Thermal Characterizations of Silver-containing Bioactive Glass-coated Sutures

This study utilized and compared a number of thermal analysis methods to characterize the thermal properties of commercial sutures with and without antimicrobial coatings of silver-doped bioactive glass (AgBG) interlocking particulates. The effect of a slurry dipping technique used to coat resorbable Vicryl® (polyglactin 910) and non-resorbable Mersilk® surgical sutures with AgBG was investigated using conventional differential scanning calorimetry (DSC), high speed calorimetry (or HYPERDSC™), and modulated temperature DSC (MTDSC). These methods were compared in terms of their ability to resolve the thermal transitions of the types of suture materials. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used to verify the thermal degradation temperatures of these materials and to quantify the AgBG coatings on the sutures.

The use of complementary thermal analysis techniques enabled the understanding of the effect of the AgBG coating technique on the morphological properties of the sutures. The slurry dipping technique had no significant effect on the thermal transitions of both types of materials. The use of high speed calorimetry through DSC offered better resolution for the transitions that appeared to be weak through conventional heating regimes, and was able to separate broad double transitions. Furthermore, it was shown not to compromise either the melting temperature or the enthalpy of melting. Therefore this method allows for the accurate determination of thermal transitions through much shorter experimental times thus allowing for an increased sample throughput. The combined DTA and TGA indicated that a greater AgBG coating was obtained in the case of the Mersilk® sutures.

Carbon dioxide extraction of residual solvents in poly(lactide-co-glycolide) microparticles

A process for the reduction of residual solvents in spray-dried poly(lactide-co-glycolide) (PLGA)-darbepoetin alfa microparticles was developed using carbon dioxide (CO(2)) as an extraction solvent. CO(2) was investigated in two phase states, liquid and gas. Detrimental effects on encapsulated protein integrity and microparticle morphology were observed with liquid CO(2) exposure. Extraction with CO(2) gas at <100 psig reduced residual solvent concentration and particle agglomeration was limited. Extraction rates and particle agglomeration increased with higher CO(2) gas pressures. The CO(2) pressures below which particles of polylactide (PLA) and PLGA microparticles significantly agglomerated were determined and the data used to develop extraction cycles. Extraction cycles were developed in which CO(2) gas pressure was increased as residual solvent concentration decreased in order to keep extraction rates high throughout the cycle. Spray dried darbepoetin alfa-PLGA microparticles were extracted with CO(2) gas and characterized for residual solvent concentration, process yield, particle size distribution, morphology, and protein integrity. The results indicated CO(2) gas may be used to reduce residual solvent to approximately 200 ppm with no significant detrimental effects on protein integrity or microparticle morphology.

Determination of copolymer ratios of poly(lactide-co-glycolide) using near-infrared spectroscopy

The near infrared (NIR) spectroscopic technique was used to determine copolymer ratios of polylactide-co-glycolide samples. Appropriate quantities of DL-polylactic acid and lactic-co-glycolic acid polymers with 86:14, 75:25, 64:36 and 52:48 lactide to glycolide ratios were dissolved in methylene chloride to obtain 5% (w/w) solutions. NIR spectra of the samples were obtained from the solutions using a Polyol Analyzer operated in the transmittance mode. Linear regression calibration models were generated at 2130 and 2288 nm from the second derivative spectral data obtained from the NIR technique. The lowest and highest standard errors of calibration (SEC) at 2130 nm were 1.29 and 1.63%, whereas those obtained from the calibration models generated at 2288 nm were 2.00 and 2.03%, respectively. Partial least squares (PLS) calibration models were also generated from the second derivative spectral data from 1100 to 2500 nm. The lowest and the highest SEC for the models were 1.46 and 1.53%, respectively. The calibration models were then used to predict the lactide contents of the unknown (test) samples. The highest percent error of prediction was 2.56% for samples with 86% lactide content when the linear regression calibration at 2130 nm was used, whereas the highest percent error of prediction was 1.56% for samples with 64% lactide content when the linear regression calibration at 2288 nm was used. The highest percent error of prediction was 1.73% for samples with 75% lactide content when the two-factor PLS calibration model was used.

High-performance liquid chromatographic determination of some of the hydrolytic decomposition products of poly(alpha-hydroxyacid)s

An HPLC procedure is described for the separation and identification of some hydrosoluble by-products resulting from the hydrolytic degradation of poly(alpha-hydroxyacid)s having biomedical interest: poly(L-lactide), poly(DL-lactide), poly-(glycolide) and poly(lactide-co-glycolide). Peak identification was performed by comparing the respective retention times with those of pure standards. It was observed that optimum shape and separation of peaks are considerably affected by the composition of the mobile phase, consisting of acetonitrile (A) and a 0.006 M K2HPO4 buffer (B), and, in particular, its pH and A:B ratio, which had to be adjusted to around 5.8 and 75:25 (v/v), respectively. Under the investigated experimental conditions (aqueous suspension, 100 degrees C for 12 h under stirring), poly(L-lactide) is quite stable, poly(glycolide) degrades easily to glycolic acid, whereas poly(DL-lactide) and poly(DL-lactide-co-glycolide) exhibit intermediate behaviour. Upon hydrolytic decomposition, these poly(alpha-hydroxyacid)s yield not only the corresponding acids, but also their linear dimers and, possibly, trimers, tetramers and higher oligomers.

Anticoagulant hydrogels derived from crosslinked dextran. Part I: Synthesis, characterization and antithrombic activity

Hydrogels have been prepared by binding various amino acids to Sephadex derivatives bearing carboxymethyl and sulphonated benzylamide groups. Depending on the chemical nature and content of the amino acid substituent, these insoluble strongly hydrophilic materials may absorb 7 to 19 volumes of buffer per volume of dry material. These hydrogels present antithrombic activity in relation to their swelling ratio. The adsorption of thrombin might partially explain the anticoagulant effect as shown by the evaluated affinity constants between the hydrogels and the enzyme i.e. 1 to 2 X 10(6) I/M.