A. Oliveros

Atomic force microscopy analysis of central nervous system cell morphology on silicon carbide and diamond substrates.

Brain machine interface (BMI) devices offer a platform that can be used to assist people with extreme disabilities, such as amyotrophic lateral sclerosis (ALS) and Parkinsons disease. Silicon (Si) has been the material of choice used for the manufacture of BMI devices due to its mechanical strength, its electrical properties and multiple fabrication techniques; however, chronically implanted BMI devices have usually failed within months of implantation due to biocompatibility issues and the fact that Si does not withstand the harsh environment of the body. Single crystal cubic silicon carbide (3C‐SiC) and nanocrystalline diamond (NCD) are semiconductor materials that have previously shown good biocompatibility with skin and bone cells. Like Si, these materials have excellent physical characteristics, good electrical properties, but unlike Si, they are chemically inert. We have performed a study to evaluate the general biocompatibility levels of all of these materials through the use of in vitro techniques. H4 human neuroglioma and PC12 rat pheochromocytoma cell lines were used for the study, and polystyrene (PSt) and amorphous glass were used as controls or for morphological comparison. MTT [3‐(4,5‐Dimethylthiazol‐2‐Yl)‐2,5‐Diphenyltetrazolium Bromide] assays were performed to determine general cell viability with each substrate and atomic force microscopy (AFM) was used to quantify the general cell morphology on the substrate surface along with the substrate permissiveness to lamellipodia extension. 3C‐SiC was the only substrate tested to have good viability and superior lamellipodia permissiveness with both cell lines, while NCD showed a good level of viability with the neural H4 line but a poor viability with the PC12 line and lower permissiveness than 3C‐SiC. Explanations pertaining to the performance of each substrate with both cell lines are presented and discussed along with future work that must be performed to further evaluate specific cell reactions on these substrates. Copyright

Single-Crystal Silicon Carbide: A Biocompatible and Hemocompatible Semiconductor for Advanced Biomedical Applications

Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culturing three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The in vivo biocompatibility was then evaluated via implantation of 3C-SiC and Si shanks into a C57/BL6 wild type mouse. The in vivo results, while preliminary, were outstanding with Si being almost completely enveloped with activated microglia and astrocytes, indicating a severe immune system response, while the 3C-SiC film was virtually untouched. The in vitro experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays and fluorescent microscopy. The neural cells were studied via atomic force microscopy (AFM) which was used to quantify filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show good indicators that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property.

Organic functionalization of 3C-SiC surfaces.

We demonstrate the functionalization of n-type (100) and (111) 3C-SiC surfaces with organosilanes. Self-assembled monolayers (SAMs) of amino-propyldiethoxymethylsilane (APDEMS) and octadecyltrimethoxysilane (ODTMS) are formed via wet chemical processing techniques. Their structural, chemical, and electrical properties are investigated using static water contact angle measurements, atomic force microscopy, and X-ray photoelectron spectroscopy, revealing that the organic layers are smooth and densely packed. Furthermore, combined contact potential difference and surface photovoltage measurements demonstrate that the heterostructure functionality and surface potential can be tuned by utilizing different organosilane precursor molecules. Molecular dipoles are observed to significantly affect the work functions of the modified surfaces. Furthermore, the magnitude of the surface band bending is reduced following reaction of the hydroxylated surfaces with organosilanes, indicating that partial passivation of electrically active surface states is achieved. Micropatterning of organic layers is demonstrated by lithographically defined oxidation of organosilane-derived monolayers in an oxygen plasma, followed by visualization of resulting changes of the local wettability, as well as fluorescence microscopy following immobilization of fluorescently labeled BSA protein.

The Development of Silicon Carbide Based Electrode Devices for Central Nervous System Biomedical Implants

Brain machine interface (BMI) technology has been demonstrated to be a therapeutic solution for assisting people suffering from damage to the central nervous system (CNS), but BMI devices using implantable neural prosthetics have experienced difficulties in that they are recognized by glial cells as being foreign material, which leads to an immune response cascade process called gliosis. One material, cubic silicon carbide (3C-SiC), may provide an excellent solution for the generation of an implantable neural prosthetic interface component of a BMI system. We have recently reported on the biocompatibility of 3C-SiC with immortalized cells, and have extended this work by demonstrating neural cell action potential instigation via an electrode type device. Biocompatibility assessment of 3C-SiC was accomplished using in vitro methodology. 96 hour MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays were performed to determine neural cell viability. Atomic force microscopy (AFM) was used to quantify attached cell morphology and determine lamellipodia/ filopodia interaction with the surface of the semiconductor. It was seen that neurons show excellent viability, cell morphology, and good lamellipodia/ filopodia permissiveness when interacting with 3C-SiC. A neuronal activation device (NAD), based on the planar Michigan microelectrode probe, was constructed from 3C-SiC with the goal of activating an action potential within a neuron. In order to illicit an action potential, neurons were seeded on the NAD device and then they were subjected to a biphasic square pulse signal. Successful action potential activation was recorded through the use of Rhod-2, a Ca 2+ sensitive fluorescent dye. Based on these results, 3C-SiC may be an excellent material platform for neural prosthetics.

Single-crystal Silicon Carbide: A Biocompatible and Hemocompatible Semiconductor for Advanced Biomedical Applications

Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culturing three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays and fluorescent microscopy. For the neural cells studied AFM was also used to quantify the filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was also used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property.

Cellular Interactions on Epitaxial Graphene on SiC (0001) Substrates

An ever-increasing demand for biocompatible materials provides motivation for the development of advanced materials for challenging applications ranging from disease detection to organ function restoration. Carbon-based materials are considered promising candidates because they combine good biocompatibility with high chemical resistance. In this work we present an initial assessment of the biocompatibility of epitaxial graphene on 6H-SiC(0001). We have analyzed the interaction of HaCaT (human keratinocyte) cells on epitaxial graphene and compared it with that on bare 6H-SiC(0001). We have found that for both graphene and 6H-SiC there is evidence of cell-cell and cell substrate interaction which is normally an indication of the biocompatibility of the material.

Biocompatibility Assessment of SiC Surfaces After Functionalization with Self Assembled Organic Monolayers

The biocompatibility of 6H-SiC (0001) surfaces was increased by more than a factor of six through the covalent grafting of NH 2 terminated self-assembled monolayers (SAM) using APDEMS and APTES molecules. Surface functionalization began with a hydroxyl, OH, surface termination. The study included two NH 2 terminated surfaces obtained through silanization with APDEMS (aminopropyldiethoxymethylsilane) and APTES (aminopropyltriethoxysilane) molecules (hydrophilic surfaces) and a CH 3 terminated surface produced via alkylation with 1-octadecene (hydrophobic surface). H4 human neuroglioma and PC12 rat pheochromocytoma cells were seeded on the functionalized surfaces and the cell morphology was evaluated with atomic force microscopy (AFM). In addition, 96 hour MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays were employed to evaluate the cell viability on the SAM modified samples. The biocompatibility was enhanced with a 2 fold (171-240%) increase with 1-octadecene, 3-6 fold (320-670%) increase with APDEMS and 5-8 fold (476-850%) increase with APTES with respect to untreated 6H-SiC surfaces.

Protein immobilization on 3C-SiC (100) as a substrate for detecting the onset of acute myocardial infarction (AMI)

Silicon Carbide (SiC), has been shown to be a bio- and hema-compatible substrate that could potentially be used in biosensor applications. The development of a viable biorecognition interface using SiC as the substrate material for bio-detection is described. Surface modification with 3-aminopropyltriethoxysilane (APTES) and immobilization via covalent conjugation of antimyoglobin (anti-Myo) on the modified surfaces is achieved, which are initial steps for immunosensing based devices. Successful formation of APTES layers and antibody immobilization were identified with surface water contact angle (SWCA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).

AFM and Cell Staining to Assess the In Vitro Biocompatibility of Opaque Surfaces

Although many current biomedical devices have been able to assist millions of people, there are still many critical needs to be addressed. Many individuals need constant diagnostics, controlled and targeted delivery of drugs, or even the replacement of motor and sensory functions. Many of the current biomedical systems that perform these functions are large, non-transportable, cumbersome or, more importantly, they cannot be in contact with the body for extended amounts of time. One solution is to utilize micro-electromechanical machines, or MEMS. With the same processes used to create computer chips, we can now generate a variety of micron sized machines which are designed to deliver drugs, detect physiological changes, and even electrically interface with cells. These micron to nanometer sized devices can potentially be implanted into the body with minimal invasiveness. There is, however, a very important issue which in turn needs to be addressed before their widespread clinical use can come to realization.

Chapter 3 – Multifunctional SiC Surfaces: From Passivation to Biofunctionalization

The integration of semiconductors with organic and biological systems is an emerging research area that holds great potential for future biomedical applications. Among the available semiconductors, silicon carbide (SiC) is particularly promising since it exhibits a range of exceptional physical properties, such as chemical stability, hardness, and biocompatibility, which make it suitable for in vivo operation in harsh biological environments. In order to make use of the full potential of silicon carbide for biomedical applications, a versatile toolkit is necessary for reliably tailoring its surface chemical reactivity, wettability, and electronic behavior using simple and scalable methods. This chapter provides a brief overview of the chemical and physical methods, which have recently been developed for the modification of silicon carbide surfaces. Furthermore, it presents the application of these methods to control the substrate permissiveness to cells. To date, the mechanical properties of this material have been exploited for medical implant coatings. However, in order to realize the full potential of SiC as an active biomedical element, it is necessary to develop methods for precisely tuning its surface properties. Identification of charge transfer pathways and mechanisms in multicomponent and multiphase systems, including SiC substrates, (bio)organic molecules, and electrolyte environments, is required. In addition, a comprehensive understanding of the effects of surface charge, morphology, and termination on cell growth on the surface must be developed.