Low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope: Monte Carlo treatment planning and dose measurements in a postmortem subject.

Objective.The goal of this study was to use Monte Carlo (MC) simulations and measurements to investigate the dosimetric suitability of an interventional radiology (IR) c-arm fluoroscope to deliver low-dose radiotherapy to the lungs.Approach.A previously-validated MC model of an IR fluoroscope was used to calculate the dose distributions in a COVID-19-infected patient, 20 non-infected patients of varying sizes, and a postmortem subject. Dose distributions for PA, AP/PA, 3-field and 4-field treatments irradiating 95% of the lungs to a 0.5 Gy dose were calculated. An algorithm was created to calculate skin entrance dose as a function of patient thickness for treatment planning purposes. Treatments were experimentally validated in a postmortem subject by using implanted dosimeters to capture organ doses.Main results.Mean doses to the left/right lungs for the COVID-19 CT data were 1.2/1.3 Gy, 0.8/0.9 Gy, 0.8/0.8 Gy and 0.6/0.6 Gy for the PA, AP/PA, 3-field, and 4-field configurations, respectively. Skin dose toxicity was the highest probability for the PA and lowest for the 4-field configuration. Dose to the heart slightly exceeded the ICRP tolerance; all other organ doses were below published tolerances. The AP/PA configuration provided the best fit for entrance skin dose as a function of patient thickness (R2 = 0.8). The average dose difference between simulation and measurement in the postmortem subject was 5%.Significance.An IR fluoroscope should be capable of delivering low-dose radiotherapy to the lungs with tolerable collateral dose to nearby organs.

Antisenescence effect of REAC biomodulation to counteract the evolution of myelodysplastic syndrome.

About 30 percent of patients diagnosed with myelodysplastic syndromes (MDS) progress to acute myeloid leukemia (AML). The senescence of bone marrow?derived mesenchymal stem cells (BMSCs) seems to be one of the determining factors in inducing this drift. Research is continuously looking for new methodologies and technologies that can use bioelectric signals to act on senescence and cell differentiation towards the phenotype of interest. The Radio Electric Asymmetric Conveyer (REAC) technology, aimed at reorganizing the endogenous bioelectric activity, has already shown to be able to determine direct cell reprogramming effects and counteract the senescence mechanisms in stem cells. Aim of the present study was to prove if the anti-senescence results previously obtained in different kind of stem cells with the REAC Tissue optimization - regenerative (TO-RGN) treatment, could also be observed in BMSCs, evaluating cell viability, telomerase activity, p19ARF, P21, P53, and hTERT gene expression. The results show that the REAC TO-RGN treatment may be a useful tool to counteract the BMSCs senescence which can be the basis of AML drift. Nevertheless, further clinical studies on humans are needed to confirm this hypothesis.

Monte Carlo simulations and phantom validation of low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope.

PURPOSE: To use MC simulations and phantom measurements to investigate the dosimetry of a kilovoltage x-ray beam from an IR fluoroscope to deliver low-dose (0.3-1.0 Gy) radiotherapy to the lungs. MATERIALS AND METHODS: PENELOPE was used to model a 125 kV, 5.94 mm Al HVL x-ray beam produced by a fluoroscope. The model was validated through depth-dose, in-plane/cross-plane profiles and absorbed dose at 2.5-, 5.1-, 10.2- and 15.2-cm depths against the measured beam in an acrylic phantom. CT images of an anthropomorphic phantom thorax/lungs were used to simulate 0.5 Gy dose distributions for PA, AP/PA, 3-field and 4-field treatments. DVHs were generated to assess the dose to the lungs and nearby organs. Gafchromic film was used to measure doses in the phantom exposed to PA and 4-field treatments, and compared to the MC simulations. RESULTS: Depth-dose and profile results were within 3.2% and 7.8% of the MC data uncertainty, respectively, while dose gamma analysis ranged from 0.7 to 1.0. Mean dose to the lungs were 1.1-, 0.8-, 0.9-, and 0.8- Gy for the PA, AP/PA, 3-field, and 4-field after isodose normalization to cover âˆ¼ 95% of each lung volume. Skin dose toxicity was highest for the PA and lowest for the 4-field, and both arrangements successfully delivered the treatment on the phantom. However, the dose distribution for the PA was highly non-uniform and produced skin doses up to 4 Gy. The dose distribution for the 4-field produced a uniform 0.6 Gy dose throughout the lungs, with a maximum dose of 0.73 Gy. The average percent difference between experimental and Monte Carlo values were -0.1% (range -3% to +4%) for the PA treatment and 0.3% (range -10.3% to +15.2%) for the 4-field treatment. CONCLUSION: A 125 kV x-ray beam from an IR fluoroscope delivered through two or more fields can deliver an effective low-dose radiotherapy treatment to the lungs. The 4-field arrangement not only provides an effective treatment, but also significant dose sparing to healthy organs, including skin, compared to the PA treatment. Use of fluoroscopy appears to be a viable alternative to megavoltage radiation therapy equipment for delivering low-dose radiotherapy to the lungs.

Polarity reversal of wakefields driven by ultrashort pulse laser.

Using an analytical model and computer simulation, we show that the wakefield driven by an ultrashort laser pulse in high-density plasma periodically reverses its polarity due to the carrier-envelope phase shift of the driver. The wakefield polarity reversal occurs on spatial scales shorter than the typical length considered for electron acceleration with the laser-wakefield mechanism. Consequently, the energies of accelerated electrons are significantly affected. The results obtained are important for the laser-wakefield acceleration under the conditions relevant to present-day high-repetition-rate laser systems.

[Mechanical Testing of Tendons Sutured with Newly Developed Biomaterial]. / Mechanické testování slach po suture nove vyvinutým biomateriálem.

PURPOSE OF THE STUDY Tendon injuries continue to be a highly topical issue. Research and clinical activities in this area aim to achieve an optimal repair of the damaged tendon. Such suture is characterised by maximum tensile strength, resistance to gapping at the repair site, preservation of smooth surface, prevention of adhesions and facilitation of fast rehabilitation and active tendon movement. The suture as such is required to show mechanical resistance in particular. Considered optimal is the use of core suture of the tendon in combination with epitendinous suture. The group of researchers has for several years already been exploring new materials. They can contribute to better balance between adequate mechanical strength of the suture and biological support of healing. MATERIAL AND METHODS The study was carried out as an ex vivo experiment on porcine tendon models. A tendon segment was obtained from slaughtered animals and a total rupture of the tendon was imitated by sharp cutting of its central portion. Subsequently, the tendon was repaired by Adelaide suture using coated braided polyester (Ethibond) and two types of new polyamide 6 based (PA6) sutures. The first suture was designed as an unabsorbable polyester core (PES silk) surrounded by absorbable PA6 nanofibres. The second suture was created by braiding a PES silk yarn and two viscose yarns with PA6 nanofibres into a composite surgical suture. As a part of the study also examined was the tensile strength of suture with the use of other stitches, effect of the shape of the needle s point on the tensile strength of the suture and the effect of secured mattress peritendinous suture. The tensile strength of the suture was tested until failure and the achieved maximum load was monitored. RESULTS The PES core yarn with PA6 nanofibre braiding showed lower tensile strength (28.5 ± 5.2 N) than the yarn braided from one PES yarn and two viscose yarns with PA6 nanofibres (45.7 ± 6.7 N). Both newly developed sutures, however, fail to achieve the tensile strength of Ethibond (100.3 ± 19.1 N). In case of Ethibond suture using various types of stitches, the lowest tensile strength was observed in McLarney 4-strand core suture (68.8 ± 18.7 N). A higher tensile strength was achieved by Adelaide 4-strand core suture (83.6 ± 11.2 N). The highest tensile strength was seen in 6-strand core Savage suture (147.4 ± 22.7 N). When the effect of the type of needle was tested, a statistically significant difference between the taper point needle (72.0 ± 7.0 N) and reverse cutting needle (63.3 ± 9.6 N) was observed. In case of McLarney suture the epitendinous stitch increased the tensile strength by 46.2% and in case of Adelaide suture by 48.3%. CONCLUSIONS For tendon core suture, the use of sutures with multiple longitudinal segments seems more appropriate. The epitendinous suture can considerably reinforce the basic load-bearing core suture. Also observed was not an insignificant effect of the needle profile on the resulting tensile strength of the suture. In materials developed by us, more suitable seems to be the design of braiding of absorbable nanofibers with a load-bearing non-absorbable yarn. While the mechanical tensile strength of new materials is lower, the benefits are expected in the form of biological support of healing. Moreover, the nanofibers can be used as a carrier of biological and therapeutic substances. Further improvement of mechanical properties of the newly developed biomaterial can be foreseen if the material of the load-bearing non-absorbable yarn is changed or the load-bearing yarn and nanofibres ratio modified. This pilot study shall use the findings for further development and modification of new materials in basic research and shall also verify the biological aspects and the course of healing in in vivo studies. Key words: tendon, suture, pig, biomaterials, nanofibres, mechanical testing, healing, polyester, Adelaide.

Stem cells and physical energies: can we really drive stem cell fate?

Adult stem cells are undifferentiated elements able to self-renew or differentiate to maintain tissue integrity. Within this context, stem cells are able to divide in a symmetric fashion, feature characterising all the somatic cells, or in an asymmetric way, which leads daughter cells to different fates. It is worth highlighting that cell polarity have a critical role in regulating stem cell asymmetric division and the proper control of cell division depends on different proteins involved in cell development, differentiation and maintenance of tissue homeostasis. Moreover, the interaction between cells and the extracellular matrix are crucial in influencing cell behavior, included in terms of mechanical properties as cytoskeleton plasticity and remodelling, and membrane tension. Finally, the activation of specific transcriptional program and epigenetic modifications contributes to cell fate determination, through modulation of cellular signalling cascades. It is well known that physical and mechanical stimuli are able to influence biological systems, and in this context, the effects of electromagnetic fields (EMFs) have already shown a considerable role, even though there is a lack of knowledge and much remains to be done around this topic. In this review, we summarize the historical background of EMFs applications and the main molecular mechanism involved in cellular remodelling, with particular attention to cytoskeleton elasticity and cell polarity, required for driving stem cell behavior.

Proteomic analysis of plasma proteins after low-level laser therapy in rats.

The laser radiation absorbed by cells induces production of reactive oxygen species (ROS), followed by the development of oxidative stress. Proteins are major targets for ROS due to their abundance in biological systems. The aim of the present pilot study was to examine the effects of transcutaneous laser blood irradiation (TLBI), i.e., low-level laser therapy (LLLT) at 830 nm on plasma proteome in Wistar rats. Rats were irradiated in the heart area (i.e. coronary arteries) daily (i.e., for 9-day period), by commercially available GaAsAl diode laser (Maestro/CCM, Medicom Prague, Czech Republic, lambda=830 nm, power density 450mW/cm(2), daily dose 60,3 J/ cm(2), irradiation time 134 sec). The comparison of blood plasma proteome from irradiated and non-irradiated rats was performed utilizing 2D electrophoresis followed by MALDI TOF/TOF mass spectrometry. LLLT led to a quantitative change in the acute phase proteins with antioxidant protection i.e., haptoglobin (log(2) fold change (FC)=3.5), hemopexin (log(2) FC=0.5), fibrinogen gamma (log2 FC=1.4), alpha-1-antitrypsin (log(2) FC=-2.2), fetuin A (log2 FC=-0.6) and fetuin B (log2 FC=-2.3). In comparison to conventional biochemical methods, the changes in protein levels in blood plasma induced by LLLT offer a deeper insight into the oxidative stress response.

PVA and PCL nanofibers are suitable for tissue covering and regeneration.

The aim of the study was to evaluate the safety and efficacy of a new therapeutic approach to skin defects resulting from split thickness grafting. Within the study, nanofiber-based dressings fabricated using polyvinyl alcohol (PVA) and poly-ε-caprolactone (PCL) were used, with different mass density. The study was performed in 1 female minipig. Nine defects (approx. 4x4 cm) were made in the superficial skin layer. The tested materials were applied to the squared skin defect and covered by a Jelonet paraffin gauze, sutured in the corners of the defects. The animal was monitored daily during the healing process (21 days). On day 5, 12, and 27, the healing of the wound was evaluated, and a biopsy was performed for further histologic testing. At the end of the study (on day 27 after the procedure), the animal was euthanized, and a standard pathologic evaluation was performed. We can conclude that the nanofiber scaffold which was well tolerated, could be used as a smart skin cover which could be functionalized with another bioactive substances directly on the surgeon table, among potential bioactive substances belong platelet derivatives, antibiotics, etc.

[Use of the Peptigel with Nanofibres in the Bone Defects Healing]. / Vyuzití peptigelu s nanovlákny k lécbe defektu kostní tkáne.

INTRODUCTION Traumatic bone injuries or pathological processes may sometimes result in very extensive bone defects. Currently, the standard procedure applied in clinical humane as well as veterinary medicine to fill a bone defect is the autogenous bone graft which, however, necessitates a more invasive procedure for the patient and in the cases of extensive defects it fails to provide adequate amount of graft. Synthetic bone replacements can be used with no further burden for the patient and can simultaneously be used as the carriers for bioactive molecules or therapeutic drugs. For clinical use, an easy and simple application is one of the requirements that have to be taken into consideration. These requirements are best satisfied by preparations in the form of gel, which may be injected into the defects of various shapes even through minimal surgical approach. MATERIAL AND METHODS Synthetic transparent PGD-AlphaProA hydro-peptide-gel was used as a basis to develop a composite hydrogel scaffold. This gel was enriched by cryogenically ground poly- -caprolactone nanofibers (PCL) in a ratio of 1 ml of gel to 16 µg of nanofibres. In experimental animals (laboratory rat Wistar, n=20), a single regular circular defect of 1.5 mm in diameter was drilled by a low speed drill machine across the whole width of distal femur diaphysis, identically in both the hind legs. In the right hindleg, this defect was filled by injection of 0.05 ml of the composite peptide gel with nanofibers (experimental defect). In the contralateral limb a similar defect was left untreated, without filling (control defect), for spontaneous healing. The group of experimental animals was subsequently divided into four sub-groups (A, B, C, D) for the purpose of further follow-up. One week after the surgical implantation, in the first group of experimental animals (Group A; n = 5) lege artis euthanasia was performed, a radiological examination of both the hind legs was carried out and a sample of the bone from both the control and experimental defect was collected for histologic examination. The other groups of experimental animals were evaluated similarly at 2, 4 and 6 weeks after the surgical procedure (Group B, C, D; n = 5). These groups of experimental animals were assessed using various histological techniques by two independent pathologists. RESULTS A difference between the control and the experimental bone defect was observed only at the healing stage at two weeks after the implantation, when a tendency for greater formation of new bone trabeculas was seen in the defect treated with the composite hydro-peptide-gel with PCL nanofibers. The results show a slightly higher angiogenesis and cellularity at the bone defect site with an increase of newly formed bone tissue and faster colonisation of lamellar bone structures by bone marrow cells at early stages of the healing process (1-2 weeks old defect). In the experimental and control groups, at the later stage of healing (4-6 weeks old defect), the process of healing and bone modelling at the defect site shows no detectable morphological differences. CONCLUSIONS The experimental use of hydro-peptide-gel with PCL nanofibers in vivo in laboratory rats shows very good applicability into the defect site and, compared to the untreated defect within two weeks after the implantation, accelerates the bone healing. This fact could be an advantage especially at the early stage of healing, and thus accelerate the healing of more extensive defects. Key words: peptide gel, polycaprolactone, PCL, replacement, bone, healing, scaffold, nanofibers, biomaterial.

Vertebral formula and congenital abnormalities of the vertebral column in rabbits.

The aim of this retrospective study of 330 rabbits (164 males, 166 females) was to determine different vertebral formulas and prevalence of congenital vertebral anomalies in rabbits from radiographs of the cervical (C), thoracic (Th), lumbar (L) and sacral (S) segments of the vertebral column. The number of vertebrae in each segment of vertebral column, position of anticlinal vertebra and localisation and type of congenital abnormalities were recorded. In 280/330 rabbits (84.8%) with normal vertebral morphology, seven vertebral formulas were identified: C7/Th12/L7/S4 (252/330, 76.4%), C7/Th12/L6/S4 (11/330, 3.3%), C7/Th13/L7/S4 (8/330, 2.4%), C7/Th12/L7/S5 (4/330, 1.2%), C7/Th12/L8/S4 (3/330, 0.9%), C7/Th12/L7/S6 (1/330, 0.3%) and C7/Th11/L7/S4 (1/330, 0.3%). The anticlinal vertebra was identified as Th10 in 56.4% of rabbits and Th11 in 42.4% of rabbits. Congenital spinal abnormalities were identified in 50/330 (15.2%) rabbits, predominantly as a single pathology (n=44). Transitional vertebrae represented the most common abnormalities (n=41 rabbits) in the thoracolumbar (n=35) and lumbosacral segments (n=6). Five variants of thoracolumbar transitional vertebrae were identified. Cervical butterfly vertebrae were detected in three rabbits. One rabbit exhibited three congenital vertebral anomalies: cervical block vertebra, thoracic hemivertebra and thoracolumbar transitional vertebra. Five rabbits exhibited congenital vertebral abnormalities with concurrent malalignment, specifically cervical kyphosis/short vertebra (n=1), thoracic lordoscoliosis/thoracolumbar transitional vertebrae (n=1), thoracic kyphoscoliosis/wedge vertebrae (n=2) and thoracolumbar lordoscoliosis/thoracolumbar transitional vertebrae/lumbosacral transitional vertebrae (n=1). These findings suggest that vertebral columns in rabbits display a wide range of morphologies, with occasional congenital malformations.

[Canine Elbow Humeroulnar Incongruity Measurements Using Computed Tomography]. / Merení humeroulnární inkongruity loketního kloubu u psu pomocí výpocetní tomografie.

PURPOSE OF THE STUDY The purpose of the study is to compare the repeatability and reproducibility of quantitative and subjective evaluation of elbow humeroulnar incongruity (HUI) using computed tomography (CT) on an in vivo canine model. MATERIAL AND METHODS HUI was evaluated on canine (n = 50) elbow joints (n = 100). The computed tomography of elbow joints was performed under intravenous sedation. Multiplanar reconstructions (MPR) were produced. HUI was evaluated on sagittal MPR images subjectively and by measuring the subluxation index (SI). The SI was defined by measuring the distance between the centres of two circles, the shape of which corresponded the most with the shape of the trochlear notch of the ulna at sagittal crest and the shape of humeral trochlea. This distance was divided by the radius of the circle (r) defining the humeral trochlea. HUI was subjectively evaluated based on the width of the joint space at the greatest caudal convexity of the trochlear notch of the ulna. Three categories of HUI were established: 0 (congruent), 1 (moderately incongruent), 2 (strongly incongruent). Measurement and evaluation of HUI was conducted by two evaluators twice at a one-month interval between the first and second measurement. The statistical analysis was carried out using the repeated measures ANOVA and the Cohen s kappa coefficient. RESULTS The mean SI was 11.14 (SD 8.703). The SI values measured by two evaluators were statistically significantly different (p < 0.05). Contrarily, there was no statistically significant difference between the two measurements of the same evaluator (p > 0.05). The subjective evaluation of HUI done by two evaluators showed a mean to substantial agreement (Kappa = 0.53-0.79). There was a substantial to almost perfect agreement between the results of two evaluations carried out by a single evaluator (Kappa = 0.79-0.83). DISCUSSION The radiographic detection of moderate incongruity is unreliable, especially on account of wrongly positioned elbow joint, superposition of bone structures and due to the evaluation of three-dimensional bone structure through a two-dimensional image. Evaluation of humeroulnar congruity by computed tomography (CT) enables to assess the congruity of joints without the superposition of neighbouring bone structures. The quantification of humeroulnar incongruity using the SI does not show a higher degree of agreement between two evaluators as against the subjective evaluation of HUI. On the contrary, the agreement between two measurements of a single evaluator was high in both the cases. CONCLUSIONS Dog is a suitable model animal for evaluation of HUI of elbow joints due to frequent incidence of elbow dysplasia associated with HUI. The quantification of HUI at the expense of subjective evaluation of HUI is often overrated in radiological studies. Key words: dog, elbow, humeroulnar incongruity.

[Comparison between the Range of Movement Canine Real Cervical Spine and Numerical Simulation - Computer Model Validation]. / Porovnání rozsahu pohybu reálné krcní pátere psa s pocítacovou simulací ­ validace pocítacového modelu.

PURPOSE OF THE STUDY In developing new or modifying the existing surgical treatment methods of spine conditions an integral part of ex vivo experiments is the assessment of mechanical, kinematic and dynamic properties of created constructions. The aim of the study is to create an appropriately validated numerical model of canine cervical spine in order to obtain a tool for basic research to be applied in cervical spine surgeries. For this purpose, canine is a suitable model due to the occurrence of similar cervical spine conditions in some breeds of dogs and in humans. The obtained model can also be used in research and in clinical veterinary practice. MATERIAL AND METHODS In order to create a 3D spine model, the LightSpeed 16 (GE, Milwaukee, USA) multidetector computed tomography was used to scan the cervical spine of Doberman Pinscher. The data were transmitted to Mimics 12 software (Materialise HQ, Belgium), in which the individual vertebrae were segmented on CT scans by thresholding. The vertebral geometry was exported to Rhinoceros software (McNeel North America, USA) for modelling, and subsequently the specialised software Abaqus (Dassault Systemes, France) was used to analyse the response of the physiological spine model to external load by the finite element method (FEM). All the FEM based numerical simulations were considered as nonlinear contact statistic tasks. In FEM analyses, angles between individual spinal segments were monitored in dependence on ventroflexion/ /dorziflexion. The data were validated using the latero-lateral radiographs of cervical spine of large breed dogs with no evident clinical signs of cervical spine conditions. The radiographs within the cervical spine range of motion were taken at three different positions: in neutral position, in maximal ventroflexion and in maximal dorziflexion. On X-rays, vertebral inclination angles in monitored spine positions were measured and compared with the results obtain0ed from FEM analyses of the numerical model. RESULTS It is obvious from the results that the physiological spine model tested by the finite element method shows a very similar mechanical behaviour as the physiological canine spine. The biggest difference identified between the resulting values was reported in C6-C7 segment in dorsiflexion (Δφ = 5.95%), or in C4-C5 segment in ventroflexion (Δφ = -3.09%). CONCLUSIONS The comparisons between the mobility of cervical spine in ventroflexion/dorsiflexion on radiographs of the real models and the simulated numerical model by finite element method showed a high degree of results conformity with a minimal difference. Therefore, for future experiments the validated numerical model can be used as a tool of basic research on condition that the results of analyses carried out by finite element method will be affected only by an insignificant error. The computer model, on the other hand, is merely a simplified system and in comparison with the real situation cannot fully evaluate the dynamics of the action of forces in time, their variability, and also the individual effects of supportive skeletal tissues. Based on what has been said above, it is obvious that there is a need to exercise restraint in interpreting the obtained results. Key words: cervical spine, kinematics, numerical modelling, finite element method, canine.

[Ex Vivo Testing of Mechanical Properties of Canine Metacarpal/Metatarsal Bones after Simulated Implant Removal]. / Ex vivo testování mechanických vlastností metakarpálních/metatarzálních kostí psu po simulovaném vyjmutí implantátu.

UNLABELLED: PURPOSE OF THE STUDY In a long-term perspective, it is better to remove implants after fracture healing. However, subsequent full or excessive loading of an extremity may result in refracture, and the bone with holes after screw removal may present a site with predilection for this. The aim of the study was to find ways of how to decrease risk factors for refracture in such a case. This involved support to the mechanical properties of a bone during its remodelling until defects following implant removal are repaired, using a material tolerated by bone tissue and easy to apply. It also included an assessment of the mechanical properties of a bone after filling the holes in it with a newly developed biodegradable polymer-composite gel ("bone paste"). The composite also has a prospect of being used to repair bony defects produced by pathological processes. MATERIAL AND METHODS Experiments were carried out on intact weight-bearing small bones in dogs. A total of 27 specimens of metacarpal/metatarsal bones were used for ex vivo testing. They were divided into three groups: K1 (n = 9) control undamaged bones; K2 (n = 9) control bones with iatrogenic damage simulating holes left after cortical screw removal; EXP (n = 9) experimental specimens in which simulated holes in bone were filled with the biodegradable self-hardening composite. The bone specimens were subjected to three-point bending in the caudocranial direction by a force acting parallel to the direction of drilling in their middiaphyses. The value of maximum load achieved (N) and the corresponding value of a vertical displacement (mm) were recorded in each specimen, then compared and statistically evaluated. RESULTS On application of a maximum load (N), all bone specimens broke in the mid-part of their diaphyses. In group K1 the average maximum force of 595.6 ± 79.5 N was needed to break the bone; in group K2 it was 347.6 ± 58.6 N; and in group EXP it was 458.3 ± 102.7 N. The groups with damaged bones, K2 and EXP, were compared and the difference was found to be statistically significant (p ≤ 0.05). CONCLUSIONS The recently developed biodegradable polymer-composite gel is easy and quick to apply to any defect, regardless of its shape, in bone tissue. The ex vivo mechanical tests on canine short bones showed that the composite applied to defects, which simulated holes left after screw removal, provided sufficient mechanical support to the bone architecture. The results of measuring maximum loading forces were statistically significant. However, before the composite could be recommended for use in veterinary or human medical practice, thorough pre-clinical studies will be required. KEY WORDS: fracture fixation, mechanical testing, bone plate, cortical screw, refracture.

Polycaprolactone foam functionalized with chitosan microparticles - a suitable scaffold for cartilage regeneration.

For biodegradable porous scaffolds to have a potential application in cartilage regeneration, they should enable cell growth and differentiation and should have adequate mechanical properties. In this study, our aim was to prepare biocompatible scaffolds with improved biomechanical properties. To this end, we have developed foam scaffolds from poly-epsilon-caprolactone (PCL) with incorporated chitosan microparticles. The scaffolds were prepared by a salt leaching technique from either 10 or 15 wt% PCL solutions containing 0, 10 and 20 wt% chitosan microparticles, where the same amount and size of NaCl was used as a porogen in all the cases. PCL scaffolds without and with low amounts of chitosan (0 and 10 wt% chitosan) showed higher DNA content than scaffolds with high amounts of chitosan during a 22-day experiment. 10 wt% PCL with 10 and 20 wt% chitosan showed significantly increased viscoelastic properties compared to 15 wt% PCL scaffolds with 0 and 10 wt% chitosan. Thus, 10 wt% PCL scaffolds with 0 wt% and 10 wt% chitosan are potential scaffolds for cartilage regeneration.

[Intra-articular reinforcement of a partially torn anterior cruciate ligament (ACL) using newly developed UHMWPE biomaterial in combination with Hexalon ACL/PCL screws: ex-vivo mechanical testing of an animal knee model]. / Intraartikulární augmentace parciální ruptury predního zkrízeného vazu (ACL) nove vyvinutým UHMWPE biomateriálem v kombinaci s Hexalon ACL/PCL srouby: ex vivo mechanické testování animálního modelu kolenního kloubu.

PURPOSE OF THE STUDY Recent trends in the experimental surgical management of a partial anterior cruciate ligament (ACL) rupture in animals show repair of an ACL lesion using novel biomaterials both for biomechanical reinforcement of a partially unstable knee and as suitable scaffolds for bone marrow stem cell therapy in a partial ACL tear. The study deals with mechanical testing of the newly developed ultra-high-molecular-weight polyethylene (UHMWPE) biomaterial anchored to bone with Hexalon biodegradable ACL/PCL screws, as a new possibility of intra-articular reinforcement of a partial ACL tear. MATERIAL AND METHODS Two groups of ex vivo pig knee models were prepared and tested as follows: the model of an ACL tear stabilised with UHMWPE biomaterial using a Hexalon ACL/PCL screw (group 1; n = 10) and the model of an ACL tear stabilised with the traditional, and in veterinary medicine used, extracapsular technique involving a monofilament nylon fibre, a clamp and a Securos bone anchor (group 2; n = 11). The models were loaded at a standing angle of 100° and the maximum load (N) and shift (mm) values were recorded. RESULTS In group 1 the average maximal peak force was 167.6 ± 21.7 N and the shift was on average 19.0 ± 4.0 mm. In all 10 specimens, the maximum load made the UHMWPE implant break close to its fixation to the femur but the construct/fixation never failed at the site where the material was anchored to the bone. In group 2, the average maximal peak force was 207.3 ± 49.2 N and the shift was on average 24.1 ± 9.5 mm. The Securos stabilisation failed by pullout of the anchor from the femoral bone in nine out of 11 cases; the monofilament fibre ruptured in two cases. CONCLUSIONS It can be concluded that a UHMWPE substitute used in ex-vivo pig knee models has mechanical properties comparable with clinically used extracapsular Securos stabilisation and, because of its potential to carry stem cells and bioactive substances, it can meet the requirements for an implant appropriate to the unique technique of protecting a partial ACL tear. In addition, it has no critical point of ACL substitute failure at the site of its anchoring to the bone (compared to the previously used PET/PCL substitute). Key words: knee stabilisation, stifle surgery, ultra-high-molecular-weight polyethylene, UHMWPE, nylon monofilament thread, biodegradable screw, bone anchor.

Achieving a long-lived high-beta plasma state by energetic beam injection.

Developing a stable plasma state with high-beta (ratio of plasma to magnetic pressures) is of critical importance for an economic magnetic fusion reactor. At the forefront of this endeavour is the field-reversed configuration. Here we demonstrate the kinetic stabilizing effect of fast ions on a disruptive magneto-hydrodynamic instability, known as a tilt mode, which poses a central obstacle to further field-reversed configuration development, by energetic beam injection. This technique, combined with the synergistic effect of active plasma boundary control, enables a fully stable ultra-high-beta (approaching 100%) plasma with a long lifetime.

Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

A low prevalence of mycobacteria in freshwater fish from water reservoirs, ponds and farms.

A survey of the occurrence of mycobacteria was conducted from 717 freshwater fish (25 species) in two water reservoirs, five ponds and two farms in the Czech Republic. A total of 2182 tissue samples from these fish were examined using the conventional culture method. Thirteen mycobacterial isolates were obtained from 12 (1.7%) fish belonging to nine species. Isolates were identified using sequence analysis of the 16SrRNA gene as: Mycobacterium algericum, M. fortuitum, M. gordonae, M. insubricum, M. kumamotonense, M. nonchromogenicum, two isolates of M. peregrinum, M. terrae and M. triplex. Mycobacteria were isolated more frequently from fish skin and gills than from internal organs or muscles.

Optimized conditions for mesenchymal stem cells to differentiate into osteoblasts on a collagen/hydroxyapatite matrix.

Collagen/hydroxyapatite (HA) composite scaffolds are known to be suitable scaffolds for seeding with mesenchymal stem cells (MSCs) differentiated into osteoblasts and for the in vitro production of artificial bones. However, the optimal collagen/HA ratio remains unclear. Our study confirmed that a higher collagen content increased scaffold stiffness but that a greater stiffness was not sufficient for bone tissue formation, a complex process evidently also dependent on scaffold porosity. We found that the scaffold pore diameter was dependent on the concentration of collagen and HA and that it could play a key role in cell seeding. In conclusion, the optimal scaffold for new bone formation and cell proliferation was found to be a composite scaffold formed from 50 wt % HA in 0.5 wt % collagen I solution.

[Treatment of a bone bridge by transplantation of mesenchymal stem cells and chondrocytes in a composite scaffold in pigs: experimental study]. / Lécba kostního mustku transplantací mezenchymových kmenových bunek a chondrocytu v kompozitním nosici u prasat - experimentální studie.

PURPOSE OF THE STUDY: The presented experimental study describes the results of using a combination of allogeneic mesenchymal cells (MSCs) with chondrocytes (CHCs) and a novel scaffold based on type I collagen and chitosan fibres. This biocomposite was transplanted into a defect produced by excision of a bone bridge to induce new cartilaginous tissue formation. The left femur was treated by transplantation into a defect of distal epiphysis; the right femur with implantation of the scaffold only served as control. A better therapeutic result was therefore expected in the left femur - the reduction of growth and angular deformities, and the histological finding of a tissue similar to the cartilage excised from the left femur.. MATERIAL AND METHODS: The miniature pig was selected as an experimental model and 10 pigs were used. Mesenchymal stem cells derived from femoral bone marrow and chondrocytes derived from a sample harvested from the non-weight-bearing articular surface of the distal end of the femur were cultured in medium. The novel scaffold was based on collagen containing chitosan nanofibres. To make manipulation during implantation easier, the cilindrical scaffolds after lyophilisation were again placed in 96-well plates for seeding. The scaffolds before implantation were seeded with 2x106 allogeneic MSCs and 1x106 allogeneic CHCs. The outcomes of treatment were assessed by measuring the length of bone and the degree of distal femoral valgus deformity, and by the histological findings obtained (properties and maturity of the newly-formed tissue, detection of type II collagen, PAS reaction). RESULTS: The right and left legs were examined for longitudinal bone growth and the valgus angle and compared. The treated left leg showed a higher average value for longitudinal growth than the untreated right leg (p = 0.004). The average degree of angular deformity was lower in the left leg than in the right leg (p = 0.008). The microscopic findings showed that a tissue similar to hyaline cartilage was more frequently present in the femoral bone defect of the left leg, as compared with that of the right leg. Type II collagen was detected more frequently and at higher amounts on the left than the right side (p = 0.033). The PAS reaction was positive in all left limbs, with a high degree of positivity in 80 % of them, while this was not achieved in any of the right limbs (p = 0.001). DISCUSSION: The use of stem cells in the indication reported here has only been the matter of time since the information on encouraging results in neurology and cardiology was published. First studies with positive results have soon been reported. The initial hydrogel scaffolds were based on tissue adhesives. However, they were not stable enough and were difficult to handle during surgery. In further studies, therefore, the use was made of a three-dimensional scaffold with a self-supporting structure of collagen fibres. This structure also facilitated its hydrodynamic seeding with MSCs and CHCs, which is an effective and sparing procedure for the transplanted cells. Studies concerned with MSCs and/or CHCs transplantation for re - pair of a physeal defect following bone bridge excision, i.e. for bone bridge treatment, in a broader experimental design, however, are still missing. CONCLUSION: Transplantation of a composite scaffold seeded with mesenchymal stem cells and chondrocytes into a physeal defect following bone bridge excision prevented growth disturbance and angular deformity development in the distal femoral epi - physis. In comparison with the control group, it resulted in a more frequent production of a tissue similar to hyaline cartilage, with a cell formation reminiscent of a typical columnar arrangement of the growth plate. Key words: mesenchymal stem cells, growth plate, bone bridge, scaffold.