China
Africa
Explore chapters and articles related to this topic
Nanocarriers as an Emerging Platform for Cancer Therapy
Published in Lajos P. Balogh, Nano-Enabled Medical Applications, 2020
Dan Peer, Jeffrey M. Karp, Seungpyo Hong, Omid C. Farokhzad, Rimona Margalit, Robert Langer
Polymers are the most commonly explored materials for constructing nanoparticle-based drug carriers. One of the earliest reports of their use for cancer therapy dates back to 1979 [62] when adsorption of anticancer drugs to polyalkylcyanoacrylate nanoparticles was described. Couvreur et al. revealed the release mechanism of the drugs from the polymer in calf serum, followed by tissue distribution and efficacy studies in a tumour model [63]. This work laid the foundation for the development of doxorubicin-loaded nanoparticles that were tested in clinical trials in the mid-1980s [64]. Polymeric nanoparticles can be made from synthetic polymers, including poly(lactic acid) (PLA) and poly(lactic co-glycolic acid) [65], or from natural polymers such as chitosan [66] and collagen [67] and may be used to encapsulate drugs without chemical modification. The drugs can be released in a controlled manner through surface or bulk erosion, diffusion through the polymer matrix, swelling followed by diffusion, or in response to the local environment. Several multifunctional polymeric nanoparticles are now in various stages of pre-clinical and clinical development [4, 56, 68, 69]. Concerns arising from the use of polymer-based nanocarriers include the inherent structural heterogeneity of polymers, reflected, for example, in a high polydispersity index (the ratio of the weight-and-number-average molecular weight (Mw/Mn)). There are, however, a few examples of polymeric nanoparticles that show near-homogenous size distribution [70].
Aptamers and Cancer Nanotechnology
Published in Mansoor M. Amiji, Nanotechnology for Cancer Therapy, 2006
Omid C. Farokhzad, Sangyong Jon, Robert Langer
Virtually every branch of medicine has been dramatically impacted by controlled drug delivery strategies during the past four decades,3,69–72 including cardiology,73 ophthalmology,74 endocrinology,75 oncology,76 immunology,77 and orthopedics.78 Drugs can be released in a controlled manner from within a material through surface or bulk erosion of the material, diffusion of the drug from the interior of the material, or swelling followed by diffusion or triggered by the environment or other external events,2 such as changes in pH,79 light,80 temperature,81 or the presence of an analyte, such as glucose.82 In general, controlled-release polymer systems deliver drugs in the optimum dosage for long periods, thus increasing the efficacy of the drug, maximizing patient compliance and enhancing the ability to use highly toxic, poorly soluble, or relatively unstable drugs.
Release mechanisms and applications of drug delivery systems for extended-release
Published in Expert Opinion on Drug Delivery, 2020
Shuying Wang, Renhe Liu, Yao Fu, W. John Kao
The situation for polymeric systems is more complex, given that both surface and bulk erosion could occur simultaneously in an erosion-controlled system. When the rate of water diffusion into the system is lower than that of polymer degradation, surface erosion becomes the primary driving force. Alternatively, if the degradation rate of the polymer exceeds the rate of water uptake, bulk erosion dominates. Burkersroda et al [39]. have explored a model to define the erosion parameter
Insulin-like growth factor-1 (IGF-1) poly (lactic-co-glycolic acid) (PLGA) microparticles – development, characterisation, and in vitro assessment of bioactivity for cardiac applications
Published in Journal of Microencapsulation, 2019
Aamir Hameed, Laura B. Gallagher, Eimear Dolan, Janice O’Sullivan, Eduardo Ruiz-Hernandez, Garry P. Duffy, Helena Kelly
PLGA undergoes non-enzymatic hydrolysis of the ester linkages in the presence of water and its metabolites, lactic acid and glycolic acid are biodegradable and are cleared by the Krebs cycle in vivo, causing minimal systemic toxicity. The degradation of PLGA microparticles results from the collective process of bulk diffusion, surface diffusion, bulk erosion, and surface erosion (Makadia and Siegel 2011) during which encapsulated drug or protein is released. The release of the encapsulated drug or protein may be affected by the factors like PLGA particle porosity and drug hydrophilicity (Shive and Anderson 1997).
Preparation and characterization of letrozole-loaded poly(d,l-lactide) nanoparticles for drug delivery in breast cancer therapy
Published in Pharmaceutical Development and Technology, 2019
Bayan Alemrayat, Abdelbary Elhissi, Husam M. Younes
Data obtained from the in vitro release study has been tested against four different kinetic modeling: zero-order, first order, Higuchi model, Hixson–Crowell model, and Korsemeyer–Peppas semi-empirical model. Release rate constants (k) and correlation coefficients (R2) of the obtained data and the corresponding kinetic models were computed for the three formulations and presented in Table 2. It can be seen that the release profiles of the three formulations were best fitted with Higuchi model where highest correlation coefficient (R2) values were obtained (Table 2). This entails that the drug is primarily released from the matrix through diffusion that is square root time-dependent; thus, as time elapses, more drug is released (Peppas 2011; Petropoulos et al. 2012). Based on the release exponent (n) values of Korsemeyer–Peppas model, it appears that the 10% LTZ formulation follows Fickian diffusion (n < 0.43), whereas 20 and 30% LTZ formulations follow non-Fickian diffusion (0.43 < n < 0.85) (Siepmann and Siepmann 2008). Fickian diffusion occurs when the drug predominantly diffuses through the water-formed pores within the polymeric matrix. On the other hand, deviation from Fickian diffusion, in case of non-Fickian diffusion, is caused by additional release mechanisms such as surface and bulk erosion which are characteristic for PDLLA and manifested as initial burst release of the drug from the 20 and 30% LTZ formulations (Siepmann and Siepmann 2008; La Saponara 2011). Bulk erosion is known to be more prominent with time as PDLLA continues to be degraded into lactic acid, increasing the acidity of the environment, and hence, resulting in further degradation of the polymer chains in an event called autocatalytic degradation (Tsuji and Tsuruno 2010). As seen in Figure 4, the bulk degradation occurred gradually since there was no sudden increase in LTZ concentration during the duration of the study, which indicates an appropriate drug release pattern.