[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.

[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.

[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.