Babak Kaffashi

Polylactic Acid in Medicine

Polylactic acid (PLA) is a biodegradable polymer with exceptional properties that has been studied extensively for the past 25 years. The possibility of using devices in human body with minimum inflammation and infection to allow natural healing has obliged researchers to search for biocompatible and biodegradable alternatives. Polylactic acid is one of the most promising biopolymers used in world today. Due to its organic source, it has attracted many attentions. This review presents information about the properties, monomer types, kinetics and different synthesis methods that are currently employed for production of polylactic acid as well as its biomedical and clinical applications in scaffolds, drug delivery systems, bone fixation devices such as screw and plates, surgical suture and meshes. GRAPHICAL ABSTRACT

Investigating composite systems based on poly l-lactide and poly l-lactide/triclosan nanoparticles for tissue engineering and medical applications

In this study, the encapsulated triclosan with a low molecular weight PLLA (LATC30) is dispersed into a PLLA having higher molecular weight via melt blending to increase the overall properties and particularly antibacterial activity of the system. The proposed method results in a completely homogenous composite as 5% LATC30 improved mechanical properties. For instance, the elongation at break was increased ca. 3%. The mechanical properties of the fabricated composites were also affected by the plasticizing role of LATC30. The kinetics of hydrolytic degradation in an accelerated condition was obtained using a novel method by the Beer-Lambert equation. It was found that the incorporation of LATC30 into the composite increases the rate of hydrolytic degradation. The calorimetry showed a reduction in crystallinity upon addition of LATC30. Moreover, the degradation of the composites was studied and fully described the kinetic analysis by the Flynn-Wall-Ozawa (FWO) method. From which, it was found that the activation energy of the system was decreased. As the LATC30 content of the composite was increased, the hydrophilicity of the composite was increased. The fabricated scaffolds with 5% LATC30 demonstrated a good osteoblast cell attachment and mineralization on the composite scaffolds. This composite is a suitable antibacterial candidate for the bone tissue engineering and medical applications since the real dosage of triclosan stays at ca. 1.5%.

Preparation and Characterization of Poly L-Lactide/Triclosan Nanoparticles for Specific Antibacterial and Medical Applications

This work aims at preparation of poly-L-lactide (PLLA)/triclosan nanoparticles as antibacterial products used in some specific medical applications. PLLA was synthesized by the reaction extrusion via the ring opening polymerization of L-lactide using a continuous single-stage process, which is a fast and easy method. The PLLA triclosan nanoparticles were prepared by the emulsification–diffusion process with few modifications. Chloroform was used for the surface reaction of triclosan without any chemical shifts. The resulting nanoparticles with various triclosan quantities were fully characterized. The release as well as its kinetics was studied using the UV-visible spectroscopy. All the results confirmed the high stability and process efficiency of molecular dispersion and attachment of triclosan to PLLA. The sample containing 30% triclosan showed the best form among the others with the highest encapsulation efficiency. The synthesized nanoparticles with the controlled antibacterial activity could be considered as an appropriate alternative for application as antibacterial agent in the implantable surgical products as well as the drug delivery and wound-dressing applications. GRAPHICAL ABSTRACT

Improving rheological properties of covalently MWCNT/epoxy nanocomposites via surface re-modification

This article describes the application of the chemical surface re-modification of carboxylated multi-walled carbon nanotubes (MWCNTs) through in-situ esterification of oligomeric unsaturated aliphatic hydroxyl terminated polyesters. The Fourier transform infrared spectroscopy and the thermogravimetric analysis proved covalent treatment of MWCNTs. Consequently, the acid–base titration method was employed to determine the population of the re-modified sites within the polyester chains. The dispersion state of the re-modified MWCNTs was investigated by the transmission electron microscopy relevant to the cured nanocomposite sample along with the Ultraviolet–Visible spectroscopy while using various solvents. The degree of dispersion was correlated to the Hansen solubility parameters. In summary, our study shows an appropriate dispersion of the re-modified MWCNTs into the solvents with a high dispersive fashion. In addition, the rheological properties of the re-modified MWCNTs/epoxy resin having various nanoinclusions were considerably studied and discussed. Also, an improved rheological response was observed in the case of the re-modified MWCNT nanocomposite samples.

Synthesis, Characterization, and Viscoelastic Behavior of Thermothickening Poly (N-Isopropylacrylamide-Methacrylicacide-Vinylpyrrolidone) Nanogels as an Injectable Biocompatible Drug Carrier

In the present work, the preparation of dual thermo-/pH-responsive nanogels composed poly (NIPAAm-MAA-VP) was investigated as an injectable carrier in which doxorubicin hydrochloride (DOX) was opted as an anticancer agent. The SEM photomicrographs showed that copolymer was almost spherical in shape with the mean diameter below 30 nm. Using dynamic oscillatory the gel-like behavior was observed at 37°C for the crosslinked polymer. Biocompatibility of the synthesized nanoparticles and superior antitumor activity of DOX-loaded nanoparticles were proved by in vitro cytotoxicity assay. The system is expected to be valuable for the delivery of chemotherapeutic agents in the treatment of solid tumors. GRAPHICAL ABSTRACT

Effect of hydroxyapatite nano-particles on morphology, rheology and thermal behavior of poly(caprolactone)/chitosan blends.

The effect of hydroxyapatite nano-particles (nHA) on morphology, and rheological and thermal properties of PCL/chitosan blends was investigated. The tendency of nHA to reside in the submicron-dispersed chitosan phase is determined using SEM and AFM images. The presence of electrostatic interaction between amide sites of chitosan and ionic groups on the nHA surface was proved by FTIR. It is shown that the chitosan phase is thermodynamically more favorable for the nano-particles to reside than the PCL phase. Lack of implementation of Cox-Merz theory for this system shows that the polymer-nano-particle network is destructed by the flow. Results from dynamic rheological measurements and Zener fractional model show that the presence of nHA increases the shear moduli and relaxation time of the PCL/chitosan blends. DSC measurements showed that nHA nano-particles are responsible for the increase in melting and crystallization characteristics of the PCL/chitosan blends. Based on thermogravimetric analysis, the PCL/chitosan/nHA nano-composites exhibited a greater thermal stability compared to the nHA-free blends.

Preparation and Rheological Properties of Functionalized Multiwalled Carbon Nanotube/Waterborne Polyurethane Nanocomposites

Waterborne polyurethane (WBPU) was synthesized by a polyaddition reaction with toluene diisocyanate (TDI), polytetramethylene ether glycol (PTMEG), dimethylol propionic acid (DMPA), and triethylamine (TEA). Aqueous polyurethane dispersions with three different weight fractions, 30, 40, and 50 wt%, were prepared. All the dispersions made with these concentrations showed Newtonian viscosity behavior. Multiwalled carbon nanotubes (CNTs) were functionalized using a mixture of sulfuric and nitric acid at a ratio of 3:1 and added to these dispersions in two different loads of 0.1 and 0.5 wt%. Ultraviolet visible spectrometry (UV/Vis) spectroscopy proved the formation of stable suspensions following ultrasonic agitation. The rheology of these suspensions was characterized using dynamic and steady-state measurements. The higher amount of CNT in the suspension imparted non-Newtonian and complex viscoelastic behavior. This was attributed to a physical network formed due to the presence of the functionalized CNTs. The Cox-Merz rule was not observed for these suspensions.

Evaluation of melt rheology of lactose-filled polyethylene glycol composites by means of capillary rheometery

In this study melt rheological behavior of lactose-filled polyethylene glycol (PEG) composites as a low melting polymeric carrier for controlled release drugs was investigated using a capillary rheometer. The effect of lactose concentration and process variables such as temperature and ram speed on the flow behavior of PEG has been studied. The composites were found to be shear thinning in behavior when extruded, and the results were well described by power-law model in each case. Stronger shear thinning behavior was observed by raising the filler concentration and decreasing the temperature, while the flow index has been decreased. In all compositions a significant increase in shear viscosity was found by an increase in the filler content. In fact, shear viscosity increased linearly by weight fraction of filler, but there was a dramatic increase after the filler content raised above 20 wt% of lactose which might be the result of the strong interaction among filler particles. Furthermore, decreasing the process temperature resulted in an increase in shear viscosity, and the temperature dependence of shear viscosity decreased as the shear rate increased. The extensional viscosity of composites was calculated in each case. The results showed that the ratio of the extensional viscosity to shear viscosity was in the range of 500–1200.

Rheological evaluation of wet masses for the preparation of pharmaceutical pellets by capillary and rotational rheometers

The rheological properties of wet powder masses used in the preparation of pharmaceutical pellets by extrusion/spheronization were evaluated utilizing capillary and rotational rheometers. A ram extruder was used as a capillary rheometer to construct flow and viscosity curves for each wet mass under different extrusion rates and die geometry. As a result, shear thinning behavior was observed for all wet masses. Among the considered rheological models Power Law and Herschel-Bulkley models fitted well with the experimental results. For the majority of the wet masses, water separation and migration occurred during extrusion which led to uneven water content in the extrudate. The effect of extrusion condition including extrusion speed, die geometry and water content on the occurrence of water separation was investigated and the surface quality of the extrudates was compared. In addition, dynamic rheometry tests were done by a parallel plate rheometer to investigate the viscoelastic properties of the wet masses. The frequency sweep tests showed that as water content of the wet masses decreases storage (G′) and loss modulus (G″) increase. The storage modulus values were much higher than those of the loss modulus showing dominated elastic rather than viscous behavior for the wet masses at low deformation rates.

Synthesis and characterization of a novel solvent-free dextran-HEMA-PNIPAM thermosensitive nanogel

ABSTRACT In recent years, the polymeric nanogels, as a group of nanostructured materials, have attracted the attention of researchers of various fields such as polymers, materials science, pharmacy, and drug delivery. Gels are mostly known for their water-swellable features and are candidates for a variety of applications. In this work, a facile solvent free synthesis procedure for production of dextran-hydroxyethyl methacrylate (Dex-HEMA) and poly N-isopropyl acryl amide (PNIPAM) copolymeric nanogels is narrated. The polymerization process was conducted by the UV irradiation and the gel size was controlled by the liposomal structures. The H-NMR and FTIR analysis were all proved a successful polymerization procedure. By implication of the dynamic light scattering (DLS), the mean diameter of particles was determined to be in the range of ca. 350 nm. The molecular weight determination by the GPC results in the Mw ranging from 16100 to 20900 gr mol−1 with a polydispersity index of ca. 1.5. The turbidity assay indicated the thermosensitive nature of the gels and a LCST of ca. 32.5 was characterized. In this work, the equilibrium swelling measurements and the water content studies at two temperatures of 25 and 37°C were also performed.