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PubMed2005

Poly(lactide) stereocomplexes: formation, structure, properties, degradation, and applications.

Poly(lactide)s [i.e. poly(lactic acid) (PLA)] and lactide copolymers are biodegradable, compostable, producible from renewable resources, and nontoxic to the human body and the environment. They have been used as biomedical materials for tissue regeneration, matrices for drug delivery systems, and alternatives for commercial polymeric materials to reduce the impact on the environment. Since stereocomplexation or stereocomplex formation between enantiomeric PLA, poly(L-lactide) [i.e. poly(L-lactic acid) (PLLA)] and poly(D-lactide) [i.e. poly(D-lactic acid) (PDLA)] was reported in 1987, numerous studies have been carried out with respect to the formation, structure, properties, degradation, and applications of the PLA stereocomplexes. Stereocomplexation enhances the mechanical properties, the thermal-resistance, and the hydrolysis-resistance of PLA-based materials. These improvements arise from a peculiarly strong interaction between L-lactyl unit sequences and D-lactyl unit sequences, and stereocomplexation opens a new way for the preparation of biomaterials such as hydrogels and particles for drug delivery systems. It was revealed that the crucial parameters affecting stereocomplexation are the mixing ratio and the molecular weight of L-lactyl and D-lactyl unit sequences. On the other hand, PDLA was found to form a stereocomplex with L-configured polypeptides in 2001. This kind of stereocomplexation is called "hetero-stereocomplexation" and differentiated from "homo-stereocomplexation" between L-lactyl and D-lactyl unit sequences. This paper reviews the methods for tracing PLA stereocomplexation, the methods for inducing PLA stereocompelxation, the parameters affecting PLA stereocomplexation, and the structure, properties, degradation, and applications of a variety of stereocomplexed PLA materials.

Absorbable Implants↗
PubMed2006

Triclosan release from coated polyglycolide threads.

Copolymerization of lactide, epsilon-caprolactone, and trimethylene carbonate is performed. The synthesis is focused on obtaining materials with adequate properties for application as a suture coating that could contain an antimicrobial agent like triclosan. An amorphous character, a low glass transition temperature, a moderate susceptibility to degradation, and a hydrophobic nature are the conditions required for the optimal behavior of this coating. These properties can be attained with a copolymer of composition 10:60:30. Triclosan is added to the surface of polyglycolide threads and its release is studied in different media with high-performance liquid chromatography. The influence of the temperature, the diameter of the thread, the initial concentration of the antibacterial agent, and the applied procedure on the incorporation of triclosan is also evaluated. A total release of triclosan is attained after a few days of exposure to a Dulbecco's based medium, whereas equilibrium concentrations are reached when a Sörensen hydrophilic medium is used. Partition and diffusion coefficients are also estimated.

Absorbable Implants↗
PubMed2006

Preparation and characterization of novel bone scaffolds based on electrospun polycaprolactone fibers filled with nanoparticles.

Novel bone-scaffolding materials were successfully fabricated by electrospinning from polycaprolactone (PCL) solutions containing nanoparticles of calcium carbonate (CaCO(3)) or hydroxyapatite (HA). The diameters of the as-spun fibers were found to increase with the addition and increasing amounts of the nanoparticles. The observed increase in the diameters of the as-spun fibers with the addition and increasing amounts of the nanoparticulate fillers was responsible for the observed increase in the tensile strength of the obtained fiber mats. An increase in the concentration of the base PCL solution caused the average diameter of the as-spun PCL/HA composite fibers to increase. Increasing applied electrical potential also resulted in an increase in the diameters of the obtained PCL/HA composite fibers. Lastly, indirect cytotoxicity evaluation of the electrospun mats of PCL, PCL/CaCO(3), and PCL/HA fibers based on human osteoblasts (SaOS2) and mouse fibroblasts (L929) revealed that these as-spun mats posed no threat to the cells, a result that implied their potential for utilization as bone-scaffolding materials.

Absorbable Implants↗
PubMed2006

Materials for peripheral nerve regeneration.

Recent efforts in scientific research in the field of peripheral nerve regeneration have been directed towards the development of artificial nerve guides. We have studied various materials with the aim of obtaining a biocompatible and biodegradable two layer guide for nerve repair. The candidate materials for use as an external layer for the nerve guides were poly(caprolactone) (PCL), a biosynthetic blend between PCL and chitosan (CS) and a synthesised poly(ester-urethane) (PU). Blending PCL, which is a biocompatible synthetic polymer, with a natural polymer enhanced the system biocompatibility and biomimetics, fastened the degradation rates and reduced the production costs. Various novel block poly(ester-urethane)s are being synthesised by our group with tailored properties for specific tissue engineering applications. One of these poly(ester-urethane)s, based on a low molecular weight poly(caprolactone) as the macrodiol, cycloesandimethanol as the chain extender and hexamethylene diisocyanate as the chain linker, was investigated for the production of melt extruded nerve guides. We studied natural polymers such as gelatin (G), poly(L-lysine) (PL) and blends between chitosan and gelatin (CS/G) as internal coatings for nerve guides. In vitro and in vivo tests were performed on PCL guides internally coated either with G or PL to determine the differences in the quality of nerve regeneration associated with the type of adhesion protein. CS/G natural blends combined the good cell adhesion properties of the protein phase with the ability to promote nerve regeneration of the polysaccharide phase. Natural blends were crosslinked both by physical and chemical crosslinking methods. In vitro neuroblast adhesion tests were performed on CS/G film samples, PCL/CS and PU guides internally coated with G to evaluate the ability of such materials towards nerve repair.

Absorbable Implants↗
PubMed2003

Functional assessment of sciatic nerve recovery: biodegradable poly (DLLA-epsilon-CL) nerve guide filled with fresh skeletal muscle.

The aim of this study was to compare functional peripheral nerve recovery in the rat sciatic nerve model after reconstruction of a 10-mm gap with a biodegradable poly (DLLA-epsilon-CL) nerve guide, as filled with either fresh skeletal muscle or phosphate-buffered saline (PBS). During 24 weeks of recovery, motor and sensory functional evaluation was tested by extensor postural thrust (EPT) and withdrawal reflex latency (WRL), respectively. At the end of the experiment, anesthetized animals were prepared for motor nerve conduction velocity (MNCV) studies, followed by gastrocnemius and soleus muscle weight measurement. Motor functional recovery was greater in the muscle-grafted group, and reached a significant difference from weeks 8-12 (P < 0.05). The results of this investigation suggest that filling a nerve guide with fresh skeletal muscle induces faster maturation of regenerated nerve fibers in comparison with traditional tubular repair.

Absorbable Implants↗
PubMedDate not supplied

Absorbable and nonabsorbable sutures in microsurgery: standardized comparable studies in rats.

In order to study the applicability and value of synthetic absorbable suture materials in microvascular surgery, 8-0 monofilament nonabsorbable polyamide sutures and 8-0 absorbable polyglycolic acid and polyglactin 910 sutures were used in end-to-end anastomoses of the aorta in rats, employing the same microsurgical model for all procedures. Comparable investigations of the anastomotic sites were carded out macroscopically and histologically at various intervals postoperatively. It was found that when placed under unphysiologic strain, microvascular anastomoses sutured with absorbable materials had less mechanical endurance than anastomoses stitched with nonabsorbable suture materials. It was also found, however, that this had no significance in vivo, inasmuch as no vascular ruptures or aneurysms appeared with either the absorbable or nonabsorbable sutures even after long-term observation. The nonabsorbable sutures were fully recognizable up to 150 days, microscopically showing clear evidence of granuloma formation. The absorbable sutures, on the other hand, could hardly be discerned after 50 days, and after 150 days the foreign body and scar reactions had almost completely disappeared. Absorbable suture materials lead to more rapid restitution of the vascular wall than nonabsorbable sutures and consequently appear to be superior.

Absorbable Implants↗
PubMed2004

Are there any complications with bioabsorbable fixation devices? A 10 year review in orthognathic surgery.

Bioabsorbable fixation devices have been used in our departments between November 1991 and November 2001 in orthognathic surgery. The aim of this retrospective study was to assess all complications experienced during this time period, when we have operated 163 patients who have undergone 329 orthognathic osteotomies fixated with bioresorbable devices. No postoperative intermaxillary fixation was used. Light guiding elastics were used for 5 to 7 weeks. Patients' acceptance was generally excellent and very few complications occurred during this follow-up of 10 years. The complications were minor and did not affect the end results of the operations. Minor complications occurred in 14 patients (8.6%). Only one patient (0.6%) had a postoperative infection with elevated infection parameters. The other minor complications consisted mainly of dehiscence of the wound and plate exposure together with granulation tissue in the operation field. The rest of the complications occurred in the beginning of our study, when large screw heads on top of the bone irritated the patient and had to be removed. Insufficient fixation resulted in open bite in three patients (1.8%) in the beginning of the trial use of new devices, which no longer are used. Based on our experience, bioresorbable devices are safe to be used in orthognathic procedures. However, there is a learning curve, as there is with all new methods introduced.

Absorbable Implants↗
PubMed2000

Soluble biodegradable polymer-based cytokine gene delivery for cancer treatment.

Transgene expression and tumor regression after direct injection of plasmid DNA encoding cytokine genes, such as mIL-12 and mIFN-gamma, remain very low. The objective of this study is to develop nontoxic biodegradable polymer-based cytokine gene delivery systems, which should enhance mIL-12 expression, increasing the likelihood of complete tumor elimination. We synthesized poly[alpha-(4-aminobutyl)-l-glycolic acid] (PAGA), a biodegradable nontoxic polymer, by melting condensation. Plasmids used in this study encoded luciferase (pLuc) and murine interleukin-12 (pmIL-12) genes. PAGA/plasmid complexes were prepared at different (+/-) charge ratios and characterized in terms of particle size, zeta potential, osmolality, surface morphology, and cytotoxicity. Polyplexes prepared by complexing PAGA with pmIL-12 as well as pLuc were used for transfection into cultured CT-26 colon adenocarcinoma cells as well as into CT-26 tumor-bearing BALB/c mice. The in vitro and in vivo transfection efficiency was determined by luciferase assay (for pLuc), enzyme-linked immunosorbent assay (for mIL-12, p70, and p40), and reverse transcriptase-polymerase chain reaction (RT-PCR) (for Luc and mIL-12 p35). PAGA condensed and protected plasmids from nuclease degradation. The mean particle size and zeta potential of the polyplexes prepared in 5% (w/v) glucose at 3:1 (+/-) charge ratio were approximately 100 nm and 20 mV, respectively. The surface characterization of polyplexes as determined by atomic force microscopy showed complete condensation of DNA with an ellipsoidal structure in Z direction. The levels of mIL-12 p40, mIL-12 p70, and mIFN-gamma were significantly higher for PAGA/pmIL-12 complexes compared to that of naked pmIL-12. This is in good agreement with RT-PCR data, which showed significant levels of mIL-12 p35 expression. The PAGA/pmIL-12 complexes did not induce any cytotoxicity in CT-26 cells as evidenced by 3-¿4, 5-dimethylthiazol-2-yl¿-2,5-diphenyltetrazolium bromide assay and showed enhanced antitumor activity in vivo compared to naked pmIL-12. PAGA/pmIL-12 complexes are nontoxic and significantly enhance mIL-12 expression at mRNA and protein levels both in vitro and in vivo.

Absorbable Implants↗
PubMed1999

Seprafilm-induced peritoneal inflammation: a previously unknown complication. Report of a case.

INTRODUCTION: Various substances and agents have been evaluated to prevent postoperative adhesion formation. Recently a sodium hyaluronate-based bioresorbable membrane was introduced with promising clinical results. Its application was regarded as safe and efficient. METHODS: We present the first reported case of a severe inflammatory reaction to a bioresorbable membrane and give a review of the related literature. CONCLUSION: Bioresorbable membranes are increasingly used by general surgeons and gynecologists to reduce postoperative adhesion formation. Bioresorbable membranes may produce extensive inflammatory reactions.

Absorbable Implants↗
PubMed1999

Single-layer continuous colon and rectal anastomosis using monofilament absorbable suture (Maxon): study of 500 cases.

PURPOSE: The study purpose was to evaluate the results of continuous, single-layer colon and rectal anastomoses using a monofilament absorbable suture material (Maxon). METHODS: Four hundred ninety-two consecutive patients undergoing five hundred colon and rectal anastomoses with the above technique were evaluated for outcome, including anastomotic leakage, stricture, and other complications, by means of chart review. RESULTS: Three patients (0.6 percent) died after surgery and 7 (1.4 percent) developed clinical evidence of anastomotic leakage. Twenty-four percent developed some postoperative complications, most of which were minor. CONCLUSIONS: Continuous, single-layer colorectal anastomosis using monofilament absorbable suture can be performed safely, quickly, and with a favorable cost ratio. Handsewn anastomoses should still be part of the armamentarium of the well-trained surgeon.

Absorbable Implants↗
PubMed2000

Use of bioresorbable membrane (sodium hyaluronate + carboxymethylcellulose) after controlled bowel injuries in a rabbit model.

PURPOSE: Patients in whom enterolysis is performed are at high risk for recurrence of adhesions and for injury during adhesiolysis. Therefore, the aim of this study was to assess the safety of sodium hyaluronate-based bioresorbable membrane (Seprafilm) after myotomy and enterotomy. METHODS: A total of 60 rabbits underwent laparotomy with equal distribution to one of three groups: creation of either three repaired, or three unrepaired myotomies, or three repaired enterotomies. Thus, a total of 180 defects were created in the same anatomic positions. One-half of the animals in each group had the surface of the myotomies or enterotomies covered by Seprafilm. Fourteen days later, after complete absorption of Seprafilm, the presence of intra-abdominal abscess, adhesions, and the integrity of the suture line were evaluated by a surgeon blinded to the use of Seprafilm and by a standard radiographic isobaric contrast study. Statistical analysis was done by use of Fisher's exact test; significance was set at P < 0.05. RESULTS: The incidence of adhesions in the repaired myotomy group were 2 (6.6 percent) and 9 (30 percent) in the Seprafilm and control (nonSeprafilm) groups, respectively (P < 0.05); in the unrepaired myotomy group, 2 (6.6 percent) and 10 (33 percent) in the Seprafilm and control groups, respectively (P < 0.05); and in the enterotomy group, 28 (94 percent) and 29 (97 percent) in the Seprafilm and control groups, respectively (P = not significant). A single phlegmon occurred in the myotomy group at a Seprafilm site (1.6 (1/60) vs. 0 percent, P = not significant). There were no leaks in this group. In the enterotomy group, the incidence of phlegmons was 33 percent (10/30) in the Seprafilm group, whereas it was 27 percent (8/30) in the nonSeprafilm group (P = not significant). The incidence of leaks was 6.6 (2/30) and 10 percent (3/30) in the Seprafilm and nonSeprafilm group, respectively (P = not significant). CONCLUSION: The use of Seprafilm at the sites of myotomies significantly reduced the incidence of adhesions. Effectiveness at the enterotomy site may have been attenuated by a greater inflammatory response. Importantly, Seprafilm did not increase septic mortality in any group.

Absorbable Implants↗
PubMed2000

Preparation of a pure autologous biodegradable fibrin matrix for tissue engineering.

Parallel to the growing role of tissue engineering, the need for cell embedding materials, which allow cells to stabilise in a three-dimensional distribution, has increased. Although several substances have been tested, fibrin is thus far the only one that permits the clinical application of cultured tissue. To date, autologous fibrinogen has usually been polymerised with bovine thrombin, which can cause severe immunological side effects. The objective of this study was to explore the practicability of obtaining autologous thrombin from a single patient in an adequate concentration and amount. Fibrinogen was cryoprecipitated from 200 ml of freshly-frozen plasma. Thrombin was isolated from the supernatant through ion-exchange chromatography. The thrombin was first bound to Sephadex A-50 and then eluated using 2 ml of a salt buffer (2.0 M NaCl in 0.015 M trisodiumcitrate, pH 7.0). The activity of the thrombin (51 NIH x ml(-1) to 414 NIH x ml(-1) reached levels comparable to those in commercially available fibrin glues (4-500 NIH x ml(-1)). The study has shown that it is possible to obtain a sufficient amount of autologous thrombin from a single donor to create a fibrin matrix of high efficiency without the risk of immunological and infectious side effects.

Absorbable Implants↗
PubMed2003

Engineering an artificial nerve graft for the repair of severe nerve injuries.

Nerve repair with tubes has a limit to regeneration depending upon the length of the gap. The characteristics of the guide, in terms of permeability, durability and adhesiveness, also influence regeneration. Considering the importance of the cellular component in regeneration, the development of artificial grafts, composed of a biocompatible nerve guide filled with a neurotropic matrix and seeded with Schwann cells (SCs), is an interesting option to enhance nerve regeneration and provide an alternative to the classical autologous nerve graft. We evaluated the ability of SCs transplanted into a nerve guide to improve regeneration after sciatic nerve resection, leaving a 6-mm gap, in the mouse. Syngeneic, isogeneic and autologous SCs were suspended in Matrigel and seeded in resorbable guides, and compared to acellular guides and to nerve autografts. The immunogenicity of the transplanted SCs clearly influenced the outcome. Transplants of autologous SCs resulted in only slightly lower levels of reinnervation than autografts, but higher recovery and number of regenerated axons than transplants of isologous and syngeneic SCs, and than acellular guides. Thus, by combined developments on nerve guides, extracellular matrix components and cell transplantation, an artificial graft has been designed that allows axonal regeneration across long gaps to levels comparable with an autograft.

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