Browsing by Subject "biocompatibility"

Now showing 1 - 3 of 3

Open Access
Characterization and corneal tissue engineering application of peptide amphiphiles
(2012) Dağdaş, Yavuz Selim
Molecular self-assembly is a powerful technique for developing novel nanostructures by using non-covalent interactions such as hydrogen bonding, hydrophobic, electrostatic, metal-ligand, π-π and van der Waals interactions. Hydrogen bonding, hydrophobic and electrostatic interactions promote self-assembly of peptide amphiphile molecules into nanofibers. Bundles of nanofibers form a three-dimensional network resulting in gel formation. Concentration and temperature dependent measurements of gel stiffness suggest that the mechanical properties of the gels are determined by a number of factors including the interfiber interactions and mechanical properties of individual nanofibers. Peptide amphiphile molecules provide a convenient model as extracellular matrix mimetic systems for regenerative medicine studies. Since the substrate stiffness is crucial for cellular behaviours such as proliferation, adhesion and differentiation, understanding the mechanisms behind the viscoelastic properties of the gels formed by self-assembling molecules can lead to development of new materials with controlled stiffness. In this study, regeneration of the corneal stroma was used as a model system for utilization of peptide amphiphile molecules in regenerative medicine studies. Corneal stroma is constituted by collagen fiber arrays that are closely packed forming a stiff environment for corneal fibroblasts. The tunability of mechanical properties of self-assembled peptide amphiphile nanostructures was aimed to be utilized in corneal stroma regeneration. Thinning of the corneal stroma is a debilitating problem that can be caused by diseases like keratoconus, infections or accidents. Since corneal stroma has a restricted regenerative capacity, thinning of stroma is usually treated with cornea transplantation, which is limited by the number of donors. In this thesis, I studied mechanical properties of self-assembled peptide amphiphile nanostructures in nanometer and micrometer scale. I found that the divergence in gel stiffness may arise from the difference of strength of interfiber bonds. An injectable, biocompatible, biodegradable and bioactive system that can be used for thickening the corneal stroma was developed. This system that is composed of nanofibers was observed to enhance viability and proliferation of keratocytes in vitro.
Open Access
In vitro biocompatibility of plasma-aided surface-modified 316L stainless steel for intracoronary stents
(Institute of Physics Publishing, 2010) Bayram, C.; Mizrak, A.K.; Aktürk, S.; Kurşaklioǧlu H.; Iyisoy, A.; Ifran, A.; Denkbaş, E.B.
316L-type stainless steel is a raw material mostly used for manufacturing metallic coronary stents. The purpose of this study was to examine the chemical, wettability, cytotoxic and haemocompatibility properties of 316L stainless steel stents which were modified by plasma polymerization. Six different polymeric compounds, polyethylene glycol, 2-hydroxyethyl methacrylate, ethylenediamine, acrylic acid, hexamethyldisilane and hexamethyldisiloxane, were used in a radio frequency glow discharge plasma polymerization system. As a model antiproliferative drug, mitomycin-C was chosen for covalent coupling onto the stent surface. Modified SS 316L stents were characterized by water contact angle measurements (goniometer) and x-ray photoelectron spectroscopy. C1s binding energies showed a good correlation with the literature. Haemocompatibility tests of coated SS 316L stents showed significant latency (t-test, p < 0.05) with respect to SS 316L and control groups in each test. © 2010 IOP Publishing Ltd.
Open Access
Novel wireless RF-bioMEMS implant sensors of metamaterials
(2010) Melik, Rohat
Today approximately one out of ten patients with a major bone fracture does not heal properly because of the inability to monitor fracture healing. Standard radiography is not capable of discriminating whether bone healing is occurring normally or aberrantly. To solve this problem, we proposed and developed a new enabling technology of implantable wireless sensors that monitor mechanical strain on implanted hardware telemetrically in real time outside the body. This is intended to provide clinicians with a powerful capability to asses fracture healing following the surgical treatment. Here we present the proof-of-concept in vitro and ex vivo demonstrations of bio-compatible radio-frequency (RF) micro-electro-mechanical system (MEMS) strain sensors for wireless strain sensing to monitor healing process. The operating frequency of these sensors shifts under mechanical loading; this shift is related to the surface strain of the implantable test material. In this thesis, for the first time, we developed and demonstrated a new class of bio-implant metamaterial-based wireless strain sensors that make use of their unique structural advantages in sensing, opening up important directions for the applications of metamaterials. These custom-design metamaterials exhibit better performance in remote sensing than traditional RF structures (e.g., spiral coils). Despite their small size, these meta-sensors feature a low enough operating frequency to avoid otherwise strong background absorption of soft tissue and yet yield higher Q-factors (because of their splits with high electric field density) compared to the spiral structures. We also designed and fabricated flexible metamaterial sensors to exhibit a high level of linearity, which can also conveniently be used on non-flat surfaces. Innovating on the idea of integrating metamaterials, we proposed and implemented a novel architecture of ‘nested metamaterials’ that incorporate multiple split ring resonators integrated into a compact nested structure to measure strain telemetrically over a thick body of soft tissue. We experimentally verified that this nested metamaterial architecture outperforms classical metamaterial structures in telemetric strain sensing. As a scientific breakthrough, by employing our nested metamaterial design, we succeeded in reducing the electrical length of the sensor chip down to λo/400 and achieved telemetric operation across thick soft tissue with a tissue thickness up to 20 cm, while using only sub-cm implantable chip size (compatible with typical orthopaedic trauma implants and instruments). As a result, with nested metamaterials, we successfully demonstrated wireless strain sensing on sheep’s fractured metatarsal and femur using our sensors integrated on stainless steel fixation plates and on sheep’s spine using directly attached sensors in animal models. This depth of wireless sensing has proved to suffice for a vast portfolio of bone fracture (including spine) and trauma care applications in body, as also supported by ongoing in vivo experiments in live animal models in collaboration with biomechanical and medical doctors. Herein, for all generations of our RF-bioMEMS implant sensors, this dissertation presents a thorough documentation of the device conception, design, modeling, fabrication, device characterization, and system testing and analyses. This thesis work paves the way for “smart” orthopaedic trauma implants, and enables further possible innovations for future healthcare.