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"Parthasarathy, A"
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Peracetic Acid: A Practical Agent for Sterilizing Heat-Labile Polymeric Tissue-Engineering Scaffolds
Advanced biomaterials and sophisticated processing technologies aim at fabricating tissue-engineering scaffolds that can predictably interact within a biological environment at the cellular level. Sterilization of such scaffolds is at the core of patient safety and is an important regulatory issue that needs to be addressed before clinical translation. In addition, it is crucial that meticulously engineered micro- and nano- structures are preserved after sterilization. Conventional sterilization methods involving heat, steam, and radiation are not compatible with engineered polymeric systems because of scaffold degradation and loss of architecture. Using electrospun scaffolds made from polycaprolactone, a low melting polymer, and employing spores of
Bacillus atrophaeus
as biological indicators, we compared ethylene oxide, autoclaving and 80% ethanol to a known chemical sterilant, peracetic acid (PAA), for their ability to sterilize as well as their effects on scaffold properties. PAA diluted in 20% ethanol to 1000 ppm or above sterilized electrospun scaffolds in 15 min at room temperature while maintaining nano-architecture and mechanical properties. Scaffolds treated with PAA at 5000 ppm were rendered hydrophilic, with contact angles reduced to 0°. Therefore, PAA can provide economical, rapid, and effective sterilization of heat-sensitive polymeric electrospun scaffolds that are used in tissue engineering.
Journal Article
Peracetic Acid Sterilization Induces Divergent Biological Response in Polymeric Tissue Engineering Scaffolds
Synthetic polymers offer control over composition, architecture, mechanical properties and degradation kinetics. Predictable sterilization of synthetic polymeric scaffolds made from low temperature melting polymers, remains a challenge to clinical translation. We previously demonstrated successful room temperature sterilization of electrospun polycaprolactone scaffolds (ePCL) using peracetic acid (PA). The current paper investigates the effects of PA sterilization on two different scaffolds types—ePCL and commercially available porous polystyrene (Alvetex®) scaffolds using mouse calvarial osteoblasts cell line (MC3T3) and Live-Dead Assay. We report cytotoxicity in PA-treated ePCL scaffolds (PA-ePCL), while control scaffolds strongly supported cell survival. Treatment of PA-ePCL scaffolds with known methods of PA residual elimination (sodium thiosulfate, catalase, washing and aeration) had minimal effect on MC3T3 survival. However, incubation in 80% ethanol for 30 min successfully eliminated the toxic PA residuals and restored scaffold cytocompatibility. On the other hand, PA treatment of Alvetex® scaffolds induced diametrically opposite effects: cell survival and proliferation was enhanced after PA exposure and these responses were reversed following ethanol wash. These results suggest that PA treatment can induce different biological effects based on polymer chemistry and scaffold architecture and presents interesting opportunities to modulate biological properties of tissue engineering scaffolds.
Journal Article
Science of nanofibrous scaffold fabrication: strategies for next generation tissue-engineering scaffolds
Native extracellular matrix (ECM) provides structural support to the multicellular organism on a macroscopic scale and establishes a unique microenvironment (niche) to tissue- and organ-specific cell types. Both these functions are critical for optimal function of the organism. These natural ECMs comprise predominantly fibrillar proteins, collagen and elastin and are synthesized as monomers but undergo hierarchical organization into well-defined nanoscaled structural units. The interaction between the cells and ECM is dynamic, reciprocal and essential for tissue development, maintenance of function, repair and regeneration processes. Tissue-engineering scaffolds are synthetic, biomimetic ECM analogues that have great promise in regenerative medicine. Ongoing efforts in mimicking the native ECM in terms of composition and dimension have resulted in three strategies that permit the generation of scaffolds in nanometer dimensions. Although excellent reviews regarding the applications of these strategies in tissue engineering are available, a comprehensive review of the science behind these fabrication techniques does not exist. This review intends to fill this critical gap in the existing knowledge in the fast-expanding field of nanofibrous scaffolds. A thorough understanding of the fabrication processes would enable us to better exploit available technologies to produce superior tissue-engineering scaffolds.
Journal Article
Visual acuity outcomes after deep anterior lamellar keratoplasty: a case-control study
AimTo compare visual outcomes between deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK). Secondarily to compare refractive outcomes, complications and graft survival between the three cohorts.MethodsRetrospective case-control study evaluating visual acuity outcomes (VA) following DALK with complete Descemet's baring (DALKa) (modified Anwar big bubble technique—51 eyes), pre-descemetic anterior lamellar keratoplasty (DALKm) (manual technique—52 eyes) and PK (103 eyes) with mean follow-up of 13.6, 19.3 and 18.6 months, respectively.ResultsThe common indications for surgery were corneal scars (36.4%), keratoconus (28.6%) and corneal dystrophies (13.6%). A best-corrected VA of 6/7.5 or better was achieved in 19.4% (PK), 21.6% (DALKm) and 38.5% (DALKa) of cases (p=0.02), and eyes that underwent DALKa had significantly better visual outcomes than PK (p=0.03). Complications following PK were glaucoma (15%), endothelial rejection (12%) and epithelial problems (11%); in the lamellar group, glaucoma (9%), epithelial problems (5%) and Descemet's detachment (3%) were more common. The 2-year estimated probability of graft survival was 90% for PK, 98% for DALKm and 100.0% for DALKa (p=0.35).ConclusionsLamellar keratoplasty with complete baring of the Descemet's membrane (DALKa) gave significantly better visual outcomes compared to PK or pre-descemetic ALK and should be the preferred from of corneal replacement in corneal disorders with healthy endothelium.
Journal Article
Isolation and characterization of microsatellite markers in Garcinia gummi-gutta by next-generation sequencing and cross-species amplification
Garcinia gummi-gutta
(L.) Roxb. (Clusiaceae) is an endemic, semidomesticated, fruit-yielding tree species distributed in the Western Ghats of India and Sri Lanka. Various bioactive phytochemicals, such as garcinol, benzophenones and xanthones are isolated from
G. gummi-gutta
and have shown antibacterial, antiviral and antioxidant activities. We sequenced the total genomic DNA using Illumina Hiseq 2000 platform and examined 241,141,804 bp high quality data, assembled into 773,889 contigs. In these contigs, 27,313 simple-sequence repeats (SSRs) were identified, among which mononucleotide repeats were predominant (44.98%) followed by dinucleotide and trinucleotide repeats. Primers were designed for 9964 microsatellites among which 32 randomly selected SSR primer pairs were standardized for amplification. Polymerase chain reaction (PCR) amplification of genomic DNA in 30
G. gummi-gutta
genotypes revealed polymorphic information content (PIC) across all 32 loci ranging from 0.867 to 0.951, with a mean value of 0.917. The observed and expected heterozygosity ranged from 0.00 to 0.63 and 0.896 to 0.974, respectively. Alleles per locus ranged from 12 to 27. This is the first report on the development of genomic SSR markers in
G. gummi-gutta
using next-generation sequencing technology. The genomic SSR markers developed in this study will be useful in identification, mapping, diversity and breeding studies.
Journal Article
Effect of fluid application conditions on grinding behaviour
Abstract
Applying copious amounts of fluid to ensure adequate lubrication and cooling during grinding creates environmental and safety hazards. The present investigation was undertaken to explore the prospects for reducing the amount of applied fluid without having a deleterious effect on grinding performance. Straight surface grinding experiments were conducted to determine the effect of fluid flowrate and nozzle set-up conditions on the grinding behaviour for both up grinding and down grinding. A high-speed camera was used to observe fluid access to the grinding zone. For up grinding at low flowrates, lack of fluid reaching the wheel and workpiece caused an increase in the forces and surface roughness. The effect of a low flowrate was much less pronounced for down grinding due to the presence of residual fluid, which had collected on the workpiece top surface. A simple fluid mechanics model was developed to determine the flowrate and nozzle set-up condition required for the fluid to reach the wheel and the workpiece.
Journal Article
The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys
More than five years ago, wrought processing was first used to produce fully lamellar (FL) microstructure in TiAl alloys having grain sizes < approx400 mu m. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such microstructural forms led to exceptional yield strengths (500-1000 MPa at low temperatures) while maintaining attractive high-temperature properties. The improvements appeared to be related to an unusually high apparent sensitivity of strength to grain sizes. Studies reported an apparent value for the slope of the Hall-Petch (HP) plot approaching 5 MParoot m for FL gamma alloys, while that for single-phase or duplex microstructures is near unity. The present investigations examine the slope of the HP plot for FL microstructures, paying particular attention to the lamellar microstructural variables. Results show that the alpha sub 2 lamellar thickness and spacing and the gamma lamellar thickness can vary over more than two orders of magnitude with typical process methods. These spacings influence the value of k sub y in the HP (grain sizes) relationship. Since they often change concomitantly with grain size in processing, they can give rise to a large scatter in the HP plot. The investigations also examine the flow behavior, glide barriers, and slip multiplicity for polysynthetically twinned (PST) crystals (the single-grain analogue of FL material), and then map this behavior into an explanation of the yield behavior of high-strength FL gamma alloys.
Journal Article