D. J. Carlsson

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N2 atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N2 APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.

Polyolefin oxidation: Quantification of alcohol and hydroperoxide products by nitric oxide reactions☆

Abstract A new procedure has been developed for the identification and quantification of key products from the oxidation of solid polyolefins, based on reactions with gaseous nitric oxide. Alcohol and hydroperoxide groups are converted to nitrites and nitrates, respectively, and can be detected with high sensitivity by infrared spectroscopy. Furthermore, the nitrate and nitrite absorptions are influenced by the primary, secondary or tertiary nature of the alkyl substituents so that it is possible to identify differing sites of attack in branched polyolefins. Preliminary results from the application of nitric oxide reactions to the analysis of polyethylene and polypropylene oxidized by γ-irradiation are used to illustrate the potential of the technique and a comparison made with other current methods.

Artificial human corneas: Scaffolds for transplantation and host regeneration

Purpose To review the development of artificial corneas (pros-theses and tissue equivalents) for transplantation, and to provide recent updates on our tissue-engineered replacement corneas. Methods Modified natural polymers and synthetic polymers were screened for their potential to replace damaged portions of the human cornea or the entire corneal thickness. These polymers, combined with cells derived from each of the three main corneal layers or stem cells, were used to develop artificial corneas. Functional testing was performed in vitro. Trials of biocompatibility and immune and inflammatory reactions were performed by implanting the most promising polymers into rabbit corneas. Results Collagen-based biopolymers, combined with synthetic crosslinkers or copolymers, formed effective scaffolds for developing prototype artificial corneas that could be used as tissue replacements in the future. We have previously developed an artificial cornea that mimicked key morphologic and functional properties of the human cornea. The addition of synthetic polymers increased its toughness as it retained transparency and low light scattering, making the matrix scaffold more suitable for transplantation. These new composites were implanted into rabbits without causing any acute inflammation or immune response. We have also fabricated full-thickness composites that can be fully sutured. However, the long-term effects of these artificial corneas need to be evaluated. Conclusions Novel tissue-engineered corneas that comprise composites of natural and synthetic biopolymers together with corneal cell lines or stem cells will, in the future, replace portions of the cornea that are damaged. Our results provide a basis for the development of both implantable temporary and permanent corneal replacements.

Bioengineered corneas: how close are we?

Bioengineered corneas are substitutes for human donor tissue that are designed to replace part or the full thickness of damaged or diseased corneas. They range from prosthetic devices that solely address replacement of the corneas function to tissue-engineered hydrogels that allow some regeneration of the host tissue. In addition, there are also bioengineered lenticules that may be implanted into the cornea to improve vision by altering the refractive properties of the eye, an alternative procedure to refractive surgery. In recent years, there have been significant developments in many areas of bioengineered corneas, such as the clinical trials of an artificial cornea designed as a prosthesis, the development of completely natural corneal replacements, and the development of biosynthetic matrices that permit host tissue regeneration. For correction of refractive errors, a synthetic corneal onlay that allows stable overgrowth of epithelium appears to be promising.

Polyethylene hydroperoxide decomposition products

Abstract The decomposition products from pre-oxidized, linear low-density polyethylene have been identified and quantified for films exposed in the absence of oxygen to ultra-violet irradiation, heat or γ-irradiation. Films were preoxidized under controlled conditions by γ-irradiation in air. Vacuum decomposition products were then analyzed by infrared derivatization techniques to allow the quantification of carboxylic acid, ketone, ester, γ-lactone, alcohol, hydroperoxide and unsaturation products. From the relative proportion of these products it is possible to compare the mechanisms of the three initiation methods. These mechanisms are compared and contrasted with previously proposed mechanisms for polyethylene degradation.

A critical comparison of methods for hydroperoxide measurement in oxidized polyolefins

Hydroperoxide products in solid oxidized polyolefins have been measured by iodometry, Fe2+ reaction and by derivatization infrared spectroscopy methods. Polyethylene, polypropylene and elastomers were oxidized by photo, thermal and γ-initiation. The traditional iodometric method appears to be highly reliable within certain constraints of reaction time imposed by sample crosslinking. The Fe2+ reaction was found to give values consistently one order of magnitude below the true level because of failure of the reagents to penetrate into the oxidized polymers even after a prior swelling step. Derivatization of hydroperoxides by reaction with nitric oxide produced nitrates which could be measured by infrared spectroscopy with high sensitivity. Total nitrate yields agreed well with iodometric determination of hydroperoxide for reaction conditions under which the nitrates were stable. Different nitrates, and hence hydroperoxides, could be identified and quantified by this method.

Polyolefin photo-stabilisation mechanisms. Reactions of tetramethylpiperidine derivatives in model systems☆

Abstract The relative rate of cyclohexyl radical scavenging by oxygen or 4-oxo-2,2,6,6-tetramethylpiperidino-N-oxyl has been measured at 25°C, together with the relative rates of cyclohexyl peroxy radical attack on cyclohexane or substituted hydroxylamines derived from 2,2,6,6-tetramethylpiperidine. These competitive processes are important in the stabilisation of polymers against photo-oxidative destruction by piperidine derivatives. Peroxy radical scavenging by the substituted hydroxylamine appears to be considerably more important than alkyl radical scavenging by the nitroxide, although both processes are essential for prolonged ultra violet (uv) stabilisation of a polymer. However, a comparison of experimental photo-protection with that predicted by the measured rate constant ratios shows that other processes are needed to account entirely for the observed stabilisation. Other factors which may be involved in piperidine photo-protection of polymers include thermal decomposition of the substituted hydroxylamine to reform nitroxide in polar(oxidised) zones and especially the association of nitroxides with hydroperoxide groups (the dominant photo-initiator in degrading polyolefins).

Photooxidation of unsaturated oils: Effects of singlet oxygen quenchers

The photooxidative deterioration of unsaturated food oils by near UV and visible light was found to be retarded by nickel (II) chelates well known to quench singlet oxygen (1O2). The rates of hydroperoxide formation during light exposure were unaffected by efficient peroxy radical scavengers such as hindered phenols. α-Tocopherol (vitamin E) underwent a relatively rapid oxidation itself when exposed to1O2 in oil solutions, despite being able to deactivate1O2 quite efficiently. From a comparison of the rates of scavenging by stabilizers and attack on allyl groups,1O2 initiated deterioration is appreciably more difficult to retard than peroxy radical processes.

Corneal regeneration following implantation of a biomimetic tissue-engineered substitute.

Per Fagerholm, Neil S Lagali, David J Carlsson, Kimberley Merrett and May Griffith, Corneal Regeneration Following Implantation of a Biomimetic Tissue-Engineered Substitute, 2009, CTS-CLINICAL AND TRANSLATIONAL SCIENCE, (2), 2, 162-164. which has been published in final form at: http://dx.doi.org/10.1111/j.1752-8062.2008.00083.x Copyright: Blackwell Publishing http://eu.wiley.com/WileyCDA/Brand/id-35.html

Genipin Cross-Linked Fibrin Hydrogels for in vitro Human Articular Cartilage Tissue-Engineered Regeneration

Our objective was to examine the potential of a genipin cross-linked human fibrin hydrogel system as a scaffold for articular cartilage tissue engineering. Human articular chondrocytes were incorporated into modified human fibrin gels and evaluated for mechanical properties, cell viability, gene expression, extracellular matrix production and subcutaneous biodegradation. Genipin, a naturally occurring compound used in the treatment of inflammation, was used as a cross-linker. Genipin cross-linking did not significantly affect cell viability, but significantly increased the dynamic compression and shear moduli of the hydrogel. The ratio of the change in collagen II versus collagen I expression increased more than 8-fold over 5 weeks as detected with real-time RT-PCR. Accumulation of collagen II and aggrecan in hydrogel extracellular matrix was observed after 5 weeks in cell culture. Overall, our results indicate that genipin appeared to inhibit the inflammatory reaction observed 3 weeks after subcutaneous implantation of the fibrin into rats. Therefore, genipin cross-linked fibrin hydrogels can be used as cell-compatible tissue engineering scaffolds for articular cartilage regeneration, for utility in autologous treatments that eliminate the risk of tissue rejection and viral infection.