Aliphatic Polyester Nanoparticles for Drug Delivery Systems

Drug delivery systems using aliphatic polyester nanoparticles are usually prepared via an emulsion process. These nanoparticles can control drug release and improve pharmacokinetics. Aliphatic polyesters are linear polymers containing ester linkages, showing sensitivity to hydrolytic degradation. The byproducts then promote autocatalytic degradation. These byproducts could enter the Krebs cycle and be eliminated from the body, resulting in the high biocompatibility of these nanoparticles. The properties of these polyesters are linked to the drug release rate due to biodegradation, i.e., polymer crystallinity, glass transition temperature, polymer hydrophobicity, and molecular weight (MW), all of which relatively influence hydrolysis. Mathematical equations have been used to study the factors and mechanisms that affect drug dissolution compared to experimental release data. The equations used as models for predicting the kinetics of drug release include the zero-order, first-order, Higuchi, Hixson-Crowell, and Korsmeyer-Peppas equations. Aliphatic polyester-based controlled drug delivery has surrounded much of the current activity in the estimation parameters of nanoparticles and stimulated additional research. Polymeric nanoparticles have potential in a wide range of applications, such as in biotechnology, vaccine systems, and the pharmaceutical industry. The main goal of this chapter is to discuss aliphatic polyester nanoparticles as drug carrier systems.

High molecular weight of polylactic acid (PLA): A Review on the effect of initiator

This article reviews various initiator used to synthesize high molecular weight (MW >10,000 g/mol) of polylactic acid (PLA) through ring-opening polymerisation (ROP) of lactide. ROP has been chosen as the best method in producing PLA. On the other hand, stannous octoate (Sn(Oct)2) has been reported as the best catalyst used for ROP method. Many researchers have studied that polymerisation rate with the presence of only Sn(Oct)2 as catalyst is slow compared to polymerisation of lactide with the presence of initiator. An initiator is also favourable in producing high molecular weight of PLA as it can initiate the synthesis of PLA. Therefore, this review focus on ROP method catalysed by Sn(Oct)2 using different solvent as initiator. Among groups of initiators being reviewed are hydroxyl, carboxylic acid, aldehyde, aliphatic polyester and organophosphorus compound. Most of the studies applied in nitrogen atmosphere with a temperature range of 125 to 200 °C, while only one study in vacuum condition. Duration of the polymerisation time is between 1 to 24 hours. Based on the review, alcohol (hydroxyl group initiator) has been reported as the best initiator to produce high molecular weight of PLA. This functional group act as co-initiator molecule that reacts with Sn(Oct)2, forming the initiating stannous alkoxide linkage. The linkage is necessary to propagate monomer addition and hence increase the MW.

Leflunomide Loaded Chitosan Nanoparticles for the Preparation of Aliphatic Polyester Based Skin Patches

In the present study, the preparation of controlled-released leflunomide (LFD)-loaded skin patches was evaluated, utilizing the combination of chitosan (CS) nanoparticles (NPs) incorporated into suitable poly(l-lactic acid) (PLLA) or poly(lactic-co-glycolic acid) (PLGA) polyester matrices. Initially, LFD-loaded CS NPs of ~600 nm and a smooth surface were prepared, while strong inter-molecular interactions between the drug and the CS were unraveled. In the following step, the prepared LFD-loaded CS NPs were incorporated into PLLA or PLGA, and thin-film patches were prepared via spin-coating. Analysis of the prepared films showed that the incorporation of the drug-loaded CS NPs resulted in a significant increase in the drug’s release rate and extent as compared to neat LFD-loaded polyester patches (i.e., prepared without the use of CS NPs). In-depth analysis of the prepared formulations showed that the amorphization of the drug within the matrix and the increased wetting properties of the prepared CS NPs were responsible for the improved thin-film patch characteristics.

Effect of Storage Conditions on the Thermal Stability and Crystallization Behaviors of Poly(L-Lactide)/Poly(D-Lactide)

Polylactide (PLA) is a biodegradable thermoplastic aliphatic polyester. The thermal stability and crystallization behavior of PLA are extremely sensitive to storage, processing, and usage conditions. This work systematically studied the thermal stability and crystallization behavior of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and a PLLA/PDLA (LD) blend, which were stored under two sets of laboratory storage conditions: (1) stored in a vacuum-free desiccator and (2) stored in vacuum-sealed bags. Both were stored at room temperature for 3 years. Gel permeation chromatography results revealed that the PLLA, PDLA, and LD samples hydrolyzed slowly when stored in vacuum-sealed bags and degraded significantly when stored in a vacuum-free desiccator; this process significantly reduced the thermal stability of the samples stored in the vacuum-free desiccator. Owing to hydrolysis, the levorotation and dextrorotation (L- and D-) molecular chains were shortened; consequently, more nuclei were formed, and this caused the melting points of the PLLA, PDLA, and LD samples to decrease and the melting enthalpy of the crystals in these samples to increase. Wide-angle X-ray diffraction analysis revealed that when the L- and D- molecular chains were packed side by side to form stereocomplex crystals and the randomly arranged L- and D- molecular chains were easy hydrolyzed and degraded, this interfered with the formation of homocrystals in LD. When PLLA, PDLA, and LD samples are stored in a vacuum-free desiccator, they will be significantly hydrolyzed, resulting in the formation of only stereocomplex crystals, and no homocrystals are observed.