Antibacterial property mechanism

Roily and Liebermeister [95] showed that bacteria introduced into the small bowel disappeared rapidly, without bile, pancreatic, and intestinal juices having antibacterial properties alone or mixed. Later studies, of which those by Dack and Petran [96], Dixon [99] and Dixon and Paulley [100] are of particular importance, provided considerable further evidence that intestinal peristalsis is the main line of defense against bacterial colonization of the small bowel. This was also concluded by Donaldson [101-103] when he reviewed host defense mechanisms in 1964. At that time, however, the insights into small bowel motility were confined to the reflex-mediated peristaltic behavior. 

Methenamine (Hiprex, Mandelamine, Urex) exerts antibacterial properties in a unique fashion. In an acidic environment, this drug decomposes into formaldehyde and ammonia. Formaldehyde is bactericidal to almost all bacteria, and bacteria do not develop resistance to this toxin. This mechanism enables methenamine to be especially useful in treating urinary tract infections, because the presence of this drug in acidic urine facilitates the release of formaldehyde at the site of infection (i.e., within the urinary tract). Use of methenamine is safe, although high doses are associated with gastrointestinal upset and problems with urination (bloody urine, pain while urinating). 

Hence, PP composites containing zinc oxide along with silver can further enhance the antimicrobial properties of this polymer. Antibacterial elastomer composites of silver zeolite/silicone could be a useful material to satisfy a range of requirements including good mechanical properties, due to the incorporation of zeolite, and good antibacterial properties. 

The bacteriostatic and antibacterial properties are in addition to pH-conditions and the nanostructural entrapping mechanism also related to the surface structure developed of the hydrated biomaterial. The nano-particle/crystal size of hydrates are in the interval 15-40 nm with a nanoporosity size of 1-3 nm. The number of pores per square micrometer is at least 500, preferably > 1000 [9]. The number of nanopores will thus be extremely high, which will affect the possibility of catching and fastening bacteria to the hydrate surface - an analogue to how certain peptides may function as antibacterial material due to a structure with nano-size holes within the structure. This may also provide a long-term antibacterial activity after the initial hydration. 

Chapter 4 then expands the diseussion on the use of nanoparticles in membrane modification processes. Materials in the form of nanoparticles have a large surface area to volume ratio, which infers many interesting properties on nanoparticulate systems due to the involved interfaeial properties. As a consequence, nanoparticles are currently receiving a lot of interest in many industries, such as membrane technology where the control of interfacial interactions is important. Nanoparticles affect the permeability, selectivity, hydrophilicity, thermal and electrical conductivities, mechanical strength, thermal stability, and the antiviral and antibacterial properties of the polymeric membranes. Chapter 4 discusses important examples of... 

Composites prepared using different types of nanoparticles can show superior properties compared to pure PU and have a wide range of applications in structural and biomedical fields. The surface morphology of nanocomposites is affected by the nature and amount of the nanoparticles embedded in polymer matrix. Different shapes and sizes of the nanoparticles play a significant role in enhancement of the mechanical, rheological, thermal, and fire retardant properties of the PU nanocomposites. Considerable improvements in antibacterial properties have been reported using nanocomposites compared to pure PU. Incorporation of the different kinds of nanoparticles in PU matrix alters the biocompatible nature of the composites, suggesting that PU composites may have use in biomaterial applications. 

Emerging work on new polyurethane scaffolds aims to enhance osteoconductivity and mechanical properties using novel methods and additives. Ionic liquids have been proposed to add antibacterial properties to polyurethanes while improving mechanical properties and increasing hydrophilicity. l-bntyl-3-methylimidazolium hexafluorophosphate ionic Uqnid blended with a thermoplastic polyurethane improved the electrospun fiber morphology and non woven mats exhibited 99.9% antibacterial efficiency against Escherichia coli and Staphylococcus aureus [78]. 

Many groups have blended PU with other polymers that possess inherent antibacterial properties to synergize the beneficial mechaifical properties of PU with the antibacterial properties of other polymers. In particular, zein and chitosan have been used most frequently (Kara et al., 2014 Umiithan et al., 2014). Both zein, a plant protein, and chitosan, derived from chitin, are natural polymers. Both are also cationic, which is thought to dismpt bacterial cell wall interactions (Chen et al., 2000 Ishitsuka et al., 2006 Kuroda and DeGrado, 2005 Tew et al., 2002) as well as having poor mechanical properties, making both polymers good candidates for copolymer blends with PUs. 

Bone cement impregnated with chitosan NPs Antibacterial and mechanical properties [385]... 

Shi Z, Neoh KG, Kang ET, Wang W. Antibacterial and mechanical properties of bone cement impregnated with chitosan nanoparticles. Biomateiials. 2006 27(ll) 2440-9. 

Wu YB, Yu SH, Mi FL, Wu CW, Shyu SS, Peng CK, Chao AC (2004) Preparation and characterization on mechanical and antibacterial properties of chitsoan/cellulose blends. Carbohydr Polym 57 435 40... 

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