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Biodegradable polymer hydrogel networks based on hydrophilic dextran derivative of allyl isocyanate (dex-AI) and hydrophobic poly (D,L) lactide diacrylate macromer (PDLLAM) were synthesized, and their swelling and morphological properties were studied. During a 2-day incubation, the higher the PDLLAM composition in the hydrogel, the slower the swelling as well as the lower the extent of swelling were. A 3D porous network structure was observed by scanning electron microscope. The rate of formation of this 3D porous network structure depended on the hydrophilicity of the components, their composition ratio, and the degradation time. The highly hydrophilic dex-AI component facilitated the formation of this 3D porous network structure at an earlier immersion period, while the degradability of the PDLLAM component would make this 3D porous network structure more open at a later immersion period. Indomethacin, a low molecular weight and moderately hydrophobic drug, was incorporated into the hydrogels for the release study in pH 7.4 phosphate buffer solution at 37 degrees C. The release kinetics suggested, as the PDLLAM composition increased, the indomethacin diffusion coefficient (D) and release half life time (t(1/2)) decreased, while the release index n increased. The controlled release mechanism was determined by the combination of three factors: the rate and degree of formation of swelling-induced 3D porous structure in the hydrogel, the hydrolytic degradation of PDLLAM components, and the hydrophobic interaction between PDLLAM and IDM., (Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 59: 318-328, 2002)

The objective of this paper was to study the release of bovine serum albumin (BSA) from a series of biodegradable hydrogels having a wide range of hydrophilicity to hydrophobicity, swelling, and biodegradation properties. BSA was incorporated into a series of biodegradable hydrogels made from a dextran derivative of allyl isocyanate (dex-AI, as the hydrophilic constituent) and poly(DL-lactic acid) diacrylate macromer (PDLLAM, as the hydrophobic constituent). The release kinetics of BSA from these dex-AI/PDLLAM hydrogels was studied. Laser confocal scanning microscopy was used to investigate the morphological change of the hydrogels, as well as BSA distribution in the hydrogels, as a function of dex-AI to PDLLAM composition ratio and incubation time. We found that the incorporation of PDLLAM into dex-AI reduced the initial burst release of BSA due to its more homogeneous distribution in the hydrogels. As the PDLLAM component increased, the rate of formation of a loose three-dimensional (3D) network structure increased; consequently, the sustained rate and extent of BSA release increased. Both release index and diffusion coefficient (from release kinetics data) increased as the PDLLAM component increased in the hydrogels. The data suggest that the release of BSA was controlled by both diffusion of BSA through swelling of the hydrophilic phase during an early stage, and degradation of the hydrophobic phase during a late stage, and also that the magnitude of diffusion versus degradation controlled release is dependent on composition ratio and immersion time., (Copyright 2000 John Wiley & Sons, Inc.)

The objectives of this study were to develop a simple and reproducible method for the preparation of the hydrogel precursor dextran-methacrylate and to conduct a visual observation of the interior structure of the swollen dextran-methacrylate hydrogel with minimum artifacts. A dextran-methacrylate hydrogel precursor was synthesized by reacting dextran with methacrylic anhydride in the presence of triethylamine as a catalyst. The effects of reaction time, temperature, concentration, and catalyst amount were studied to obtain a wide range of degree of substitution (DS) in dextran by methacrylate. The dextran-methacrylate synthesized showed an enhanced solubility in water and common organic solvents. UV irradiation of dextran-methacrylate by a long-wave UV lamp (365 nm) generated a photocrosslinked hydrogel. This dextran-methacrylate hydrogel showed a range of swelling ratio from 67 to 227% and exhibited an increase in swelling ratio with a decrease in methacrylate substitution. The pH of the swelling media did not affect the swelling behavior of the dextran-methacrylate hydrogels at all the degrees of substitution used. Special cryofixation and cryofracturing techniques were used to prepare aqueous swollen dextran-methacrylate hydrogel samples for SEM observation of their surface and interior structures. A unique three-dimensional porous structure was observed in the swollen hydrogel but was absent in the unswollen hydrogel. Different pore sizes and morphologies between the surface and the interior of swollen hydrogels also were observed., (Copyright 2000 John Wiley & Sons, Inc.)

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., (Copyright 2000 John Wiley & Sons, Inc.)

The objectives of this study were to visually examine the surface and interior morphology of a new class of biodegradable hydrogels based on dextran-methacrylate and to quantify the porous structure of these hydrogels in swollen state. Two techniques (scanning electron microscopy and mercury intrusion porosimetry) were used to analyze pore structure of dextran-methacrylate hydrogels as a function of the degree of methacrylate substitution. SEM was used to observe 3-dimensional network structure of cryofixed and fractured swollen dextran-methacrylate hydrogels. Image analysis of the SEM data revealed different pore shapes and sizes, depending on the degree of substitution and the location within the hydrogel. A higher methacrylate-substituted dextran hydrogel showed a compact and rigid pore structure, while a lower substituted hydrogel showed a delicate and fragile pore structure. Mercury intrusion porosimetry analysis of the pore structure of dextran-methacrylate hydrogels provided useful and more reliable quantitative data of pore characteristics, such as total pore area, average pore diameter, their distribution, and bulk density. The total pore area and average pore diameter of swollen dextran-methacrylate hydrogels decreased with an increase in degree of methacrylate substitution, while bulk density increased with an increase in degree of substitution., (Copyright 2000 John Wiley & Sons, Inc.)

A new class of hydrogel precursor, dextran-maleic acid (Dex-MA), was synthesized by the reaction of dextran with maleic anhydride in the presence of the catalyst triethylamine. The effects of temperature, time, catalyst amount, and reactant concentration on the degree of substitution (DS) by MA was studied to establish an optimum reaction condition. The new hydrogel precursor had excellent solubility in various common organic solvents. The hydrogels based on Dex-MA precursor were made by the irradiation of Dex-MA with a long wave UV lamp. The Dex-MA hydrogels showed a very high swelling ratio in water, and the magnitude of swelling depended on the pH of the medium and the DS by MA. The Dex-MA hydrogels exhibited the highest swelling ratio in neutral pH, followed by acidic (pH 3) and alkaline pH (10). The most distinctive characteristic of Dex-MA hydrogels was that a carboxylic acid group was generated by the reaction of dextran with maleic anhydride. As a result, the swelling ratio increased with an increase of the DS of the MA segment (ionizable moiety that affects swelling ratio) in the Dex-MA hydrogel.

In this study, a new visual characterization method was developed using laser scanning confocal microscopy (LSCM) to study morphologic properties, particularly at the fiber-matrix interface, by optical sectioning of bioabsorbable single-fiber composites. The interface gap width (IGW) between the fiber and matrix, and the changes in IGW after in vitro hydrolysis, named the gap rate (Rg), were measured from images obtained using the LSCM. Higher values for IGW and Rg showed faster degradation of the fiber-matrix interface. These parameters were used to investigate the effects of strain, wicking, different reinforcing fibers, and gamma-irradiation on the fiber-matrix interface morphology. The component materials used were nonbioabsorbable AS4 carbon (C) fibers, bioabsorbable calcium phosphate (CaP), poly(glycolic acid) (PGA), and chitin fibers, and bioabsorbable poly(L-lactic acid) (PLLA) matrix. The application of strain on CaP/PLLA composites increased the IGW up to about 15%, after which there was no change up to 25%. The Rg for CaP/PLLA composites with the fiber ends exposed in vitro (permitting wicking) was greater than for CaP/PLLA with the fiber ends embedded completely within the matrix (preventing wicking). Open-end C/PLLA composites had the slowest rate of interface degradation in vitro, followed by chitin/PLLA, PGA/PLLA, and CaP/PLLA. The exposure of closed-end CaP/PLLA composites to 4 Mrad of gamma-irradiation, in air at room temperature or in vaccuum at 77K, accelerated the rate of interface degradation in vitro. In conclusion, an effective new visual characterization method was developed using LSCM, and it was used to show that (a) moderate strain could accelerate the degradation of the interface, (b) fiber-matrix interface wicking could accelerate the rate of degradation of the interface, (c) the rate of interface degradation depends on the type of fiber used, and (d) gamma-irradiation could accelerate the rate of interface degradation. Furthermore, the results of LSCM analysis of different reinforcing fibers with a PLLA matrix agree with measurements of interfacial shear strength (IFSS) and single-fiber tensile strength reported in Part I of this study.

The objective of this study was to characterize and evaluate the performance of various fiber-matrix composite systems by studying the mechanical, thermal, and physical properties of the fiber and matrix components, and by studying the fiber-matrix interface adhesion strength using both microbond and fragmentation methods. The composites studies were poly(L-lactic acid) (PLLA) matrix reinforced with continuous fibers of either nonabsorbable AS4 carbon (C), absorbable calcium phosphate (CaP), poly(glycolic acid) (PGA), or chitin. Carbon and CaP single fibers had high Young's moduli and failed in a brittle manner. PGA and chitin single fibers had relatively lower Young's moduli and relatively higher ductility. Upon in vitro hydrolysis, CaP fibers retained 17% of their tensile strength and 39% of their Young's modulus after 12 h, PCA fibers retained 10% of their tensile strength and 52% of their Young's modulus after 16 days, and chitin fibers retained 87% of their tensile strength and 130% of their Young's modulus after 25 days. PLLA films had much lower strength and Young's moduli, but much higher ductility relative to the single fibers. Using the microbond method, the initial fiber-matrix interfacial shear strength (IFSS) of C/PLLA and CaP/PLLA microcomposites was 33.9 and 12.6 MPa, respectively. Upon in vitro hydrolysis, C/PLLA retained 49% of IFSS after 15 days and CaP/PLLA retained 46% of IFSS after 6 h. Using a fiber fragmentation method, the initial IFSS of C/PLLA, CaP/PLLA, and chitin/ PLLA was 22.2, 15.6, and 28.3 MPa, respectively. The performance of carbon fibers and C/PLLA composites was superior to the other fibers and fiber/PLLA systems, but the carbon fiber was nonabsorbable. CaP had the most suitable modulus of the absorbable fibers for fixing cortical bone fracture, but its rapid deterioration of mechanical properties and loss of IFSS limits its use. PGA and chitin fibers had suitable mechanical properties and their retention for fixing cancellous bone fractures, but likely had insufficient stiffness for applications such as bone plates for fixing cortical bone fractures.

The purpose of this study was to derive new mathemtic formulae that could be used reliably to predict water permeability of surgical fabrics before they are made and tested for water permeability. Such a theoretical prediction of water permeability, Qprd, of surgical fabrics is needed for not only timely characterization but also for assisting in more efficient future design and development of better surgical fabrics. Two mathematic formulae, Qw and Qk, were derived from the Buckingham Pi Theorem, in which relevant fiber and fabric parameters were placed into dimensionless pi groups and computed for 25 commercial and experimental vascular fabrics. Linear regression analysis of the relationship between these pi groups with water permeability on the woven and knitted grafts yielded coefficients for the corresponding pi groups that were required for constructing appropriate mathematic formulae to predict water permeability of vascular fabrics. When proper sources of the experimentally determined water permeability, Qexp, were chosen for comparison, we found that 86% of woven fabrics (6 of 7) and 77% of knitted fabrics (14 of 18) had their Qprd within 10% of their Qexp. This high percentage of close matching (within 10%) between Qprd and Qexp should be considered satisfactory because the experimental error for obtaining Qexp is generally higher than 10%. The difference between Qprd and Qexp ranged from as small as 0.27% to as high as 74.2%, depending on the type of fabrics and source of Qexp.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this work was threefold: to enhance the adhesion between the reinforced absorbable calcium phosphate (CaP) fibers and the absorbable polyglycolide acid (PGA) matrix, to improve the hydrolytic degradation of the CaP fibers, and preliminarily to evaluate the cytotoxicity of the plasma treated surface of CaP fibers. A CH4 plasma treatment was used to achieve these goals. The microbond method was used to evaluate the effects of the plasma treatment on the interfacial shear strength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system by 30%. AFM data showed that CH4-treated CaP fibers had considerable microscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and plasma-treated fibers were also subjected to in vitro hydrolytic degradation in a phosphate buffer solution of pH 7.44 at 37 degrees C for up to 15 h. CH4 plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms may reduce the capillary wicking phenomena of water through the CaP fiber/PGA matrix interface. The CaP fiber dissolution studies revealed that both CH4 and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was higher in an acidic than a physiologic pH environment. A preliminary cytotoxicity test revealed that both CH4 and Parylene plasma-treated CaP fibers were noncytotoxic. Additional research should be done to determine the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers.

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.

The objective of this study is to determine the effects of the location and concentration of synthetic absorbable yarn components in bicomponent vascular graft fabrics on their structure and properties in a controlled in vitro hydrolytic environment. Bicomponent vascular fabrics were made from Dacron and polyglycolic acid (PGA) yarns with a range of composition ratios of PGA to Dacron and a range of locations of PGA. Both woven and single jersey knit fabrics were made. These fabrics were characterized by standard textile methods and subject to in vitro hydrolytic degradation study. In vitro hydrolytic degradation study showed that the most dramatic changes in the bicomponent fabric characteristics and properties occurred 30 and 60 days of hydrolysis. This schedule coincided with the hydrolytic degradation rate of PGA absorbable sutures. In the woven (W) group, the incorporation of absorbable yarns in the weft direction (W3) of the bicomponent fabrics resulted in the velour-like, loose, and porous surface morphology of the fabric for potential subsequent tissue ingrowth, while those woven fabrics with absorbable yarns in the warp direction (W1) did not have this unique velour-like surface. In the knitted (K) group, the concentration of absorbable yarns appeared to be closely related to the observed changes in fabric properties and structure. The incorporation of absorbable yarns into knitted fabrics did not result in the same level change in fabric structure and property as woven fabrics. In both W and K groups, a minimal level of mechanical strength of the fabrics was maintained due to the remaining Dacron yarns. Structural integrity of these fabrics was retained at the end of hydrolytic degradation study. The data obtained could be used to correlate with the subsequent in vivo performance of these bicomponent vascular grafts. If correlations exist, they could be used to improve the design of future bicomponent vascular grafts for improved performance.

The in vitro hydrolytic degradation of 2-0 size PDS monofilament suture was studied for the purpose of revealing its morphologic structure and degradation mechanism. The sutures were immersed in phosphate buffer of pH 7.44 for up to 120 days at 37 degrees C. These hydrolyzed sutures were examined by the changes in tensile properties, weight, thermal properties, x-ray diffraction structure, surface morphology, and dye diffusion phenomena. It was found that hydrolysis had significant effects on the change of PDS fiber morphology and properties. Hydrolysis, however, had no significant effect on overall molecular orientation of the fiber until the very late stage. PDS suture fibers retained their skeleton throughout the earlier periods of hydrolysis concurrent with mass and tensile strength losses. PDS sutures exhibited an absorption delay of 120 days. Both heat of fusion and melting point exhibited a maximum function of hydrolysis time. Hydrolysis of PDS suture fibers proceeded through two stages: random scission of chain segments located in the amorphous regions of microfibrils and intermicrofibrillar space, followed by stepwise scission of chain segments located in the crystalline regions of microfibrils. Dye diffusion data showed that the passage along the longitudinal direction of the fiber was relatively easier than the lateral direction as evident in the diffusion coefficient, activation energy, and flexibility of chain segments. Swiss-cheese model of fiber structure appears to describe the observed dye diffusion phenomena and their dependence on hydrolysis time and dying temperature.

This article reports the morphological observations on the surface changes of poly-(glycolic acid) sutures which have been exposed to various dosages of gamma irradiation (0, 2.5, 5.0, 10, 20 and 40 Mrad) and duration of immersion (0, 7, 14, 28, 48, 60, and 90 days) in a physiological saline buffer. The most important gross morphological characteristics of PGA suture hydrolytic degradation is the formation of surface cracks on the filaments. The regularity of the surface cracks increased with an increase in the gamma irradiation and the duration of hydrolysis. Surface cracks were not observed in irradiated sutures that had not been subjected to hydrolytic degradation. The arrangement of the surface cracks, their orientation on the filaments, and the direction of crack propagation provide very useful information for depicting the mechanism of hydrolytic degradation in this class of fibrous material. The microfibrillar model of fiber structure has been used as the basis for the proposed degradation mechanism of PGA in vitro. It is believed that hydrolysis occurs initially in the amorphous regions sandwiched between two crystalline zones, as tie-chain segments, free chain ends, and chain folds in these regions degrade into fragments. As degradation proceeds, the size of the fragments reaches the stage at which they can be dissolved into the buffer medium. This dissolution removes the fragments from the amorphous regions, and surface cracks appeared.

The evaluation of the efficiency of polymer additives with special emphasis on uv absorbers and antioxidants in polyurethane elastomers has been completed. Aliphatic polyurethanes were chosen for this study because their properties closely relate to the requirements of maxillofacial prosthesis. The polyurethane elastomers were either synthesized by ourselves or formulated according to the manufacturer's recommendation. Eleven different types of uv absorbes, coupled with one antioxidant, were incorporated into the polyurethane systems. The Atlas twin-lamp carbon arc Weatherometer was used as the source of uv. The samples were periodically withdrawn for examination of yellowing and tackiness. It was found that, although the incorporation of uv stabilizers enhanced the uv resistance of polyurethanes, the problem of tackiness resulting from uv aging was not solved satisfactorily. The phenomenon of yellowing, however, was significantly improved, mainly due to the aliphatic structure of polyurethanes. The most promising uv absorbers are Tinuvin 770 and the combination of Tinuvin 328, ZnO, and an antioxidant. Their effectiveness in other polyurethane systems is not known and further research is underway to explore this field. Hopefully, these findings will greatly assist the successful application polyurethane elastomers in maxillofacial prosthesis.

The objective of this study is to use standard testing methods to characterize the currently available synthetic mesh fabrics in terms of their chemical, physical, mechanical, and morphologic properties. Three commonly used surgical mesh fabrics, Mersilene (Ethicon), Marlex (Davol), and Teflon (USCI), were used, and the tests reveal that they differ from one another chemically as well as configurationally. The experiment included an identification of the structure of the yarn and fabrics; a measurement of the porosity, pore size and shape; and a determination of tensile and bursting strength, flexural rigidity, and wrinkle recovery. A wide variation in structure and performance was observed among the three mesh fabrics. Mersilene mesh fabrics have the highest relative porosity, while Marlex and Teflon meshes have an equivalent, but lower value. Marlex meshes have the highest tensile and bursting strength followed by Teflon and Mersilene meshes. All three meshes have one common strength characteristic--a distinctive difference in tensile strength between the wale and course directions. Marlex mesh fabrics exhibit an immense flexural rigidity and poor wrinkle recovery, due mainly to the monofilament structure of the yarn. Mersilene and Teflon mesh fabrics have similar but considerably lower, flexural rigidity than Marlex. Thus, it is evident that the chemical nature of the constituent fibers, as well as the yarn and fabric structure, have a great effect on the performance of the resulting mesh fabrics. The availability of this characterization data can serve as the basis for a surgeon's selection of the most appropriate commercial surgical mesh fabric for each case, as well as to provide a foundation for the subsequent comparison of their in vivo performance.

The tensile strengths of poly(glycolic acid) (PGA) sutures immersed in buffered and unbuffered aqueous media were compared. The media used were an unbuffered physiological saline solution (pH = 5.0) and a phosphate-buffered physiological saline solution (pH = 7.4). PGA samples were immersed for various periods in each medium, and kept at 37 +/- 1 degree C in a constant temperature oven. The tensile strengths of the specimens were tested immediately after removal from the medium. Stress-strain curves of the specimens were expressed in terms of the stress unit "tenacity," commonly used in the study of fibrous polymers; it is an appropriate unit for materials of fibrous nature. These stress-strain curves were investigated as functions of buffering and duration of immersion. Degradation reduced the tensile strength of PGA more in the buffered saline solution than in the unbuffered. This higher rate of degradation in the buffered solution might be due to the presence of Na2HPO4, which removed the degradation products, shifted the reaction toward increased hydrolosis, and accelerated the loss of tensile strength in the PGA. A continuous decrease in the pH of the unbuffered solution supports this explanation. Tied-chain segments of macromolecules, a theory widely used in the study of mechanical strength of fibrous polymer may be the key to a comprehensive description of the degradation phenomenon of PGA.

The effect of selected UV stabilizers on the stability of mechanical properties of a polyurethane material, Calthane ND2300, was evaluated. The addition of UV stabilizers prolonged the service life of the systems studied but did not achieve completely satisfactory results. The tensile strength and modulus of elasticity decreased after extended exposure to UV. The rate of decrease, however, was much less for the specimens with UV stabilizers. The polyurethane system that contains a mixture of a UV stabilizer and an antioxidant is considered to be the best of the groups tested, in terms of the percentage of retention of tensile strength and modulus of elasticity. It was also found that elongation at break was increased when the duration of UV aging was increased. This phenomenon occurred in all the systems, with or without UV stabilizers, and can be understood in terms of the concepts of the fragmentation of macromolecules that resulted from UV aging. The physical appearance in conjunction with mechanical property tests are needed to ensure the successful performance of any UV stabilizer.

The purpose of this research was to examine the effect of annealing treatments on the mechanical properties of polyglycolic acid sutures, and their subsequent influence on PGA degradation properties. An attempt was made to develop a better understanding of the degradation mechanism of synthetic absorbable sutures, including the relationship of their structure, morphology, and mechanical properties. PGA sutures were annealed under selected axial strain (freely hung, 0%, 1%, 10%), at four temperatures (150 degrees C, 170 degrees C, 180 degrees C, 190 degrees C), and two times (5 and 20 min). The annealed PGA specimens were then subjected to hydrolysis in phosphate-buffer solutions (pH = 7.4) for up to 28 days at 37 degrees C. Tensile properties were used to evaluate the effect of annealing treatments. The data were subjected to statistical analysis using the SAS system. All of the one-, and many of the two- and three-factor interactions were found to be statistically significant. Annealing treatments did alter the mechanical properties of PGA sutures, as well as their degradation properties. Except for the increase in tenacity of samples with increasing percent extension, all other respects of the annealing treatments resulted in lower tenacity and breaking elongation when compared with the control samples. Sutures that have been exposed to any level of axial tension during annealing, however, exhibited a lower rate of hydrolytic degradation than the freely hung suture samples. The reduction of the characteristics of fiber structure due to the tendency of the tie-chain molecules to acquire the less constrained conformations and thus to bring the crystal blocks they connect back to the original arrangement before drawing is believed to be responsible for the freely hung specimens to behave quite differently from the clamped and stressed PGA samples.

A new type of braided nylon thread with a silver compound coating was made for the purpose of designing a biocidal suture material. The study used standard bacterial culture techniques to evaluate the antibacterial property of the new Ag-coated nylon thread. Seven types of bacterial species were tested; S. aureus, E. coli, P. aeruginosa, K. pneumoniae, S. dysenteriae, S. maruslens, and P. mirabilis. The commercial size 2/0 Nurolon suture from Ethicon served as the control. A weak direct current ranging from 0.4-400 microA was applied to the specimens to examine whether the biocidal property of silver could be enhanced by current. The antibacterial property was evaluated by the width and sterility of the clear zone in the bacterial culture plates. It was found that the new nylon thread exhibited very good to moderate bactericidal property toward these seven bacterial species. P. aeruginosa was the most sensitive species, while P. mirabilis was the least sensitive one. Application of direct current through the Ag-coated specimens positively enhanced their antibacterial property and the degree of enhancement depended on the direct current level. The material also exhibited an antibacterial property toward well-established bacterial colonies, but the effect was less strong than the case when direct current was applied simultaneously with incubation. Silver ions released from the coated nylon thread were responsible for the observed antibacterial property; and the application of a weak direct current to the material enhanced this effect. A preliminary biocompatibility study of this new material in rat gluteal muscle indicated that the new material caused less inflammatory reaction than the control Nurolon suture up to 60 days after implantation.

The purpose of the study was to examine the effect of gamma irradiation on the enzymatic as well as the in vivo degradation of polyglycolic acid sutures. The sutures of size 2-0 were irradiated at dosage levels of 0-20 mrad. The three enzymes chosen for this study were esterase, alpha-chymotrypsin, and trypsin. The irradiated sutures were both immersed in the enzyme solutions; their corresponding buffer controls, and implanted in inbred black-and-white hooded hister rats (Liverpool strain). The degradation of PGA sutures was determined mechanically. Among the three enzymes studied, esterase showed the highest enzymatic effect on the degradation of the unirradiated and irradiated PGA sutures. Trypsin's effect on PGA sutures was not observed until 20 mrad. The findings of trypsin demonstrated the hypothesis that synthetic high molecular weight polymers, which are initially resistant to enzymatic degradation, could become prone to enzymatic attack after altering their physical and chemical structures. Implanted PGA sutures maintained a similar or slightly higher mean tensile breaking strength in in vivo degradation compared to in vitro degradation (0.1M tris buffer of pH = 7.5); these degradation profiles suggest that PGA does not display similar behavior in in vivo and in vitro degradations. The magnitude of dissimilarity depends on the radiation dosage and on the duration of degradation, and is speculated to be attributable to the specific action of enzymes with respect to the configuration and chemical structure of the PGA sutures.

The objective of this study is to alter the fiber morphology of a linear aliphatic polyester, polyglycolic acid, by annealing treatment and to examine the changes of its degradation properties. The annealing was done at 150 degrees C, 170 degrees C, and 190 degrees C, and the specimens were annealed in four different strained conditions, freely hung, 0, 1, and 10%. After annealing treatments, the specimens were subject to in vitro hydrolytic degradation by immersing them in phosphate-buffer solution of pH 7.4 at 37 degrees C for up to 28 days. The thermal properties and gross morphology of the specimens were obtained. It was found that annealing treatments resulted in initial higher levels of crystallinity, which, in turn, influenced the hydrolytic degradation of the fiber. Among all the annealing conditions, the freely hung specimens annealed at 190 degrees C exhibited the most pronounced annealing effect on hydrolytic degradation, and was consistent with the observed gross morphologic changes. The change in the characteristics of fiber structure (i.e., the return to the stage of less oriented conformation upon freely hung annealing) was thought to be the cause.

The pH effect on the hydrolytic degradation of Polyglactin 910 copolymer was studied in terms of the tensile properties of the suture specimens. The use of a cord/yarn grip, newly designed specifically for fibrous materials, eliminated the grip-induced failure. Different degrees of hydrolytic degradation of this copolymer at 3 different pH levels were observed. The suture specimens exhibited the best retentions of breaking strength at the physiological pH of 7.44, while the specimens at pH = 10.09 showed the fastest loss of breaking strength. Thus, a maximum retention of tensile properties occurred around the pH level of 7.0, whereas smaller percentages of retention of tensile properties were observed at both acidic and strong alkaline solutions. This synthetic absorbable suture material exhibits the basic characteristic of hydrolysis which is catalyzed by both acid and base.

Tensile strength of poly(glycolic acid) suture (PGA) of size 2-0 was examined as a function of three pH levels, 5.25, 7.44, and 10.09 of the buffer. Cord and yarn grip was used to eliminate grip-induced failure of breaking strength tests. It was found that Dexon sutures degraded significantly faster in pH = 10.09 buffer than the other two lower pH buffers. There was no significant difference in degradation rate at pH = 5.25 and 7.44. At 7 days, PGA sutures lost almost half of its original tensile strength at pH = 10.09, while the same sutures still remained more than 95% of their original breaking strength at buffers of pH = 5.25 and 7.44. After 21 days, no trace of sutures could be detected in the buffer of pH = 10.09 while about 20% strength still remained in the buffers of pH = 7.44 and 5.25. Cage effect in the crystalline phase and pH dependent hydrogen bonding were introduced to explain the difference in degradation phenomenon of PGA at buffers of various pH.