Nureddin Ashammakhi

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 epsilon-caprolactone and L-lactic acid 50/50 copolymer (PCL/LLA) film and mesh and poly 96L,4D-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 70L,30DL-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.

Absorbable polyglycolide devices in trauma and bone surgery

Poly(glycolic acid) or polyglycolide (PGA) is a polymer of glycolic acid. Glycolic acid is produced during normal body metabolism and is known as hydroxyacetic acid. Strong implants can be manufactured from this polymer with a self-reinforcing (SR) technique and used in the treatment of fractures and osteotomies. Since 1984, SR-PGA implants have been used routinely in our hospital for internal fixation of bone fractures. These implants were studied extensively in experimental animals and proved biocompatible. In 1.7% of human cases, sinus formation may develop after the use of these implants, which does not disturb healing. Use of these absorbable implants is justified as it obviates the need for a second operation for implant removal and avoids the risks associated with biostable implants.

Strength retention properties of self-reinforced poly l-lactide (SR-PLLA) sutures compared with polyglyconate (MaxonR) 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) and polydioxanone (PDS) sutures in vitro. Sutures made of SR-PLLA (0.3, 0.5 and 0.7 mm diameter), Maxon (0.3 and 0.5 mm diameter) and PDS (0.3 and 0.5 mm diameter) were studied by immersion in phosphate-buffered distilled water (pH 7.4) at 37 degrees 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 sutures of 0.3 and 0.5 mm diameter were of comparable initial tensile strength. Initial knot tensile strength values were lower than those of their counterpart straight sutures. Maxon sutures had lost their tensile strength by 12 weeks; PDS sutures by 20 weeks. SR-PLLA sutures of 0.3 mm diameter had a strength of 161.6 MPa and those of 0.5 mm diameter 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 strength properties of poly-L/D-lactide (PLDLA) 96/4 and polyglyconate (Maxon®) sutures: In vitro, in the subcutis, and in the Achilles tendon of rabbits

Achilles tendon rupture is a common injury. Absorbable sutures are not commonly used because of their limited strength properties. Recently, sutures with prolonged strength retention properties have been developed. The aim of the study is to test the mechanical properties of recently developed poly-L/D-lactide (PLDLA) sutures in comparison with polyglyconate (Maxon) sutures. PLDLA (0.2 mm thick) and Maxon (4.0) sutures were studied in vitro by immersion in a buffered saline solution (pH 7.4). Tensile strength tests were done on sutures retrieved after 1-26 weeks. In vivo, they were implanted in the subcutis of 32 rabbits. Tensile strength tests were done on sutures retrieved after 1-6 weeks. The sutures were also used to repair the Achilles tendon in rabbits. Maximum force before breaking and percentage elongation of tendons were determined. Although PLDLA had a lower initial tensile strength than Maxon, PLDLA showed more prolonged tensile strength retention than Maxon. Tendons repaired with PLDLA, however, had a lower strength than Maxon-repaired tendons at six weeks (insignificant difference). PLDLA has more prolonged tensile strength properties compared with Maxon. Thus, PLDLA offers an alternative to Maxon in repair of the Achilles tendon.

A new technique for correction of trigonocephaly in an infant: application of an absorbable endocranial plate.

Abstractu2002We report on a new method of cranial bone osteofixation using absorbable material, which is applied endocranially to avoid the application of a thick, cosmetically inferior system epicranially in the frontal area. This is especially important in the correction of deformity in trigonocephaly cases. A 9-month-old boy presented with a prominent trigonocephalic deformity. Cranioplasty was performed, in which a supraorbital bar (bandeau) was removed, reinforced with a self-reinforced polylactide (SR-PLA) plate and reshaped to correct the deformity. The plate was applied on the inner side of the bony bar, with its ends fixed epicranially to the temporal bones by means of SR-PLA miniscrews. 3-D CT scans and rapid prototypes were used to evaluate the results. Stable and secure fixation was obtained, and the cosmetic result appeared excellent. No complications occurred during the postoperative period of 1 year. Hence, stabilisation of cranial bone can be achieved endocranially using an absorbable plate and screws, with an encouraging cosmetic result. The method is thought to be reliable.

Neomembranes: A concept review with special reference to self-reinforced polyglycolide membranes

Absorbable implants are being increasingly used in various fields of medicine. Important materials for these applications include the polyesters polylactide and polyglycolide. Following implantation of any absorbable device there occurs a proliferation of fibrous tissue, which along with material from the degrading implant forms a composite membranous structure-a neomembrane. Neomembranes can be exploited in guiding tissue regeneration. Success in this respect has been achieved in treatment of bone defects, nerve defects, and periodontal ligaments. Future research may ultimately permit taking advantage of neomembranes in the reconstruction of more complex organs such as the liver. Gaining an understanding of implant characteristics and implant-tissue interaction is essential for further progress in this area.

Strength retention of self-reinforced drawn poly-L/DL-lactide 70/30 (SR-PLA70) rods and fixation properties of distal femoral osteotomies with these rods. An experimental study on rats

Self-reinforced polylevo-dextro-lactic acid(SR-PLA)70 composite rods,(2 mm×26 mm) were implanted in the dorsal subcutaneus tissue of sixteen rats. Osteotomies of the distal femur were fixed with SR-PLA70 composite rods (2 mm × 15 mm) in 39 rats. The follow-up times varied from 1 week to 1 year. After sacrifice three-point bending and shear tests were performed for subcutaneously placed rods, and radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of osteotomized and intact control femora were performed. At 52 weeks the shear strength and flexural modulus of the rods were 41% of the initial value, and the flexural strength was 43% of the initial value. In the osteotomies seven specimens had to be excluded due to postoperative infection or dislocation of the fragment. Six of the thirty-two evaluated osteotomies showed signs of postoperative infection. Twenty-six osteotomies healed uneventfully. No signs of inflammatory or foreign-body reaction were observed. The present investigation demonstrated that the mechanical strength and fixation properties of the SR-PLA70 rods are suitable for fixation of cancellous bone osteotomies in rats. The present article is the first report on successful application of SR-PLA70 rods for fixation of cancellous bone osteotomies studied.

Strength retention of self-reinforced polyglycolide membrane: An experimental study

Self-reinforced polyglycolide (SR-PGA) devices are stronger than non-reinforced ones. To study the strength retention of SR-PGA membrane, in vitro and in vivo, membranes were either immersed in distilled water at 37 degrees C, or implanted in the subcutis or around the femoral bone of rats. The SR-PGA membranes lost their strength in vitro by 6 wk, while they retained it for 15 wk in vivo due to the fibrous tissue that formed around and inside the implant (biomembrane). This is an advantage when clinical application of the membrane is being considered.

Tissue engineering of bone in muscle by using free periosteal grafts with a self-reinforced polyglycolide membrane scaffold. An experimental study in growing rabbits

Abstractu2002For tissue engineering of predesigned rectangular bone from free tibial and calvarial periosteal grafts, using self-reinforced polyglycolide membrane (SR-PGA) as a scaffold, fourteen growing New Zealand White rabbits were used. In twelve animals, free tibial and calvarial periosteal grafts wrapped around membranes and grafts without membranes were implanted in muscle. In two control animals membranes only were implanted. Follow-up periods were 6 and 12 weeks. Bone formation and tissue reactions were evaluated macroscopically and histologically. Tibial grafts produced bone more often than calvarial grafts (11/12 vs. 5/12). At 6 weeks mature rectangular bone was obtained from tibial grafts with membranes, whereas none was obtained from calvarial grafts with membranes. At 12 weeks, bone ossicles obtained from both types of graft with membranes were clearly smaller than at 6 weeks and the rectangular form was lost. SR-PGA membrane can be used as a scaffold to obtain predesigned rectangular bone from free tibial periosteal grafts in growing rabbits. Transplantation should be performed before resorption occurs.

Absorbable membranes for bone repair: An experimental study on rabbits

To study the use of absorbable self-reinforced polyglycolide (SR-PGA) membranes for bone repair, distal femoral metaphyseal osteotomies were created in 10 rabbits and diaphyseal osteotomies in five. Osteotomies were fixed with intramedullary PLLA rods and PGA membranes were applied over the osteotomy. They were followed up for 6, 12 and 24 weeks. Radiography, histology, microradiography and oxytetracycline fluorescence labelling studies were used to evaluate the outcome. Healing occurred without complications in the metaphyseal series while failure was recorded in the diaphyseal series. In metaphyseal osteotomies, new bone formation was seen medially (on the side of PGA membrane), more proximal and medial to the membrane than at the inlet of osteotomy.