SAN) as matrix. Emulsion polymerization (batch or continuous), suspension polymerization (batch), bulk polymerization (continuous), and combined processes and compounding. In this paper, suspension process of ABS production, and the morphology and properties of obtained will be studied.