China
Africa
Explore chapters and articles related to this topic
Design, Development, Manufacturing, and Testing of Transdermal Drug Delivery Systems
Published in Tapash K. Ghosh, Dermal Drug Delivery, 2020
Timothy A. Peterson, Steven M. Wick, Chan Ko
Silicone PSAs are made of two major components: a resin and a polymer dissolved in solvent. The resin component is a three-dimensional structure having Si-O-Si siloxane bonds. Typically, Si resins and polymers have residual silanol (SiOH) functionality. A condensation reaction takes place between silanols on the resin and polymer to form the silicone PSA (Sobieski 1986, Ho and Dodou 2007). The molecular structure of silicone PSAs imparts unique properties such as low glass transition temperature (Tg) (−120°C) and a high degree of flexibility within the polysiloxane chains. Silicone PSAs are also known for their physiological inertness. Silicone PSAs may be modified by endcapping the reactive silanol groups to make them more compatible with amine-functional drugs (Pfister et al. 1992, Lin et al. 2007). Recently, “soft” silicone PSAs have been developed and incorporated in medical tapes (Grove et al. 2013) which result in very minimal skin trauma following removal (Figure 4.5) and may provide a useful adhesive option for TDD patches as well.
Accuracy Requirements for 3D Dosimetry in Contemporary Radiation Therapy
Published in Ben Mijnheer, Clinical 3D Dosimetry in Modern Radiation Therapy, 2017
Jacob Van Dyk, Jerry J. Battista, Glenn S. Bauman
A more recent analysis (Nelms et al., 2015) used DICOM RT structure sets imported into two different TPSs: (1) to test for the accuracy of various DVH parameters such as total volume, Dmax, Dmin, and various doses to percent volumes, and (2) to determine volume errors along the DVH curves. Significant deviations were found for the different treatment planning algorithm implementations. The errors were related to inadequate 3D dose grid sampling and inconsistencies in the implementation of “endcapping” of 3D structures. As noted previously, there is a tacit assumption that the regions are accurately contoured and this is normally only done “slice by slice” rather than in a 3D view.
Silicones in Cosmetics
Published in E. Desmond Goddard, James V. Gruber, Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
E. Desmond Goddard, James V. Gruber
The basis of current silicone chemistry nomenclature was established by Alfred Stock in 1916 (16). He referred to silicone hydride compounds as silanes; e.g., was a monosilane, a disilane, and so forth. Derivatives were named by adding the appropriate prefixes such as dichlorodisilane for When oxygen joined two silicon atoms, the compound was referred to as a siloxane, and polymeric versions became known as polydimethylsiloxanes. This system was eventually adopted by the International Union of Pure and Applied Chemistry (IUPAC). Although these descriptors are accurate and informative, they are somewhat cumbersome. Silicone chemists thus frequently use an abbreviated notation when referring to the basic groups that comprise typical silicone polymers. According to this system, there are four primary building blocks in silicone chemistry, as illustrated in Table 6. The chainstopper, or end-capping unit, is “monovalent,’ or reactive through only one bond to the silicone atom, and has been given the shorthand notation of “ M “ ‘This group is also commonly known as a “trimethylsilyl” unit in cosmetic applications, such as in trimethylsilylamodimethicone. The onchain repeat unit is referred to as “ D,” or difunctional, as there are two bonds through which the polymer chain can grow and two unreactive methyl units attached to the silicone atom. Thus, the structure of a linear dimethicone polymer would be represented as . Should one or both of the methyl groups in a D unit be replaced with an organic moiety
An overview of PLGA in-situ forming implants based on solvent exchange technique: effect of formulation components and characterization
Published in Pharmaceutical Development and Technology, 2021
Tarek Metwally Ibrahim, Nagia Ahmed El-Megrab, Hanan Mohammed El-Nahas
Furthermore, the end-capping can reduce the PLGA hydrolysis rates since it can increase the lipophilicity of the polymer and decrease the water uptake. The acid-capped PLGA can also increase the autocatalysis of the ester bond degradation. Thus, esterified end groups could minimize the rates of PLGA hydrolysis (Kamaly et al. 2016). On the other hand, reduced burst release may be obtained with the acid-capped polymers compared to ester-capped polymers. This can be seen in the case of active drugs that possess functional groups interacting with polymer acidic ends. For instance, Chhabra et al. (2007) reported that a great reduction in burst release was obtained by using acid-capped polymers. This might be attributed to the chemical linkages formed between the amino acid residues of studied lysozyme with the carboxylic acid end groups of the polymer.
Advances with weak affinity chromatography for fragment screening
Published in Expert Opinion on Drug Discovery, 2019
Fotios Tsopelas, Anna Tsantili-Kakoulidou
For in situ immobilization standard columns (dimensions 30 × 2.1 mm containing porous silanized diol-based spherical silica particles are commonly used. First, oxidation of diol silica to aldehyde silica by periodic acid is performed, followed by covalent coupling to primary amino groups of the protein by reductive amination chemistry to create a Schiff base. Stable covalent bonds (amino links) are formed between the high-performance silica support and the protein, mediated by the lysine side chains on the protein surface. Deactivation of any remaining aldehyde functional groups is necessary since they may lead to non-specific interactions with the analytes. This is usually carried out by end-capping with amine reagents containing hydroxyl groups. The most popular reagent, in this case, is ethanolamine. Ethanolamine is used also to prepare a reference column which does not contain immobilized protein. Such reference column is produced simply by coupling the reactive aldehyde silica groups to ethanolamine. Figure 2 illustrates the reaction scheme followed for protein immobilization (A) and for preparation of ethanolamine silica (B). The whole procedure of WAC column preparation is described in detail in ref [54].
Effects of N-terminal and C-terminal modification on cytotoxicity and cellular uptake of amphiphilic cell penetrating peptides
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Mehdi Soleymani-Goloujeh, Ali Nokhodchi, Mehri Niazi, Saeedeh Najafi-Hajivar, Javid Shahbazi-Mojarrad, Nosratollah Zarghami, Parvin Zakeri-Milani, Ali Mohammadi, Mohammad Karimi, Hadi Valizadeh
In conclusion, the coupling of anticancer drug to CPPs provides a powerful tool in drug delivery with increased solubility, intracellular uptake and improved bio-distribution as well as pharmacokinetic profiles. We have obtained satisfactory results demonstrating that, the use of CPPs with a chemotherapeutic agent could lead to improved therapy. Some modified peptides interacted with MTX which included BA-QGR-[WK]3-pGlu and BA-WRWQGRWRW-pGlu, that could successfully increase toxic effects of the drug in comparison with their unmodified counterparts. The cytotoxicity of modified peptides which were physically linked to MTX, showed higher cytotoxicity than both physically linked unmodified peptides and chemically conjugated peptides with MTX, even though they had lower loading. Also, we have obtained comprehensive results proving that peptide end-capping will result in reduced internalization as well as direct site localization inside a cell. In contrary, increased drug toxic effects was seen in the case of drug delivery using these sequences. Uptake studies also approved the negative effects of our designed peptides in cell internalization, by increasing concentration or E8 addition. Finally, a number of potential shortfalls need to be considered. Firstly, the present study has only investigated the effects of unmodified peptides as well as N- and C-terminal modifications without peptide purification which can be responsible for some unpredictable errors and secondly, this study has only investigated all these procedures in vitro. Consequently, to obtain more accurate and reliable results, we recommend doing this research in vivo. Also, peptide stability assessment procedures should be considered before modification of CPPs.