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

A fully biodegradable spherical nucleic acid nanoplatform for self-codelivery of doxorubicin and miR122 for innate and adaptive immunity activation

Facile construction of a fully biodegradable spherical nucleic acid (SNA) nanoplatform is highly desirable for clinical translations but remains rarely explored. We developed herein the first polycarbonate-based biodegradable SNA nanoplatform for self-codelivery of a chemotherapeutic drug, doxorubicin (DOX), and a human liver-specific miR122 for synergistic chemo-gene therapy of hepatocellular carcinoma (HCC). Ring-opening polymerization (ROP) of a carbonate monomer leads to a well-defined polycarbonate backbone for subsequent DOX conjugation to the pendant side chains via acidic pH-cleavage Schiff base links and miR122 incorporation to the chain termini via click coupling, affording an amphiphilic polycarbonate-DOX-miR122 conjugate, PBis-Mpa30-DOX-miR122 that can self-assemble into stabilized SNA. Besides the desired biodegradability, another notable merit of this nanoplatform is the use of miR122 not only for gene therapy but also for enhanced innate immune response. Together with the ICD-triggering effect of DOX, PBis-Mpa30-DOX-miR122 SNA-mediated DOX and miR122 codelivery leads to synergistic immunogenicity enhancement, resulting in tumor growth inhibition value (TGI) of 98.1 % significantly higher than those of the groups treated with only drug or gene in a Hepa1-6-tumor-bearing mice model. Overall, this study develops a useful strategy toward biodegradable SNA construction, and presents a drug and gene-based self-codelivery SNA with synergistic immunogenicity enhancement for efficient HCC therapy. STATEMENT OF SIGNIFICANCE: Facile construction of a fully biodegradable SNA nanoplatform is useful for in vivo applications but remains relatively unexplored likely due to the synthetic challenge. We report herein construction of a polycarbonate-based SNA nanoplatform for co-delivering a chemotherapeutic drug, DOX, and a human liver-specific miR-122 for synergistic HCC treatment. In addition to the desired biodegradability properties, this SNA nanoplatform integrates DOX-triggered ICD and miR-122-enhanced innate immunity for simultaneously activating adaptive and innate immunities, which leads to potent antitumor efficiency with a TGI value of 98.1 % in a Hepa1-6-tumor-bearing mice model.

How Long Do Implanted Triclosan Sutures Inhibit Staphylococcus aureus in Surgical Conditions? A Pharmacological Model

(1) Background: Sutures with triclosan (TS) are used to reduce the risk of surgical site infections (SSI), but most clinical trials are inconclusive. The traceability of SSI risk to antimicrobial activity in operated tissues is needed. (2) Objectives: This study aimed to predict triclosan antistaphylococcal activity in operated tissues. (3) Methods: Three TS were exposed to static water for 30 days, and triclosan release was recorded. Polyglactin TS explanted from sheep seven days after cardiac surgery according to 3Rs provided ex vivo acceleration benchmarks. TS immersion up to 7 days in ethanol-water cosolvency and stirring simulated tissue implantation. Controls were 30-day immersion in static water. The release rate over time was measured and fitted to a predictive function. Antistaphylococcal activity and duration were measured by time-kill analysis with pre-immersed polyglactin TS. (4) Fifteen to 60-fold accelerated in vitro conditions reproduced the benchmarks. The rate prediction with double-exponential decay was validated. The antistaphylococcal activity was bactericidal, with TS pre-immersed for less than 12 h before then S. aureus began to grow. The residual triclosan level was more than 95% and played no detectable role. (5) Conclusions: Polyglactin, poliglecaprone, and polydioxanone TS share similar triclosan release functions with parametric differences. Polyglactin TS is antistaphylococcal in surgical conditions for 4 to 12 h.

In Vivo Versus In Vitro Degradation of a 3D Printed Resorbable Device for Ligation of Vascular Tissue in Horses

A resorbable 3D printed polydioxanone (PDO) device is manufactured to facilitate ligation of vascular tissue during surgery. The device must provide sufficient mechanical performance throughout the healing period. Therefore, degradation and mechanical performance of the device are investigated as a function of in vivo and in vitro aging. During aging the PDO device released cyclic and linear water-soluble products. In vivo aging resulted in higher relative number of linear oligomers in comparison to in vitro aging. A major loss of mechanical performance is observed after only 10 days in vivo and the Young's modulus (E) and tensile strength at break (σ_b ) decreased by 28% and 54%, respectively. This is in contrast to in vitro aging, where no loss of mechanical properties is observed during the same period. The in vivo aged devices exhibit clear holes in the matrices after 28 days, while apparent cracks are observed first after 140 days in vitro. These results highlight the sensitivity of the degradation process of resorbable devices with regards to the interactions of the device with the surrounding environment (tissues) and demonstrate the importance of in vivo testing as compliment to in vitro testing before clinical use of devices.

Structure-property relationships in 3D-printed poly(l-lactide-co-ε-caprolactone) degradable polymer

The recent growth of polymer 3D-printing has brought innovation to the medical implant field. Implants with complex porous structures can be fabricated by printing to tune mechanical behavior and enable diffusion, consequently improving integration with tissues in the human body. Poly(L-lactide-co-ε-caprolactone) (PLCL) is a 3D-printable polymer that possess a wide range of possible mechanical properties depending on its monomer composition. It is often used in biomedical applications requiring degradability. In this study, we explore 1) the effect of annealing 3D-printed PLCL and 2) the degradation profile of both annealed and unannealed 3D-printed PLCL scaffolds. The degraded samples were characterized for its molecular weight, mass loss, microstructure, and mechanical properties. By annealing the 3D-printed PLCL, we reveal the structure-property relationship of PLCL. Crystallization was found to be a crucial factor in the resulting mechanical properties, increasing stiffness significantly. The subsequent degradation study revealed that there was no significant difference brought about by pre-annealing the scaffolds. The scaffolds were found to maintain their mechanical properties until up to 8 weeks, at which point the scaffolds reached a critical molecular weight and lost their mechanical integrity.

In Vivo Degradation Mechanisms of Aliphatic Polycarbonates and Functionalized Aliphatic Polycarbonates

Aliphatic polycarbonates (APCs) have been studied for decades but have not been as utilized as aliphatic polyesters in biomaterial applications such as drug delivery and tissue engineering. With the recognition that functionalized aliphatic polymers can be readily synthesized, increased attention is being paid to these materials. A frequently provided reason for utilizing these polymers is that they degrade to form diols and carbon dioxide. However, depending on the structure and molecular weight of the APC, degradation may not occur. In this review, the mechanisms by which APCs and functionalized APCs have been found to degrade in vivo are examined with the objective of providing guidance in the continued development of these polymers as biomaterials.

A combined approach for the development of novel sutures with antibacterial and regenerative properties: the role of silver and silk sericin functionalization

Chronic wounds and related infections cause physical and psychological distress in patients, increased mortality, disability and high health care costs. The healing process can be delayed by several factors and in particular by the risk of infections, which can be further complicated by the increasing number of antibiotic-resistant microorganisms. New approaches in wounds management have been encouraged, aiming at preventing infections and improving wound healing. In this scenario, silver has emerged as an ideal antimicrobial agent due to its recognized efficacy against bacteria, viruses and fungi. Moreover, silk and in particular silk sericin from Bombyx mori has demonstrated excellent biological properties and can be considered a good candidate for skin tissue engineering. In this study absorbable PLGA sutures were functionalized with silk sericin and, then, they were treated with silver through an in situ photochemical deposition technology in order to develop an antibacterial and regenerative biomedical device. Morphological analysis was performed by Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDX) in order to evaluate the presence and distribution of silver deposited on the sutures. The stability and durability of the sericin/silver coatings were tested and the results were related to both antibacterial properties and sample degradation. The biological analyses also aimed at studying the biocompatibility and wound healing properties of the device, evaluating the synergistic effect between sericin and silver.

Controllable degradation kinetics of POSS nanoparticle-integrated poly(ε-caprolactone urea)urethane elastomers for tissue engineering applications

Biodegradable elastomers are a popular choice for tissue engineering scaffolds, particularly in mechanically challenging settings (e.g. the skin). As the optimal rate of scaffold degradation depends on the tissue type to be regenerated, next-generation scaffolds must demonstrate tuneable degradation patterns. Previous investigations mainly focussed on the integration of more or less hydrolysable components to modulate degradation rates. In this study, however, the objective was to develop and synthesize a family of novel biodegradable polyurethanes (PUs) based on a poly(ε-caprolactone urea)urethane backbone integrating polyhedral oligomeric silsesquioxane (POSS-PCLU) with varying amounts of hard segments (24%, 28% and 33% (w/v)) in order to investigate the influence of hard segment chemistry on the degradation rate and profile. PUs lacking POSS nanoparticles served to prove the important function of POSS in maintaining the mechanical structures of the PU scaffolds before, during and after degradation. Mechanical testing of degraded samples revealed hard segment-dependent modulation of the materials’ viscoelastic properties, which was attributable to (i) degradation-induced changes in the PU crystallinity and (ii) either the presence or absence of POSS. In conclusion, this study presents a facile method of controlling degradation profiles of PU scaffolds used in tissue engineering applications.

Effect of chemotherapy and heat on biomechanical properties of absorbable sutures

BACKGROUND

The quality of tissue repairs depends on tissue integrity, surgical technique, and material properties of the sutures used. Currently, there is no clear consensus on which is the best suture to use during cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy. The aim of this study was to evaluate the impact of heat and chemotherapy on sutures' biomechanical properties.

METHODS

Six different 3.0 absorbable sutures (Biosyn, Dexon II, Maxon, Monocryl, PDS II, and Vicryl Plus) were tested. All suture strands were incubated for a 24-h period in saline, mitomycin-c, and oxaliplatin at 37 and 45°C. Suture loops were then loaded to failure using a servohydraulic testing machine. Data for tensile breaking force (TBF) and elongation rate were collected for all samples.

RESULTS

Under basal condition, Maxon was the strongest of all sutures with a TBF of 59.6 ± 4.3 N (P < 0.01), and no significant difference in TBF was observed between other sutures. Heat alone had no impact on sutures' biomechanical parameters. Exposition to mitomycin-c at 45°C did not significantly affect sutures' basal tensile properties, with Maxon remaining the strongest suture. When incubated in oxaliplatin at 45°C, the six suture types had a similar TBF. In all experimental conditions, multifilament sutures had a significantly lower elongation rate than monofilament sutures, and no correlations were demonstrated between elongation rate and the TBF of sutures.

CONCLUSIONS

This study showed that exposition to heated chemotherapy did not significantly affect absorbable sutures biomechanical properties.

The Present and the Future of Degradable Dendrimers and Derivatives in Theranostics

Interest in dendrimer-based nanomedicines has been growing recently, as it is possible to precisely manipulate the molecular weight, chemical composition, and surface functionality of dendrimers, tuning their properties according to the desired biomedical application. However, one important concern about dendrimer-based therapeutics remains-the nondegradability under physiological conditions of the most commonly used dendrimers. Therefore, biodegradable dendrimers represent an attractive class of nanomaterials, since they present advantages over conventional nondegradable dendrimers regarding the release of the loaded molecules and the prevention of bioaccumulation of synthetic materials and subsequent cytotoxicity. Here, we present an overview of the state-of-the-art of the design of biodegradable dendritic structures, with particular focus on the hurdles regarding the use of these as vectors of drugs and nucleic acids, as well as macromolecular contrast agents.

Effect on the tensile strength of human acellular dermis (Epiflex®) of in-vitro incubation simulating an open abdomen setting

Background

The use of human acellular dermis (hAD) to close open abdomen in the treatment process of severe peritonitis might be an alternative to standard care. This paper describes an investigation of the effects of fluids simulating an open abdomen environment on the biomechanical properties of Epiflex® a cell-free human dermis transplant.

Methods

hAD was incubated in Ringers solution, blood, urine, upper gastrointestinal (upper GI) secretion and a peritonitis-like bacterial solution in-vitro for 3 weeks. At day 0, 7, 14 and 21 breaking strength was measured, tensile strength was calculated and standard fluorescence microscopy was performed.

Results

hAD incubated in all five of the five fluids showed a decrease in mean breaking strength at day 21 when compared to day 0. However, upper GI secretion was the only incubation fluid that significantly reduced the mechanical strength of Epiflex after 21days of incubation when compared to incubation in Ringer’s solution.

Conclusion

hAD may be a suitable material for closure of the open abdomen in the absence of upper GI leakage and pancreatic fistulae.

Effect of the addition of a labile gelatin component on the degradation and solute release kinetics of a stable PEG hydrogel

Characterization of the degradation mechanisms and resulting products of biodegradable materials is critical in understanding the behavior of the material including solute transport and biological response. Previous mathematical analyses of a semi-interpenetrating network (sIPN) containing both labile gelatin and a stable cross-linked poly(ethylene glycol) (PEG) network found that diffusion-based models alone were unable to explain the release kinetics of solutes from the system. In this study, degradation of the sIPN and its effect on solute release and swelling kinetics were investigated. The kinetics of the primary mode of degradation, gelatin dissolution, was dependent on temperature, preparation methods, PEGdA and gelatin concentration, and the weight ratio between the gelatin and PEG. The gelatin dissolution rate positively correlated with both matrix swelling and the release kinetics of high-molecular-weight model compound, FITC-dextran. Coupled with previous in vitro studies, the kinetics of sIPN degradation provided insights into the time-dependent changes in cellular response including adhesion and protein expression. These results provide a facile guide in material formulation to control the delivery of high-molecular-weight compounds with concomitant modulation of cellular behavior.

Fabrication and characterization of chitosan coated braided PLLA wire using aligned electrospun fibers

The development of functionalized braided wires coated with chitosan that can be used for tissue suturing and tissue regeneration is the subject of this work. Poly(L: -lactic acid) (PLLA) braided wires were successfully fabricated by combining an electrospinning technique and alignment collection with a mini-type braiding method. The resulting PLLA wires with and without chitosan coating were characterized through a variety of methods including scanning electron microscopy (SEM), X-ray photoelectronic spectra (XPS) and tensile mechanical testing. Hemolytic property, kinetic hemostasis behavior, platelet adhesion, erythrocyte adhesion, and water uptake ability of the wires were explored. The results showed that a nearly comparable mechanical behavior of the braided wires with some commercial suture could be obtained with well-aligned fibers, and no significant difference in tensile performances were recognized with and without the introduction of chitosan. The PLLA wires coated with chitosan were found to have better prohemostatic activity than those without a chitosan coating.

Role of NADPH oxidase in formation and function of multinucleated giant cells

Macrophages play essential roles in a wide variety of physiological and pathological processes. One of the unique features of these phagocytic leukocytes is their ability to fuse, forming multinucleated giant cells. Multinucleated giant cells are important mediators of tissue remodeling and repair and are also responsible for removal or sequestration of foreign material, intracellular bacteria and non-phagocytosable pathogens, such as parasites and fungi. Depending on the tissue where fusion occurs and the inflammatory insult, multinucleated giant cells assume distinctly different phenotypes. Nevertheless, the ultimate outcome is the formation of large cells that can resorb bone tissue (osteoclasts) or foreign material and pathogens (giant cells) extracellularly. While progress has been made in recent years, the mechanisms and factors involved in macrophage fusion are still not fully understood. In addition to cytokines and a number of adhesion proteins and receptors, it is becoming increasingly clear that NADPH oxidase-generated reactive oxygen species (ROS) also play an important role in macrophage fusion. In this review, we provide an overview of macrophage multinucleation, with a specific focus on the role of NADPH oxidases and ROS in macrophage fusion and in the function of multinucleated giant cells. In addition, we provide an updated overview of the role of these cells in inflammation and various autoimmune diseases.

Kinetics of solid-state NMR cross-polarization from protons to carbon-13 in surgical sutures

Commercial Dexon surgical sutures, made of polyglycolide (PGA), were examined using (13)C CP/MAS NMR. The study shows that detailed analysis of the cross-polarization (CP) process is useful in the peak assignments and in the assessment of molecular mobility in the polymer domains. Crystallinity of PGA in the sutures was estimated at ca. 55%.

Vaterite deposition on biodegradable polymer foam scaffolds for inducing bone-like hydroxycarbonate apatite coatings

Hydroxycarbonate apatite (HCA) coatings on the surface of bioresorbable materials for bone tissue engineering scaffolds were produced using macroporous poly(DL-lactide) (PDLLA) foams impregnated by calcium carbonate in vaterite crystalline form. Stable and homogeneous vaterite deposition on PDLLA foams was achieved using a slurry dipping technique. In vitro studies in simulated body fluid (SBF) were performed to induce formation of (HCA) on the surface of vaterite/PDLLA composite foams. HCA was detected after immersion of foams in SBF for 7 days. Hence, depositing vaterite on materials followed by immersion in SBF is confirmed to induce HCA coatings on the surface of the material. The HCA coated, bioactive and resorbable PDLLA foams are intended for use as bone tissue engineering scaffolds.

Tissue reaction and surface morphology of absorbable sutures after in vivo exposure

Tissue reaction to suture materials depends mainly on how the polymer they are composed of interacts with the tissues. There are few in vivo studies evaluating the suture material modifications resulting from its interaction with tissues. This paper aimed to study rat subcutaneous tissue reaction to irradiated polyglactin 910, polydioxanone, poliglecaprone 25 and chromic gut and its correlation with the ultra-structural alterations the materials undergo. The histological alterations were studied on the 1st, 2nd, 3rd, 7th and 14th day after suture implantations. In these periods, the materials were removed from the tissues and their surfaces were analyzed by scanning electron microscopy. Irradiated polyglactin 910 stimulated the formation of multinucleated giant cells and its filaments underwent cleavage and dissolution. In potydioxanone, a few inflammatory cells and scar fibrosis was observed, and triangular cracks appeared on its surface. Around the poliglecaprone 25, a diffused infiltration of a few mononuclear cells and fibrosis was recorded and formation of craters was observed on its surface. Chromic gut induced necrosis and granulation tissue and underwent dissolution in the tissues during the studied periods. In this study, it was observed that suture materials induced differentiated tissue reactions and morphologic surface changes, suggesting that indications should be individualized.

Alkaline-treated poly(ε-caprolactone) films: Degradation in the presence or absence of fibroblasts

In the first stage, we observed the study of the degradation behavior of alkaline-treated poly(epsilon-caprolactone) (PCL) in two biologically-related media: phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) for 18 months, finding a much accelerated degradation in the last one. As expected, the degradation in the presence of cells is much pronounced even considering that the study is limited to 6 months. The characterization of the degraded substrates by chemiluminescence (CL) allows to explain the modifications of the substrate and their relations with transitory oxidative stress phenomena described in the fibroblasts seeded onto the PCL membranes.

Bioactive and mechanically strong Bioglass®-poly(D,L-lactic acid) composite coatings on surgical sutures

New coating processes have been investigated for degradable (Vicryl) and nondegradable (Mersilk) sutures with the aim to develop Bioglass coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the aqueous phase of a Bioglass particle slurry was replaced with a poly(D,L-lactic acid) (PDLLA) polymer dissolved in solvent dimethyle carbonate (DMC) to act as third phase. SEM observations indicated that this alteration significantly improved the homogeneity of the coatings. Second, a new coating strategy involving two steps was developed: the sutures were first coated with a Bioglass-PDLLA composite film followed by a second PDLLA coating. This two-step process of coating has addressed the problem of poor adherence of Bioglass particles on suture surfaces. The coated sutures were knotted to determine qualitatively the mechanical integrity of the coatings. The results indicated that adhesion strength of coatings obtained by the two-step method was remarkably enhanced. A comparative assessment of the bioactivity of one-step and two-step produced coatings was carried out in vitro using acellular simulated body fluid (SBF) for up to 28 days. Coatings produced by the two-step process were found to have similar bioactivity as the one-step produced coatings. The novel Bioglass/PDLLA/Vicryl and Bioglass/PDLLA/Mersilk composite sutures are promising bioactive materials for wound healing and tissue engineering applications.

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.

Biodegradation of absorbable sutures in body fluids and pH buffers

OBJECTIVE

This study measures the influence of body fluids on the loss of tensile strength of absorbable sutures in vitro.

METHODS

Nine synthetic absorbable sutures were incubated in different gastrointestinal fluids, as well as in blood and three buffers. Stretch tests were performed after days 0, 7, 14, and 21.

RESULTS

Tensile strength varied from 18.5 to 32.8 N, and elasticity varied from 9.5 to 51% of the initial length. The influence of pH, blood, and gastric juice was negligible on all sutures except PDS II. Except for Monocryl, all sutures, especially Polysorb and Vicryl, lost tensile strength much faster in bile, jejunal and pancreatic juices than in the corresponding buffers.

CONCLUSION

The biodegradation of sutures varies greatly in different body fluids independent of differences in pH.

The effect of polylactide membranes on the levels of reactive oxygen species in periodontal flaps during wound healing

It is consented that reactive oxygen species (ROS) are deleterious to wound healing process due to the harmful effects on cells and tissues. Absorbable synthetic biomaterials are considered to be degraded via ROS. Free-radical-scavenging enzymes (FRSE) are a cytoprotective enzymal group that has an essential role in the reduction, de-activation and removal of ROS as well as regulating wound healing process. In the present study, synthetic and absorbable polylactide (PLA) barrier membranes were evaluated by means of ROS activity levels during degradation in the healing periodontal flaps measuring the activity of FRSE superoxide dismutase (SOD) and catalase (CAT). Gingival biopsies taken from 10 patients allowing both guided tissue regeneration (test) and conventional flap surgery (control) before and 1 month after the operations were processed and the supernatants were studied by Mc Cord and Fridovich, Flohe and Otting, and Luck methods to measure total SOD and CAT levels respectively. A significantly increased enzyme activity of SOD and CAT was observed in both groups (p<0.05). SOD activity change was 62.92% in the test and 3.97% in the control group, and, CAT activity change was 48.04% in the test and 11.58% in the control group. Our results suggest that ROS, particularly superoxide anions, may contribute to the degradation phase of PLA membranes and this may affect the wound healing of periodontium at least for one-month period.

Development and characterisation of silver-doped bioactive glass-coated sutures for tissue engineering and wound healing applications

A novel silver-doped bioactive glass powder (AgBG) was used to coat resorbable Vicryl (polyglactin 910) and non-resorbable Mersilk surgical sutures, thereby imparting bioactive, antimicrobial and bactericidal properties to the sutures. Stable and homogeneous coatings on the surface of the sutures were achieved using an optimised aqueous slurry-dipping technique. Dynamic mechanical analysis (DMA) was used to investigate the viscoelastic parameters of storage modulus and tandelta and thermal transitions of the as-received and composite (coated) sutures. The results generally showed that the bioactive glass coating did not affect the dynamic mechanical and thermal properties of the sutures. The in vitro bioactivity of the sutures was tested by immersion in simulated body fluid (SBF). After only 3 days of immersion in SBF, bonelike hydroxyapatite formed on the coated suture surfaces, indicating their enhanced bioactive behaviour. Resorbable sutures with bioactive coatings as fabricated here, in conjunction with 3-D textile technology, may provide attractive materials for producing 3-D scaffolds with controlled porosities for tissue engineering applications. The bactericidal properties imparted by the Ag-containing glass coating open also new opportunities for use of the composite sutures in wound healing and body wall repair.

Composite surgical sutures with bioactive glass coating

A processing method was developed to coat polyglactin 910 (Vicryl) sutures with bioactive glass powder (45S5 Bioglass). High reproducibility and homogeneity of the coating in terms of microstructure and thickness along the suture length were achieved. Bioglass-coated sutures exhibited a high level of chemical reactivity in simulated body fluid (SBF), indicating their bioactive behavior. This was evident by the prompt formation of hydroxyapatite (HA) crystals on the surface after only 7 days of immersion in SBF. These crystals grew to form a thick HA layer (15 microm thickness) after 3 weeks in SBF. The tensile strength of the sutures was tested before and after immersion in SBF in order to assess the effect of the bioactive glass coating on suture degradation. The tensile strength of composite sutures was lower than that of as-received Vicryl sutures, 385 and 467 MPa, respectively. However, after 28 days of immersion in SBF the residual tensile strengths of coated and uncoated sutures were similar (83 and 88 MPa, respectively), indicating no negative effect of the HA layer formation on the suture strength. The effect of bioactive glass coating on the polymer degradation is discussed. The developed bioactive sutures represent interesting materials for applications in wound healing, fabrication of fibrous three-dimensional scaffolds for tissue engineering, and reinforcement elements for calcium-phosphate temporary implants.

PEO-like plasma polymerized tetraglyme surface interactions with leukocytes and proteins: in vitro and in vivo studies

Polyethylene oxide (PEO) surfaces reduce non-specific protein and cell interactions with implanted biomaterials and may improve their biocompatibility. PEO-like polymerized tetraglyme surfaces were made by glow discharge plasma deposition onto fluorinated ethylene propylene copolymer (FEP) substrates and were shown to adsorb less than 10 ng/cm2 of fibrinogen in vitro. The ability of the polymerized tetraglyme surfaces to resist leukocyte adhesion was studied in vitro and in vivo. Polymerized tetraglyme and FEP were implanted subcutaneously in mice and removed after 1 day or 4 weeks. Histological analysis showed a similar degree of fibrous encapsulation around all of the 4-week implants. Darkly stained wells were present in the fibrous tissues at the tissue-material interface of both FEP and tetraglyme. Scanning electron micrographs showed that in vivo macrophage adhesion to polymerized tetraglyme was much higher than to FEP. After 2-hour contact with heparinized whole blood, polymorphonuclear leukocyte (PMN) adhesion to polymerized tetraglyme was much higher than to FEP, while platelet adhesion to polymerized tetraglyme was lower than to FEP. When PMNs isolated from blood were suspended in 10% autologous plasma, cell adhesion to polymerized tetraglyme was higher than to FEP; however when the cells were suspended in heat inactivated serum, cell adhesion to FEP was higher than to polymerized tetraglyme. The surface chemistry of polymerized tetraglyme did not change after 2-hour blood contact, but displayed nitrogen functional groups after 1-day implantation and became slightly degraded after 4-week implantation. The surface chemistry of FEP did not change significantly after blood contact or implantation. Loosely bound proteins such as fibrinogen on polymerized tetraglyme may contribute to the adhesion of PMNs and macrophages and ultimately to fibrous encapsulation (the foreign body response) around the implants.

The pH dependence of monofilament sutures on hydrolytic degradation

Hydrolytic degradation of two nonabsorbable sutures, four absorbable sutures, and a new type of absorbable suture was studied in buffered media of various pHs at 37 degrees C. The pH levels fixed in this study were 1.0, 7.4, 8.5, and 10.5. Physical measurements were made on the retention of tensile strength and melting temperature of the sutures after hydrolysis for 12 weeks. Sutures containing glycolic acid as a comonomer exhibited enhanced degradation in alkaline media, similar to polyglycolide multifilament sutures. Poly-p-dioxanone (PDS II) suture lost strength to a significant extent at pH 1.0, suggesting that care should be taken when this suture is used for closing tissues in contact with acidic media, such as the stomach. In marked contrast, the degradation of lactide-epsilon-caprolactone copolymer [P(LA/CL)] suture was not sensitive to the pH of media. The surface morphology of hydrolyzed sutures varied, depending on the pH of media. Particularly, moon-crater-shaped impressions were observed on glycolide-epsilon-caprolactone copolymer (MONOCRYL) and glycolide-trimethylene carbonate-dioxanone copolymer (BIOSYN) sutures. Among the nonabsorbable sutures, nylon (ETHILON) exhibited the fastest loss of strength in acidic buffer solution, and polypropylene (PROLENE) suture retained most of its initial strength at all pHs studied.