Browsing by Author "Velayudhan, S"

Now showing 1 - 8 of 8
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    Dynamic mechanical properties of hydroxyapatite-ethylene vinyl acetate copolymer composites
    (MATERIALS CHEMISTRY AND PHYSICS, 2005) Velayudhan, S; Ramesh, P; Varma, HK; Friedrich, K
    Dynamic mechanical thermal analysis (DMTA) was carried out to explore the dependence of temperature on the viscoelasticity of composites consisting of synthetic hydroxyapatite (HAP) particulate filled ethylene vinyl acetate copolymer (EVA). Two forms of HAP, differing in their surface characteristics and particle size, were used for the study. The freeze-dried HAP (FDHAP) had a mean particle size of 49.18 mum and an irregular surface morphology. In the contrary the spray dried form of HAP (SDHAP) had a mean particle size of 5.84 (m and a spherical morphology. The dynamic mechanical analysis of the composites showed that both, particle size and morphology, had a significant effect on viscoelastic properties. A tremendous increase of the storage modulus was noted with the addition of HAP. Above the T-g of the polymer matrix, the values were marginally higher for the composites containing FDHAP than for those with SDHAP. The damping (tan delta) was found to decrease with the inclusion of HAP. A marginal upper shift in the value of the glass transition temperature (T-g) was observed for the composites fabricated from SDHAP indicating a slightly strong interaction between this HAP and the EVA matrix. (C) 2004 Elsevier B.V. All rights reserved.
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    Effect of vinyl acetate content on the sintering behavior of hydroxyapatite-ethylene vinyl acetate copolymer composites
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 2002)
    Ethylene vinyl acetate copolymer (EVA) alone could be used as a binder material for the fabrication of hydroxyapatite (HAP) into intricate shapes for various bone substitute applications. It was observed that as the vinyl acetate content in the polymer was increased from 12 to 28 wt % an increase in the sintered density of the HAP was observed. Retention of the shapes of HAP in the molded form was also observed. (C) 2002 Kluwer Academic Publishers.
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    Extrusion of hydroxyapatite to clinically significant shapes
    (MATERIALS LETTERS, 2000) Velayudhan, S; Ramesh, P; Sunny, MC; Varma, HK
    Synthetic hydroxyapatite (HAP) particles were incorporated into ethylene vinyl acetate (EVA) co-polymer and then shaped into various forms by simple plastic-forming techniques. Composites with HAP volume of fraction from 10-60% were prepared and shaped. The shapes thus formed were subjected to thermal debinding and subsequent sintering to 1150 degreesC. Retention of shapes was found after thermal debinding and sintering of composites above 30 vol.% of HAP. (C) 2000 Elsevier Science B.V. All rights reserved.
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    Hydroxyapatite filled chitosan-polyacrylic acid polyelectrolyte complexes
    (JOURNAL OF MATERIALS SCIENCE, 2003) Sailaja, GS; Velayudhan, S; Sunny, MC; Sreenivasan, K; Varma, HK; Ramesh, P
    Chitosan (CHI) has been complexed with polyacrylic acid (PAA) in the presence of hydroxyapatite (HAP) to prepare composites intended for bone substitute applications. Thermogravimetric analysis of the composite showed that the presence of HAP had little effect on the degradation profile of the polyelectrolyte complex (PEC), except for the onset of degradation. Optimum compressive strength was observed for 70-weight percentage HAP filled PEC. The morphological analysis revealed that the HAP particles were uniformly distributed in the PEC matrix. The results indicate that HAP filled PEC of CHI and PAA could be prepared following the proposed simple route. (C) 2003 Kluwer Academic Publishers.
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    Mechanical Properties of Hydroxyapatite-Filled Ethylene Vinyl Acetate Copolymer Composites: Effect of Particle Size and Morphology
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2011) Velayudhan, S; Ramesh, P; Varma, HK
    Pliable and bioactive composites made of hydroxyapatite (HAP) and ethylene vinyl acetate (EVA) copolymer were developed for the repair of defective cranium. This article describes the mechanical properties of HAP-EVA composites. The effects of HAP particle size and morphology of HAP on the properties of resultant composites were investigated using various techniques. It was found that the composites containing smaller HAP particles had higher values of tensile modulus, flexural modulus, and impact strength. Examination of the fracture surfaces revealed that only a mechanical bond existed between the filler and the matrix. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1594-1601, 2011
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    A Novel, Single Step, Highly Sensitive In-Vitro Cell-Based Metabolic Assay Using Honeycomb Microporous Polymer Membranes
    (J. Biomed. Nanotechnol., 2015-04) Velayudhan, S; Anilkumar, PR; Nair, PD
    This study describes a novel, simple and versatile system for cell-based assays at the bench-top. The system consists of Polyurethane (PU) based honeycomb membrane with the active compounds/assay reagents dispensed on its pore linings. Membranes with functionalized pores were thus created and used for conducting cell based assays. As proof-of-concept Flourocein acetate (FDA) and Propidium iodide (PI) were embedded on the pore linings and live/dead assays were performed on L929 and Hacat cell lines. The results proved the sensitivity of the membrane based cell assay. To ensure the capacity of this system for high throughput applications, membrane based live/dead assay was performed on L929 cells with varying levels of viability. The results from this experiment were quantified by microscopic and spectrofluourimetric techniques both of which were found to correlate well. It was concluded that this simple membrane based cell assay is highly versatile and enables multiple compounds to be tested on the same cell/tissue. Furthermore, this method requires low volumes of assay reagents and eliminates many of the wet techniques that are involved in a conventional assay, without compromising on the sensitivity. It is anticipated that this functionalized membrane system could be easily adapted for both manual and automated high content screening experiments including in vitro biomaterial evaluation as well as cytotoxicity of nanomaterials.
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    Stamp forming of hydroxyapatite filled ethylene vinyl acetate co-polymers: Process optimization using a right angle V-mould
    (COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, 2007) Velayudhan, S; Ramesh, P; Varma, HK; Schmitt, S; Friedrich, K
    Hydroxyapatite (HAP) filled ethylene vinyl acetate co-polymer (EVA) composites are developed in an attempt to formulate a surgeon friendly material for renovating impaired skull contours. A cost effective technique for obtaining these composites in the clinically significant forms would indeed be a landmark accomplishment. Stamp forming is one of such processes where the cost as well as the performance of the product strikes the right balance. This study was carried out prior to the stamp forming process optimization of the composites into three-dimensional (3-D) contours, essential for applications like cranioplasty. This paper discusses the V-bending results for HAP filled EVA and an attempt to identify a processing window for real manufacturing situations (3-D forming) is made. The processing conditions, such as the stamping temperature, time, and stamping rate, required to give high-quality right angle bends, have been established. The quality of stamped forms is also examined in terms of shape conformance and variation in wall thickness. It has been found that the stamping temperature and velocity were the key factors, which determined the quality of the stamped part. Too high temperatures as well as too high stamping rates lead to severe thinning and degradation of the formed parts. On the other hand, when the temperatures and the stamping rates are too low, the composites do not conform to the mould contour. (c) 2007 Elsevier Ltd. All rights reserved.