There are no efficient treatment options for osteoarthritis (OA) that delay further progression. Besides osteoinduction, there is growing evidence of also anti-inflammatory, angiogenetic and neuroprotective effects of biodegradable magnesium-based biomaterials. Their use for the treatment of cartilage lesions in contrast is not well-evaluated yet.

Mg-cylinders were analysed in an in vitro and in vivo OA model. In vitro, SCP-1 stem cell line was analysed under inflammatory conditions and Mg-impact. In vivo, small Mg- and WE43 alloy-cylinders (1mm × 0,5mm) were implanted into the subchondral bone of the knee joint of 24 NZW rabbits after establishment of OA. As control, another 12 rabbits received only drill-holes. µCT-scan were performed and assessed for changes in bone volume and density. After euthanasia, cartilage was evaluated macroscopically and histologically after Safranin-O-staining. Furthermore, staining with CD271 directed antibody was performed to assess neuro-reactivity.

In vitro, an increased gene expression of extracellular matrix proteins as collagen II or aggrecan even under inflammatory conditions was observed under Mg-impact. In vivo, µCT evaluation revealed twice-elevated values for bone volume in femoral condyles with Mg-cylinders compared to controls while density remained unchanged. Cartilage showed no significant differences between the groups. Mg- and WE-samples showed significantly lower levels of CD271+ cells in the cartilage and bone of the operated joints than in non-operated joints, which was not the case in the Drilling-group. Furthermore, bone in operated knees of Drilling-group showed a strong trend to an increase in CD271+ cells compared to both Cylinder-groups. Counting of CD271+ vessels revealed that this difference was attributable to a higher amount of these vessels.

The in vitro results indicate a potential cartilage regenerative activity of the degradable Mg-based material. While so far there was no positive effect on the cartilage itself in vivo, implantation of Mg-cylinders seemed to reduce pain-mediating vessels.

Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 404534760). We thank Björn Wiese for production of the cylinders.

Osteoarthritis (OA) is an inflammatory disease affecting the complete synovial joint including the cartilage layer and the subchondral bone plate. Due to the multifactorial causes and the not yet completely resolved molecular mechanisms, it lacks a gold standard treatment to mitigate OA. Hence, biomaterials capable of delaying or preventing OA are a promising alternative or supplement to antiphlogistic and surgical interventions. Magnesium (Mg) and its alloys are among the promising biomaterials with osteoinductive effects. This work investigated the impact of Mg micro cylinders (length ≈of 1.0 mm and width of 0.5 mm) in vitro, in favoring joint regeneration together with preventing OA progression. Therefore, a mesenchymal stem cell line (SCP-1) was applied in order to assess the compatibility of the degradable material. Furthermore, an in vitro OA model utilizing SCP-1 cells based on the supplementation of the cytokines; IL-1β, TNF-α was established and disclosed the capability of Mg microparticles in differentiating SCP-1 cells into chondrogenic and osteogenic lineages proven through extracellular matrix staining and gene marker analysis. A concentration above 10 mM revealed a reduction in the cell viability by 50 %. An increase in the expression of collagens especially and proteoglycans (COL2A1, Aggrecan) as extracellular matrix proteins as well as an increase in osteogenic marker (ALP, BMP2) favoring the mineralization process were observed. The inflammatory condition reduced the viability and productivity of the applied stem cell line. However, the application of Mg microparticles induced a cell recovery and reduction of inflammation marker such as MMP1 and IL6. The cytocompatible and the ability of Mg microparticles in supporting bone and cartilage repair mechanisms in vitro even under inflammatory conditions make biodegradable Mg microparticles a suitable implant material to treat OA therapy.

Acknowledgements: This project OAMag was funded by the German Research Foundation (project number 404534760). The author thank Dr. Björn Wiese (hereon) for the production of Mg based material and Prof. Böcker (MUM Musculoskeletal University Center Munich) for the provision of SCP-1 cell line.

In orthopedic surgery, implant infections are a serious issue and difficult to treat. The aim of this study was to use superparamagnetic nanoporous silica nanoparticles (MNPSNP) as candidates for directed drug delivery. Currently, short blood circulation half-life due to interactions with the host's immune system hinder nanoparticles in general from being clinically used. PEGylation is an approach to reduce these interactions and to enhance blood circulation time. The effect of PEGylation of the used ⁶⁸Ga-labelled MNPSNP on the distribution and implant accumulation was examined by PET/CT imaging and gamma counting in an implant mouse model.

Female Balb/c mice (n=24) received a magnetic implant subcutaneously on the left and a titanium implant on the right hind leg. On day one, 12 of these mice received an additional clodronate®-injection for macrophage depletion. On the second postoperative day, mice were anaesthetized and MNPSNP (native or PEGylated) injected intravenously, followed by a dynamic PET-scan over 60 minutes, a CT- and a static PET-scan at 120 min. As control, 12 mice received only ⁶⁸Ga-MNPSNP (native or PEGylated). Gamma counting of inner organs, urine, blood and implant area was performed as further final analysis. Although PEGylation of the nanoparticles already resulted in lower liver uptakes, both variants of ⁶⁸Ga-labeled MNPSNP accumulated in liver and spleen. Combination of PEGylation with clodronate®-injection led to a highly significant effect whereas clodronate®-injection alone could not reveal significant differences. In gamma counting, a significantly higher %I.D./g was found for the tissue surrounding the magnetic implants compared to the titanium control, although in a low range. PEGylation and/or clodronate®-injection revealed no significant differences regarding nanoparticle accumulation at the implantation site. PEGylation increases circulation time, but MNPSNP accumulation at the implant site was still insufficient for treatment of infections. Additional efforts have to further increase circulation time and local accumulation.

Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 280642759).

There is no optimal therapy to stop or cure chondral degeneration in osteoarthritis (OA). Beside cartilage, subchondral bone is involved. The often sclerotic bone is mechanically less solid which in turn influences negatively chondral quality. Microfracturing as therapeutic technique aims to enhance bone quality but is applied only in smaller cartilage lesions. The osteoproliferative properties of Magnesium (Mg) have been shown repeatedly^1-3. The present study examined the influence of micro-scaled Mg cylinders compared to sole drilling in an OA model.

Ten New Zealand White rabbits underwent anterior crucial ligament transection. During 12 weeks after surgery, the animals developed OA as previously described⁴. In a second surgery, half of the animals received 20 drill holes (ø 0.5mm) and the other half received 20 drill holes, which were additionally filled with one Mg cylinder each. Extracapsular plication was performed in all animals. During the follow-up of 8 weeks three µ-computed tomographic (µCT) scans were performed: immediately after surgery and after four and eight weeks. Changes of bone volume, trabecular thickness and bone density were calculated and compared.

µCT evaluation showed an increase in bone volume and trabecular thickness in both groups. This increase was significantly higher in rabbits which received Mg cylinders showing thrice as high values for both parameters (bone volume: Mg group +44.5%, drilling group +15.1%, p≤0.025; trabecular thickness: Mg group +53.2%, drilling group +16.9%, p≤0.025). Also bone density increased in both groups, but on a distinctly lower level and with no significant difference.

Although profound higher bone volume was found after implantation of Mg cylinders, µCT showed similar levels of bone density indicating adequate bone quality in this OA model. Macroscopic and histological evaluation of cartilage condition have to reveal possible impact on OA progression. Additionally, current examination implement different alloys and influence on lameness.

Introduction and Objective

In the elderly population, chronic rotator cuff tears are often associated with high re-rupture rates after surgical tendon refixation. Implant materials, especially in combination with additives are supposed to positively influence healing outcome. Furthermore, adequate mechanical properties are crucial. In order to realize degradable implants with high specific surface area, polycaprolactone (PCL) was chosen as basic material and processed by electrospinning to achieve a high surface area for growth factor implementation and subsequent cell attachment.

Chronic rotator cuff tears are a major problem especially in the elderly population. Refixation is associated with high re-rupture rates. Therefore new implants or healing methods are needed. For a control of success biomechanical characteristics of native as well as treated tendons are of particular importance.

Currently, tensile tests with static material testing machines are the most common technique for the biomechanical characterization of tendons. Resulting values are the maximum force (Fmax), stiffness and the Young´s modulus. However, no information is given about the allocation of strains over the tendon area. In addition, the determination of Fmax results in tissue destruction thus foreclosing further evaluation like histology.

The Digital Image Correlation (DIC) is a contact-free non-destructive optical measuring method which gives information about distribution of strains by tracking the areal shift of an applied speckle pattern. The needed speckle pattern has to have a high contrast, a homogeneous distribution and a good adhesion to the surface. The method is established for the characterization of construction materials [1] to detect e.g. weak points. The present study examined if DIC is applicable for the complementary biomechanical evaluation of the sheep infraspinatus tendon.

Fine ground powder extracted from a printer cartridge was chosen as a starting point. Preliminary to the in vitro experiments, the powder was applied on sheets with different methods: brushing, blowing, sieving and stamping. Stamping showed best results and was used for further in vitro tests on cadaveric native tendons (n=5). First, the toner powder was transferred to coarse-grained abrasive paper using a brush and stamped on the tendon surface. Afterwards DIC analysis was performed. For the in vivo tests, the left infraspinatus tendon of two German black-headed Mutton Sheep was detached and then refixed with bone anchors, the right tendon was used as native control (authorization: AZ 33.19-42502-04-17/2739). 12 weeks after surgery the animals were euthanized, the shoulders were explanted and DIC measurement performed.

The speckle pattern could be applied adequately on the smooth tendon surfaces of native tendons. All specimens could be analyzed by DIC with sufficient correlation coefficients. The highest displacements were measured in the peripheral areas, whereas the central part of the tendon showed a low displacement. Repaired left tendons showed obvious differences already macroscopically. The tendons were thicker and showed inhomogeneous surfaces. Application of the toner powder by stamping was distinctly more complicated, DIC analysis could not produce sufficient correlation coefficients.

In summary, transfer of DIC to native infraspinatus tendons of sheep was successful and can be further transferred to other animal and human tendons. However, irregular surfaces in tendon scar tissues affect the application of an adequate speckle pattern with a stamp technique. Therefore, further modifications are necessary.

This research project has been supported by the German Research Foundation “Graded Implants FOR 2180 – tendon- and bone junctions” WE 4262/6-1.

Implant infection is an increasing problem in orthopedic surgery, especially due to progressive antibiotic resistance and an aging population with rising numbers of implantations. As a consequence, new strategies for infection prevention are necessary. In the previous study it was hypothesized that laser-structured implant surfaces favor cellular adhesion while hindering bacterial ongrowth and therewith contribute to reduce implant infections. Cuboid titanium implants (0.8 × 0.8 × 12 mm³, n=34) were used. Seventeen were laser-structured by ultra-short pulsed laser ablation to create a spike structure; the others were polished and served as controls. In general anesthesia, implants were inserted in rat tibiae and infected with a S. aureus suspension. During a 21 day postoperative follow-up, daily clinical control was performed. Radiographs were taken at day 14 and day 21. After euthanasia, bacterial load and biofilm formation on the implant surface was evaluated semi quantitatively by confocal laser scanning microscopy and computational acquisition of bacteria and cells by Imaris®-software. Additionally, histology of the surrounding bone was performed. Clinically, no differences were observed between the groups. However, contrary to our hypothesis, bacterial load was increased in the laser-structured implant group although cellular adhesion was even more pronounced. Radiographical and histological evaluations showed increased bone alterations in the group with laser-structured implants compared to the control group. These findings did not confirm prior in vitro studies, where a reduction of bacterial load was found for similar surfaces and demonstrate the necessity of in vivo trials prior to the clinical use of new materials.

The field of nanoparticle related research for the diagnosis and therapy of diseases evolves rapidly. Magnetic nanoparticles in combination with magnetizable implant materials for the treatment of implant related infections present a possible implementation in orthopedics. Magnetic nanoporous silica nanoparticles (MNPSNPs) were developed and equipped with fluorescent dyes. In vitro/in vivo biocompatibility and in vivo biodistribution were examined to appraise their potential applicability. Cell culture tests with NIH-3T3 and HepG2 cell lines indicated a good in vitro biocompatibility. Ferritic and titanium alloy (control) plates were implanted subcutaneously at the hind legs of Balb/c mice. Immediately after i.v. or s.c. injection of MNPSNPs, the caudal half of the mice was placed between the poles of an electro magnet. Exposure to the electromagnetic field of approx. 1.7 T was maintained for 10 minutes. 10 animals each were euthanized at days 0, 1, 7, 21 or 42, respectively. Quantity of MNPSNPs in liver, spleen, kidney, lung and skin/muscle samples was assessed by fluorescent microscopic methods. MNPSNP existence on the implant surface was also appraised after several steps of detachment. MNPSNPs showed a time-dependent accumulation in the organs after i.v. injection with initial accumulation in the lungs followed by redistribution to liver and spleen. After s.c. injection no systemic distribution but local appearance of MNPSNPs could be found. First histological evaluation showed no pathological changes after i.v. injection. With good in vivo biocompatibility, future focus will be laid on increasing circle life time of MNPSNPs and evaluation in an infection model.

After the implantation of endoprotheses or osteosynthesis devices, implant-related infections are one of the major challenges. The surface of implants offers optimal conditions for the formation of a biofilm. Effective carrier systems for the delivery of adequate therapeutics would reduce the concentrations needed for successful treatment and improve cure rates. In cancer diagnosis and therapy, magnetic nanoparticles are concentrated in the target area by an external magnetic field. For orthopaedic applications, in vitro examinations showed that the addition of a magnetic implant in combination with an external magnetic field could increase the amount of MNPSNPs that accumulated in direct vicinity to the implant. The present examinations implemented an electromagnet to increase magnetic field strength and should show if the in vitro set up can be transferred to an in vivo mouse model. Additionally, the loading capacity of the MNPSNPs with enrofloxacin and its release kinetics were determined.

Fluorescein-isothiocyanate (FITC) was covalently attached to MNPSNPs. For the in vitro set up, a peristaltic pump was used to establish a closed circuit which contained the MNPSNP dispersion and a magnetic platelet. After 5 minutes fluid samples were taken from the area around the magnetic platelet and analysed using a microplate reader. For the in vivo set up, a BALB/c mouse was implanted subcutaneously with the metallic platelet at the hind leg. The MNPSNP dispersion was injected into the tale vein and the hind leg of the mouse was placed immediately in a magnetic field of 1.9 T. After one week the implant was retrieved and examined by confocal laser scanning microscopy (CLSM). Liver, spleen and kidneys of the mouse were examined by magnetic resonance imaging (MRI). The loading capacity of the MNPs with enrofloxacin was examined by quantification of the enrofloxacin content in the incubation and washing solution after incubation. The release kinetics weres tested in PBS using UV/Vis-spectrometry.

The solution in the remaining tube contained no detectable MNPs while the concentration in the vicinity of the platelet was 150 µg/ml. The mouse showed no clinical adverse effects. The CLSM examination revealed a considerable accumulation of the MNPs at the implant surface. MRI could show neither accumulated MNPs nor changes of organ structure. The loading capacity of the MNPs for enrofloxacin was approximately 95 µg/mg. A burst release of nearly a third of the loaded antibiotic occurred within the first 6 hours followed by a further steady release.

Purpose

In patients with multiple trauma delayed fracture healing is often diagnosed, but the pathomechanisms are not well known yet. The purpose of the study is to evaluate the effect of a severe hemorrhagic shock on fracture healing in a murine model.

Aim

The aim of this study was to establish an implant-associated osteomyelitis model in rats with the ability to quantify biofilm formation on implants for prospective evaluation of antibacterial effects on micro-structured implant surfaces.

Magnesium calcium alloys are promising candidates for an application as biodegradable osteosynthesis implants [1,2]. As the success of most internal fracture fixation techniques relies on safe anchorage of bone screws, there is necessity to investigate the holding power of biodegradable magnesium calcium alloy screws. Therefore, the aim of the present study was to compare the holding power of magnesium calcium alloy screws and commonly used surgical steel screws, as a control, by pull-out testing.

Magnesium calcium alloy screws with 0.8wt% calcium (MgCa0.8) and conventional surgical steel screws (S316L) of identical geometries (major diameter 4mm, core diameter 3mm, thread pitch 1mm) were implanted into both tibiae of 40 rabbits. The screws were placed into the lateral tibial cortex just proximal of the fibula insertion and tightened with a manual torque gauge (15cNm). For intended pull-out tests a 1.5mm thick silicone washer served as spacer between bone and screw head. Six animals with MgCa0.8 and four animals with S316L were followed up for 2, 4, 6 and 8 weeks, respectively. Thereafter the rabbits were sacrificed. Both tibiae were explanted, adherent soft tissue and new bone was carefully dissected around the screw head. Pull-out tests were carried out with an MTS 858 MiniBionix at a rate of 0.1mm/sec until failure of the screw or the bone. For each trial the maximum pull-out force [N] was determined. Statistical analysis was performed (ANOVA, Student's t-test).

Both implant materials were tolerated well. Radiographically, new bone was detected at the implantation site of MgCa0.8 and S316L, which was carefully removed to perform pull-out trials. Furthermore, periimplant accumulations of gas were radiographically detected in MgCa0.8. The pull-out force of MgCa0.8 and S316L did not significantly differ (p = 0.121) after two weeks. From 6 weeks on the pull-out force of MgCa0.8 decreased resulting in significantly lower pull-out values after 8 weeks. Contrary, S316L pull-out force increased throughout the follow up. Thus, S316L showed significantly higher pull-out values than MgCa0.8 after 4, 6 and 8 weeks (p<0.001).

MgCa0.8 showed good biocompatibility and pull-out values comparable to S316L in the first weeks of implantation. Thus, its application as biodegradable osteosynthesis implant is conceivable. Further studies are necessary to investigate whether the reduced holding power of MgCa0.8 is sufficient for secure fracture fixation. In addition, not only solitary screws, but also screw-plate-combinations should be examined over a longer time period.

Introduction: Rabbits are a well-established animal model for orthopaedic research

and the tibia is commonly used for investigations of fracture repair with different implant materials

Therefore, a new method for the direct measurement of forces in the rabbit tibia was developed. The aim of this study was to determine maximal forces during weight bearing in the rabbit for future implementation into FEM-simulation.

Animals and Methods: An external ring fixation was attached to the left tibiae of 5 rabbits and an ostectomy followed. Force sensors were included into the collateral rods to incur the emerging forces completely. On each side, a measurement amplifier was applied to transfer the collected data telemetrically. During the study, the animals were weighted and x-rays were taken regularly. Measurements started 8 days postoperatively and were repeated 8 times until day 50 post-op. The rabbits were placed in a run and animated to move while the forces were registered. Force peaks were filtered from the collected data of each measurement as absolute values and relative to the animals’ weight (force-weight ratio/FWR).

Results: All included animals tolerated the external fixa-tion well and no clinical intolerances occurred. Beginning of callus formation was detected radiographically about 3 weeks post-op and all fixations could be removed 12–14 weeks after application without any permanent detriments. The maximal force amounted to 6950 g and 172 % FWR in animal 4 during the first recording. Means of the 5 maximal values for each measurement were located between 55 % FWR and 152 % FWR for the first measurement, converged to approx. 80 % FWR during the second recording 3 days later and descended to 20–40 % FWR until the end of the experiment.

Discussion: Aim of this study was to determine maximal forces during weight bearing in a rabbit model. Our model for in-vivo monitoring of these forces was practicable and provided profound data. The highest values occurred during the first or second recording. That coincides with the radiographic detection of callus after 3 weeks. Therefore, reliable measurements have to be carried out during the first 2 weeks postoperatively. Detected values show that the rabbit tibia is strained with up to 170 % of the body weight, which is the compressive force an implant in a weight bearing bone has to be able to bear. Future research will focus on the in-vivo monitoring of bending and torsion forces and the implementation of these data into FEM-simulation.