Pentablock Copolymers Research Articles

Synthesis and characterization of novel biodegradable pentablock copolymers from L‐lactide, p‐dioxanone and poly (ethylene glycol)

AbstractABCBA type pentablock copolymers, in which the A, B and C blocks are poly (p‐Dioxanone) (PPDO), poly (L‐Lactide) (PLLA), and polyethylene glycol (PEG), respectively, were synthesized via a two‐step ring‐opening polymerization in bulk using stannous octoate as the catalyst. PLA‐b‐PEG‐b‐PLA Triblock copolymer was synthesized at first and then p‐Dioxanone monomers as the other blocks were added to it. In the first step, poly ethylene glycol and, in the second step, triblock copolymer acts as the macro initiator. The obtained copolymers were identified by ⊃1&/sup;H&/I;, ⊃13&/sup;CNMR&/I; and IR&/I; spectroscopy. The intrinsic viscosity of copolymers was measured in chloroform/phenol (3/1 v/w) solution. The thermal properties, such as melting point, melting enthalpy and crystallinity, were studied. From the results of differential scanning calorimetry and thermal gravimetric analysis, it was observed that the PPDO blocks show similar crystallization behavior like homopolymer and also melting temperature of two PPDO end blocks raise with an increase in DON content in copolymer.

Synthesis and Characterization of Amphiphilic Multiblock Copolymers: Effect of the Number of Blocks on Micellization

Five linear amphiphilic multiblock copolymers based on 2-(dimethylamino)ethyl methacrylate (“D”) and methyl methacrylate (“M”), bearing from two to six blocks, were synthesized using sequential group transfer polymerization. All copolymers were obtained from the same polymerization flask (by the withdrawal of a sufficient amount of sample and appropriate adjustment of subsequent monomer loadings) to ensure better comparison between the various multiblocks. A theoretical degree of polymerization (DPth) of 20 was targeted for all D blocks, whereas a DPth of 10 was aimed for the M blocks. Upon characterization using gel permeation chromatography and 1H NMR spectroscopy, the copolymers were confirmed to have the expected values of molecular weights and compositions. Subsequently, the aqueous micellization behavior of these copolymers was probed using dye solubilization, dynamic light scattering, and small-angle neutron scattering. Dye solubilization experiments indicated that micelles readily formed at low copolymer concentrations equal to or less than 0.03% w/w. The scattering measurements revealed that despite the differences in their overall DPth values, the triblock, the tetrablock, and the pentablock copolymers self-assembled in water to form micelles with radii of gyration and hydrodynamic radii very similar to each other, suggesting chain looping and the formation of flowerlike micelles, which is in agreement with recent Monte Carlo simulations.

Synthesis, characterization and surface modification of low moduli poly(ether carbonate urethane)ureas for soft tissue engineering

Flexible scaffolds are of great interest in engineering functional and mechano-active soft tissues as such scaffolds might allow mechanical stimuli to transfer effectively from the scaffolds to cells during tissue development. Towards this end, we have developed a family of flexible poly(ether carbonate urethane)ureas (PECUUs) with a triblock copolymer poly(trimethylene carbonate)–poly(ethylene oxide)–poly(trimethylene carbonate) (PTMC–PEO–PTMC) or pentablock copolymers PTMC–PEO–PPO–PEO–PTMC (PPO, polypropylene oxide) as soft segments, linked by 1,4-diisocyanatobutane and putrescine. All of the PECUUs had low glass transition temperatures (<−46 °C). The PTMC–PEO–PTMC-containing PECUUs had low tensile strength and breaking strain. Replacing PEO with the similar length PEO–PPO–PEO resulted in highly flexible and soft PECUUs possessing breaking strains of 362–711%, tensile strengths of 8–18 MPa and moduli of 5.5–7.4 MPa at room temperature in air. Under aqueous conditions at 37 °C, these polymers remained flexible while their moduli were decreased to 3.4–4.0 MPa. PECUUs based on PTMC–PEO–PPO–PEO–PTMC were thermosensitive as the water content at 37 °C was lower than that at 4 °C. PECUU using PTMC–PEO–PTMC as a soft segment showed 30% weight loss over 6 weeks in PBS at 37 °C, while that using PTMC–PEO–PPO–PEO–PTMC as a soft segment had weight loss <6%. Degradation products were found to lack cytotoxicity. The mechanical stresses and moduli of PECUUs based on PTMC–PEO–PPO–PEO–PTMC were unchanged during the degradation. To enhance cell adhesion, PECUUs were surface modified with Arg-Gly-Asp-Ser (RGDS). Smooth muscle cell adhesion was 114% of tissue culture polystyrene for unmodified PECUU and >180% for RGDS-modified PECUUs, with cell viability on both surfaces increasing during culture. These low moduli polyurethanes may find applications in engineering cardiovascular or other soft tissues.

Molecular design of novel pH/temperature-sensitive hydrogels

A series of poly(β-amino ester)–poly(ɛ-caprolactone)–poly(ethylene glycol)–poly(ɛ-caprolactone)–poly(β-amino ester) pentablock copolymers (PAE–PCL–PEG–PCL–PAE) were designed and prepared to examine factors affecting sol–gel phase transition behavior. First, the composition of a series of PCL–PEG–PCL copolymers was controlled by changing the feed ratios of PCL/PEG and the molecular weight of PEG. Second, the composition of pentablock copolymers was varied using different PCL–PEG–PCL copolymers and several feed ratios of PAE monomers. The physicochemical properties of triblock and pentablock copolymers were characterized by 1H NMR and gel permeation spectroscopy. The PAE–PCL–PEG–PCL–PAE copolymers in aqueous solution (20–30 wt%) underwent sol–gel transitions with changes in both pH change and temperature. With increasing molecular weight of PAE, the sol–gel transition zone became narrower because the hydrophobic character of the copolymers decreased. Also, with increases in PCL/PEG ratio and PEG molecular weight, changes in the hydrophobic/hydrophilic balance within copolymers resulted in alterations in sol–gel phase transitions.

Controlled release of insulin from pH/temperature-sensitive injectable pentablock copolymer hydrogel

A pH- and temperature-sensitive hydrogel of poly(β-amino ester)-poly(ε-caprolactone)-poly (ethylene glycol)-poly(ε-caprolactone)-poly(β-amino ester) (PAE-PCL-PEG-PCL-PAE) pentablock copolymer was evaluated as a sustained injectable insulin delivery system. Insulin was readily loaded into the matrix, forming an ionically linked insulin–PAE complex. Complex mixtures containing various concentrations of insulin and copolymer were subcutaneously injected into male Sprague–Dawley rats to study the profile of insulin release in vivo. The insulin-release profile showed that insulin was maintained at a constant steady-state level for 15 days, and further demonstrated that insulin levels were controlled by the amount of insulin loaded into the copolymer and the copolymer concentration in the hydrogel. The effect of the insulin–gel complex was further investigated in the streptozotocin (STZ) diabetic rat model. After subcutaneously injecting complex mixtures into STZ-induced diabetic rats, blood glucose and plasma insulin levels were measured. The results showed that the diabetic rats could be treated for more than 1 week with a single injection of the complex mixture containing 10 mg/mL insulin in a 30 wt.% copolymer solution, suggesting that this pH/temperature-sensitive insulin–hydrogel complex system may have therapeutic potential.

Chain bridging in a model of semicrystalline multiblock copolymers

Recent experimental observations have suggested an intimate connection between the chain conformations and mechanical properties of semicrystalline multiblock copolymers. Motivated by these studies, we present a theoretical study evaluating the bridging/looping fractions in a model of semicrystalline multiblock copolymers. We model the noncrystalline block (A) as a flexible Gaussian chain and the crystalline block (B) as a semiflexible chain with a temperature dependent rigidity and interactions that favor the formation of parallel oriented bonds. Using self-consistent field theory, the bridging fractions of the various domains in different multiblock copolymers (ABA, BAB, ABABA, and BABAB) are evaluated and compared with their flexible counterparts. In general, we observe that for both triblock and pentablock copolymers, rendering one of the blocks crystallizable promotes bridging in that component while reducing the bridging in the other noncrystallizable component. Moreover, the bridging fractions in tri- and pentablock copolymers were seen to be quantitatively similar except insofar as being normalized by the volume fraction of bridgeable units.

Novel Pentablock Copolymers for Selective Gene Delivery to Cancer Cells

In this study, the novel poly(diethylaminoethylmethacrylate) (PDEAEM)/Pluronic F127 pentablock copolymers were found to be able to mediate high-efficiency transfection of human epithelial ovarian carcinoma (SKOV3) cell line while showing significantly lower efficacy in human epithelial retinal (ARPE-19) cell line and Swiss Mouse Fibroblast (3T3) cell line. The intracellular routes of polyplexes were investigated by confocal microscopy after appropriately labeling the polymer and DNA. It was found that lesser nuclear entry in the ARPE-19 cells may result in the lower efficiency of transfection. Since the SKOV3 proliferation rate was found to be much higher than that of the ARPE-19 cells, the nuclear entry of polyplexes was assumed to be correlated with the proliferation rate, and it was hypothesized that the novel pentablock copolymers could mediate gene delivery selectively in fast growing cells. The different intracellular barriers to gene transfer may also account for the observed difference of transfection efficacy. Although the validity of the hypothesis that our pentablock copolymer could selectively transfect hyperproliferative cells needs further examination, this present work provides a new perspective to design targeting vectors for cancer therapies based on different characteristics among specific cell types.

Comparison between the self‐assembling behaviors of PLLA‐PEO‐PLLA triblock copolymers and PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers

AbstractPoly(L‐lactic acids) (PLLAs) were grafted to both ends of poly(ethylene oxide) (PEO) to produce biocompatible amphiphilic PLLA‐PEO‐PLLA triblock copolymers. The self‐assembling behaviors of two PLLA‐PEO‐PLLA copolymers in aqueous solutions were examined by Dynamic Light Scattering and Transmission Electron Microscopic techniques. PLLA‐PEO‐PLLA formed spherical micelles, whereas PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers were reported to produce vesicles. It is believed that the PPO segment within the PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers has a dominant role in the formation of vesicles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

PH- and temperature-dependent phase behavior of a PEO-PPO-PEO-based pentablock copolymer in aqueous media

We investigated the structural features of micelles formed by the self-association of the pentablock copolymer poly[ N,N -(diethyl amino)ethyl methacrylate]-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethyleneoxide)-block-poly[ N,N -(diethylamino)ethyl methacrylate] (PDEAEM-PEO-PPO-PEO-PDEAEM) in aqueous solutions by using small-angle neutron scattering SANS. The pentablock copolymer solutions exhibit micellar and gel phases in response to changes in both the temperature and pH by virtue of (1) the lower critical solution temperature of the PPO blocks and (2) the polyelectrolyte character of the pendant PDEAEM blocks. Two modeling schemes were employed to describe the SANS data of semidilute copolymer solutions at higher temperature as they contain interacting charged micelles at pH<7.5 and interacting neutral micelles at higher pH. We have elucidated the structures of the micelles in terms of size, shape, polydispersity, association number, number density, and surface charge. At low pH the charged spherical micelles are less packed with the copolymers presumably due to the electrostatic repulsion between the charged pendant groups. On the other hand, at higher pH the hydrophobic character of the neutral pendant groups enable them to sequester within the micelle core along with the PPO, thus increasing the number density and the core size of the spherical micelles. At higher copolymer concentration reversible thermoresponsive sol-gel transitions were observed at all pH conditions and the rheological behavior of the gels nicely correlates with different organization of micelles with different shapes.

Synthesis and Characterization of Ionic Block Copolymer Templated Calcium Phosphate Nanocomposites

Self-assembling thermo-reversibly gelling anionic and zwitterionic pentablock copolymers were used as templates for precipitation of calcium phosphate nanostructures, controlling their size and ordered structural arrangement. Calcium and phosphate ions were dissolved in a block-copolymer micellar dispersion at low temperatures. Aging at ambient temperature produced inorganic nanoparticles, presumably nucleated by ionic interactions. The self-assembled nanocomposites were characterized by small-angle X-ray and neutron scattering (SAXS/SANS), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). 1H−31P NMR with 1H spin diffusion from polymer to phosphate proved the formation of nanocomposites, with inorganic particle sizes from ∼2 nm, characterized by 1H−31P dipolar couplings, to >100 nm. TEM analysis showed polymer micelles surrounded by calcium phosphate. SAXS attested that a significant fraction of the calcium phosphate was templated by the polyme...

Synthesis of ABC and CABAC Triphilic Block Copolymers by ATRP Combined with ‘Click’ Chemistry

AbstractATRP using poly(propylene oxide) monofunctional macroinitiator was carried out with solketal methacrylate (SMA) and the non‐reactive PPO having two N3 terminal groups was removed by dissolution in an excess of n‐hexane. The resulting azido terminated AB diblock copolymer was ‘clicked’ with an α‐alkyne fluorinated compound, followed by acid hydrolysis of the SMA units, a triphilic ABC triblock copolymer was prepared. ATRP of SMA with a difunctional PPO macroinitiator to give ABA triblock copolymer was also carried out. The terminal Br was again exchanged with N3, ‘clicked’ with the α‐alkyne fluorinated compound and likewise hydrolyzed to give a triphilic CABAC pentablock copolymer, i.e., hydrophilic, oleophilic, and fluorophilic blocks were combined.magnified image

Pentablock copolymers of poly(ethylene glycol), poly((2-dimethyl amino)ethyl methacrylate) and poly(2-hydroxyethyl methacrylate) from consecutive atom transfer radical polymerizations for non-viral gene delivery

Well-defined pentablock copolymers (PBPs) of P(HEMA)- b-P(DMAEMA)- b-PEG- b-P(DMAEMA)- b-P(HEMA) (in which PEG = poly(ethylene glycol), P(DMAEMA) = poly((2-dimethyl amino)ethyl methacrylate), and P(HEMA) = poly(2-hydroxyethyl methacrylate)), with different block lengths of P(DMAEMA), for non-viral gene delivery were prepared via consecutive atom transfer radical polymerizations (ATRPs) from the same di-2-bromoisobutyryl-terminated PEG (Br–PEG–Br) center block. The PBPs demonstrate good ability to condense plasmid DNA (pDNA) into 100–160 nm size nanoparticles with positive zeta potentials of 25–35 mV at PBPs/pDNA weight ratios of 5–25. The PBPs exhibit very low in vitro cytotoxicity and excellent gene transfection efficiency in HEK293 and COS7 cells. In particular, the transfection efficiencies of all the PBPs in HEK293 cells are comparable to, or higher than those of polyethylenimine (PEI, 25 kDa) at most weight ratios. The ability of the copolymers to condense plasmid DNA and the transfection efficiency of the resulting complexes are dependent on the chain length of P(DMAEMA) blocks. In addition to reducing the cytotoxicity and increasing the stability of the plasmid complexes, the PEG center block and the short P(HEMA) end blocks also help to enhance the gene transfection efficiency. Thus, the approach to well-defined block copolymers via ATRP provides a versatile means for tailoring the structure of non-viral gene vectors to meet the requirements of low cytotoxicity, good stability and high transfection capability for gene therapy applications.

Synthesis and characterization of amphiphilic fluorinated pentablock copolymers based on Pluronic F127

AbstractThe synthesis and self‐assembly behavior of pentablock copolymers consisting of Pluronic F127 (PEO100‐PPO65‐PEO100) and poly(2, 2, 3, 3, 4, 4, 5, 5‐octafluoropentyl methacrylate) (POFPMA) is herein described. Using the difunctional potassium alcoholate of F127, K+O–‐(PEO100‐PPO65‐PEO100)‐O–K+, as the macroinitiator, the POFPMA‐F127‐POFPMA pentablock copolymers were synthesized via oxyanion‐initiated polymerization. The chain length of POFPMA can be controlled by the original molar ratio of macroinitiator to OFPMA monomer, that is, F‐monomer. The composition and chemical structure of POFPMA‐F127‐POFPMA pentablock copolymers have been characterized by FTIR, 1HNMR, and 19F NMR spectroscopy, and gel permeation chromatography techniques. The solution behavior of POFPMA‐F127‐POFPMA copolymers was investigated by the methods of surface tension, cloud point, transmission electron microscopy, and high performance particle sizer (HPPS). The results indicate that these Pluronic F127‐based block copolymers modified with fluorinated segments possess relatively high surface activity and low cloud points, depending on various factors, such as the length of fluorinated block, the concentration of the copolymers in aqueous solution, and the adscititious inorganic salt. TEM measurements showed that the pentablock copolymers can self‐assemble in aqueous solution to form various micellar morphologies. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3029–3041, 2008

Functionalized injectable hydrogels for controlled insulin delivery

The concept of this research is using poly(β-amino ester) (PAE) as a duo-functional group for synthesis of the novel sensitive injectable hydrogel for controlled drug/protein delivery. Firstly, PAE made of 1,4-butanediol diacrylate and 4,4′-trimethylene dipiperidine is used as a pH-sensitive moiety to conjugat to the temperature-sensitive biodegradable triblock copolymer of poly(ethylene glycol)–poly(ɛ-caprolactone) (PCL–PEG–PCL) to manufacture pH/temperature-sensitive injectable hydrogel of pentablock copolymer PAE–PCL–PEG–PCL–PAE. Furthermore, the cationic nature of PAE is used as the second function to make the ionic complexes with anionic biomolecule loaded into the hydrogel such as insulin. As a result, the release of drug/protein from this hydrogel device can be controlled by the degradation of copolymer. Sol–gel phase transition behavior of PAE–PCL–PEG–PCL–PAE block copolymer was investigated; the results showed that the aqueous media of the pentablock copolymer changed from a sol to a gel phase with increasing temperature and pH. The effect of anionic biomolecule such as insulin on sol–gel phase transition, degradation of the complex gel of the material with insulin was studied in vitro. Then the schematic of the ionic complexes between positive charges in PAE and the negatively charges in protein was simulated. In addition, the mechanism of controlled release behavior of insulin from the complex gel was supposed, which includes the chemically-controlled and diffusion-controlled stages. To prove the simulations, the cumulative release of the protein from the complex gel was investigated in vitro with different methods. Furthermore, the pharmacokinetic release of insulin from the complex gel in vivo on male Sprague-Dawley (SD) rats was compared with that from triblock copolymer hydrogel of PCL–PEG–PCL.

Synthesis of Amphiphilic ABCBA‐Type Pentablock Copolymer from Consecutive ATRPs and Self‐Assembly in Aqueous Solution

AbstractSummary: A novel amphiphilic ABCBA‐type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2‐dimethylaminoethyl methacrylate)‐block‐poly(2,2,2‐trifluoroethyl methacrylate)‐block‐poly(ε‐caprolactone)‐block‐poly(2,2,2‐ trifluoroethyl methacrylate)‐block‐poly(2‐dimethylaminoethyl methacrylate) (PDMAEMA‐ b‐PTFEMA‐b‐PCL‐b‐PTFEMA‐b‐PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and 1H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self‐assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.

The Chemoenzymatic Synthesis of a Novel CBABC-Type Pentablock Copolymer and Its Self-Assembled “Crew-Cut” Aggregation

A symmetric linear CBABC pentablock copolymer consisting of poly(ethylene oxide) (PEO), polycaprolactone (PCL), and polystyrene (PSt) was synthesized by the combination of enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Dihydroxyl-capped PEO first initiated eROP of ε-CL in the presence of biocatalyst Novozyme 435. Subsequently, the resulting dihydroxyl-terminated copolymer PCL-b-PEO-b-PCL was converted to bromine-ended triblock macroinitiator by the esterification with α-bromopropionyl bromide. Pentablock copolymer PSt-b-PCL-b-PEO-b-PCL-b-PSt was obtained via a subsequent ATRP of styrene(St), and its kinetics analysis indicated a “living”/controlled radical polymerization. The self-assembly behavior of pentablock copolymer was investigated in aqueous media. The “crew-cut” aggregates of various morphologies were observed, such as normal spherical micelles, rodlike micelles, vesicles, lamellae, and large compound micelles (LCMs). In addition, it was found that both the copolymer composition and the copolymer concentration in THF had a great influence on the morphologies of the aggregates.

Thermoreversible Ion Gels with Tunable Melting Temperatures from Triblock and Pentablock Copolymers

We demonstrate a way to tune the critical gelation temperature (Tgel) for thermoreversible ion gels. Thermoreversible ion gels were prepared previously through the self-assembly of poly(N-isopropyl acrylamide-b-ethylene oxide-b-N-isopropyl acrylamide) (PNIPAm-PEO-PNIPAm) triblock copolymers in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). The resulting Tgel was 17 °C, as judged by the intersection of the dynamic moduli (G‘ and G‘ ‘) at a fixed low frequency on increasing the temperature. These gels are of interest in various applications, including gate dielectric materials in organic field effect transistors. However, it is desirable to bring the Tgel significantly above room temperature in order to realize device applications. By incorporating solvatophobic blocks of polystyrene (PS) into the PNIPAm-PEO-PNIPAm triblock copolymers to produce well-defined PNIPAm-PS-PEO-PS-PNIPAm pentablock copolymers, we are able to adjust the Tgel of the re...

Synthesis of azobenzene-centered (co)polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization

Abstract An azobenzene-based dithiocarbamate, 4,4'-bis[2-(carbazole-N-dithio formatyl)-2-methyl-propionatyl]-azobenzene (CDMPA), was synthesized and used as the chain transfer agent (CTA) for reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in anisole solution. Well-defined azobenzene-centered and carbazole-ended polystyrene (PS) with well-controlled molecular weight (Mn) and narrow molecular weight distributions (Mw/Mn) was obtained. The good agreement between the theoretical molecular weight (Mn,th) and the 1H NMR determined molecular weight (Mn,NMR) indicated that most of the polymer chains contained an azo-functional center-group end-capped with the carbazole moieties, which were derived from the RAFT agent. The obtained polystyrene (PS) showed a strong ultraviolet absorption in tetrahydrofuran (THF) and emitted fluorescence after excited by UV-irradiation in N,N’-dimethyl formamide (DMF) solutions. The PS was used as the macro-RAFT agent to carry out the polymerization of methyl acrylate (MA) and N-isopropylacrylamide (NIPAAM). Triblock copolymers (PMA-b-PS-b-PMA), and pentablock copolymers (PNIPAAM-b-PMA-b-PS-b-PMA-b-PNIPAAM) were obtained, respectively. These copolymers were characterized by gel permeation chromatography (GPC), FT-IR spectroscopy and NMR spectroscopy.

Dual-role self-assembling nanoplexes for efficient gene transfection and sustained gene delivery

Novel cationic pentablock copolymers with poly(diethylamino ethyl methacrylate) blocks covalently attached to parent triblock Pluronic copolymers have been designed and developed as sustained release non-viral gene delivery vectors. These copolymers electrostatically condense plasmid DNA into nanostructures (nanoplexes) and further self-assemble above critical concentration to form thermoreversible hydrogels at physiological temperatures. Unlike other sustained gene delivery systems of non-ionic copolymers that release naked DNA, hydrogels of pentablock copolymer/DNA nanoplexes dissolve in excess buffers to release DNA compacted inside the nanoplexes. These hydrogels permit aqueous pharmaceutical formulations that do not involve organic solvents and are non-invasively injectable with syringes into localized tissues where they instantly form hydrogels in situ. The hydrogels were found to have better mechanical strength than Pluronic gels. Hydrogels of nanoplexes containing 15 wt% copolymer dissolved to release nanoplexes up to 5 days in vitro, compared to rapid release of up to 90% entrapped naked DNA from only Pluronic gels by day 1. The release profile of the nanoplexes from the hydrogels could be modulated by changing the concentration of copolymer or plasmid DNA in the hydrogel formulation. Since DNA is electrostatically bound to copolymer molecules, it does not freely diffuse out of the polymeric network, preventing initial release bursts observed with other such controlled release gels/matrices/microspheres. The released nanoplexes were colloidally stable, preserved the integrity of supercoiled plasmid DNA, and gave good transfection efficiencies in vitro upon dissolution. These novel copolymers, thus, act as both nanoscale gene delivery vectors and macroscale sustained delivery agents, and make a clinically viable long-term sustained gene delivery system.

Branched Pentablock Poly(L-lactide-co-∊-caprolactone) Synthesis in scCO2

Pentablock poly(L-lactide-co-∊-caprolactone) (PLLA/PCL), with a central fluorinated segment and four PLLA/PCL side chains was synthesized by sequential ring-opening polymerization (ROP) with stannous octoate catalyst in an environmentally benign and clean medium, scCO2. Copolymers of PLLA and PCL are extensively researched for biomedical applications. Fluorinated hydrocarbons are similarly promising for biomedicine, and especially for oxygen-carrying substitute applications. Initially, a fluorinated reactive triblock stabilizer (prepolymer, PCL-FLKT-PCL) with inner fluorinated segment and PCL side chains was synthesized in bulk from a tetraol fluorinated alcohol (FLKT) with a 99% conversion. The prepolymer was then utilized for the synthesis of copolymers in scCO2, where PLLA segments were successively incorporated to the ends of the prepolymer, forming a pentablock structure with four polyester side chains. Reactions were carried out at 75°C and 4000-4500 psi. Solubility studies of the prepolymer and the pentablock copolymer in scCO2 showed effective solubilization at the reaction temperature and pressure. The molecular weights of the products were measured with the aid of gel permeation chromatography; the prepolymer and the copolymer possessed average number molecular weights (Mn) in the range of 13 000 and 24 000 (for 96% conversion of LLA), respectively. Low poly-dispersity indexes were obtained: 1.34 for the prepolymer and 1.08-1.34 for the pentablock copolymer. Material characterization was carried out by 1H NMR, 13C NMR, 19F NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and scanning electron microscopy (SEM).