Self-reinforced poly-L-lactide Research Articles

Biocompatibility and strength retention of biodegradable Mg‐Ca‐Zn alloy bone implants

The biocompatibility and strength retention of a Mg-Ca-Zn alloy were studied to evaluate its efficacy for osteosynthesis applications. Mg-Ca-Zn alloy and self-reinforced poly l-lactide (SR-PLLA) bone screws were implanted into New Zealand rabbits for radiography analysis, micro computed tomography analysis, histomorphometry, hematology, serum biochemistry, histopathology, and inductively coupled plasma mass spectrometry analysis. Bending and torsion tests were performed on intact specimens to find the initial mechanical strength of these Mg-Ca-Zn alloy bone screws. Strength retention of the Mg-Ca-Zn alloy implants were calculated from in vivo degradation rates and initial mechanical strength. Based on the animal study, Mg-Ca-Zn alloy bone screw showed absence of subcutaneous gas pockets, characteristic surface erosion properties, faster degradation rate than SR-PLLA bone screw, normal reference range of hematology and serum biochemistry, better histopathological response than SR-PLLA bone screw, and stable concentrations of each constituent element in soft tissues surrounding the implants. The initial strength and strength retention of Mg-Ca-Zn alloy were compared with those of various biomaterials. The initial strength of Mg-Ca-Zn alloy was higher than those of biostable and biodegradable polymers. The strength retention of Mg-Ca-Zn alloy bone screws was similar to those of biodegradable polymer. Therefore, this Mg-Ca-Zn alloy represents an excellent biodegradable biomaterial candidate for osteosynthesis applications.

The effect of low-intensity pulsed ultrasound on bone healing in SR-PLLA rod fixed experimental distal femur osteotomy in rat

The effects of low-intensity pulsed ultrasound (30 mW/cm2) were investigated in experimental cancellous bone fracture healing in bioabsorbable self-reinforced poly-L-lactide (SR-PLLA) rod fixed distal femur osteotomy in rats. A transverse transcondylar osteotomy was fixed with one SR-PLLA rod in 32 male Wistar rats of the age of 20 weeks. Half of the rats had a daily 20-min ultrasound exposure for three weeks. The follow-up times were three, six, and 12 weeks. Radiographical, histological, microradiographical, oxytetracycline labeling, and histomorphometrical analyses were performed. No foreign-body reactions were noted. The biocompatibility of SR-PLLA and ultrasound was found to be good. In the radiological and histological assessments there was a slight tendency for enhanced healing in the ultrasound group at three weeks, but at six and 12 weeks no differences were observed. The histomorphometrical and oxytetracycline labeling analyses showed that ultrasound exposure had no significant effects on bone healing. The present study shows that there were no obvious findings to support the hypothesis that low-intensity pulsed ultrasound enhances bone healing in self-reinforced poly-L-lactide (SR-PLLA) rod fixed experimental metaphyseal distal femur osteotomy in rats. The observed good biocompatibility provides a safe starting-point for clinical trials on bioabsorbable fixation combined with low-intensity ultrasound.

Bioabsorbable screw fixation for the treatment of ankle fractures

BackgroundSelf-reinforced poly(L/DL)lactide 70:30 (SR-PLA70) retains its strength in bone for 24 weeks, whereas self-reinforced poly-L-lactide (SR-PLLA) retains its strength for over 36 weeks. In this prospective randomized study, bioabsorbable 4.5-mm SR-PLA70 screws were compared with SR-PLLA screws in the treatment of displaced ankle fractures in adults. MethodsSixty-two patients with ankle fractures needing operative treatment were randomized into two groups. Comminuted fractures needing plating were excluded. In total 54 of 62 patients were followed up for 1 year by clinical evaluation, radiographs, and Olerud-Molander score. ResultsThe study groups differed significantly only in the mean duration of sick leave (SR-PLA70, 60 days; SR-PLLA, 65 days; P = 0.02). At the 1-year follow-up, syndesmotic ossification was more common in the SR-PLA70 group (5 versus 1 patient, not significant). Radiologically, the screw channel had not disappeared in any of the patients by the 1-year follow-up. ConclusionsBoth implant types proved to have good biocompatibility. SR-PLA70 and SR-PLLA screws are suitable in selected cases for the fixation of ankle fractures, but the mechanical stability of the fixation has to be carefully monitored perioperatively.

In vitro properties of PLLA screws and novel bioabsorbable implant with elastic nucleus to replace intervertebral disc

The suitability of two different implant types for the replacement of the intervertebral disc was studied in vitro. Self-reinforced poly-L-lactide (SR-PLLA) screws Ø 4.5 mm were studied 24 weeks in vitro and cylindrical implants with elastic nucleus made of poly(L/D)lactide 96/4, poly(L/DL)lactide 70/30, Bioactive Glass n:o 13-93 and Polyactive 1000PEOT70PBT30 were studied 15 weeks in vitro. The cylindrical implant mimics the size and shape of the intervertebral disc. During the in vitro, there were no changes in compression properties with either implant types. The screws had sufficient modulus for intervertebral ossification in the canine model and the cylindrical implant showed also sufficient mechanical properties. These results suggest that both implant types could be used in clinical testing.

Assessment of material- and technique-related complications following sagittal split osteotomies stabilized by biodegradable polylactide screws

Objective The aim of this retrospective clinical study was to determine whether there are any material-related problems and increased occurrence of postoperative mandibular nerve and temporomandibular joint dysfunctions in connection with the use of biodegradable self-reinforced poly-L-lactide (SR-PLLA) screws for bone fixation after bilateral sagittal split osteotomies (BSSO). Study design Forty consecutive patients who underwent BSSO and mandibular advancement that included fragment fixation using SR-PLLA screws were monitored for an average of 2.2 years postoperatively. Results The osteotomy sites healed uneventfully with no adverse reactions. The incidence of postoperative sensory disturbances of the inferior alveolar nerve was 27%. Symptoms of temporomandibular joint disorders (TMJD) observed preoperatively in 73% of patients were reduced to 48% after surgery. Conclusion The occurrence of postoperative sensory disturbances and TMJD symptoms in this study did not deviate strikingly from that of other studies using conventional osteosynthesis. No specific complications related to the screw material were observed.

Preliminary assessment of skeletal stability after sagittal split mandibular advancement using a bioresorbable fixation system

We studied skeletal stability during the first year after mandibular advancement and fixation with bioresorbable self-reinforced poly- l-lactide (SR-PLLA) screws in 11 patients by cephalometric measurements. We compared these with a cohort of 11 patients, in whom titanium screws were used for fixation. We found no significant difference between the two groups in the median preoperative cephalometric values and the median changes after operation. There was also no significant difference between the two groups regarding the median extent of relapse 1-year after operation. We conclude that bioresorbable SR-PLLA screws are comparable to metallic screws for fixation of bone after sagittal split mandibular advancement.

Treatment of pectus excavatum with bioabsorbable polylactide plates: Preliminary results

Background/Purpose: Pectus excavatum usually is corrected by thoracoplasty using metal plates. Recently bioabsorbabe polylactide plates have been developed. The aim of this study was to compare outcome after use of metal and bioasorbable plates in thoracoplasty performed for correction of pectus excavatum. Methods: Eighty-three children (<16 years old) underwent thoracoplasty (Sulamaa's technique). In 75 patients, metallic plates, and in 8 patients, self-reinforced poly-L-lactide (SR-PLLA) plates, were used. Seven patients in the SR-PLLA group and 13 patients in the metal plate group were assessed 0.5 to 13 years postoperatively. Results: The mean operating time was 121 minutes in the metal plate group, and 87 minutes in the SR-PLLA plate group. In the metal plate group, complications were pain caused by instability of the metal plates (n = 17), wound infection (n = 3), recurrence of deformity (n = 3), postoperative pain (n = 3), pneumothorax (n = 1), and nonspecific postoperative fever (n = 1). Thirteen patients underwent reoperation to refix the position of the metallic plates. In the SR-PLLA group, one case of pneumothorax occurred, and plate fragment palpability caused local pain in one patient. Cosmetic results and lung function values were similar. Conclusion: Our preliminary results show that bioabsorbable plates are a useful option in the treatment of pectus excavatum in children. J Pediatr Surg 37:1281-1286. Copyright 2002, Elsevier Science (USA). All rights reserved.

Self-reinforced bioabsorbable versus metallic fixation systems for metacarpal and phalangeal fractures: a biomechanical study.

Bioabsorbable fixation devices offer a useful option to treat small bone fractures of the hand if the prerequisite of reliable and stable osteofixation is met. We compared the stabilities of various bioabsorbable fixation devices with metallic fixation devices by using an oblique osteotomy model in radial to ulnar orientation. The 1.5-mm, self-reinforced, poly-L-lactide (SR-PLLA) pins provided fixation rigidity comparable with 1.5-mm K-wires in dorsal and palmar apex bending, whereas in lateral apex bending and in torsion the rigidity was equal to that of 1.25-mm K-wires. The 2.0-mm, self-reinforced, poly-L/DL-lactide (SR-P(L/DL)LA) 70/30 screws provided rigidity comparable with that of 1.5-mm K-wires in all testing modes. The bioabsorbable plate considerably enhanced the bending stabilities of the fixation system, but a single interfragmentary screw provided only limited rotational rigidity. The results show that by using ultra-high strength self-reinforced implants adequate fixation stability for hand fracture fixation can be achieved.

Complications in the first 1,043 operations where self-reinforced poly-L-lactide implants were used solely for tissue fixation in orthopaedics and traumatology.

This is an analysis from one hospital of the first 1043 operations where pure self-reinforced poly-L-lactide (SR-PLLA) implants have been used alone. The operations were performed between 1988 and 1999 and included 407 orthopaedic patients and 636 trauma patients. There was a total of 107 complications. There were 21 infections but no sinus formation. Failure of fixation was seen in 46 patients. In 936 operations the healing was uneventful.

Healing of subcapital femoral osteotomies fixed with self-reinforced poly-L-lactide screws: an experimental long-term study in sheep.

Subcapital femoral osteotomies of ten young adult sheep were fixed with two bioabsorbable, self-reinforced, poly- L-lactide (SR-PLLA) lag screws of 4.5 mm in diameter. At 3 weeks radiographs were taken to check the reduction and fixation achieved. After follow-up periods of 12 weeks, 1 year and 3 years with three sheep in each group, and of 7 years and 4 months with one sheep, the sheep were killed, and the healing of the osteotomies, degradation and tissue response of the implants were examined radiographically, histologically and microradiographically. All osteotomies healed with a firm bony union. There was no dislocation or wound infection. Histologically, there was no marked tissue response in the bone tissue. At 12 weeks the implants were grossly intact, at 1 year granulation tissue and new bone formation had started to penetrate into the implant, and at 3 years the implant area was mostly replaced by connective tissue and new bone, but implant material was still seen as little islands surrounded by some lymphocytes. At 7 years and 4 months, the implant material had been degraded and replaced by tight bone. Self-reinforced poly- L-lactide lag screws seem to possess adequate mechanical properties and good biocompatibility for this demanding fixation.

The effects of low-intensity pulsed ultrasound on bioabsorbable self-reinforced poly l-lactide screws

The effects of low-intensity pulsed ultrasound on the mechanical and molecular properties of self-reinforced poly l-lactide (SR-PLLA) screws were studied in vitro. SR-PLLA screws of 4.5 mm diameter were exposed on low-intensity ultrasound for 1, 3, 6, 9, and 12 weeks. After exposure, the bending strength, shear strength, and molecular weight were investigated. There were no differences in the investigated properties between the ultrasound exposure and control groups. We found no evidence that low-intensity ultrasound has any effect on the mechanical or molecular properties of SR-PLLA screws in vitro. The present results suggest that biodegradable SR-PLLA fixation devices are compatible with low-intensity ultrasound in vitro.

Strength retention properties of self-reinforced poly l-lactide (SR-PLLA) sutures compared with polyglyconate (Maxon R) and polydioxanone (PDS) sutures. An in vitro study

Recent developments in manufacturing techniques have led to the development of strong bioabsorbable materials such as self-reinforced poly l-lactide (SR-PLLA) sutures. The aim of the study was to investigate the mechanical properties of SR-PLLA sutures in comparison with polyglyconate (Maxon R) and polydioxanone (PDS) sutures in vitro. Sutures made of SR-PLLA (0.3, 0.5 and 0.7 mm ∅), Maxon R (0.3 and 0.5 mm ∅) and PDS (0.3 and 0.5 mm ∅) were studied by immersion in phosphate-buffered distilled water (pH 7.4) at 37°C for 40 weeks. The breaking force of straight sutures and suture knots was measured. Tensile strength and percentage elongation were calculated. Means, standard deviations, differences between means, and confidence intervals for differences between means were evaluated. SR-PLLA, PDS and Maxon R sutures of 0.3 and 0.5 mm ∅ were of comparable initial tensile strength. Initial knot tensile strength values were lower than those of their counterpart straight sutures. Maxon R sutures had lost their tensile strength by 12 weeks; PDS sutures by 20 weeks. SR-PLLA sutures of 0.3 mm ∅ had a strength of 161.6 MPa and those of 0.5 mm ∅ had a strength of 134 MPa at 40 weeks. The highest percentage elongation of straight sutures (62.8% and 62%) was exhibited by PDS; the lowest by SR-PLLA (35.6% and 35%). In loop tests, PDS showed the highest percentage elongation (43.7% and 58.1%) and SR-PLLA had the lowest values (19.7% and 33%). SR-PLLA sutures had the most prolonged strength retention in vitro, but the lowest elongation (elasticity). Compared with straight sutures, knots had lower tensile strength and elongation values. SR-PLLA sutures can be applied to the closure of wounds that need prolonged support, such as bone.

Comparison of absorbable poly-l-lactide and metallic intramedullary rods in the fixation of femoral shaft osteotomies: an experimental study in rabbits

An osteotomy of the distal femoral diaphysis was fixed with an intramedullary self-reinforced poly-l-lactide (SR-PLLA) rod in 22 and with a metallic rod in 38 skeletally mature rabbits. Histomorphometric and quantitative computed tomography (QCT) were performed to assess timerelated changes in the consolidation process of the osteotomy of cortical bone and development of the external callus. The follow-up times were 8, 16, 24, and 48 weeks for radiologic and 16, 24, and 48 weeks for histologic studies; 19/22 of the SRPLLA and 34/38 of the metallic fixed osteotomies healed during the observation periods. On microscopic evaluation, no difference was found in histologic parameters such as external callus area and fraction, and endosteal callus area and fraction between SR-PLLA and metallic fixed osteotomies. The total external callus area increased up to 16 weeks and subsequently decreased linearly over time in both experimental groups. However, the mean endosteal bone area and fraction decreased after 16 weeks in metallic fixated femora, while in the SR-PLLA fixated femora, both these values increased, being greater in the SR-PLLA group. The mean external callus QCT density decreased after 8 weeks in both experimental groups, the decrease being greater in the SR-PLLA group. Nevertheless, no significant difference was detected between SR-PLLA and metallic fixed femora in any of the follow-ups. These results suggest that both SR-PLLA and metallic rods are suitable in the fixation of femoral shaft osteotomies in rabbits. Furthermore, SR-PLLA rod fixation seems to have a minor stress-shielding effect.

Prefabricating bone in muscle by using free tibial periosteal grafts and self-reinforced polyglycolide and poly-L-lactide pins

To investigate the possibility of prefabricating bone of predetermined form in muscle using free tibial periosteal grafts and biodegradable pins, operations were performed on 12 growing rabbits. In each animal, (1) a graft around a self-reinforced polyglycolide (SR-PGA) pin, (2) a graft around a self-reinforced poly-L-lactide (SR-PLLA) pin, (3) a SR-PGA pin, and (4) a SR-PLLA pin were implanted in the dorsal muscles for 6 weeks. Histological and histomorphometric evaluations were performed. Bone formation from periosteal grafts was observed in all 12 animals. The shape of the newly-formed bone was grossly cylindrical in all specimens except one. Bone formation was stronger around the SR-PGA pins than around the SR-PLLA pins. The pins without grafts did not induce any bone formation, but fibrous tissue encapsulation instead. A mild foreign body reaction was elicited by SR-PGA pins, while it was almost absent with SR-PLLA pins. It is thus possible to prefabricate bone in a cylindrical form in growing rabbits using free tibial periosteal grafts and SR-PGA or SR-PLLA pins implanted in muscle.

Bioabsorbable scaffolds for guided bone regeneration and generation

Several different bioabsorbable scaffolds designed and manufactured for guided bone regeneration and generation have been developed. In order to enhance the bioactivity and potential osteoconductivity of the scaffolds, different bioabsorbable polymers, composites of polymer and bioactive glass, and textured surface structures of the manufactured devices and composites were investigated in in vitro studies and experimental animal models. Solid, self-reinforced polyglycolide (SR-PGA) rods and self-reinforced poly l–lactide (SR-PLLA) rods were successfully used as scaffolds for bone formation in muscle by free tibial periosteal grafts in animal experiments. In an experimental maxillary cleft model, a bioabsorbable composite membrane of ε-caprolactone and l-lactic acid 50/50 copolymer (PCL/LLA) film and mesh and poly 96 l,4 d-lactide (PLA96) mesh were found to be suitable materials for guiding bone regeneration in the cleft defect area. The idea of solid layer and porous layer combined together was also transferred to stiff composite of poly 70 l,30 dl-lactide (PLA70) plate and PLA96 mesh which structure is introduced. The osteoconductivity of several different biodegradable composites of polymers and bioactive glass (BG) was shown by apatite formation in vitro. Three composites studied were self-reinforced composite of PLA70 and bioactive glass (SR-(PLA70+BG)), SR-PLA70 plate coated with BG spheres, and Polyactive ® with BG.

SR-PLLA and SR-PGA miniscrews: biodegradation and tissue reactions in the calvarium and dura mater

The biocompatibility and degradation of self-reinforced poly-L-lactide (SR-PLLA) and polyglycolide (SR-PGA) miniscrews, vs titanium miniscrews, was studied in frontal bone osteotomies in 20 lambs, where they were used for plate fixation. At follow-up at 4, 6, 12, 26, 52 and 104 weeks, no clinical foreign body reaction, infection or other complications had occurred. Histologically, PGA material was hydrolyzed and fragmented at 4-6 weeks and was resorbed by 12 weeks, whereas the SR-PLLA miniscrews retained their integrity and holding power for 26 weeks and were mostly resorbed at 2 years. According to histological and histomorphometric analyses and plain film radiography, the degradation of PGA miniscrews was accompanied by a typical non-specific foreign-body reaction and initial transient osteolysis with decreased osteoid formation around the screw channel, but compensatory intense osteoid formation and bone remodelling followed after resorption of the polymer. The foreign body reactions to PLLA and titanium were considerably milder. All miniscrews were commendably strong and could be satisfactorily tightened against the plate. SR-PLLA miniscrews offer fixation stability for half a year, whereas rapidly degrading SR-PGA miniscrews may be used when short-term fixation is needed.

Bioabsorbable Self-reinforced Poly-l-Lactide, Metallic, and Silicone Stents in the Management of Experimental Tracheal Stenosis

The aim of the present study was to compare, in rabbits, the biocompatibility and suitability of a bioabsorbable spiral stent made of self-reinforced poly-L-lactide (SR-PLLA) in the management of experimental tracheal stenosis with stents made of metal and silicone. Tracheobronchial stenosis, and its management, is still problematic because stenoses are not always amenable to surgical resection and reconstruction, especially concerning anastomotic problems and stenosis after lung transplantation. Stenosis can be handled with stenting, although the ideal stent has yet to be developed; all the stents available have their disadvantages. Because stenting of the airways can be only temporary, stents made of bioabsorbable materials, theoretically, offer benefits. Tracheal stenosis was created in rabbits by the extramucosal resection of cartilaginous arches of the cervical trachea. After a few weeks, the animals were operated on again, and those stenoses that had developed were dilated with a balloon. Stents then were implanted in the area of stenosis to keep the dilated trachea open. All the animals in the group with silicone stents had to be killed because of respiratory difficulties: their stents had a tendency to occlude because of internal encrustation, and they developed a hyperplastic polyp at the ends of the stents. The SR-PLLA and metallic stents were tolerated well, and after follow-up ended the animals were put to death. This experimental study showed that silicone stents had a tendency to occlude and that stents made of metal and of SR-PLLA were well tolerated and can be used in the management of airway stenosis.

Tissue response to bioabsorbable self-reinforced polylevolactide and polyglycolide pins implanted intra-articularly and directly into the bone on different levels. An experimental study on rats.

Self-reinforced poly-L-lactide (SR-PLLA) and self-reinforced polyglycolide (SR-PGA) pins were implanted intra-articularly and directly into the bone of the distal femur of rats at three levels: above, on the same level, and under the surface. For the controls only channels were drilled, or the controls were not operated at all. The follow-up times were 3, 6, and 12 weeks for SR-PGA and 3, 6, 12, and 24 weeks for SR-PLLA. The macroscopic appearance and histologically the villus reaction, the mononuclear phagocytosis and giant cells, the neutrophils, the lymphocytes, the plasma cells, the eosinophils, and the mast cells were analyzed. In the histologic analysis, the most favorable implantation depth was found to be under the surface where the contact between the implants and bone was best, and the orifice was covered with new trabecular bone at 3 weeks. This was especially seen in intra-articular implantation. In general, the tissue responses were mild, and could also be explained in the statistical analysis by a normal postoperative tissue response and faster biodegradation of PGA.

A 5-year in vitro and in vivo study of the biodegradation of polylactide plates

Purpose: The purpose of this study was to investigate the long-term tissue response and duration of degradation of self-reinforced poly-L-lactide (SR-PLLA) multilayer plates in vivo. Materials and Methods: Mandibular osteotomies in sheep were fixed with SR-PLLA multilayer plates. The animals were followed for 1, 2, 3, 4, and 5 years, after which histologic studies were performed. Results: The foreign-body reaction was mainly mild, and the osteotomies were well united. After 5 years in vivo, the material was almost completely resorbed, but small particles of polymer could still be detected at the implantation site. SR-PLLA plates were also incubated in vitro for 5 years. The material degraded considerably faster in vivo than in vitro. Molecular weight, melting temperature, and crystallinity of the plates remained at a constant level after 2 years in vitro, indicating very slow degradation of the oligomeric (molecular weight [Mw], 3500 daltons), highly crystalline (heat of fusion, 70 J/g), PLLA residue solely as a result of hydrolysis. Although the plates became increasingly fragile as they degraded, they retained their macroscopic form until the end of the 5-year follow-up. Loss of mass of the plates was 52% ± 8% after 5 years of incubation in vitro. Conclusions: Although the long degradation period may seem to be a minor drawback to the use of such plates, it does not appear to affect the healing process.

Tissue response to polyglycolide and polylactide pins in cancellous bone.

An absorbable self-reinforced polyglycolide (SR-PGA) pin, 2.0 mm in diameter and 15 mm in length, was implanted in the trabecular bone areas of the distal femur of 51 rats and a biodegradable self-reinforced poly-L-lactide (SR-PLLA) pin of the same size was inserted into the distal femur of the other hind leg of the same rats. The intact femora of eight non-operated rats were used as controls. Tissue reaction to the implants was examined within standardized sample fields radiographically, histologically, histomorphometrically, microradiographically and using oxytetracycline fluorescence studies. The follow-up periods of the groups consisting of five operated rats and one intact control rat were 1, 3, 6, 12, 24, 36, 48 and 52 weeks. Eleven extra rats were operated on to ensure five samples in each follow-up group for the final analyses. The first signs of degradation of the SR-PGA pin were seen at 3 weeks, and the pin was totally degraded by 36 weeks. No signs of degradation of the SR-PLLA pin were observed during the follow-up period. Active new bone formation was seen close to the implant profile at 1 week in both groups. At 12 weeks the mean fractional osteoid formation surface was statistically significantly (P < 0.01) higher in the SR-PGA-implanted specimens than in the SR-PLLA-implanted specimens. At that time there were also statistically significantly (P < 0.05) more phagocyting macrophages in the SR-PGA-implanted specimens than in the SR-PLLA-implanted specimens, which is in accordance with the degradation behaviour of both implants. The biocompatibility of polyglycolide and polylactide proved to be good.