Harikrishna Varma

Publications of Harikrishna Varma

• Preparation and analysis of chemically gradient functional bioceramic coating formed by pulsed laser deposition.

  Authors: P Rajesh, C V Muraleedharan, S Sureshbabu, Manoj Komath, Harikrishna Varma

  Journal of materials science. Materials in medicine. 11/2011; 23(2):339-48.

  Bioactive ceramic coatings based on calcium phosphates yield better functionality in the human body for a variety of metallic implant devices including orthopaedic and dental prostheses. In theBioactive ceramic coatings based on calcium phosphates yield better functionality in the human body for a variety of metallic implant devices including orthopaedic and dental prostheses. In the present study chemically and hence functionally gradient bioceramic coating was obtained by pulsed laser deposition method. Calcium phosphate bioactive ceramic coatings based on hydroxyapatite (HA) and tricalcium phosphate (TCP) were deposited over titanium substrate to produce gradation in physico-chemical characteristics and in vitro dissolution behaviour. Sintered targets of HA and α-TCP were deposited in a multi target laser deposition system. The obtained deposits were characterized by X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. Inductively coupled plasma spectroscopy was used to estimate the in vitro dissolution behaviour of coatings. The variation in mechanical property of the gradient layer was evaluated through scratch test and micro-indentation hardness. The bioactivity was examined in vitro with respect to the ability of HA layer to form on the surface as a result of contact with simulated body fluid. It could be inferred that chemically gradient functional bioceramic coating can be produced by laser deposition of multiple sintered targets with variable chemical composition.

• Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite.

  Authors: P Rajesh, C V Muraleedharan, Manoj Komath, Harikrishna Varma

  Journal of materials science. Materials in medicine. 05/2011; 22(7):1671-9.

  Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for theBiomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500-18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400 °C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.

• Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer.

  Authors: P Rajesh, C V Muraleedharan, Manoj Komath, Harikrishna Varma

  Journal of materials science. Materials in medicine. 01/2011; 22(3):497-505.

  Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate forPulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.

• The treatment of goat femur segmental defects with silica coated hydroxyapatite - one year follow up.

  Authors: Manitha Balachandran Nair, Harikrishna Varma, Sachin J Shenoy, Annie John

  Tissue engineering. Part A. 10/2009;

  Segmental bone defects caused by tumor resections, trauma and skeletal abnormalities like osteomyelitis is still a major problem in orthopaedics due to the lack of predictability in attainingSegmental bone defects caused by tumor resections, trauma and skeletal abnormalities like osteomyelitis is still a major problem in orthopaedics due to the lack of predictability in attaining functional bone after the treatment. The objective of this study was to propose an indigenous porous biodegradable triphasic ceramic (calcium silicate, tricalcium phosphate and hydroxyapatite) coated hydroxyapatite (core) - HASi, for the repair of such segmental defects. With respect to the synthesis of HASi, HA blocks were prepared by wet precipitation; dipped in silica sol (sol gel method); sintered at 1200oC; polished in the form of hollow cylinder (2 cm long with an outer and inner diameter of 2 cm and 7 mm respectively) and implanted into a 2 cm segmental defect created in the goat femur diaphysis. This study prolonged for 12 uneventful months and thereafter neo-osteogenesis in par with material degradation was analyzed through radiography, histology, histomorphometry, SEM-EDS, micro-CT and inductively coupled plasma spectrometry. HASi proved to be osteoconductive, osteointegrative and degradative in nature without the intervention of fibrous tissue formation at the defect site. Histologically the newly formed bone reorganized, mineralized and attained the appearance and contour of the original femoral diaphysis in one year. The interconnected porous structure with silica composition aided the progressive bone regeneration and repair in par with the degradation of the material. Thus the study proposes the possibility of using HASi as a suitable material in clinical orthopaedic reconstructive surgery, which still remains a formidable challenge.

• SURFACE PHOSPHORYLATED COPOLYMER PROMOTES DIRECT BONE BONDING.

  Authors: Sailaja Sivkamiammal Gopalakrishnanchettiar, Mira Mohanty, Kumary T V, Mohanan P V, Ramesh P, Harikrishna Varma

  Tissue engineering. Part A. 04/2009;

  Abstract The bone bonding potential of surface phosphorylated poly (2-hydroxyethyl methacrylate-co-methyl methacrylate), poly (HEMA-co-MMA) has been investigated and compared with commerciallyAbstract The bone bonding potential of surface phosphorylated poly (2-hydroxyethyl methacrylate-co-methyl methacrylate), poly (HEMA-co-MMA) has been investigated and compared with commercially available poly (methyl methacrylate) PMMA bone cement (CMW1 radiopaque, Depuy, Johnson & Johnson, UK) as control. Poly(HEMA-co-MMA) is synthesized by free radical initiated copolymerization and surface functionalized by phosphorylation. The X-ray photoelectron spectroscopy confirms the presence of surface bound phosphate groups on poly (HEMA-co-MMA). The surface phosphorylated poly(HEMA-co-MMA) promotes in vitro biomineralization, cell viability, cell adhesion, and expression of bone specific markers such as osteocalcin and alkaline phosphatase. The bone implantation study performed in rabbits as per ISO 10993-6; 1994 (E), shows that surface phosphorylated poly (HEMA-co-MMA) elicits bone bonding and new bone formation. New woven bone trabeculae are formed at the defect site of surface phosphorylated poly (HEMA-co-MMA) within one week, while for control sample, inflammatory cells predominantly macrophages, fibroblasts and fibrocytes are present at the cortical margins around the defect. The four and twelve weeks post implantation results show that, the major part of the defects around the surface phosphorylated poly (HEMA-co-MMA) implant is bridged with new woven bone, with significant remodeling (evident from resorption bays) along both the margins of the defect. But, for control implants, the defects are only partially closed, with slight remodeling along the margins, but most of them are separated by fibrous tissue.

• A bioactive triphasic ceramic-coated hydroxyapatite promotes proliferation and osteogenic differentiation of human bone marrow stromal cells.

  Authors: Manitha B Nair, Anne Bernhardt, Anja Lode, Christiane Heinemann, Sebastian Thieme, Thomas Hanke, Harikrishna Varma, Michael Gelinsky, Annie John

  Journal of biomedical materials research. Part A. 07/2008;

  Hydroxyapatite (HA) ceramics are widely used as bone graft substitutes because of their biocompatibility and osteoconductivity. However, to enhance the success of therapeutic application, manyHydroxyapatite (HA) ceramics are widely used as bone graft substitutes because of their biocompatibility and osteoconductivity. However, to enhance the success of therapeutic application, many efforts are undertaken to improve the bioactivity of HA. We have developed a triphasic, silica-containing ceramic-coated hydroxyapatite (HASi) and evaluated its performance as a scaffold for cell-based tissue engineering applications. Human bone marrow stromal cells (hBMSCs) were seeded on both HASi and HA scaffolds and cultured with and without osteogenic supplements for a period of 4 weeks. Cellular responses were determined in vitro in terms of cell adhesion, viability, proliferation, and osteogenic differentiation, where both materials exhibited excellent cytocompatibility. Nevertheless, an enhanced rate of cell proliferation and higher levels of both alkaline phosphatase expression and activity were observed for cells cultured on HASi with osteogenic supplements. These findings indicate that the bioactivity of HA endowed with a silica-containing coating has definitely influenced the cellular activity, projecting HASi as a suitable candidate material for bone regenerative therapy. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2008.