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Project Topic: Comparing Nitric Oxide-Releasing Biomaterials and Discussing Viability of Nitric Oxide-Releasing Therapy

Outline of Article: Peter N. Coneski, Kavitha S. Rao, and Mark H. Schoenfisch. " Degradable Nitric Oxide-Releasing Biomaterials via Post-Polymerization Functionalization of Cross-Linked Polyesters." //Biomacromolecules// 2010, 11, 3208–3215

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I) Abstract II) Introduction III) Experimental VI) Results and Discussion V) Conclusion
 * By varying temperature and chemical, polyesters were generated with different thermal an degradation properties
 * Polyesters synthesized resulted in a maximum nitric oxide flow rate of 0.81 //μ//mol cm-2
 * The adhesion of // Pseudomonas aeruginosa //to the polymers decreased by % 80.
 * Reducing infection in implantable biomedical devices is important
 * Over 2 million infections per year developed at hospitals in the U.S.
 * Microbe proliferation occurs at surgical sites and biofilm is created around implanted devices
 * This film protects microbes and encourages them to thrive
 * NO has been shown to eliminate //Pseudomonas aeruginosa// and//Staphylococcus aureus// which account for many hospital-acquired infections
 * NO is highly reactive and must be released in a controlled manner to be used to therapeutic purposes
 * //S//-Nitrosothiols release NO in the presence of heat, light and some trace metals
 * //N//-diazeniumdiolates release NO in the presence of H +
 * NO has a short half-life under physiological conditions (~3s)
 * Must be released near desire site
 * NO releasing coatings have been developed but they are non-degradable
 * Preparation of melt phase reactions and variation of temperature allows “tuning” of NO releasing degradable biomaterials for different applications
 * Static adhesion assay was used to quantify //Pseudomonas aeruginosa// adhesion to polymers
 * Polyesters were synthesized by curing mixtures of diacid/polyol/thiol
 * Polymers were cut to 1 cm x 1 cm squares
 * //N//-hydroxysuccinimide (NHS) and //N//-(3-dimethylaminopropyl)-//N//′-ethylcarbodiimide hydrochloride (EDC) were used to functionalize the polymers
 * Polymers were then nitrosated using 10 mg/mL NaNO2
 * 250mg squares were incubated at 37⁰C and pH 7.4 and percent mass was calculated
 * Nitric Oxide released from polymers was determined using chemiluminescence analyzer
 * Zeiss Axiovert 200 inverted microscope was used to quantify //P. aeruginosa//
 * //Grown in colonies of// 108 colony forming units (CFU) mL-1
 * L929 mouse fibroblasts used in mitogenic MTS assay to assess cell viability
 * 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2//H//-tetrazolium) reduced to purple formazan derivative in viable cells and compared to non-treated control
 * Various polyesters synthesized using different diacid (glutaric acid, adipic acid), polyol (glycerol, pentaerythritol) and thiols (penicillamine, cysteamine)
 * Labeled PE1-PE6
 * Higher curing temperature needed for prepolymer mixes containing adipic acid versus glutaric acid and glycerol versus pentaerythritol
 * Glass transition temperatures (Tg ) for all polyesters were below physiological temperature
 * No appreciable thermal degradation of polymers below 200⁰C
 * GA-based polyesters exhibited higher Tg and thermal degradation
 * Glycerol-based polyesters degraded more quickly in vitro than pentaerythritol-based
 * GA-based polyesters degraded more quickly than AA-based in vitro
 * To prevent harmful nitrite absorption into polyesters S-nitrosothiols were prepared by exposing material to acidified nitrite aqueous solution.
 * Aliphatic polyesters are susceptible to hydrolysis in acidic conditions
 * 0.25M HCl with 30 min exposure (in the prescence of NaNO2) were the maximum effective exposure conditions
 * NO release in polyesters
 * High wattage, broad spectrum irradiation used to liberate NO in S-nitrosothiols
 * Cysteamine analogs produced larger NO release than penicillamine
 * Less steric hindrance for NO storage
 * GA polyesters stored more NO than AA
 * AA cured at higher temperature
 * 21 pmol cm-2 s-1 NO flux required for % 65 decrease in //P. aeruginosa//
 * Achieved in all cases when submerged in PBS at 37⁰C
 * Bacteria Adhesion
 * Compared to controls all NO-releasing polyesters reduced bacterial adhesion
 * PE3 which had a large NO flux showed less reduction in bacteria
 * Too large of a flux for quickly degrading material was not ideal
 * Slowly degrading material with flux less than maximum was proposed to be best mechanism for reducing bacterial adhesion
 * Cytotoxicity
 * PE1 and PE2 showed greatest toxicity (34 ± 2 and 53 ± 20% viable cells, respectively)
 * It is suggested that unpolymerized material was leaching from these polyesters
 * All other materials exhibited > % 65 cell viability in L929 mouse fibroblasts
 * Polyester composition could be managed by controlling melt-phase reaction stoichiometry of diacids and polyols
 * Thermal polycondensation was a viable mode of generating NO-releasing degradable polyesters
 * NO-releasing moiety incorporation was greatest for materials with lower Tg
 * Under physiological conditions, cysteamine- and penicillamine-polyesters released 0.01-0.81 //μ//mol NO cm-2
 * Reduced bacterial adhesion by % 80
 * Future studies will require //in vivo// testing of materials