Copolymerization Of Glycolide Research Articles

A new pathway for developing in vitro nanostructured non-viral gene carriers

Extracellular and intracellular barriers typically prevent the efficient transfection of non-viralgene vectors. The formulation of a gene delivery carrier that can overcome the barriers wouldbe a key for successful gene therapy. We have developed a novel pathway for the preparation ofcore-shelled DNA nanoparticles by invoking solvent-induced condensation of plasmid DNA(β-galactosidase) in a poor solvent mixture and subsequent encapsulation of the condensedDNA globule in a tri-block copolymer (e.g. polylactide-poly(ethylene glycol)-polylactide,L8E78L8). The polylactide shell can protect the encapsulated DNA from degradation duringelectrospinning of a mixture of encapsulated DNA nanoparticles and biodegradable PLGA(a random copolymer of lactide and glycolide) to form a non-woven nanofibrousDNA-containing scaffold. The bioactive plasmid DNA can then be released in an intactform and in sufficient quantity from the scaffold with a controlled release rate and totransfect cells in vitro. Further consideration of the stability of the DNA in extracellularand intracellular environments is proposed. In particular, the use of block copolymers witha positively charged block and a hydrophilic block, as well as tri-arm block copolymers withan additional hydrophobic, biodegradable block to stabilize the DNA chain of interest, isdiscussed.

Application of the lithium and magnesium initiators for the synthesis of glycolide, lactide, and ϵ‐caprolactone copolymers biocompatible with brain tissue

The subject of this work is new method of the synthesis of biodegradable copolymers compatible with brain tissue. Copolymerization of glycolide with lactide was conducted in solution or in bulk in the presence of LiBu, LiAcac, MgBu(2), Mg(acac)(2) as initiators. In all cases, copolymers with molecular weight of 20000-40000 were obtained, which enables to use them as drug carriers. During the reactions of copolymer chain growth, the intermolecular transesterification occurs, changing the distribution of comonomeric units in copolymer chain. Magnesium initiators showed a lower contribution to transesterification in comparison with lithium and calcium compounds. The copolymerization of glycolide with epsilon-caprolactone using magnesium compounds as initiators was also described. The random glycolide/epsilon-caprolactone copolymer (10/90) obtained with MgBu(2) was used in in vivo study in the forms of microspheres and foils. Complete degradation of microspheres during 6 weeks was observed after the implantation to brain tissue. All implanted copolymers are compatible with brain tissue.

Copolymerization of glycolide and trimethylene carbonate

AbstractThe bulk ring‐opening copolymerization of glycolide with trimethylene carbonate was performed under different conditions. The influence of the composition, temperature, reaction time, and catalyst on the chain microstructure was studied by means of 1H and 13C NMR spectroscopy. The final microstructure was found to be highly dependent on the transesterification reactions. The thermal behavior was sensitive to the composition and to the length of the glycolyl microblocks. Differential scanning calorimetry and X‐ray diffraction demonstrated that glycolyl‐rich sequences could give rise to a single crystalline phase, whereas trimethylene carbonyl units were incorporated into the amorphous phase. The synthesis of copolymers from the melt‐state transesterification of polyglycolide and poly(trimethylene carbonate) homopolymer mixtures was also studied. The hydrolytic degradation rate of the copolymers was found to depend on the microstructure and in general was enhanced with the degree of randomness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 993–1013, 2006

In vitro non-viral gene delivery with nanofibrous scaffolds

Extracellular and intracellular barriers typically prevent non-viral gene vectors from having an effective transfection efficiency. Formulation of a gene delivery vehicle that can overcome the barriers is a key step for successful tissue regeneration. We have developed a novel core-shelled DNA nanoparticle by invoking solvent-induced condensation of plasmid DNA (β-galactosidase or GFP) in a solvent mixture [94% N,N-dimethylformamide (DMF) + 6% 1× TE buffer] and subsequent encapsulation of the condensed DNA globule in a triblock copolymer, polylactide-poly(ethylene glycol)-polylactide (L8E78L8), in the same solvent environment. The polylactide shell protects the encapsulated DNA from degradation during electrospinning of a mixture of encapsulated DNA nanoparticles and biodegradable PLGA (a random copolymer of lactide and glycolide) to form a nanofibrous non-woven scaffold using the same solution mixture. The bioactive plasmid DNA can then be released in an intact form from the scaffold with a controlled release rate and transfect cells in vitro.

Synthesis of Biodegradable Diblock Copolymers of Glycolide and Poly(oxyethylene) Using a Montmorillonite Clay as Catalyst

Biodegradable diblock copolymers were prepared from glycolide and poly(oxyethylene) of Mn=600 (POE 600), 1500 (POE 1500) and 2000 (POE 2000). The copolymerization of glycolide and POE was induced in heterogeneous phase by “Maghnite-H+” under suitable conditions. Maghnite-H+ is a montmorillonite sheet silicate clay exchanged with protons. Various techniques, including 1H NMR, 13C NMR, IR, DSC and Ubbelohde viscometer were used to elucidate structural characteristics and thermal properties of the resulting copolymers. The effect of the [glycolide]/[POE] molar ratio on the rate of copolymerization and on intrinsic viscosity of the resulting copolymers was studied. Data showed that the rate of copolymerization and intrinsic viscosity of copolymers increase with increasing [glycolide]/[POE] molar ratio.

Microstructural analysis and structure-property relationship of poly(glycolide-co-1,3-trimethylene carbonate)

A series of linear copolymers of glycolide and 1,3-trimethylene carbonate were synthesized by bulk ring-opening polymerization. The copolymers were characterized by 1H NMR, 13C NMR, viscometry, and differential scanning calorimetry (DSC). The dependency of reaction temperature, reaction time, and the feed composition on the microstructure of the copolymers was examined by 13C NMR analysis. The microstructural analysis using 13C NMR was useful to calculate the average block length of the glycolyl (LG) and trimethylene carbonyl (LT) sequence. The structural change such as transesterification, which was assigned by TGT sequence, was reflected in the average block length and the sequence of each monomeric unit in the copolymer. The average length of glycolyl sequence (LG) was much longer than that of trimethylene carbonyl sequence (LT) in polymerization temperature of 100–150°C. Upon further increasing the polymerization temperature, the LG decreased, but the change of LT was insignificant. During the polymerization, transesterification did not occur at 100°C, but it was observed at a polymerization temperature range of 130–200°C resulting in the decrease in LG. As the composition of trimethylene carbonate increased, LG decreased, but LT do not show remarkable change. DSC results showed a close relationship between crystallinity and nature of microstructural sequence. The crystallinity of block copolymers was mainly decided by the average length of the glycolyl block.

Glycolide Copolymer Staple-Line Reinforcement Reduces Staple Site Bleeding During Laparoscopic Gastric Bypass

The use of staple-line reinforcement sleeves during laparoscopic gastric bypass reduces staple-line bleeding, which may translate into a reduction in the rate of gastrointestinal hemorrhage. Prospective randomized trial. University hospital. Thirty-four patients undergoing laparoscopic gastric bypass were randomly assigned to receive either no reinforcement (control group, n = 17) or reinforcement of the staple line with glycolic copolymer sleeves (treatment group, n = 17). Demographic data, the number of stapler loads used, the number of staple-line bleeding sites, the amount of blood loss, the length of time required to obtain hemostasis of the staple lines, operative time, intraoperative and postoperative complications, and serial hemoglobin levels. The mean number of stapler loads used was similar between groups. The mean number of staple-line bleeding sites was significantly fewer in the treatment group for division of gastric tissue (0.4 vs 2.5 bleeding sites), jejunal tissue (0.1 vs 0.6 bleeding site), and mesenteric tissue (0 vs 0.8 bleeding site). The mean blood loss was lower in the treatment group (84 vs 129 mL). Staple misfire occurred in 1 (0.7%) of 143 stapler loads used in the treatment group compared with 0 (0%) of 138 stapler loads used in the control group. The time to obtain staple-line hemostasis was shorter in the treatment group (1.2 vs 10.1 minutes). The total operative time was similar between groups. There was no mortality or postoperative leaks. One patient in the control group had postoperative gastrointestinal hemorrhage requiring blood transfusion and reoperation. There was no significant difference in the mean hemoglobin level between groups on the first postoperative day. The use of glycolide copolymer staple-line reinforcement sleeves in patients undergoing laparoscopic gastric bypass is safe and significantly reduces staple-line bleeding sites and may reduce the incidence of gastrointestinal hemorrhage.

An Implantable Immunosuppressive Cyclosporine Drug Delivery System

In the article a kind biodegradable drug carrier (glycolide-co-lactide-co-caprolactone) tricomponent copolymer (PGLC) was synthesized by ring opening copolymerization of glycolide (GA), lactide (LA) and ε-caprolactone (CL), and was used to manufacture an implantable drug preparation---Cyclosporine-PGLC drug delivery system (Cs-PGLC DDS).The Cs could slowly release from the Cs-PGLC DDS near linearly and last for a long time in vitro. A clinically significant Cs concentration in the cornea and anterior chamber could be achieved by implanting the Cs-PGLC DDS in anterior chamber. It was demonstrated that the Cs-PGLC DDS is a long-effective intraocular immunosuppressive agent for remaining corneal allograft clear and significantly prolong its survival time.

Uniform Encapsulation of Stable Protein Nanoparticles Produced by Spray Freezing for the Reduction of Burst Release

Stable protein nanostructured particles, produced by spray freezing into liquid (SFL) nitrogen, were encapsulated uniformly into microspheres to reduce the burst release over the first 24 h. The denaturation and aggregation of these bovine serum albumin (BSA) high‐surface area particles were minimal due to ultra‐rapid freezing and the absence of a liquid–air interface. Upon sonication, these friable highly porous, solid protein particle aggregates broke up into submicron particles. These particles were encapsulated into DL‐lactide/glycolide copolymer (PLGA) and poly(lactic acid) (PLA) microspheres by anhydrous solid‐in‐oil‐in‐oil (s/o/o) techniques. For 5% loading of protein, the burst release after 24 h was only 2.5–4.1%, that is, values fivefold to tenfold lower than those observed for larger more conventional BSA particles. At a loading of 10%, the burst was only 6 and 13% for PLGA and PLA, respectively, and at 15% loading it was only 12% for PLGA. As shown with confocal and scanning electron microscopy (SEM), the low burst is consistent with a uniform distribution of protein nanoparticles, which were about 100 times smaller than the microspheres. Changes in aggregation and secondary structure, which were monitored by size exclusion chromatography and FTIR, respectively, indicated only slight monomer loss (3.9%) and high structural integrity (38% α‐helix) in the encapsulated protein. © 2004 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:56–69, 2005

Measurement and modeling of CO 2 absorption in poly(lactic-co-glycolic acid)

High-pressure CO 2 absorption into polymers was measured by a gravimetric method. The amount of CO 2 absorbed in the polymer was extrapolated using the CO 2 release profile from polymeric samples measured at standard conditions by an external balance. The polymers studied were poly-(methyl methacrylate) (PMMA) and poly(lactic-co-glycolic acid) (PLGA) with different molecular weights (MW) and lactide–glycolide copolymer ratios. Experimental results for PMMA well agree with literature data of Wissinger and Paulaitis [J. Polym. Sci.: Part B: Polym. Phys. 25 (1987) 2497] and Chang et al. [J. Supercrit. Fluids 13 (1998) 113]. For PLGA, CO 2 absorption measurements were performed at 313 K and in the pressure range 0.6–4.0 MPa. The method gave reproducible results within the accuracy of ±0.002 for mass fraction, ±0.1 MPa for pressure and ±0.15 K for temperature. A perturbed-hard-sphere-chain equation of state (PHSC EOS) was used to correlate CO 2–PLGA absorption isotherms. Pure EOS parameters were estimated by a group contribution method, whereas only one interaction parameter was necessary to fit the measured data. The model fairly describes the experimental data points for all PLGAs considered in this work. These results may be very useful to examine the possibility of successfully using a biodegradable amorphous PLGA polymer for developing effective pharmaceutical products by high-pressure CO 2 techniques.

Guided Bone Regeneration with Novel Bioabsorbable Membranes

Guided Bone Regeneration (GBR) is a method for bone tissue regeneration. In this method, membranes are used to cover bone defects and to block the invasion of the surrounding soft tissues. It would provide sufficient time for the osteogenic cells from bone marrow to proliferate and form new bony tissues. In spite of the potential usefulness of this method, no appropriate materials for the GBR membrane have been developed. Here we design the ideal mechanical properties of the GBR membranes and created novel materials, which is the composite of β-tricalcium phosphate and block copolymer of L-lactide, glycolide and e-caplolactone. In the animal experiments with the use of the trial products, we observed significant enhancement in the bone regeneration and proved the effectiveness of the materials.

Controllable delivery of non-viral DNA from porous scaffolds

The inductive approach to tissue engineering combines three-dimensional porous scaffolds with drug delivery to direct the action of progenitor cells into a functional tissue. We present an approach to fabricate scaffolds capable of controlled, sustained delivery by the assembly and subsequent fusion of drug-loaded microspheres using a gas foaming/particulate leaching process. DNA-loaded microspheres were fabricated from the copolymers of lactide and glycolide (PLG) using a cryogenic double emulsion process. Microspheres were fabricated in four populations with mean diameters ranging from 12.3 μm to 92.5 μm. Scaffolds fabricated by fusion of these microspheres had an interconnected open pore structure, maintained DNA integrity, and exhibited sustained release for 21 days. Control over the release was obtained through manipulating the properties of the polymer, microspheres, and the foaming process. Decreasing the microsphere diameter or the molecular weight of the polymer used for microsphere fabrication led to increased rates of release from the porous scaffold. Additionally, increasing the pressure of CO2 increased the DNA release rate. The ability to create porous polymer scaffolds capable of controlled release rates may provide a means to enhance and regulate gene transfer within a developing tissue, which will increase their utility in tissue engineering.

Local delivery of basic fibroblast growth factor (bFGF) using adsorbed silyl-heparin, benzyl-bis(dimethylsilylmethyl)oxycarbamoyl-heparin.

A growth factor delivery system was developed that is based on the use of silyl-heparin, a chemically modified analogue of heparin. The silyl-heparin was adsorbed onto surfaces by hydrophobic interaction via the prosthetic unit and can then be used as a solid-phase adsorbent for bFGF. All the coating steps were performed by adsorption, a process that allowed preparation of surfaces by immersion or "dip-coating". In this study a series of silyl-heparins were synthesized and each of the analogues found to function similar to unmodified heparin relative to their binding of antithrombin III and also the binding of bFGF. The silyl-heparins were found to be adsorbed onto a wide variety of substrates including polystyrene and lactide:glycolide copolymer. Enzyme-linked immumosorbant assay (ELISA) was used to establish that bFGF was readily bound to surface adsorbed silyl-heparin, and that the amount bound was directly related to amount offered for binding. Once adsorbed the silyl-heparin/FGF was able to induce capillary tube formation of endothelial cells and to increase the growth of endothelial cells. When coated onto suture material and implanted in muscle, the FGF/silyl-heparin coating caused an increased density of mesenchymal cells in the area of the implant. This coating method could prove to be useful in a number of tissue engineering applications for the local delivery of FGF and other growth factors.

1H and 13C NMR Studies of Molecular Dynamics in the Biocopolymer of Glycolide and ε-Caprolactone

Copolymers of glycolide and ε-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T 1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson–Cole model. T 1 relaxation is dominated by trans–gauche isomerisation, with an activation energy of 34–35 kJ mol −1.

Synthesis of biodegradable copolymers with low‐toxicity zirconium compounds. III. Synthesis and chain‐microstructure analysis of terpolymer obtained from L‐lactide, glycolide, and ϵ‐caprolactone initiated by zirconium(IV) acetylacetonate

AbstractZirconium(IV) acetylacetonate [Zr(acac)4] is a very good initiator for the terpolymerization of glycolide with L‐lactide and ϵ‐caprolactone. The microstructure of the obtained terpolymer was determined by NMR spectroscopy and then compared with terpolymers obtained in the presence of stanous(II) octoate [Sn(oct)2]. Samples obtained with Zr(acac)4 were characterized by a segmental‐chain microstructure. Apart from relatively long lactidyl microblocks, there were also segments made of random copolymer of glycolide with lactide. Such a structure is formed as a result of strong transesterification caused by active caproyl chain endings attacking the glycolidyl groups. Domination of this type of transestrification is shown. The growth of terpolymer chains and the influence of transesterification on gradual changes of the microstructure of the forming terpolymer chain were examined. Significant differences among glycolide, lactide, and the least reactive caprolactone were observed. The results of differential scanning calorimetric examinations of the obtained terpolymers are presented. Differences between the structures of random terpolymers obtained during terpolymerization initiated by Sn(oct)2 and those obtained by Zr(acac)4 influence their thermal properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3129–3143, 2002

Synthesis of biodegradable copolymers with low‐toxicity zirconium compounds. II. Copolymerization of glycolide with ϵ‐caprolactone initiated by zirconium(IV) acetylacetonate and zirconium(IV) chloride

AbstractThe aim of this article is to show a new method of copolymerizing glycolide and caprolactone with the low‐toxicity zirconium(IV) acetylacetonate and zirconium(IV) chloride as initiators. Such initiators enabled us to obtain copolymers with very good efficiency and good mechanical properties. The reactivity of the initiators was defined, and the chain‐propagation process was examined. On the basis of an NMR examination and differential scanning calorimetry thermograms, we found that the samples obtained at 100 °C with the initiators were characterized by a segmental chain microstructure, which provided good mechanical properties. When the synthesis was carried out at 150 °C, a more randomized structure was obtained, which caused crucial changes in the properties of the copolymers and decreases in the mechanical properties. Because of their properties, the obtained copolymers could be successfully applied as degradable surgical implants or drug carriers. The results show that the copolymers obtained with zirconium(IV) acetylacetonate and chloride could successfully replace ones obtained in the presence of tin compounds as far as medical applications are concerned. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1379–1394, 2002

Treatment of tuberculosis using a combination of sustained-release rifampin-loaded microspheres and oral dosing with isoniazid.

Previously, we reported on the use of rifampin-loaded microspheres to effectively treat Mycobacterium tuberculosis-infected macrophages and mice. Using similar biocompatible polymeric excipients of lactide and glycolide copolymers, we have increased the rifampin loading of small microsphere formulations (1 to 10 microm) by fourfold. Improved formulations were evaluated individually and in combination with oral regimens of isoniazid for the treatment of Mycobacterium tuberculosis H37Rv-infected mice. Groups (10 mice per group) consisted of mice that received (i) oral dosages of isoniazid (25 to 0.19 mg/kg of body weight/day), (ii) two intraperitoneal injections of rifampin-loaded microspheres on days 0 and 7, (iii) a combination of small rifampin-loaded microspheres on days 0 and 7 and isoniazid orally for 25 days (12.5 to 0.39 mg/kg/day), (iv) placebo injections, and (v) no treatment. Treatment with rifampin-loaded microspheres alone resulted in significant reductions in the numbers of CFU in the lungs and spleens by day 26. A bioassay revealed that plasma rifampin levels from the microspheres exceeded the MICs by more than twofold throughout the 26-day experimental period. Susceptibility testing demonstrated continued sensitivity to rifampin during the treatment period. Whereas isoniazid alone significantly reduced the numbers of CFU for dosages ranging from 12.5 to 1.56 mg/kg, combination therapy with rifampin-loaded microspheres increased the effective range to 0.39 mg/kg. In many cases, complete elimination of CFU was obtained with the combination therapy, something not achieved with most of the single therapies. These results demonstrate the ability to use small microsphere formulations alone to achieve significant results in a murine tuberculosis model and also the ability to use them safely in combination with another antimycobacterial agent.

Emulsion copolymerization ofD,L-lactide and glycolide in supercritical carbon dioxide

Biodegradable polyesters were synthesized via an emulsion polymerization in supercritical carbon dioxide (SC-CO2). Copolymers of lactide and glycolide were synthesized in SC-CO2 with stannous octoate as the ring-opening catalyst and a fluorocarbon polymer surfactant as an emulsifying agent. The conversion of lactide and glycolide was monitored with respect to the reaction time and temperature with 1H NMR spectroscopy. The conversion of glycolide surpassed 99% within 72 h for an SC-CO2 phase maintained at 200 bar and 70 °C. Under the same conditions, lactide conversion reached 65% after 72 h of polymerization. Unpolymerized monomer was removed after the reaction by extraction with an SC-CO2 mobile phase. The molecular weights of all the copolymers were measured by gel permeation chromatography. Weight-average molecular weights (Mw) ranged between 2500 and 30,200 g/mol and polydispersity indices ranged from 1.4 to 2.3 for polymerization times of 6 and 48 h, respectively. Although the molecular weight increased significantly during the first 48 h of reaction, there was no significant difference in the Mw for polymerization times of 48 and 72 h. Emulsion polymerization within the benign solvent SC-CO2 demonstrated improved conversion and molecular weight versus polymers synthesized without surfactant. The emulsion polymerization of lactide and glycolide copolymers in SC-CO2 is proposed as a novel production technique for high-purity, biodegradable polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 562–570, 2001

Fibroblast culture on surface-modified poly (glycolide-co-ε-caprolactone) scaffold for soft tissue regeneration

Novel porous matrices made of a copolymer of glycolide (G) and ε-caprolactone (CL) (51 : 49, Mw 103 000) was prepared for tissue engineering using a solvent-casting particulate leaching method. Poly(glycolide-co-ε-caprolactone) (PGCL) copolymer showed a rubber-like elastic characteristic, in addition to an amorphous property and fast biodegradability. In order to investigate the effect on the fibroblast culture, PGCL scaffolds of varying porosity and pore size, in addition to surfacehydrolysis or collagen coating, were studied. The large pore-sized scaffold (pore size >150 μm) demonstrated a much greater cell adhesion and proliferation than the small pore-sized one. In addition, the higher porosity, the better the cell adhesion and proliferation. The surface-hydrolyzed PGCL scaffold showed enhanced cell adhesion and proliferation compared with the unmodified one. Type I collagen coating revealed a more pronounced contribution for increased cell interactions than the surface-hydrolyzed one. These results demonstrate that surface-modified PGCL scaffold can provide a suitable substrate for fibroblast culture, especially in the case of soft tissue regenerations.

The manufacturing techniques of various drug loaded biodegradable poly(lactide- co-glycolide) (PLGA) devices

A considerable research has been conducted on drug delivery by biodegradable polymeric devices, following the entry of bioresorbable surgical sutures in the market about two decades ago. Amongst the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) like poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide, poly(lactide-co-glycolide) (PLGA) have generated immense interest due to their favorable properties such as good biocompatibility, biodegradability, and mechanical strength. Also, they are easy to formulate into different devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Also, they have been approved by the Food and Drug Administration (FDA) for drug delivery. This review discusses the various traditional and novel techniques (such as in situ microencapsulation) of preparing various drug loaded PLGA devices, with emphasis on preparing microparticles. Also, certain issues about other related biodegradable polyesters are discussed.