Prevention of oxidative degradation of polyurethane by covalent attachment of di-tert-butylphenol residues

Fungal Enzymes Involved in Plastics Biodegradation

Plastic pollution is a growing environmental problem, in part due to the extremely stable and durable nature of this polymer. As recycling does not provide a complete solution, research has been focusing on alternative ways of degrading plastic. Fungi provide a wide array of enzymes specialized in the degradation of recalcitrant substances and are very promising candidates in the field of plastic degradation. This review examines the present literature for different fungal enzymes involved in plastic degradation, describing their characteristics, efficacy and biotechnological applications. Fungal laccases and peroxidases, generally used by fungi to degrade lignin, show good results in degrading polyethylene (PE) and polyvinyl chloride (PVC), while esterases such as cutinases and lipases were successfully used to degrade polyethylene terephthalate (PET) and polyurethane (PUR). Good results were also obtained on PUR by fungal proteases and ureases. All these enzymes were isolated from many different fungi, from both Basidiomycetes and Ascomycetes, and have shown remarkable efficiency in plastic biodegradation under laboratory conditions. Therefore, future research should focus on the interactions between the genes, proteins, metabolites and environmental conditions involved in the processes. Further steps such as the improvement in catalytic efficiency and genetic engineering could lead these enzymes to become biotechnological applications in the field of plastic degradation.

Biodegradation of plastics for sustainable environment

Plastics are a kind of utility product that has become part and parcel of one's life. Their continuous usage, accumulation, and contamination of soil and water pose a severe threat to the biotic and abiotic components of the environment. It not only increases the carbon footprints but also contributes to global warming. This calls for an urgent need to develop novel strategies for the efficient degradation of plastics. The microbial strains equipped with the potential of degrading plastic materials, which can further be converted into usable products, are blessings for the ecosystem. This review comprehensively summarizes the microbial technologies to degrade different plastic types, such as polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyurethane (PU). The study also describes the utilization of degraded plastic material as feedstock for its conversion into high-value chemicals.

Electrochemically-active carbon nanotube coatings for biofouling mitigation: Cleaning kinetics and energy consumption for cathodic and anodic regimes

Biofouling is a major obstacle in engineered systems exposed to aqueous conditions. Many attempts have been made to engineer the surface properties of materials to render them resistant to biofouling. These modifications typically rely on passive antimicrobial or anti-adhesive surface coatings that prevent the deposition of bacteria or inactivate them once they reach the surface. However, no surface modification strategy completely prevents biofilm formation, and, over time, surfaces will be fouled and require cleaning. In this work, we demonstrate the capacity of electrochemical carbon nanotube coatings in dispersing biofilms formed on the surface. A systematic analysis of the biofilm removal kinetics in function of applied current density is made to identify the optimal current conditions needed for efficient surface cleaning. Operating the electrochemically active surface as a cathode produces superior results compared to when it is operated as an anode. Specifically, the 5.00 A m^-2 and 2.50 A m^-2 cathodic conditions produced rapid cleaning, with complete biofilm dispersal after 2 min of operation. Surface cleaning is attributed to the generation of microbubbles on the surface that scours the surface to remove the adhered biofilm. Energy consumption analyses indicate that the 2.50 A m^-2 cathodic condition offers the best combination of cleaning kinetics and energy consumption achieving 99% biofilm removal at an energy cost of ~$ 0.0318 m^-2. This approach can be competitive compared to the current chemical cleaning strategies, while offering an opportunity for a more sustainable and integrated approach for biofouling management in engineered systems.

Degradable poly(ester-ether) urethanes of improved surface calcium deposition developed as novel biomaterials

Bones, which are considered as hard tissues, work as scaffold for human body. They provide physical support for muscles and protect intestinal organs. Percentage of hard tissues in human body depends on age, weight, and gender. Human skeleton consists of 206 connected bones. Therefore, it is natural that the hard-tissue damage such as fractures, osteoporosis, and congenital lack of bone may appear. The innovative way of bone healing is an application of so-called tissue scaffolds. There are many synthetic polymers used in this field, but polyurethanes play a great role in this field. It is due to the possibility to control their degradation rate and to tune their surface to improve the calcification process, required for proper bone regeneration. In this article, we described the fabrication of degradable poly(ester-ether)urethane materials, having different hard-segment content (28% or 47%). PEEURs-28HS and PEEURs-47HS materials were obtained by two-step polymerization method and characterized by mechanical properties, ability to undergo oxidative degradation and surface calcification. Performed studies indicated that the PEEURs-28HS material possessed suitable properties to be proposed as a material for possible application in the bone tissue engineering.

New insights into the microbial degradation of polyurethanes

Frequent and frequently deliberate release of plastics leads to accumulation of plastic waste in the environment which is an ever increasing ecological threat.

The effect of CD47 modified polymer surfaces on inflammatory cell attachment and activation

CD47 is a transmembrane protein that is a marker of "self". CD47 binding to its cognate receptor in leukocytes and macrophages, signal-regulatory protein alpha (SIRPα), causes inhibition of inflammatory cell attachment. We hypothesized that immobilization of recombinant CD47 on polymeric surfaces would reduce inflammation. Recombinant CD47 was appended to polyvinyl chloride (PVC) or polyurethane (PU) surfaces via photoactivation chemistry. Cell culture studies showed that CD47 immobilization significantly reduced human neutrophil (HL-60) and human monocyte derived macrophage (MDM) (THP-1) attachment to PVC and PU respectively. A neutralizing antibody, directed against SIRPα, inhibited THP-1 and HL-60 binding to PU and PVC surfaces respectively. This antibody also increased the level of SIRPα tyrosine phosphorylation, thereby indicating a direct role for SIRPα mediated signaling in preventing inflammatory cell attachment. Studies using human blood in an ex vivo flow-loop showed that CD47 modified PVC tubing significantly reduced cell binding and neutrophil activation compared to unmodified tubing or poly-2-methoxy-ethylacrylate (PMEA) coated tubing. In ten-week rat subdermal implants, CD47 functionalized PU films showed a significant reduction in markers of MDM mediated oxidative degradation compared to unmodified PU. In conclusion, CD47 functionalized surfaces can resist inflammatory cell interactions both in vitro and in vivo.

Prevention of polyurethane oxidative degradation with phenolic antioxidants covalently attached to the hard segments: structure-function relationships

Oxidative degradation of the polyurethane elastomeric (PU) components greatly reduces the efficacy of PU-containing cardiovascular devices. Covalently appending the phenol-based antioxidant, 4-substituted 2,6-di-tert-butylphenol (DBP), to PU hard segments effectively reduced oxidative degradation of the PU in vivo and in vitro in prior studies by our group. In these experiments, we analyze the contribution of the tethering molecule to the antioxidant capabilities of the DBP-modified PU. Bromoalkylation chemistry was used to link DBP to the hard segment of the polyether PU, Tecothane, via our original linker (PU-DBP) or variants containing side chains with one (PU-C-DBP) or three (PU-3C-DBP) carbons. Two additional DBP variants were fabricated in which the DBP group was appended to the alkyl chain via an oxygen atom (PU-O-DBP) or an amide linkage in the middle of the tether (PU-NHCO-DBP). All DBP variant films and unmodified control films were subject to oxidative degradation via 15-day immersion in a solution of 20% H(2)O(2) + 0.1M CoCl(2). At the end of the oxidation protocol, films were analyzed for the presence of oxidation-related endpoints via scanning electron microscopy, contact angle measurements, and Fourier transformation infrared spectroscopy (FTIR). All DBP-containing variants resisted oxidation damage significantly better than the unmodified control PU. SEM analysis of oxidized PU-C-DBP and PU-O-DBP showed evidence of surface cracking, consistent with oxidative degradation of the PU surfaces. Similarly, there was a trend in increased ether crosslinking, a marker for oxidative degradation, in PU-C-DBP and PU-NHCO-DBP films. Consistent with these FTIR results, both PU-C-DBP and PU-NHCO-DBP had significant reductions in measured surface hydrophobicity as a result of oxidation. These data show for the first time that the choice of linker molecule significantly affects the efficiency of the linked phenolic antioxidant.

Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders

Biodegradable segmented polyurethanes (BSPUs) were prepared with poly(caprolactone) as a soft segment, 4,4'-methylene bis (cyclohexyl isocyanate) and either butanediol (BSPU1) or dithioerythritol (BSPU2) as a chain extender. BSPU samples were characterized in terms of their physicochemical properties and their hemocompatibility. Polymers were then degraded in acidic (HCl 2N), alkaline (NaOH 5M) and oxidative (H(2)O(2) 30wt.%) media and characterized by their mass loss, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Undegraded BSPU1 and BSPU2 exhibited different properties, such as the glass transition temperature T(g) of the soft segment (-25 vs. 4 degrees C), mechanical properties (600% vs. 900% strain to break) and blood coagulating properties (clotting time=11.46 vs. 8.13min). After acidic and alkaline degradation, the disappearance of the 1728cm(-1) band of polycaprolactone (PCL) on both types of BSPU was detected by FTIR. However, the oxidative environment did not affect the soft segment severely as the presence of PCL crystalline domains were observed both by DSC (melting temperature T(m)=52.8 degrees C) and XRD (2theta=21.3 degrees and 23.7 degrees ). By TGA three decomposition temperatures were recorded for both BSPU samples, but the higher decomposition temperature was enhanced after acidic and alkaline degradation. The formation of the porous structure on BSPU1 was observed by SEM, while a granular surface was observed on BSPU2 after alkaline degradation.

Biological stability of polyurethane modified with covalent attachment of di-tert-butyl-phenol

Polyurethane cardiovascular implants are subject to oxidation initiated surface degradation, which is mediated by monocyte-derived macrophages (MDM); this often leads to surface cracking and device failure. The present studies examined the hypothesis that covalently attaching antioxidant, di-tert-butylphenol (DBP), to the urethane nitrogens of a polyether polyurethane (PU) via bromo-alkylation reactions could prevent this problem. PU was configured with two dosages of DBP, 0.14 mM DBP/g PU of DBP (PU-DBP) and a more highly modified (HM) 0.40 mM DBP/g PU (PU-DBP-HM). THP-1 cells, a human MDM cell line, stimulated with phorbol ester and seeded on PU, PU-DBP, and PU-DBP-HM films were assessed for reactive oxygen species (ROS) production via a fluorescent based dihydrorhodamine-123 assay. Results from these studies showed a significant dose-dependent reduction of ROS levels for THP-1 cells seeded on PU-DBP versus unmodified PU. PU, PU-DBP, or PU-DBP-HM films were implanted into subdermal pouches of Sprague-Dawley rats. Films were explanted after 10 weeks and assessed for oxidative degradation via light and scanning electron microscopy (SEM) and Fourier transformation infrared spectroscopy (FTIR). Light microscopy showed extensive surface cracking, which was confirmed via SEM, on unmodified PU surfaces that was absent in both PU-DBP and PU-DBP-HM explanted films. FTIR analysis showed reduction in oxidation-induced ether crosslinking that was directly related to DBP dosages. It is concluded that modifying PU with the covalent attachment of an antioxidant confers biodegradation resistance in vivo in a dose dependent manner; this effect is likely due to quenching of the ROS generated by the adherent macrophages.