Biotribology of alternative bearing materials for unicompartmental knee arthroplasty

The objective of our wear simulator study was to evaluate the suitability of two different carbon fibre-reinforced poly-ether-ether-ketone (CFR-PEEK) materials for fixed bearing unicompartmental knee articulations with low congruency. In vitro wear simulation was performed according to ISO 14243-1:2002 (E) with the clinically introduced Univation® F fixed bearing unicompartmental knee design (Aesculap AG, Tuttlingen, Germany) made of UHMWPE/CoCr29Mo6 in a direct comparison to experimental gliding surfaces made of CFR-PEEK pitch and CFR-PEEK PAN. Gliding surfaces of each bearing material (n = 6 + 2) were γ-irradiated, artificially aged and tested for 5 million cycles with a customized four-station knee wear simulator (EndoLab, Thansau, Germany). Volumetric wear assessment, optical surface characterization and an estimation of particle size and morphology were performed.The volumetric wear rate of the reference PE1–6 was 8.6 ± 2.17 mm³ per million cycles, compared to 5.1 ± 2.29 mm³ per million cycles for PITCH1–6 and 5.2 ± 6.92 mm³ per million cycles for PAN1–6; these differences were not statistically significant. From our observations, we conclude that CFR-PEEK PAN is obviously unsuitable as a bearing material for fixed bearing knee articulations with low congruency, and CFR-PEEK pitch also cannot be recommended as it remains doubtful wether it reduces wear compared to polyethylene. In the fixed bearing unicompartmental knee arthroplasty examined, application threshold conditions for the biotribological behaviour of CFR-PEEK bearing materials have been established. Further in vitro wear simulations are necessary to establish knee design criteria in order to take advantage of the biotribological properties of CFR-PEEK pitch for its beneficial use to patients.     

Biotribology of a new bearing material combination in a rotating hinge knee articulation

The objective of the present study was to evaluate the biotribological behaviour, in terms of wear and particle release, of bushings and flanges made of carbon fibre reinforced poly-ether-ether-ketone (CFR-PEEK) in articulation with a zirconium nitride (ZrN) multilayer surface coating in a rotating hinge knee system. For the bushings of the rotational and flexion axles and the medial and lateral flanges, a CFR-PEEK with 30% polyacrylonitrile fibre content was used in a new bearing combination with ZrN. In vitro wear simulation was performed for patients with metal ion hypersensitivity, using a new rotating hinge knee design with a ZrN surface articulation in comparison with the clinically established cobalt–chromium version. For the bushings and flanges made of CFR-PEEK subjected to wear simulation, the volumetric wear rates were 2.3 ± 0.48 mm³ million^?1 cycles in articulation to cobalt–chromium as reference and 0.21 ± 0.02 mm³ million^?1 cycles in the coupling with ZrN, a 10.9-fold decrease. The released CFR-PEEK particles were comparable in size and shape for the coupling to cobalt–chromium and ZrN with most of the particles in a size range between 0.1 and 2 μm. The study reveals comparable low wear and no macroscopic surface fatigue in a new rotating hinge knee design with highly congruent flanges and axles bushings made of CFR-PEEK articulating to a ZrN multilayer surface coating. Favourable wear behaviour of the newly introduced CFR-PEEK/ZrN coupling in comparison with the clinically established CFR-PEEK/cobalt–chromium articulation was found.     

Anti-infective and osteointegration properties of silicon nitride,poly(ether ether ketone), and titanium implants

Silicon nitride (Si₃N₄) is an industrial ceramic used in spinal fusion and maxillofacial reconstruction. Maximizing bone formation and minimizing bacterial infection are desirable attributes in orthopedic implants designed to adhere to living bone. This study has compared these attributes of Si₃N₄ implants with implants made from two other orthopedic biomaterials, i.e. poly(ether ether ketone) (PEEK) and titanium (Ti). Dense implants made of Si₃N₄, PEEK, or Ti were surgically implanted into matching rat calvarial defects. Bacterial infection was induced with an injection of 1 × 10⁴ Staphylococcus epidermidis. Control animals received saline only. On 3, 7, and 14 days, and 3 months post-surgery four rats per time period and material were killed, and calvariae were examined to quantify new bone formation and the presence or absence of bacteria. Quantitative evaluation of osteointegration to adjacent bone was done by measuring the resistance to implant push-out (n = 8 rats each for Ti and PEEK, and n = 16 rats for Si₃N₄). Three months after surgery in the absence of bacterial injection new bone formation around Si₃N₄ was ～69%, compared with 24% and 36% for PEEK and Ti, respectively. In the presence of bacteria new bone formation for Si₃N₄, Ti, and PEEK was 41%, 26%, and 21%, respectively. Live bacteria were identified around PEEK (88%) and Ti (21%) implants, whereas none were present adjacent to Si₃N₄. Push-out strength testing demonstrated statistically superior bone growth onto Si₃N₄ compared with Ti and PEEK. Si₃N₄ bioceramic implants demonstrated superior new bone formation and resistance to bacterial infection compared with Ti and PEEK.     

In vivo roughening of retrieved total knee arthroplasty femoral components

BackgroundJoint registry data highlights the higher rates of cumulative revision for younger patients undergoing TKR. One of the reasons associated with this higher revision rate may be due to the wear of the UHMWPE leading to loosening. Alternate bearing surfaces have been developed to address this problem; however, roughening of the metal bearing surface has not been demonstrated in vivo.MethodWe recorded roughness measurements of retrieved femoral components.ResultsAverage lateral condyle roughness was 0.032 μm, compared to control values of 0.020 μm, p = 0.002; average medial condyle roughness was 0.028 μm, compared to a control value of 0.019, p < 0.001.ConclusionThere was a small but statistically significant roughening of femoral components in vivo compared to controls. This may have important implications for aseptic loosening of knee arthroplasty components and the decision to use scratch resistant components.     

Wear rate evaluation of a novel polycarbonate-urethane cushion form bearing for artificial hip joints

There is growing interest in the use of compliant materials as an alternative to hard bearing materials such as polyethylene, metal and ceramics in artificial joints. Cushion form bearings based on polycarbonate-urethane (PCU) mimic the natural synovial joint more closely by promoting fluid-film lubrication. In the current study, we used a physiological simulator to evaluate the wear characteristics of a compliant PCU acetabular buffer, coupled against a cobalt–chrome femoral head. The wear rate was evaluated over 8 million cycles gravimetrically, as well as by wear particle isolation using filtration and bio-ferrography (BF). The gravimetric and BF methods showed a wear rate of 9.9–12.5 mg per million cycles, whereas filtration resulted in a lower wear rate of 5.8 mg per million cycles. Bio-ferrography was proven to be an effective method for the determination of wear characteristics of the PCU acetabular buffer. Specifically, it was found to be more sensitive towards the detection of wear particles compared to the conventional filtration method, and less prone to environmental fluctuations than the gravimetric method. PCU demonstrated a low particle generation rate (1–5 × 10⁶ particles per million cycles), with the majority (96.6%) of wear particle mass lying above the biologically active range, 0.2–10 μm. Thus, PCU offers a substantial advantage over traditional bearing materials, not only in its low wear rate, but also in its osteolytic potential.     

Effects of molecular weight of grafted hyaluronic acid on wear initiation

Hyaluronic acid (HA) of different molecular weights (M_w) was grafted onto mica surfaces to study the effects of M_w on the conformation and wear protection properties of a grafted HA (gHA) layer in lubricin (LUB) and bovine synovial fluid (BSF) using a surface forces apparatus. The M_w of gHA had significant effects on the wear pressure (P_w), at which point the wear initiates. Increasing the gHA M_w from 51 to 2590 kDa increased P_w from 4 to 8 MPa in LUB and from 15 to 31 MPa in BSF. The 2590 kDa gHA in BSF had the best wear protection (P_w ∼ 31 MPa), even though it exhibited the highest friction coefficient (μ ∼ 0.35), indicating that a low μ does not necessarily result in good wear protection, as is often assumed. The normal force profile indicated that BSF confines the gHA structure, making it polymer brush-like, commonly considered as an excellent structure for boundary lubrication.     

Mechanical properties and in vitro response of strontium-containing hydroxyapatite/polyetheretherketone composites

Strontium-containing hydroxyapatite/polyetheretherketone (Sr-HA/PEEK) composites were developed as alternative materials for load-bearing orthopaedic applications. The amount of strontium-containing hydroxyapatite (Sr-HA) incorporated into polyetheretherketone (PEEK) polymer matrix ranged from 15 to 30 vol% and the composites were successfully fabricated by compression molding technique. This study presents the mechanical properties and in vitro human osteoblast-like cell (MG-63) response of the composite material developed. The bending modulus and strength of Sr-HA/PEEK composites were tailored to mimic human cortical bone. PEEK reinforced with 25 and 30 vol% Sr-HA exhibited bending modulus of 9.6 and 10.6 GPa, respectively; alternatively, the bending strengths of the composites were 93.8 and 89.1 MPa, respectively. Based on the qualitative comparison of apatite formation in SBF and quantitative measurement of MG-63-mediated mineralization in vitro, the Sr-HA/PEEK composite was proven to outperform HA/PEEK in providing bioactivity. However, no difference was found in the trend of cell proliferation and alkaline phosphatase activity between different composites. Strontium, in the form of strontium-containing hydroxyapatite (Sr-HA), was confirmed to enhance bioactivity in the PEEK composites.     

Biocompatibility of injectable chitosan–phospholipid implant systems

Injectable biomaterials are desirable therapeutic platforms due to minimal invasiveness and improved patient compliance, and are applicable in such areas as compound delivery and tissue engineering. The present work examined the biocompatibility of injectable blends composed of chitosan, phospholipid and lauric aldehyde (PoLi_gel-LA) or lauric chloride (PoLi_gel-LCl). In vitro cytotoxicity was evaluated in L929 and HeLa cell lines. Both blends resulted in acceptable biocompatibility, although greater cell viability was seen with PoLi_gel-LA. In vivo biocompatibility was investigated in healthy CD-1 mice. Subcutaneous injection of the PoLi_gel-LA blend caused no local or systemic toxicities over a four-week period while the PoLi_gel-LCl caused immediate local toxicity. Mice injected intraperitoneally with PoLi_gel-LA did not show physical or behavioural alterations, and body weight changes did not differ from control animals. Furthermore, histological examination of spleen and liver showed unaltered morphology. Interleukin-6 levels in mice injected with PoLi_gel-LA did not differ from levels of control animals (6.91 ± 3.61 pg/mL versus 6.92 ± 5.02 pg/mL, respectively). Biodegradation occurred progressively, with 7.4 ± 5.02% of the original injected mass remaining after four weeks. Results obtained herein establish the biocompatibility of PoLi_gel-LA and indicate its potential for use in various localized therapeutic applications.     

Less polyethylene wear in monobloc compared to modular ultra-high-molecular-weight-polyethylene inlays in hybrid total knee arthroplasty: A 5-year randomized radiostereometry study

BackgroundA modular polyethylene (PE) inlay in total knee arthroplasty (TKA) may wear on both sides. PE particles may induce osteolysis, which can lead to implant loosening. The aim of this study was to determine if PE wear in monobloc TKA differs from that of modular TKA at 60-month follow-up.Patients and methodsIn a prospective, patient-blinded trial, 50 patients were randomized to hybrid TKA surgery with either a cementless high-porosity trabecular-metal tibial component with a monobloc UHMWPE inlay (MONO-TM) or a cementless low-porosity screw-augmented titanium fiber-mesh tibial component with a modular UHMWPE inlay (MODULAR-FM). Radiostereometry was used to measure PE wear and tibial component migration.ResultsAt 60-month follow-up, mean PE wear of the medial compartment was 0.24 mm and 0.61 mm and mean PE wear of the lateral compartment was 0.31 mm and 0.82 mm for the MONO-TM and the MODULAR-FM groups, respectively (p < 0.01). The PE wear-rate was 0.05 mm (95% CI 0.03–0.08) in the MONO-TM group and 0.14 mm (95% CI 0.12–0.17) in the MODULAR-FM group (p < 0.01). Total translation at 60 months was mean 0.30 mm (95% CI 0.10–0.51) less (p < 0.01) for MONO-TM compared with MODULAR-FM tibial components. The majority of tibial components were stable (<0.2 mm MTPM) from 12 to 24-month and 24 to 60-month follow-up.ConclusionAt mid-term follow-up, monobloc PE inlay wear was approximately 40% of that of the modular PE inlay wear, which suggest that back-side wear of modular PE inlays is a significant contributor of PE wear in hybrid TKA.     

A novel silk-based artificial ligament and tricalcium phosphate/polyether ether ketone anchor for anterior cruciate ligament reconstruction – Safety and efficacy in a porcine model

Loss of ligament graft tension in early postoperative stages following anterior cruciate ligament (ACL) reconstruction can come from a variety of factors, with slow graft integration to bone being widely viewed as a chief culprit. Toward an off-the-shelf ACL graft that can rapidly integrate to host tissue, we have developed a silk-based ACL graft combined with a tricalcium phosphate (TCP)/polyether ether ketone anchor. In the present study we tested the safety and efficacy of this concept in a porcine model, with postoperative assessments at 3 months (n = 10) and 6 months (n = 4). Biomechanical tests were performed after euthanization, with ultimate tensile strengths at 3 months of ∼370 N and at 6 months of ∼566 N – comparable to autograft and allograft performance in this animal model. Comprehensive histological observations revealed that TCP substantially enhanced silk graft to bone attachment. Interdigitation of soft and hard tissues was observed, with regenerated fibrocartilage characterizing a transitional zone from silk graft to bone that was similar to native ligament bone attachments. We conclude that both initial stability and robust long-term biological attachment were consistently achieved using the tested construct, supporting a large potential for silk–TCP combinations in the repair of the torn ACL.     

High-throughput laser printing of cells and biomaterials for tissue engineering

In parallel with ink-jet printing and bioplotting, biological laser printing (BioLP) using laser-induced forward transfer has emerged as an alternative method in the assembly and micropatterning of biomaterials and cells. This paper presents results of high-throughput laser printing of a biopolymer (sodium alginate), biomaterials (nano-sized hydroxyapatite (HA) synthesized by wet precipitation) and human endothelial cells (EA.hy926), thus demonstrating the interest in this technique for three-dimensional tissue construction. A rapid prototyping workstation equipped with an IR pulsed laser (τ = 30 ns, λ = 1064 nm, f = 1–100 kHz), galvanometric mirrors (scanning speed up to 2000 mm s^?1) and micrometric translation stages (x, y, z) was set up. The droplet generation process was controlled by monitoring laser fluence, focalization conditions and writing speed, to take into account its mechanism, which is driven mainly by bubble dynamics. Droplets 70 μm in diameter and containing around five to seven living cells per droplet were obtained, thereby minimizing the dead volume of the hydrogel that surrounds the cells. In addition to cell transfer, the potential of using high-throughput BioLP for creating well-defined nano-sized HA patterns is demonstrated. Finally, bioprinting efficiency criteria (speed, volume, resolution, integrability) for the purpose of tissue engineering are discussed.     

The influence of suture material on the strength of horizontal mattress suture configuration for meniscus repair

PurposeComparison of the mechanical characteristics of meniscal repair fixation using horizontal sutures and six different sutures under submaximal cyclic and load to failure test conditions may aid physicians in selecting a suture type.MethodsA 2-cm long anteroposterior vertical longitudinal incision was created in six groups of bovine medial menisci. Lesions were repaired using a No. 2 suture either composed of polyester or polyester and ultra high-molecular weight polyethylene (UHMWPE), or UHMWPE and polydioxanone or pure UHMWPE. Endpoints included ultimate failure load (N), pull-out stiffness (N/mm), pull-out displacement (mm), cyclic displacement (mm) after 100 cycles, after 500 cycles, and mode of failure.ResultsPolyester suture had lower ultimate load than all groups except the suture composed of polyester and UHMWPE (P < .05). Pure UHMWPE suture had higher ultimate failure load than sutures composed of either polyester or polyester plus UHMWPE (P < .05).Predominant failure mode was suture cutting through the meniscus for the groups except for polyester suture which failed by suture rupture.ConclusionUnder cyclic loading conditions in bovine meniscus, braided polyester suture fixation provided lower initial fixation strength than fixation with various high strength sutures composed of pure UHMWPE or a combination of absorbable monofilament polydioxanone and UHMWPE, except for combination of polyester and UHMWPE sutures.Clinical relevancePresent study does not support the usage of the braided polyester sutures instead of high strength sutures composed either partially or totally of ultra-high molecular weight polyethylene for the horizontal suture configuration of meniscus repair.     

Anterior cruciate ligament fixation: Is radial force a predictor of the pullout strength of soft-tissue interference devices?

BackgroundIn anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.PurposeThe objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.Study DesignControlled laboratory study.MethodsA resultant force (F_R) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F_R was measured while each device was inserted into synthetic bone mounted on a test machine (n = 5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50 mm/min. The pullout strength was measured as the ultimate load before failure (n = 10 for each device).ResultsThe F_R values generated during insertion into synthetic bone were 777 ± 86 N, 865 ± 140 N, 1313 ±198 N, and 1780 ± 255 N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125 N, 716 ± 249 N, 1147 ± 142 N, and 1233 ± 190 N, respectively.ConclusionsThese results suggest that the F_R generated during interference fixation affects the pullout strength with sheath-based devices providing superior F_R compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.Clinical relevanceThese results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.     

Response of human bone marrow stromal cells to a novel ultra-fine-grained and dispersion-strengthened titanium-based material

A novel titanium-based material, containing no toxic or expensive alloying elements, was compared to the established biomaterials: commercially pure titanium (c.p. Ti) and Ti6Al4V. This material (Ti/1.3HMDS) featured similar hardness, yield strength and better wear resistance than Ti6Al4V, as well as better electrochemical properties at physiological pH 7.4 than c.p. Ti grade 1 of our study. These excellent properties were obtained by utilizing an alternative mechanism to produce a microstructure of very fine titanium silicides and carbides (<100 nm) embedded in an ultra-fine-grained Ti matrix (365 nm). The grain refinement was achieved by high-energy ball milling of Ti powder with 1.3 wt.% of hexamethyldisilane (HMDS). The powder was consolidated by spark plasma sintering at moderate temperatures of 700 °C. The microstructure was investigated by optical and scanning electron microscopy (SEM) and correlated to the mechanical properties. Fluorescence microscopy revealed good adhesion of human mesenchymal stem cells on Ti/1.3HMDS comparable to that on c.p. Ti or Ti6Al4V. Biochemical analysis of lactate dehydrogenase and specific alkaline phosphatase activities of osteogenically induced hMSC exhibited equal proliferation and differentiation rates in all three cases. Thus the new material Ti/1.3HMDS represents a promising alternative to the comparatively weak c.p. Ti and toxic elements containing Ti6Al4V.     

Knee wear simulation under conditions of highly demanding daily activities – Influence on an unicompartmental fixed bearing knee design

The objectives of our in vitro study were to evaluate a knee wear simulation based on patient daily activities in combination with artificial ageing of polyethylene inserts to create an optimised simulation of in vivo wear modes.A wear simulation was performed on fixed bearing unicompartmental knee arthroplasty (UKA) devices in a direct comparison of level walking (as given by the ISO 14243-1:2002(E) profiles) and in a customised test configuration based on activities for level walking (10%), stairs ascending (40%), stairs descending (40%), chair rising (8%) and deep squatting (2%).The cumulative gravimetric wear was estimated to be 15.3 mg for level walking (ISO) and 69.6 mg for high demanding activities (HDA). The gravimetric wear rate of the ISO group was 3.0 mg/million cycles, compared to 11.7 mg/million cycles for the HDA protocol. Level walking wear testing conditions (ISO) and artificial ageing alone is not sufficient to reproduce in vivo failure modes. After 3 million cycles all gliding surfaces of the HDA group developed in the tibio-femoral articulation markable areas of structural material fatigue and delamination.In conclusion a combination of artificial ageing to clinical relevant oxidation grades and a sequence of various high demanding daily patient activities is necessary to represent a revised in vitro behaviour of abrasive–adhesive wear and delamination in artificial knee replacements.     

Distribution of polyethylene wear particles and bone fragments in periprosthetic tissue around total hip joint replacements

Ultra-high molecular weight polyethylene (UHMWPE) wear particles play a significant role in failures of total joint replacements (TJRs). In this work, we investigated the distribution of these wear particles in periprosthetic tissues obtained from nine revisions of hip TJR. In the first step, all periprosthetic tissues were combined and mechanically separated into granuloma tissue (containing hard granules visible to the naked eye) and surrounding tissue (without visible granules). In the second step, the tissues were hydrolyzed by protease from Streptomyces griseus and granules were separated by filtration; this divided the sample into four groups: (i) lyzate and (ii) non-degraded large granules from the granuloma tissue plus (iii) lyzate and (iv) non-degraded small granules from the surrounding tissue. In the third step, the large as well as small granules were hydrolyzed by collagenase from Clostridium histolyticum. In the last step, the UHMWPE wear particles from all four groups were purified by HNO₃ digestion and weighed. The purity of the isolated particles was verified by scanning electron microscopy, infrared spectroscopy and energy-dispersive X-ray analysis. Of the total amount of polyethylene particles in the whole granuloma tissue, 72% of particles in the size range 0.1–10 μm and 68% of those larger than 10 μm were found in granules. Therefore, the formation of granules significantly lowers the effective amount of wear particles available for interaction with reactive cells and seems to be a natural defense mechanism.     

Microwave-processed nanocrystalline hydroxyapatite: Simultaneous enhancement of mechanical and biological properties

Despite the excellent bioactivity of hydroxyapatite (HA) ceramics, poor mechanical strength has limited the applications of these materials primarily to coatings and other non-load-bearing areas as bone grafts. Using synthesized HA nanopowder, dense compacts with grain sizes in the nanometer to micrometer range were processed via microwave sintering between 1000 and 1150 °C for 20 min. Here we demonstrate that the mechanical properties, such as compressive strength, hardness and indentation fracture toughness, of HA compacts increased with a decrease in grain size. HA with 168 ± 86 nm grain size showed the highest compressive strength of 395 ± 42 MPa, hardness of 8.4 ± 0.4 GPa and indentation fracture toughness of 1.9 ± 0.2 MPa m^1/2. To study the in vitro biological properties, HA compacts with grain size between 168 nm and 1.16 μm were assessed for in vitro bone cell–material interactions with human osteoblast cell line. Vinculin protein expression for cell attachment and bone cell proliferation using MTT assay showed that surfaces with finer grains provided better bone cell–material interactions than coarse-grained samples. Our results indicate simultaneous improvements in mechanical and biological properties in microwave sintered HA compacts with nanoscale grain size.     

Comparison of graft healing in anterior cruciate ligament reconstruction with and without a preserved remnant in rabbits

BackgroundThe remnant of the native anterior cruciate ligament (ACL) might contribute to the biological integration of the graft in ACL reconstruction. The aim of this study was to explore whether the preserved remnant enhanced graft healing in ACL reconstruction.MethodsForty New Zealand rabbits underwent bilateral anterior cruciate ligament reconstructions. One knee was treated with a 2-mm remnant preserved on the tibial side (remnant-preservation, RP group) while the contralateral knee underwent a complete removal of the remnants by cauterization (remnant-resection, RR group) in each animal. Gross observations combined with microangiography, histological evaluation, and uniaxial load testing were performed after 4, 8, and 12 weeks.ResultsThe vascular density on the graft surface was statistically higher in the RP group as compared to that of the RR group at 4 (P = 0.002) and 8 weeks (P = 0.020). Additionally, the accelerated intra-articular and intra-tunnel graft integration were histologically observed in the RP group. Histological scores in the RP group were statistically higher than the RR group at 4 weeks (P = 0.028 for the intra-articular healing and P = 0.046 for the intra-tunnel healing) and 8 weeks (P = 0.031 for the intra-articular healing and P = 0.014 for the intra-tunnel healing). The ultimate failure load (P = 0.017), yield load (P = 0.025), and stiffness (P = 0.004) were statistically higher in the RP group as compared to those of the RR group, with corresponding significant differences in the failure mode (P = 0.020) between the two groups at 8 weeks.ConclusionsThe preserved remnant enhanced ACL graft healing with improved biomechanical properties in the rabbit model.Level of evidenceLevel II.     

PET imaging of a collagen matrix reveals its effective injection and targeted retention in a mouse model of myocardial infarction

Injectable biomaterials have shown promise for cardiac regeneration therapy. However, little is known regarding their retention and distribution upon application in vivo. Matrix imaging would be useful for evaluating these important properties. Herein, hexadecyl-4-[¹⁸F]fluorobenzoate (¹⁸F-HFB) and Qdot labeling was used to evaluate collagen matrix delivery in a mouse model of myocardial infarction (MI). At 1wk post-MI, mice received myocardial injections of ¹⁸F-HFB- or Qdot-labeled matrix to assess its early retention and distribution (at 10 min and 2 h) by positron emission tomography (PET), or fluorescence imaging, respectively. PET imaging showed that the bolus of matrix at 10 min redistributed evenly within the ischemic territory by 2 h. Ex vivo biodistribution revealed myocardial matrix retention of ∼65%, which correlated with PET results, but may be an underestimate since ¹⁸F-HFB matrix labeling efficiency was ∼82%. For covalently linked Qdots, labeling efficiency was ∼96%. Ex vivo Qdot quantification showed that ∼84% of the injected matrix was retained in the myocardium. Serial non-invasive PET imaging and validation by fluorescence imaging confirmed the effectiveness of the collagen matrix to be retained and redistributed within the infarcted myocardium. This study identifies matrix-targeted imaging as a promising modality for assessing the biodistribution of injectable biomaterials for application in the heart.     

The effect of heat treatment of wood on osteoconductivity

Wood is a natural porous fibre composite, which has some structural similarities to bone. Recently, it has been used as a modelling material in developing synthetic fibre-reinforced composite to be used as load-bearing non-metallic artificial bone material. In this study, the behaviour of wood implanted into bone was studied in vivo in the femur bone of the rabbit. Wood was pre-treated by heat, which altered its chemical composition and structure, as well as the biomechanical properties. In the heat treatment, wood’s dimensional stability is enhanced, equilibrium moisture content reduces and the biological durability increases. Cone-shaped implants were manufactured from heat-treated (at 200 and 140 °C) birch wood (Betula pubescens) and from untreated birch. A total of 62 implants were placed in the distal femur of 50 white New Zealand rabbits. The behaviour of the implants was studied at 4, 8 and 20 weeks with histological and histometrical analysis. Osteoconductive contact line and the presence of fibrous tissue and foreign body reaction were determined. The amount of fibrous tissue diminished with time, and the absence of foreign body reaction was found to be in correlation to the amount of heat treatment. Histologically found contact between the implant and the host bone at the interface was significantly more abundant in the 200 °C group (avg. 12.8%) vs. the 140 °C (avg. 2.7%) and the untreated groups (avg. 0.6%). It was observed that the heat treatment significantly modified the biological behaviour of the implanted wood. The changes of the wood by heat treatment showed a positive outcome concerning osteoconductivity of the material.