Samar J. Kalita

Development of controlled porosity polymer-ceramic composite scaffolds via fused deposition modeling

This research is focused on development and fabrication of controlled porosity polymer-ceramic composite scaffolds, with 3-D interconnectivity designed to promote richer supply of blood, oxygen and nutrients for healthy in-growth of bone cells. Particulate-reinforced polymer-ceramic composites were developed by high shear mixing of polypropylene (PP) polymer and tricalcium phosphate (TCP) ceramic. Processing aids were used to improve plasticity and processibility to the composites. Controlled porosity scaffolds were fabricated via the fused deposition process, one of the commercially available rapid prototyping (RP) techniques. These porous scaffolds were characterized for their use as bone grafts in terms of physical, mechanical and biological properties. Hg-porosimetry was performed to determine pore size and their distribution. Scaffolds with different complex internal architectures were also fabricated using this composite material. Tensile properties of neat PP (as received), PP with processing aids (without TCP) and PP-TCP composite (with processing aids) were evaluated and compared using standard dog bone samples. Uniaxial compression tests were performed on cylindrical porous samples with an average pore size of 160 μm and varying vol.% porosity (36%, 48% and 52%). Samples with 36 vol.% porosity showed the best compressive strength of 12.7 MPa. Cytotoxicity and cell proliferation studies were conducted with a modified human osteoblast cell-line (HOB). Results showed that these samples were non-toxic with excellent cell growth during the first two weeks of in vitro testing.

Nanocrystalline hydroxyapatite bioceramic using microwave radiation: Synthesis and characterization

In this work, we synthesized bioactive hydroxyapatite (Ca10(PO4)6(OH)2, HAp) ceramic powder in the lower-end of nano-regime using microwave radiation, which offers several advantages. The powder was synthesized using calcium nitrate tetrahydrate and sodium phosphate dibasic anhydrous as the starting materials. EDTA served as the complex reagent. The pH of the final suspension was adjusted to 9 by adding ammonium hydroxide. Applied microwave power of 600W, pH of the suspension, mole ratio of Ca/P in the staring chemicals, and the chelating effect of EDTA served as the factors in the synthesis of nanocrystalline HAp powder. The synthesized powder was studied using various characterizing techniques viz., XRD, SEM, HR-TEM, EDS, TG/DTA and FT-IR to determine powder morphology, particle-size, crystallinity, phases, elemental composition and thermal behavior. Results confirmed highly crystalline nano-powder (5-30nm) with elemental composition of Ca and P in HAp phase and possessed mixed (elliptical and rod-shape) morphology. Using the Scherrer formula, the average crystallite size was found to be 12nm. The FT-IR confirmed that the powder is of typical apatite structure. Thermal analysis showed a remarkably lower initial dehydroxylation temperature, compared to micron sized HAp, as reported in literature.

Assessment of Endotracheal Cuff Pressure by Continuous Monitoring: A Pilot Study

BACKGROUND Endotracheal tube cuff pressure must be maintained within a narrow therapeutic range to prevent complications. Cuff pressure is measured and adjusted intermittently. OBJECTIVES To assess the accuracy and feasibility of continuous monitoring of cuff pressure, describe changes in cuff pressure over time, and identify clinical factors that influence cuff pressure. METHODS In a pilot study, data were collected for a mean of 9.3 hours on 10 patients who were orally intubated and receiving mechanical ventilation. Sixty percent of the patients were white, mean age was 55 years, and mean intubation time was 2.8 days. The initial cuff pressure was adjusted to a minimum of 20 cm H2O. The pilot balloon of the endotracheal tube was connected to a transducer and a pressure monitor. Cuff pressure was recorded every 0.008 seconds during a typical 12-hour shift and was reduced to 1-minute means. Patient care activities and interventions were recorded on a personal digital assistant. RESULTS Values obtained with the cufflator-manometer and the transducer were congruent. Only 54% of cuff pressure measurements were within the recommended range of 20 to 30 cm H2O. The cuff pressure was high in 16% of measurements and low in 30%. No statistically significant changes over time were noted. Endotracheal suctioning, coughing, and positioning affected cuff pressure. CONCLUSIONS Continuous monitoring of cuff pressure is feasible, accurate, and safe. Cuff pressures vary widely among patients.

Porous calcium aluminate ceramics for bone-graft applications

Calcium aluminate scaffolds with controlled porosity were processed for bone-graft applications. Indirect fused deposition process was used to fabricate these structures. Phase analyses were done using x-ray diffraction technique on powdered samples of calcium aluminates at different compositions. Hg porosimetry was used to determine the pore sizes and the pore volumes present in these controlled porosity structures at different calcium aluminate compositions. Cylindrical samples were tested under uniaxial compressive loading as a function of composition and volume fraction porosity (VFP). Samples of 29% and 44% VFP (designed) with average pore size of 300 μm showed compressive strength between 2 and 24 MPa. Cytotoxicity and cell proliferation studies were conducted with a modified human osteoblast cell line (HOB). These materials showed good cell attachment and a steady cell growth behavior with HOB cells during the first three weeks of in vitro analyses.

Calcium Carbonate Reinforced Natural Polymer Composite For Bone Grafts

Abstract : Challenges in tissue engineering have always-motivated scientists and engineers to develop new biomaterials that can restore the structural features and physiological functions of natural tissues. A novel ceramic-polymer composite was processed with bio-active ceramics dispersed in a natural bio-active polymer for bone graft applications. A commercially available caster bean extract polymer (CBP) was used. It is a natural polymer extracted from the oily caster beans of the dicotyledonous class. During processing of these composites, in situ random interconnected porosity was generated similar to natural bone. Hg-porosimetry results of these composites show that most of the pores are between 50 to 150 microns. Compression tests were performed on cylindrical samples to determine the mechanical properties. Average compression modulus was calculated as 173 MPa, while the average failure strength was 6.7 MPa. Cytotoxicity and cell proliferation studies were conducted with modified human osteoblast cell-line (OPC-1) to show that these composites are biocompatible. Composites showed good cell attachment with a continuous increase in cell growth for at least up to two weeks.