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Engineered Nanoparticles for Drug Delivery in Cancer Therapy *
Published in Valerio Voliani, Nanomaterials and Neoplasms, 2021
Tianmeng Sun, Yu Shrike Zhang, Pang Bo, Dong Choon Hyun, Miaoxin Yang, Younan Xia
Bulk erosion occurs if water molecules can imbibe into the polymer more rapidly than erosion takes place [71]. In this case, chain scission occurs throughout the matrix, leading to a very complex degradation/erosion process for the polymer. Polyesters, the most commonly used biodegradable polymers for controlled release, work by bulk erosion. The release of drug from a bulk-eroding polymer typically undergoes three stages [86]. In the first stage, drug is released from the surface or from pores that are connected to the surface. During the second stage, the remaining drug is released at a slow to intermediate rate when the polymer gradually degrades. In the last stage, the trapped drug is rapidly released upon complete destruction of the polymer matrix.
Synergistic Combinations of Hyperthermia and Inhibitors of Nucleic Acids and Protein Synthesis
Published in Leopold J. Anghileri, Jacques Robert, Hyperthermia In Cancer Treatment, 2019
It is important to note the difference between the bifunctional agents (resulting largely in cytotoxicity) and monofunctional alkylating agents, the latter having greater capacity for both mutagenesis and carcinogenesis. Monofunctional agents which produce depurination and chain scission may cause permanent modifications in DNA structure that are compatible with continued life of the cell and transmission to subsequent generations; such modifications may result in mutagenesis or carcinogenesis rather than cytotoxicity. In contrast, the bifunctional alkylating agents cross-link DNA strands which cannot be easily removed or repaired, resulting eventually in cell death.55
Friction, Lubrication, Wear and Corrosion
Published in Manoj Ramachandran, Tom Nunn, Basic Orthopaedic Sciences, 2018
Gurdeep Biring, Iain McNamara, Marcus Bankes, Jay Meswania, Gordon Blunn
Sterilization methods can be divided into non-energetic (no radiation) and energetic (using radiation) methods. Non-energetic methods use ethylene oxide or gas plasma to sterilize the polyethylene (PE). Conversely, energetic techniques utilize gamma irradiation at either low or high doses. Non-energetic methods have no effect upon the cross-linking of PE. Conversely, irradiation of UHMWPE causes PE chain scission and then cross-linking of the chains. Cross-linking the UHMWPE has advantageous effects in improving the adhesive and abrasive wear resistance. The disadvantages of cross-linking are decreased tensile strength, fatigue strength, fracture toughness and increased brittleness. These factors might be particularly relevant if the polyethylene is edge loaded, e.g. in an open acetabular cup.
Fluid flow effects on the degradation kinetics of bioresorbable polymers
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Zhitao Liu, Hongbo Zhang, Huanxin Lai
Hydrolysis is known to be the dominant mechanism in hydrolytic degradation. The diffusion and accumulation of water molecules causes hydrolysis of the ester bonds in the polymer matrix. As a result, these chains are split into water soluble shorter chains (oligomers and monomers) characterized by carboxylic ends. Because of the chain scission, the molecular weight of the polymer decreases gradually. The degradation products then diffuse into the surrounding environment, which results in the mass loss of polymers. The diffusion is generally slower in a large-size device, due to the greater diffusion distance (Siepmann et al. 2005; Xu et al. 2017). The slow diffusion may result in accumulation of acidic products inside the polymer matrix, and they accelerate the degradation process. The phenomenon is known as the autocatalysis (Gentile et al. 2014; Laycock et al. 2017).
Physico-chemical and antimicrobial properties and the shelf life of experimental endodontic sealers containing metal methacrylates
Published in Biofouling, 2020
Victoria Burmann da Silva Guimarães, Andressa da Silva Barboza, Carlos Enrique Cuevas-Suárez, Tiago Collares, Thaís Larré Oliveira, Anderson Schwingel Ribeiro, Meibel Teixeira Lisboa, Fernanda Geraldo Pappen, Rafael Guerra Lund
The alkalinization capacity (increase in pH) may be considered an important chemical property because it may induce repair by stimulating the mineralization process (Holland et al. 2002). Moreover, the release of ions from monomers, such as Ca2+ and Sn2+, generally results from the hydrolytic degradation that involves a chain scission process during which polymer chains are cleaved to form oligomers and finally to form monomers, which have different functional groups from polymers. This process presents an interrelationship with erosion that designates the loss of material owing to monomers and oligomers leaving the matrix. Basically, water enters the polymer bulk, which might be accompanied by swelling. The intrusion of water triggers chemical polymer degradation, and leads to the creation of oligomers and monomers. Progressive degradation changes the microstructure of the bulk through the formation of pores, through which degradable components are released (Gopferich 1996). This study showed that AH Plus and the experimental sealers did not promote a significant pH increase, in agreement with the findings of Vertuan et al. (2018), in which the pH of the sealers remained below 6. The present results also differed from those of Almeida et al. (2018), in which the release of cationic ions (silver particles) alkalinized the pH of the eluate.
Lipid-based solubilization technology via hot melt extrusion: promises and challenges
Published in Expert Opinion on Drug Delivery, 2022
Ožbej Zupančič, Martin Spoerk, Amrit Paudel
For the milled or pelletized extrudates, powder and bulk characterization methods, such as flowability, angle of repose, bulk/tapped density, compressibility, etc. are employed. Also, self-emulsification ability and/or reconstitution ability, wetting, dispersion, dissolution profile, solubilization capacity of the formulation and its in vitro performance under a biorelevant environment (e.g. under in vitro lipolysis assay) need to be evaluated to ascertain the true success of HME-SEDDS formulation. The compositional distribution, physical structure, miscibility and molecular interactions among PWSD, lipid, surfactants and polymers of HME-SEDDS can be thoroughly characterized using calorimetry, hyperspectral (infrared, Raman, NIR) imaging, solid-state NMR spectroscopy, X-ray photoelectron spectroscopy, etc. While most of polymer excipients are expected to remain in amorphous states, the solid state of lipids and surfactants in HME-SEDDS can be highly complex. Therefore, crystallite size and distribution, polymorphic and packing structures can be analyzed using X-ray scattering, polarized optical microscopy, solid-state NMR spectroscopy, scanning and transmission electron microscopy, etc. [123]. Various forms of molecular mobility of drugs within the solidified polymer-lipid matrix can be important in terms of their dispersity as well as physical and chemical stability. These properties can be interrogated using NMR relaxometry, differential scanning calorimetry (DSC), dielectric spectroscopy, etc. Microstructure as well as pore volume distribution can be analyzed using gas physisorption, mercury intrusion and electron microscopy [124]. In addition to physical states, chemical characterization of HME-SEDDS is important because HME is reputed to risk not only PWSD degradation but also for the potential chemical alteration of lipids, surfactants and polymers. Besides traditional drug assay and impurity profiling using chromatographic analysis, a thorough chemical characterization of lipid composition (e.g. possible thermal hydrolysis of higher glycerides) and polymer chain structure (chain scission or cross-linking) in HME-SEDDS using NMR spectroscopy, mass spectrometry, size exclusion chromatography can help generating a robust drug product [125]. In addition, oxidation states of excipients as well as possible generation of any oxidizing species such as free radicals via HME can be elucidated using electron spin spectroscopy.