Self-reinforced Polylactide Research Articles

In-situ self-reinforcement of amorphous polylactide (PLA) through induced crystallites network and its highly ductile and toughened PLA/poly(butylene adipate-co-terephthalate) (PBAT) blends

Crystallites of a semicrystalline polylactide (cPLA) were induced in an amorphous PLA (aPLA) and its blends with poly(butylene adipate-co-terephthalate) (PBAT) to achieve in-situ self-reinforced PLA based structures. The approach involved the melt blending of cPLA as a minor phase with aPLA and its blends with PBAT at processing temperatures below the crystal melting peak of cPLA. An injection molding (IM) process was first adopted to obtain self-reinforced PLA (SR-PLA) structures at aPLA/cPLA weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20. IM barrel and mold temperatures revealed crucial impacts on preserving the cPLA crystallites and thereby enhancing the final mechanical performance of SR-PLA (i.e., aPLA/cPLA) samples. SR-PLA samples at various aPLA/cPLA weight ratios of 100/0, 90/10, 80/20, and 70/30 were then melt blended with PBAT to produce SR-PLA/PBAT at a given ratio of 85/15. These blends were first prepared in an internal melt mixer (MM) to evaluate the rheological properties. The rheological analysis confirmed the significance of cPLA reinforcing efficiency within SR-PLA and its corresponding blends with PBAT. Similar SR-PLA/PBAT blends were also prepared using the IM process to explore their thermal and mechanical characteristics. The effect of cPLA concentrations in blends was distinctive, leading to significant enhancements in stain at break and toughness values. This was due to the increased crystallite network within the matrix, further refining PBAT droplets. Morphological analysis of the melt-processed blends through MM and IM also revealed that the PBAT droplets were further refined when the IM process was applied. The induced shear during the molding could have further elongated the cPLA crystallites towards a fiberlike structure, which could additionally cause the matrix viscosity to increase and refine the PBAT droplets.

Transparent, Heat-Resistant, Ductile, and Self-Reinforced Polylactide through Simultaneous Formation of Nanocrystals and an Oriented Amorphous Phase

Imparting polylactide (PLA) films with great heat resistance, transparency, and balanced mechanical performance simultaneous is a big challenge in academia and industry due to mutual exclusiveness of properties. In this work, a newfound strategy that combines elongational stress field and thermal field is proposed to reorganize the crystalline and amorphous structure of PLA films. It is discovered that the oriented PLA films with high draw ratios form a unique structure of the oriented amorphous phase restricted by the oriented nanosized crystal during thermal treatment at an appropriate temperature. Superb stiffness–toughness balance of the film is achieved as the elongation at break increases from 16 to 91.9% after the thermal treatment at 150 °C, while the yield strength increases from 50.0 to 76.0 MPa. It is worth noting that the PLA film also has excellent transparency, i.e., a transmittance as high as 86.6% (550 nm), owing to crystallites formed on the nanometer scale. Excellent heat resistance is also obtained, with the onset decline temperature increasing from 63.7 (for the unstructured casting film) to 77.1 °C due to increased crystallinity. Furthermore, a new understanding of the orientation of the amorphous phase promoted by the confinement effect to the toughening of PLA is obtained, and a phenomenal model for the thermal-treatment-induced toughening effect is proposed. This work could provide a significant guidance for the facile preparation of a PLA film with promising comprehensive properties of toughness–stiffness balance, high transparency, and good heat resistance.

Interface characterization of hybrid biocompatible fiber-metal laminates after laser-based surface treatment

Fiber metal-laminates, which are based on titanium and a self-reinforced biocompatible polylactide (srPLA), are a promising approach to extend the range of materials for medical implants. A laser-based surface pre-treatment results in a strong bond between the metallic and polymeric part that are joined via hot-pressing. An extensive parameter study supported by scanning electron microscopy of the titanium sheets as well as shear edge testing with the hybrid material, allowed for a direct definition of suitable laser structures for the pre-treatment of the metallic component. A post-mortem optical examination also gave a qualitative insight into the failure mechanisms. It was possible to show that a laser induced pre-treatment significantly enhanced interface strength compared to an untreated surface with the considered testing method. Hence, a laser-induced surface treatment is a suitable pre-treatment process for the selected material combination, titanium and self-reinforced polylactide (PLA), to achieve increased interface strength.

Treatment of medial humeral epicondyle fractures in children using absorbable self-reinforced polylactide pins.

The best treatment for medial humeral epicondyle fractures in children has been debated. In case of incarceration of the epicondylar fragment, particularly after elbow dislocation, several materials are used for fixation, including Kirschner wires (K-wires), metallic compression screws, tension band wire, and suture anchors. Herein, we introduce a new fixation material: the absorbable self-reinforced polylactide (SR-PLA) pin.The aim of the study was to prove the feasibility of a new fixation material (absorbable SR-PLA pins) for the treatment of medial epicondyle fracture in children.Thirty-two patients who underwent surgery in our hospital from August 2007 to January 2012 were retrospectively analyzed. The patients were divided into group A (K-wires) and group B (absorbable SR-PLA pin). Group A comprised 11 males and 4 females, aged 8 to 14 years (average, 12.6 years), with 12 patients with elbow dislocation. Group B comprised 13 males and 4 females, aged 7 to 15 years (average, 11.8 years), with 13 patients with elbow dislocation. The same approach was used for all patients by the same team of surgeons, and all the patients were followed up for over 12 months. In all patients, rehabilitation training was started after 3 weeks. The Broberg and Morrey elbow scale was used to evaluate elbow function at follow-up.Four patients from group A developed pin-track infections that gradually resolved after removal of the K-wires, whereas no infections occurred in group B. One patient refractured her humerus after K-wire removal. Using the Broberg and Morrey elbow scale, outcomes in group A were classified as excellent in 5 patients (33.33%), good in 7 patients (46.67%), fair in 2 patients (13.33%), and poor in 1 (0.07%). Group B outcomes were scored as excellent in 12 patients (70.58%), good in 4 (23.53%), and fair in 1 (0.06%) and no patient (0.00%) had a poor outcome. The average Broberg and Morrey score for group A was significantly lower than that for group B (83.27 ± 7.02 vs 95.21 ± 5.04; P = .0238).Absorbable SR-PLA pins can be safely used for medial epicondyle fractures in children. Our results indicate that SR-PLA pins are associated with better short-term functional outcome than K-wires.Level of evidence: III

Thermomechanical properties of highly transparent self-reinforced polylactide composites with electrospun stereocomplex polylactide nanofibers

Stereocomplex polylactide (sc-PLA) nanofibers with the average diameter of 367 nm were prepared by the conductivity-controlled electrospinning using 7 wt% PLA solution in the mixed solvents of dichloromethane and pyridine. The sc-PLA nanofibers were used as reinforcement materials for poly(l-lactide) (PLLA) to fabricate a self-reinforced PLA composite, while the fibers were compounded into the PLLA by compression molding. Thermomechanical and optical properties of the resulting self-reinforced PLA composites were investigated. It was found that highly transparent (above 75%) self-reinforced PLA composites were obtained up to the sc-PLA fiber concentration of 15 wt%. Also, at higher temperature in the rubbery state, the storage moduli of the composites increased by adding sc-PLA nanofibers. At the fiber concentration of 15 wt%, the storage modulus of the composite became 70 MPa, which was 24.1 times higher than that of the original pure PLLA. It was therefore concluded that the self-reinforced PLA composite with high transparency and high thermomechanical properties was successfully obtained.

Aligned unidirectional PLA/bacterial cellulose nanocomposite fibre reinforced PDLLA composites

In an effort to enhance the properties of polylactide (PLA), we have developed melt-spinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly(L-lactide) (PLLA) fibres were filled with 2wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6GPa) and strength (127MPa), over monolithic PLLA, previously measured at 1.3GPa and 61MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7wt.% cellulose nanocrystals (CNCs), which is higher than the percolation threshold (equivalent to 6vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60vol.% PLLA fibres reinforced with 7wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%.

Fabrication of a biodegradable calcium polyphosphate/polyvinyl‐urethane carbonate composite for high load bearing osteosynthesis applications

The formation of biodegradable implants for use in osteosynthesis has been a major goal of biomaterials research for the past 2-3 decades. Self-reinforced polylactide systems represent the most significant success of this research to date, however, with elastic constants up to 12-15 GPa at best, they fail to provide the initial stiffness required of devices for stabilizing fractures of major load-bearing bones. Our research has investigated the use of calcium polyphosphate (CPP), an inorganic polymer in combination with polyvinyl-urethane carbonate (PVUC) organic polymers for such applications. Initial studies indicated that composite samples formed as interpenetrating phase composites (IPC) exhibited suitable as-made strength and stiffness, however, they displayed a rapid loss of properties when exposed to in vitro aging. An investigation to determine the mechanism of this accelerated in vitro degradation for the IPCs as well as to identify possible design changes to overcome this drawback was undertaken using a model IPC system. It was found that strong interfacial strength and minimal swelling of the PVUC are very important for obtaining and maintaining appropriate mechanical properties in vitro.

Repair of Radial Fractures in Toy Breed Dogs with Self‐Reinforced Biodegradable Bone Plates, Metal Screws, and Light‐Weight External Coaptation

To describe a surgical technique for, and outcome after, treatment of radial fractures with biodegradable self-reinforced polylactide plates and metal screws, and external coaptation. Prospective clinical study. Eleven Toy breed dogs. Radial fractures were repaired by application of a single or 2 stacked biodegradable self-reinforced polylactide plates (poly-L/D, L-lactide, stereocopolymer [LL-and DL-lactide ratio 70/30]; SR-PLA (70/30) implants) secured with metal screws, and light-weight external coaptation. Healing was evaluated clinically and by radiography at 2, 4, 6, 8, 9, 12, 24-26 weeks, and at 1 and 2 years. Owners were interviewed 3 years after surgery. Radial fracture lines disappeared within 4-14 weeks in 10 dogs; an implant failed in 1 dog. Ambulation was excellent for healed fractures. Excessive skin tension led to removal of implants in 1 dog and suture repair in another dog. No foreign body reaction from implant degradation was observed and the plate was usually no longer palpable at 2 years. One dog had a fracture through a screw hole at 1 year. Healing and complication rates after repair of radial fractures with SR-PLA (70/30) plates were considered similar or better than reported after repair with metallic plates or external fixation in Toy breed dogs. No radiographic signs of osteopenia were identified under the plate during follow-up. Biodegradable polylactide plates could be considered as an alternative to metal plates for radial fracture repair in Toy breed dogs, however available plates are likely not strong enough when used as a single plate. Implant removal is usually not needed.

A retrospective evaluation of rigid fixation in orthognathic surgery using a biodegradable self-reinforced (70L:30DL) polyactide

Objective: This study was designed to evaluate clinical and radiological evidence of osteotomy site healing in orthognathic surgery after rigid fixation using a biodegradable plating system. Study design: A follow up of 30 patients who underwent orthognathic surgery using a biodegradable self-reinforced (70L:30DL) polylactide plating system was presented. The follow-up schedule for all patients consisted of regular appointments at 1–180 days after surgery. Clinical evaluation involved notation of any abnormal swelling, infection, discoloration, or discharge at the osteotomy sites. Stability was evaluated by manual palpation. For radiographic evaluation, panoramic radiographs were taken immediately after surgery, and again at 7–180 days. The radiographs were analyzed for any visual changes in osteotomy fragments, resorptive changes in osteotomy fragments, callus formation, and union of the osteotomy segments. Results: No clinical complications and no radiological changes in the osteotomy sites were observed. Regarding the clinical usefulness of the biodegradable fixation system, fixation at the time of operation was considered as excellent in all 30 cases. Conclusions: The conclusions of this study were that self-reinforced (70L:30DL) polylactide was considered to be comparable to other forms of rigid internal fixation for orthognathic surgery.

The effect of transforming growth factor- β1, released from a bioabsorbable self-reinforced polylactide pin, on a bone defect

Transforming growth factor-beta 1 (TGF- β1)is a polypeptide growth factor which has been shown to increase bone formation in experimental studies. In this study it was combined to a bioabsorbable self-reinforced poly- ld-lactic acid fracture fixation pin. To assess the effect of TGF- β1 on the healing of a bone defect, the pins were implanted in the rat distal femur next to a bone defect filled with a viscose cellulose sponge. The pins used in the study group (13 rats) contained 50 μg of TGF- β1, whereas in the control group of nine rats an identical pin without the growth factor was used. In the histologic examination at 1, 3 and 6 weeks no difference was detected in the amount of bone inside the viscose cellulose sponge between the rats treated with TGF- β1 and those with no added growth factor. At 3 weeks there was more fibroblast-rich mesenchymal tissue inside the viscose cellulose sponge in the rats treated with TGF- β1. In the radiographic examination at 3 weeks there was an increase in the amount of new periosteal bone on the bone defect in the TGF- β1-treated rats.

Holding power of bioabsorbable ciprofloxacin-containing self-reinforced poly-L/DL-lactide 70/30 bioactive glass 13 miniscrews in human cadaver bone.

Antibiotics-plus bioactive glass-containing bioabsorbable self-reinforced (SR) polylactide screws have been developed for antibacterial osteoconductive bone fixation. The aim of the present study was to test the pullout properties of these recently developed miniscrews. Ciprofloxacin-plus bioactive glass-containing SR-polylactide miniscrews (BC) were compared with miniscrews made of neat SR-polylactide (A), SR-polylactide with bioactive glass (B), and ciprofloxacin-containing SR-polylactide (C). BC miniscrews and their controls (A, B, C) (all of length 6.0 mm, core diameter 1.45 mm, thread diameter 2.0 mm) were applied to one pair of cadaveric fibulae. Pullout force was measured using a materials testing machine. We carried out 49-50 pullout tests for each implant type. The Mann-Whitney test and Student's t-test were used for statistical evaluation. The pullout force for BC miniscrews was 114.9 +/- 34.0 (SD) N. Pullout forces for control miniscrews were 162.7 +/- 37.8 N (A), 99.1 +/- 16.2 N (B), and 142.9 +/- 26.9 N (C). Differences between the four groups were statistically significant (p < 0.001). Ciprofloxacin-plus bioactive glass-containing polylactide miniscrews have good holding power to human cadaver fibulae. However, adding bioactive glass and ciprofloxacin components to neat SR-polylactide results in lower pullout values.

Shear-load carrying capacities of the distal rat femora after osteotomy fixed with self-reinforced polyglycolic acid and poly-L-lactic acid pins.

Distal femora of 40 rats were osteotomized and fixed with self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) pin 2.0 mm in diameter and 15 mm in length. The shear-load carrying capacities of the osteotomized bones were compared with each other and with the intact control rat distal femora of the same age of 20 pairs. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities reached their highest values at 24 weeks in the SR-PGA-fixed specimens, after that decreasing to the level where they remained. In the SR-PLLA-fixed specimens the strength values of the pins increased after three weeks, but there was a decrease at 24 weeks. After that the shear-load carrying capacities started to raise because of the influence of the healed osteotomy. In the control bones the shear-load carrying capacities were weaker than in the SR-PGA-and SR-PLLA-fixed specimens except at three weeks, as the osteotomies had not yet healed. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA-fixed specimens was 199.1 N, in the SR-PLLA-fixed specimens 214.6 N, the corresponding value of the control specimens being 148.2 N.

The Biodegradable Intramedullar Nail - Biomechanical Results and Tissue Response 4 Years after Implantation in Sheep -

The conventional metal intramedullar nail has considerable drawbacks. A second operation is often needed to remove the nail after fracture healing. The stress-shield phenomenon can cause impaired fracture healing, and there is the possibility of infection, allergic reaction and corrosion.To avoid these problems a biodegradable interlocking nail was developed. Ideally, the biodegradable intramedullar nail will lose its strength gradually during a controlled degradation pattern and the load on the fractured bone will gradually shift from implant to bone.The results of a long term follow up study (4 years) in an animal model using adult sheep are presented in this paper.A self-reinforced polylactide intramedullar nail was used for the fixation of an artificially made femoral fracture.The following parameters were subject of investigation: clinical fracture healing, radiological results, mechanical properties of the bones and local and regional histological response.Macroscopically some shortening and angulation of the fractured femora was observed. The clinical healing was unimpaired and the mechanical tests were excellent in four sheep. Histological analysis showed a mild tissue response and a partial degradation of the implant.

Effect of gamma, ethylene oxide, electron beam, and plasma sterilization on the behaviour of SR-PLLA fibres in vitro

- The aim of this study was to evaluate the effect of various sterilization processes on the physical and mechanical properties of self-reinforced bioabsorbable fibres made out of polylactide (PLLA). The samples were sterilized using plasma, ethylene oxide (one and two cycles), gamma (25 kGy at room temperature, 25 kGy in dry ice, and 2 × 25 kGy at room temperature), and electron beam (15, 25, and 55 kGy) sterilization. The intrinsic viscosity, crystallinity, and mechanical properties (modulus of elasticity, yield strength, and ultimate tensile strength) were tested before and immediately after each sterilization treatment, as well as up to 30 weeks in vitro. Compared with unsterilized fibres, the intrinsic viscosity was markedly decreased after radiation sterilization (gamma and electron beam) and the loss in mechanical properties was accelerated during in vitro degradation. Plasma and ethylene oxide (one and two cycles) did not markedly alter the properties of the samples after sterilization or during in vitrodegradation. These data are important for determining the effect of various sterilization processes on the physical and mechanical properties of polylactidebased materials and can be used to predict how fast degradation of the mechanical properties of the self-reinforced PLLA will occur. They can also be used to tailor the degradation kinetics to optimize implant design.

Causes of the clinical tissue response to polyglycolide and polylactide implants with an emphasis on the knee.

The causes of a clinical tissue response to self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) implants were studied in the first 2500 polymeric fixations. The incidence was 8.0% in fixations with implants made of SR-PGA (n = 1879) and 0% in SR-PLLA fixations (n = 621). A small number of fixations per site seemed to increase the incidence of a tissue response. In diagnoses involving over 50 fixations, except for ankle fractures, the incidence was 4.2%. The site of fixation influenced the incidence; the lowest incidence was seen for radial head fracture fixation (1.1%). The aromatic dye which has not been used since 1988 in the SR-PGA implant increased the response. A large total implant volume and a large number of implants increased the incidence of a tissue response. In the knee (n = 131), the incidence of a clinical tissue response was 4.3%, with four fluid accumulations and one synovitis of the knee after fixation with SR-PGA implants.

Use of self-reinforced polylactide osteosynthesis devices in craniofacial surgery: a long-term follow-up study.

Self-reinforced polylactic acid or polylactide (SR-PLA) is a biodegradable polymer, which is strong enough to fix weight-bearing cortical bone fractures and osteotomies. We report our experience and follow-up of the use of SR-PLA plates in 15 clinical cranioplasties. Two of the cases are described in greater detail. In one of them SR-PLA plates were used in addition to titanium plates, and in the other an SR-PLA plate fixed with mini-titanium screws was used as the only fixation material. In the other patients SR-PLA plates or wire were used in addition to titanium. So far no complications have been observed in these 15 patients. The only small superficial fistula was associated with a titanium plate and titanium screws. The longest follow-up has been over eight years. Recent results show metal-like deformation properties in addition to complete late resorption, making SR-PLA osteosynthesis devices promising for use in craniofacial surgery.

Poly-L-lactic acid plate for covering of small cranial bone holes: an experimental study in rabbits

Cranioplasty was performed on 13 adult New Zealand white rabbits to investigate the potential of poly-L-lactic acid (PLLA) plates for cover of small cranial bone holes. Two holes of 5 mm in diameter were drilled through the parietal bone, one on each side of the skull. One was covered with a self-reinforced polylactide (SR-PLLA) plate while the other one was left empty, with only the periosteum covering. The results were analysed by taking X-rays and samples for histological examination 3, 6, 24 and 48 weeks postoperatively. There were no special radiological findings. Histologically, new bone formation was clearly seen on the implant side at 24 and 48 weeks after the operation, while there was only a slight reaction on the control side in the same rabbit. We conclude that SR-PLLA appears to enhance the healing of cranial bone.

Operative treatment of osteochondritis dissecans of the knee: a retrospective comparison of fixation with autologous bone pegs vs. bioabsorbable rods

Osteochondritis dissecans fragment of medial femoral condyle was fixed with cortical bone pegs in 18 patients and in 22 patients using bioabsorbable rods (self-reinforced polyglycolide, SR-PGA rods or self-reinforced polylactide, SR-PLLA rods). After cortical bone peg fixation the Lysholm functional knee score was median 79.5 (range 32–100) and after bioabsorbable rod fixation it was 86.5 (range 49–100, NS). The Tegnér activity scale level was lower (median 4.0; range 2–7), after bone peg fixation than after bioabsorbable rod fixation where it was 5.0 (range 2–9; P=0.005). No statistical difference was noted in clinical outcomes. The complication rate was similar in the groups. We conclude that both methods produce a reliable fixation of osteochondritis dissecans with no need for removal of the implant.

Combining transforming growth factor-β1 to a bioabsorbable self-reinforced polylactide pin for osteotomy healing: an experimental study on rats

The effect of a bioabsorbable pin containing transforming growth factor-β1 on fracture healing was studied in a rat model. The growth factor was mixed into a bioabsorbable polymer paste (a blend of an L-lactic acid oligomer and a copolymer of ε-caprolactone and DL-lactide) that was used to fill the grooves of a self-reinforced fracture fixation pin made of a poly-LD-lactic acid copolymer. In an in vitro assay, sustained release of the growth factor from the pins over a 7-day period was demonstrated. A distal femoral osteotomy was made in 60 rats and stabilized with the fracture fixation pin in 48 of them; In the remaining 12 rats, no fixation was performed. The pin used in the study group contained either 5μ (15 rats) or 50 μg (15 rats) of the growth factor, while in a control group of 18 rats an identical pin without the growth factor was used. After a follow-up of 1, 3, or 6 weeks, the femurs were examined radiographically, histologically, histomorphometrically, and microradiographically, and also used in tetracycline labeling studies. Faster callus formation was evident in the growth factor-treated rats but no acceleration in the healing of the osteotomy was detected.

Fixation of mandibular body osteotomies using biodegradable amorphous self-reinforced (70L:30DL) polylactide or metal lag screws: an experimental study in sheep

Mandibular body osteotomies were fixed in nine sheep using new totally amorphous (70L:30DL), self-reinforced, polylactide (SR-PLA) lag screws and in nine sheep using standard stainless steel lag screws. No intermaxillary fixation was used. During follow-up, radiological, histological and microradiological studies were undertaken at 3, 6, 12 and 24 weeks. In both groups, all osteotomies consolidated at similar rates and no adverse reaction to the screws was seen. However, displacements of the fixed osteotomy fragments were common in both groups during the first 3 weeks. The biocompatibility of SR-PLA during the follow-up period was found to be good. Only initial signs of biodegradation were seen. The results of this study indicate that (70L:30DL) SR-PLA has potential for use as a fixation screw material in oral and maxillofacial surgery, and that further studies using this material are justified.