Daniel Kaltbeitzel

Preliminary results in anterior cervical discectomy and fusion with an experimental bioabsorbable cage - clinical and radiological findings in an ovine animal model

BackgroundBioabsorbable implants are not widely used in spine surgery. This study investigated the clinical and radiological findings after anterior cervical discectomy and fusion (ACDF) in an ovine animal model with an experimental bioabsorbable cage consisting of magnesium and polymer (poly-ϵ-caprolactone, PCL) in comparison to a tricortical bone graft as the gold standard procedure.Materials and Methods24 full-grown sheep had ACDF of C3/4 and C5/6 with an experimental bioabsorbable implant (magnesium and PCL) in one level and an autologous tricortical bone graft in the second level. The sheep were divided into 4 groups (6 sheep each). After 3, 6, 12, or 24 weeks postoperatively, the cervical spines were harvested and conventional x-rays of each operated segment were conducted. The progress of interbody fusion was classified according to a three-point scoring system.ResultsThere were no operation related complications except for one intraoperative fracture of the anterior superior iliac spine and two cases of screw loosening and sinking, respectively. In particular, no vascular, neurologic, wound healing or infectious problems were observed. According to the time of follow-up, both interbody fusion devices showed similar behaviour with increasing intervertebral osseointegration and complete arthrodesis in 10 of 12 (83.3%) motion segments after 24 weeks.ConclusionsThe bioabsorbable magnesium-PCL cage used in this experimental animal study showed clinically no signs of incompatibility such as infectious or wound healing problems. The radiographic results regarding the osseointegration are comparable between the cage and the bone graft group.

Bioabsorbable Interbody Magnesium-polymer Cage: Degradation Kinetics, Biomechanical Stiffness, and Histological Findings From an Ovine Cervical Spine Fusion Model

Study Design. An experimental study using a sheep cervical spine interbody fusion model. Objective. First, to compare anterior cervical discectomy and fusion of an experimental bioabsorbable cage consisting of a magnesium alloy and a polymer (poly-&egr;-caprolactone, PCL) with an autologous tricortical iliac crest bone graft. Second, to determine the degradation kinetics of the cage, assess the 2 fusion devices for biomechanical stability, and determine their histological characteristics. Summary of Background Data. Bioabsorbable cages are not routinely used in spine surgery at present, due to some undesirable effects such as cracks and foreign body reactions. This study involved the manufacture of a bioabsorbable cage from a magnesium alloy and the polymer PCL, which was then used as a device for anterior cervical discectomy and fusion in a sheep cervical spine fusion model. Methods. Twenty-four sheep had anterior cervical discectomy and fusion of C3–C4 and C5–C6 with an experimental bioabsorbable cage consisting of the magnesium alloy AZ31, which was infiltrated and covered with PCL at 1 level and with an autologous tricortical iliac crest bone graft at a second level. The sheep were divided into 4 groups. After 3, 6, 12, or 24 weeks postimplantation, the animals were killed and the cervical spines were harvested. The intervertebral spaces with the cage were investigated using &mgr;-computed tomographic images to calculate degradation kinetics. Stiffness of all monosegments was determined through biomechanical testing. Histological analysis was performed to evaluate fusion status and to detect any foreign body reactions. The results from both implants were compared. Results. The magnesium-PCL cage showed nonlinear degradation over time. Both implants demonstrated time-dependent increases in stability, with a significantly greater stiffness of the bone graft after 24 weeks in all directions of motion. Histologically, the cage showed no signs of fusion with progressive encapsulation over time. Conclusion. In comparison with the bone graft, the bioabsorbable cage showed inferior stiffness and fusion properties. Thus, further component modifications are necessary. Level of Evidence: N/A

Molecular modeling study of CO2 plasticization and sorption onto absorbable polyesters

Drug delivery systems are often made of porous polymer matrices. One method used to prepare a foamed polymer matrix is the controlled expansion of saturated polymers process in which amorphous polymer is exposed to CO2 at high pressure with a significant lowering of glass transition temperature. This plasticizing effect allows us to process temperature-sensitive polymers at relatively low temperatures. In the present study, computational tools were applied to estimate plasticizing effect of CO2 and calculate CO2- and H2O-loading capacities for three absorbable polyesters: polycaprolactone and two copolymers of (poly-d,l-lactid-co-glycolid)-co-polyethylenglycol. Plasticization caused by CO2 was estimated by solubility parameter and radial distribution function at several CO2 concentrations and by enlargement of free volume detected by mean square displacement of helium atoms, calculated after dynamic simulation. It was found that the maximal values of the solubility parameter and density can serve as a tool to predict saturation concentration. The loading capacities of the biopolymers that were preloaded with CO2 molecules were significantly higher than those of the nontreated polymers. Similar results were obtained for H2O molecules loading.

Artificial urine and FBS supplemented media in cytocompatibility assays for PLGA-PEG-based intravesical devices using the urothelium cell line UROtsa

European and German directives for approval of new medical devices require tests for cytotoxicity in relevant media, since urine can influence cytotoxicity of biodegradable devices. The aim of this study was to determine the long-term cytotoxicity of PLGA-b-mPEG (PLGA-PEG) polymer carriers and artificial urine (AU) to human UROtsa cells. Benign urothelial UROtsa cells were incubated in fetal bovine serum-containing RPMI 1640 medium supplemented with a range of concentrations of AU for 24 h and 7 days. Cell viability was determined by the XTT assay and by live/dead staining. The cytotoxicity of medium containing degradation products from PLGA-PEG carriers was also tested on the UROtsa cells in AU-containing and control medium. PLGA-PEG carriers exhibited no cytotoxicity to UROtsa cells after 24 h of incubation. However, after 7 days, cytotoxicity was observed, but this was largely attributable to the effects of 30% AU on the cells. Compared to phosphate buffer saline (PBS) and normalized to RPMI 1640 medium, significant cytotoxicity was observed by 24 h in medium containing 50% AU and by 7 days in medium containing 30% AU. Live/Dead staining confirmed proliferation results and no pH-changes could be observed. Here we demonstrate for the first time the impact of AU on standard cytotoxicity tests related to biomaterials for urinary-tract applications. Our study showed cytotoxic effects of high concentrations of 50% AU by 24 h and by physiological concentrations of AU (i.e., 30%) by 7 days. We have also demonstrated that PLGA-PEG has no cytotoxic effects in the appropriate AU-containing test environment.