Scanning electron microscopic study of the hydrolytic degradation of poly(glycolic acid) suture

Effect of segmental motion on hydrolytic degradation of polyglycolide in electro-spun fiber mats

Recently, environmentally degradable polymers have received great attention from the perspective of sustaining the aquatic environment. To control the degradation behavior of solid polymer materials in an aqueous phase, it is crucial to better understand the thermal molecular motion of polymer chains in water. We herein focus on polyglycolide (PGA), which is one of the representative aliphatic polyesters that are hydrolytically degradable. Three kinds of fiber mats of PGA with different fiber diameters and comparable crystallinities were prepared using an electrospinning method. Our choice of fiber mats was because the ratio of the surface area, where the hydrolytic degradation starts to occur, to the volume was larger than that for the films. Dynamic mechanical analysis (DMA) enabled us to gain direct access to the dynamic glass transition temperature (Tgα) of PGA in the fiber mats both in dry gaseous nitrogen and liquid water. The Tgα value varied not only with the presence of water molecules, but also with the fiber diameter, or the specific surface area. The degradation behavior of PGA fiber mats was examined by immersing the samples in phosphate-buffered saline at various temperatures. When the segmental motion of PGA in the fiber mats was released, the apparent crystallinity of the mats increased, meaning that PGA amorphous chains were cleaved and thus partially eluted into the aqueous phase. It was also shown that partially cleaved chains crystallized.

Adjustable degradation properties and biocompatibility of amorphous and functional poly(ester-acrylate)-based materials

Tuning the properties of materials toward a special application is crucial in the area of tissue engineering. The design of materials with predetermined degradation rates and controlled release of degradation products is therefore vital. Providing a material with various functional groups is one of the best ways to address this issue because alterations and modifications of the polymer backbone can be performed easily. Two different 2-methylene-1,3-dioxepane/glycidyl methacrylate-based (MDO/GMA) copolymers were synthesized with different feed ratios and immersed into a phosphate buffer solution at pH 7.4 and in deionized water at 37 °C for up to 133 days. After different time intervals, the molecular weight changes, mass loss, pH, and degradation products were determined. By increasing the amount of GMA functional groups in the material, the degradation rate and the amount of acidic degradation products released from the material were decreased. As a result, the composition of the copolymers greatly affected the degradation rate. A rapid release of acidic degradation products during the degradation process could be an important issue for biomedical applications because it might affect the biocompatibility of the material. The cytotoxicity of the materials was evaluated using a MTT assay. These tests indicated that none of the materials demonstrated any obvious cytotoxicity, and the materials could therefore be considered biocompatible.

Distinctive degradation behaviors of electrospun polyglycolide, poly(DL-lactide-co-glycolide), and poly(L-lactide-co-epsilon-caprolactone) nanofibers cultured with/without porcine smooth muscle cells

Biodegradable nanofibers have become a popular candidate for tissue engineering scaffolds because of their biomimetic structure that physically resembles the extracellular matrix. For certain tissue regeneration applications, prolonged in vitro culture time for cellular reorganization and tissue remodeling may be required. Therefore, extensive understanding of cellular effects on scaffold degradation is needed. There are only few studies on the degradation of nanofibers, and also the studies on degradation throughout cell culture are rare. In this study, polyglycolide (PGA), poly(DL-lactide-co-glycolide) (PLGA) and poly(L-lactide-co-epsilon-caprolactone) [P(LLA-CL)] were electrospun into nanofibrous meshes. The nanofibers were cultured with porcine smooth muscle cells for up to 3 months to evaluate their degradation behavior and cellular response. The results showed that the degradation rates are in the order of PGA >> PLGA > P(LLA-CL). PGA nanofibers degraded in 3 weeks and supported cell growth only in the first few days. PLGA nanofiber scaffolds facilitated cell growth during the first 30 days after seeding, but cell growth was slow thereafter. P(LLA-CL) nanofibers facilitated long-term (1-3 months) cell growth. mRNA quantification using real-time polymerase chain reaction revealed that some smooth muscle cell markers (alpha-actinin and calponin) and extracellular matrix genes (collagen and integrin) seemed to be downregulated with increased cell culture time. Cell culture significantly increased the degradation rate of PGA nanofibers, whereas the effect on PLGA and P(LLA-CL) nanofibers was limited. We found that the molecular weight of P(LLA-CL) and PLGA nanofibers decreased linearly for up to 100 days. Half lives of PLGA and P(LLA-CL) nanofibers were shown to be 80 and 110 days, respectively. In summary, this is the first study to our knowledge to evaluate long-term polymeric nanofiber degradation in vitro with cell culture. Cell culture accelerated the nanofibrous scaffold degradation to a limited extent. P(LLA-CL) nanofibers could be a good choice as scaffolds for long-term smooth muscle cell culture.

Degradation behaviors of electrospun resorbable polyester nanofibers

Biodegradable materials are widely used in the biomedical field because there is no postoperative surgery after implantation. Widely used synthetic biodegradable materials are polyesters, especially those used in tissue engineering. Advances in the tissue engineering field have brought much attention in terms of scaffold fabrication, such as with biodegradable polyester nanofibers. The rationale for using nanofibers for tissue engineering is that the nonwoven polymeric meshwork is a close representation of the nanoscale protein fiber meshwork in native extracellular matrix (ECM). Electrospinning technique is a promising way to fabricate controllable continuous nanofiber scaffold mimicking the ECM structure. Electrospun nanofibers provide high surface-to-volume ratio and high porosity as a promising scaffold for tissue engineering. Because the degradation behaviors of scaffolds significantly affect new tissue regeneration, the degradation of the material becomes one of the crucial factors when considering using polyester nanofibers as scaffolds in tissue engineering. In this review paper, we focus on the degradation studies of several bioresorbable polyester nanofibrous scaffolds used in tissue engineering. The degradable properties of nanofibers were compared with the corresponding degradable materials in macroscale. The factors that might affect the degradation behaviors were analyzed.

Holmium-loaded PLLA nanoparticles for intratumoral radiotherapy via the TMT technique: preparation, characterization, and stability evaluation after neutron irradiation

This article describes the preparation of biocompatible radioactive holmium-loaded particles with appropriate nanoscale size for radionuclide intratumoral administration by the targeted multitherapy (TMT) technique. For this objective, holmium acetylacetonate has been encapsulated in poly-L-lactide (PLLA)-based nanoparticles (NP) by oil-in-water emulsion-solvent evaporation method. NP sizes ranged between 100 and 1,100 m being suitable for the TMT administration method. Elemental holmium loading was found to be around 18% wt/wt and the holmium acetylacetonate trihydrate (HoAcAc) encapsulation efficacy was about 90%. Different experiments demonstrated an amorphous state of HoAcAc after incorporation in NPs. The NPs were irradiated in a nuclear reactor with a neutron flux of 1.1 x 10(13) n/cm(2)/s for 1 h, which yielded a specific activity of about 27.4 GBq/g of NPs being sufficient for our desired application. Microscopic analysis of irradiated NPs showed some alteration after neutron irradiation as some NPs looked partially coagglomerated and a few pores appeared at their surface because of the locally released heat in the irradiation vials. Furthermore, differential scanning calorimetry (DSC) results indicated a clear decrease in PLLA melting point and melting enthalpy reflecting a decrease in polymer crystallinity. This was accompanied by a clear decrease in polymer molecular weights, which can be ascribed to a radiation-induced chain scission mechanism. However, interestingly, other experiments confirmed the chemical identity retention of both HoAcAc and PLLA in irradiated NPs despite this detected decrease in the polymer crystallinity and molecular weight. Although neutron irradiation has induced some NPs damage, these NPs kept out their overall chemical composition, and their size distribution remained suitable for the TMT administration technique. Coupled with the TMT technique, these NPs may represent a novel potential radiopharmaceutical agent for intratumoral radiotherapy.

Electrospun matrices made of poly(α-hydroxy acids) for medical use

Biomaterials are widely used in diverse applications as substances, materials or important elements of biomedical devices. Biodegradable polymers, both natural and synthetic, have been utilized in applications in which they act as temporary substitutes. Poly(α-hydroxy acids), especially lactic acids and glycolic acid and their copolymers with ε-caprolactone, are the most widely known and used among all biodegradable polymers. They degrade in vivo into safe end products mainly by hydrolysis in a few weeks to several months, depending on several factors, including molecular structure/morphology, average molecular weight, size and shape. They are processed into tailor-made materials for diverse applications, although mainly for soft and hard tissue repair. Electrospinning is a method of producing nanofibers and nonwoven matrices from their solutions and melts. Several factors affect fiber diameter and resulting nonwoven structures/morphologies. Recently, electrospun matrices made of lactic acids, glycolic acid and ε-caprolactone homo- and co-polymers have been attracting increasing attention for fabrication of novel materials for medical use. This review briefly describes poly(α-hydroxy acids) and the elecrospinning process, and gives some selected recent applications of electrospun matrices made from these polymers.

Mathematical modeling and simulation of drug release from microspheres: Implications to drug delivery systems

This article aims to provide a comprehensive review of existing mathematical models and simulations of drug release from polymeric microspheres and of drug transport in adjacent tissues. In drug delivery systems, mathematical modeling plays an important role in elucidating the important drug release mechanisms, thus facilitating the development of new pharmaceutical products by a systematic, rather than trial-and-error, approach. The mathematical models correspond to the known release mechanisms, which are classified as diffusion-, swelling-, and erosion-controlled systems. Various practical applications of these models which explain experimental data are illustrated. The effect of gamma-irradiation sterilization on drug release mechanism from erosion-controlled systems will be discussed. The application of existing models to nanoscale drug delivery systems specifically for hydrophobic and hydrophilic molecules is evaluated. The current development of drug transport modeling in tissues utilizing computational fluid dynamics (CFD) will also be described.

Sterilization of gentamicin containing collagen/PLGA microparticle composites

In order to achieve implants which provide sustained release of gentamicin, microparticles based on a 50/50 Resomer 503/Resomer 502H blend were combined with collagen in order to achieve their fixation and to utilize the favorable effect of collagen on wound healing. Ethylene oxide treatment as well as beta- and gamma-irradiation were tested for sterilization of the collagen/PLGA-microparticle composite. All methods resulted in a decrease of molecular weight and glass transition temperature of polymer raw material and microparticles. In addition, ethylene oxide treatment yielded aggregation of microparticles leading to a substantial increase in the initially liberated gentamicin dose. Furthermore, chemical changes of gentamicin after ethylene oxide sterilization could be identified using NMR spectroscopy. Despite a decrease in the molecular weight and glass transition temperature after irradiation, neither morphological changes of the composites nor changes regarding the gentamicin release profile from beta- and gamma-sterilized material were observed. Free radicals, which could only be detected in gentamicin drug substance and at marginal level in gentamicin-loaded MPs, disappeared within 4 weeks. Additional microbiological testing verified the microbiological activity of gentamicin liberated from beta-sterilized composites. Storage of beta-sterilized composite at 4 degrees C/35% r.h. for 3 months did not influence morphology, molecular weight, glass transition temperature, and release profiles of microparticles and composites. However, at 25 degrees C/60% r.h. and 40 degrees C/75% r.h. a marked decrease in molecular weight and glass transition temperature resulted. This effect was due to a higher humidity, water uptake into polymers, and subsequent hydrolysis of polymers and microparticles, which was more pronounced for RG 502H because of its hydrophilicity. Upon storage at 25 degrees C/60% r.h. and 40 degrees C/75% r.h. particles collapsed resulting in an increased gentamicin liberation. Thus, all sterilization techniques have their pros and cons, but based on drug release profile and chemical changes of gentamicin irradiation treatment appears to be more suitable for collagen/gentamicin-loaded PLGA microparticle composites.

Effect of load and temperature on in vitro degradation of poly(glycolide-co-l-lactide) multifilament braids

The effects of load and temperature on in vitro degradation behaviors of poly(glycolide-co-L-lactide) 90/10 multifilament braids were investigated in phosphate buffer solution at pH 7.4. The property changes of the braids with time were monitored by tensile test, gel permeation chromatography analysis, and scanning electron microscopy. The interrelationships between material properties, time and experimental conditions were explored. The results showed that the polymer braids gradually lost their strength and molecular weight with the increasing in vitro time. While the load levels applied had no effect on the materials, raising temperatures significantly accelerated the degradation. It was found that for a given tensile breaking strength retention (BSR), the dependence of degradation time on temperature could be illustrated by an Arrhenius-type equation, from which the activation energy could be derived. Further analysis indicated that there are well-defined relationships between molecular weight, BSR and breaking strain retention, and these relationships can be illustrated mathematically. Finally, the surface morphology of the fiber showed visible change during the degradation process.

Fixation with poly-L-lactic acid screws in hip osteotomy: 68 hips followed for 18-46 months

This study evaluated 68 consecutive hip osteotomies in 61 patients using absorbable poly-L-lactic acid screws for fixation. 47 hips underwent a rotational acetabular osteotomy, 17 hips Chiari's pelvic osteotomy, and 4 hips transtrochanteric rotational osteotomy. Cortical screws were used to transfix the osteotomized acetabulum, and cancellous screws to reattach the intraoperatively osteotomized greater trochanter. The average age at surgery was 35 (12-49) years. The mean duration of follow-up was 32 (18-46) months. All the osteotomized acetabulums united well, but 4 of 54 trochanteric osteotomies failed to unite.

Biodegradable implants in sports medicine: the biological base

Biodegradable implants are increasingly used in the field of operative sports medicine. Today, a tremendous variety of implants such as interference screws, staples, sutures, tacks, suture anchors, and devices for meniscal repair are available. These implants consist of different biodegradable polymers that have substantially different raw material characteristics such as in vivo degradation, host-tissue response, and osseous replacement. Because these devices have become the standard implant for several operative procedures, it is essential to understand their biological base. The purpose of this report is to provide a comprehensive insight into biodegradable implant biology for a better understanding of the advantages and risks associated with using these implants in the field of operative sports medicine. In particular, in vivo degradation, biocompatibility, and the osseous replacement of the implants are discussed. A standardized classification system to document and treat possible adverse tissue reactions is given, with special regard to extra-articular and intra-articular soft-tissue response and to osteolytic lesions.

The role of superoxide ions in the degradation of synthetic absorbable sutures

The objective of this study was to examine the effect of superoxide ion-induced degradation on synthetic absorbable biomaterials. Synthetic absorbable sutures were used as the model compounds. Inflammatory cells, particularly leukocytes and macrophages, are able to produce highly reactive oxygen species, such as superoxide (. O(2)(-)), during inflammatory reactions to foreign materials. Superoxide ions may act as oxygen nucleophile agents to attack biomaterials. In this study, the changes in tensile breaking force, thermal properties, and the surface morphology of five commercial (2/0 in size) synthetic absorbable sutures (Dexon, Vicryl, PDS II, Maxon, and Monocryl) as a function of superoxide ion concentration at 25 degrees C for 24 h were studied. Among the five absorbable sutures and over the concentration range of this study, the monofilament Monocryl suture was the most sensitive toward superoxide ion-induced degradation, followed by Maxon, Vicryl, Dexon, and PDS II sutures. The amount of tensile breaking force loss over a 24 h period ranged from as low as 3% to as high as 80%, depending on the type of absorbable sutures, the reaction time, and the superoxide ion concentration. All five absorbable sutures showed significant reductions in both the T(m) and T(g). Unlike the surface morphological changes of absorbable sutures in conventional buffer solutions, the effect of superoxide ion-induced degradation on the surface morphologies of these five absorbable sutures was unique, particularly the moon-crater-shaped impressions of various sizes and depths found in Monocryl and Maxon sutures, which defied the anisotropic characteristics of fibers.

Gamma irradiation for terminal sterilization of 17beta-estradiol loaded poly-(D,L-lactide-co-glycolide) microparticles

17beta-Estradiol-loaded microparticles using poly-(D, L-lactide-co-glycolide) polymer (PLG) were prepared by a modified spray-drying method and the effects of gamma-irradiation on drug substance, polymer and microparticles were investigated. Irradiation doses ranging from 5.1 to 26.6 kGy were applied using a 60Co-radiation source. 17beta-Estradiol drug substance showed excellent stability against gamma-irradiation in the investigated dose range, whereas microencapsulated estradiol seems to be converted to conjugation products with PLG, and to a lesser extent to the degradation product 9,11-dehydroestradiol. The weight-average molecular weight of the PLG polymers decreased with increasing irradiation dose while polydispersity indices (M(w)/M(n)) remained nearly unchanged, compatible with a random chain scission mechanism in lactide/glycolide-copolymer degradation. In vitro drug release studies showed accelerated kinetics with increasing irradiation doses due to dose dependent polymer degradation. Microbiological process monitoring showed decreasing bioburden with increasing spraying time, which was successfully further reduced by applying irradiation sterilization. Microencapsulated test spore suspensions of Bacillus pumilus ATCC 27142, the official test specimen for the gamma-sterilization process, revealed effective reduction of bioburden, confirming its published D(10) value. In conclusion, our studies demonstrated efficacy of gamma-irradiation as terminal sterilization method for poly-(D,L-lactide-co-glycolide) polymer-based drug delivery systems. The sterilization conditions need to be carefully adjusted for the final dosage form.

Tetracycline-HCl-loaded poly(DL-lactide-co-glycolide) microspheres prepared by a spray drying technique: influence of gamma-irradiation on radical formation and polymer degradation

Tetracycline-HCl (TCH)-loaded microspheres were prepared from poly(lactide-co-glycolide) (PLGA) by spray drying. The drug was incorporated in the polymer matrix either in solid state or as w/o emulsion. The spin probe 4-hydroxy-2,2,6, 6-tetramethyl-piperidine-1-oxyl (TEMPOL) and the spin trap tert-butyl-phenyl-nitrone (PBN) were co-encapsulated into the TCH-loaded and placebo particles. We investigated the effects of gamma-irradiation on the formation of free radicals in polymer and drug and the mechanism of chain scission after sterilization. Gamma-Irradiation was performed at 26.9 and 54.9 kGy using a 60Co source. The microspheres were characterized especially with respect to the formation of radicals and in vitro polymer degradation. Electron paramagnetic resonance (EPR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), gas chromatography-mass spectroscopy (GC-MS), and scanning electron microscopy (SEM) were used for characterization of the microspheres. Using EPR spectroscopy, we successfully detected gamma-irradiation induced free radicals within the TCH-loaded microspheres, while unloaded PLGA did not contain radicals under the same conditions. The relatively low glass transition temperature of the poly(dl-lactide-co-glycolide) (37-39 degrees C) seems to favor subsequent reactions of free radicals due to the high mobility of the polymeric chains. Because of the high melting point of TCH (214 degrees C), the radicals can only be stabilized in drug loaded microspheres. In order to determine the mechanism of polymer degradation after exposure to gamma-rays, the spin trap PBN and the spin probe TEMPOL were encapsulated in the microspheres. gamma-Irradiation of microspheres containing PBN resulted in the formation of a lipophilic spin adduct, indicating that a polymeric radical was generated by random chain scission. Polymer degradation by an unzipping mechanism would have produced hydrophilic spin adducts of PBN and monomeric radicals of lactic or glycolic acid. These degradation products were not detected by EPR. This result is confirmed by the observation that possible diamagnetic reaction products of low molecular weight, consisting of TEMPOL and lactide or glycolide monomers, could not be detected by GC-MS. While an irradiation dose-dependent decrease in molecular weight of PLGA could be verified in agreement with the literature, TCH content of the microspheres was not affected by the exposure to gamma-rays. It can be concluded that EPR spectroscopy in combination with GPC, DSC, and HPLC allows a detailed characterization of the impact of gamma-sterilization on biodegradable parenteral drug delivery systems.

Plasma surface modification of synthetic absorbable sutures

The aim of the study was to examine the feasibility of using plasma surface modification technology to alter the hydrolytic degradation rate of commercial synthetic absorbable sutures. Size 2-0 Dexon, Vicryl, PDSII, and Maxon sutures were tested. They were treated by two different surface modification techniques: parylene deposition and plasma gases (Methane, trimethylsilane, and tetrafluoroethene). The thickness of surface treatment ranged from 200 to 1000 A. The treated sutures were subject to in vitro hydrolytic degradation in phosphate buffer of pH = 7.4 at 37 degrees C for up to 120 days. The tensile breaking strength, weight loss, surface wettability, bending stiffness, and surface morphology were evaluated. The results indicated that the concept of plasma surface treatment for altering the hydrolytic degradation of synthetic absorbable sutures was feasible, and the level of improvement depended on the type of sutures, the treatment conditions, and the duration of hydrolysis. Vicryl and PDSII sutures showed overall the best improvement in tensile strength retention among the four commercial sutures. Dexon and Maxon sutures, however, exhibited only marginal improvement. The observed improvement in tensile strength retention appeared to be related to the increasing hydrophobicity of the sutures. The surface treatments did not adversely affect the bending stiffness of the sutures and no visible surface morphological changes were observed. Refinements and optimization of the surface treatment conditions are needed for achieving the maximum advantage of the proposed concept, particularly shielding the harmful effect of uv during plasma treatment.

Biodegradable osteosynthesis material for stabilization of midface fractures: experimental investigation in sheep

The most frequently tested biodegradable osteosynthesis materials have up to now largely consisted of poly-L-lactide (PLLA). The PLLA polymers appear to have sufficient mechanical strength for fracture treatment in the midface, but their degradation does not seem to be uniform enough to allow their clinical use. During the degradation process the disintegration products elicit a foreign body reaction due to non-uniform degradation rates. The foreign body reaction is sometimes combined with a fluctuant swelling at the implantation site. Implants injection-moulded from 90:10 PLLA/PGA (polyglycolic acid) have a more uniform degradation rate and seem to lead to a milder foreign body reaction. We bridged Le Fort I osteotomies in sheep using a system of injection-moulded PLLA/PGA 90:10 plates and screws and compared it with 2 mm AO miniplates and mini-screws made from titanium. Light microscopy evaluation showed that the PLLA/PGA copolymer system experienced its highest mechanical stress at the transition from screw head to screw shaft. Nevertheless, the fragments fixed with the copolymers were on the whole only slightly less stable than those fixed with the titanium system. The foreign body reaction solely due to co-polymer degradation was not severe, considering the fibrous tissue response that was found associated with the titanium components. The study does show that the copolymer investigated is adequate for clinical use as a biodegradable osteosynthesis material, at least in low stress bearing areas.

Effect of in vivo and in vitro degradation on molecular and mechanical properties of various low-molecular-weight polylactides

The in vivo and in vitro degradation of low-molecular-weight poly(L-lactide), poly(L/D-lactide), and poly (L/DL-lactide) rods was investigated. The low-molecular-weight fast-degrading materials were used to accelerate the degradation process and make the test conditions more critical. In the in vivo study the rods were implanted in the soft tissue of sheep and explanted at 1, 3, 6, and 12 months. In the in vitro experiments the samples were subjected to aging at 37 degrees C in the phosphate buffer using two different modes. In the so-called pseudodynamic mode the aging buffer was regularly replaced if the pH dropped more than 0.5. In the static mode the buffer was not changed over the whole testing period of 52 weeks. The mechanical, molecular, and crystalline properties of the rods were measured and their appearance in the course of aging was evaluated using scanning electron microscopy. It was found that the changes in the mechanical properties of poly(L-lactide), poly(L/D-lactide), and poly(L/DL-lactide) samples subjected to in vitro degradation tests in both the static and pseudodynamic modes are in good approximation with data obtained from the in vivo study. The pH of the buffer solution had no evident effect on the mechanical properties or the rate of degradation as estimated from the drop in molecular weight of the aged samples. The replacement of the aging buffer to maintain a constant pH at 7.4 does not seem to be critical for the degradation of the polylactides. In vitro degradation tests can be used as a relevant procedure for predicting the in vivo functionality of implants from the polylactides used if the criteria for assessing such a functionality are the changes in mechanical properties and molecular weight.

Strength retention of self-reinforced polyglycolide membrane: an experimental study

Self-reinforced polyglycolide (SR-PGA) devices are stronger than non-reinforced ones. To study the strength retention of SR-PGA membrane, in vitro and in vivo, membranes were either immersed in distilled water at 37 degrees C, or implanted in the subcutis or around the femoral bone of rats. The SR-PGA membranes lost their strength in vitro by 6 wk, while they retained it for 15 wk in vivo due to the fibrous tissue that formed around and inside the implant (biomembrane). This is an advantage when clinical application of the membrane is being considered.

Prolongation of epidural anesthesia in the rabbit with the use of a biodegradable copolymer paste containing lidocaine

Prolongation of the drug effect using a drug-delivery system has recently been introduced in local anesthesia. In this study, we investigated the prolonging effect of an epidurally injected biodegradable copolymer paste containing 10% lidocaine (Lid-CoPol). Twenty-nine rabbits were studied. A catheter was placed in the epidural space at the level of L6-7 in each animal. A solution of 10% lidocaine (Group I, n = 12), or a copolymer containing 10% lidocaine (Lid-CoPol), (Group II, n = 12) or copolymer paste only (Group III, n = 5) was injected epidurally at a dose of 0.15 mL/kg. The effect of each drug was assessed by evaluation of response to pain stimulation and of the degree of motor block produced. The plasma lidocaine concentration was also measured consecutively in five animals of both Groups I and II. The duration of sensory and motor block of Lid-CoPol was 800% and 975% longer, respectively, than that of plain lidocaine solution. Plasma lidocaine concentration reached a maximum 5 min after injection (5.5 +/- 0.5 micrograms/mL) in Group I. In Group II, the level reached a maximum 30 min after injection (3.7 +/- 1.5 micrograms/mL). The findings are attributed in part to the slow release of lidocaine from the biodegradable copolymer paste, which is suggested as a new drug-delivery system for local anesthetics.

Effect of a combined gamma irradiation and Parylene plasma treatment on the hydrolytic degradation of synthetic biodegradable sutures

The aim of this study was to alter the hydrolytic degradation property of synthetic absorbable suture fibers so that their mass loss would occur at a shorter time without significantly compromising their tensile strength loss profile. A two-step treatment concept (gamma-irradiation followed by Parylene plasma deposition) was introduced for achieving this aim. Vicryl and Maxon were used as the model compounds to test this new concept. After the treatment, the in vitro hydrolytic degradation properties of Vicryl and Maxon were evaluated by weight loss, tensile breaking strength, heat of fusion and melting temperature, intrinsic viscosity, surface wettability, and surface morphology. The results suggested that gamma-irradiation at a dosage level between 0.2-2.0 Mrad for Vicryl sutures and about 2.0 Mrad for Maxon sutures were the most effective dosages to accelerate the suture mass loss. The subsequent Parylene plasma deposition treatment statistically significantly improved the retention of tensile strength for both gamma-irradiated Vicryl and Maxon sutures and hence counteracted the undesirable gamma-irradiation induced acceleration of tensile strength loss. However, this second-step Parylene plasma treatment extended the suture mass loss to longer periods. These findings were consistent with the observed surface wettability, surface morphology, intrinsic viscosity, and thermal properties. A thin hydrophobic Parylene skin layer wrapped around a suture was responsible for the slower rate in mass and strength loss. This outer skin layer acted as a barrier to not only water but also degradation fragments.