Surface pretreatments for medical application of adhesion

Bone adhesive materials: From bench to bedside

Biodegradable bone adhesives represent a highly sought-after type of biomaterial which would enable replacement of traditional metallic devices for fixation of bone. However, these biomaterials should fulfil an extremely large number of requirements. As a consequence, bone-adhesive biomaterials which meet all of these requirements are not yet commercially available. Therefore, this comprehensive review provides an extensive overview of the development of bone adhesives from a translational perspective. First, the definition, classification, and chemistry of various types of bone adhesives are highlighted to provide a detailed overview of this emerging class of biomaterials. In this review we particularly focused studies which describe the use of materials that are capable of gluing two pieces of bone together within a time frame of minutes to days. Second, this review critically reflects on i) the experimental conditions of commonly employed adhesion tests to assess bone adhesion and ii) the current state-of-the-art regarding their preclinical and clinical applicability.

Development prospects of curable osteoplastic materials in dentistry and maxillofacial surgery

The article presents classification of the thermosetting materials for bone augmentation. The physical, mechanical, biological, and clinical properties of such materials are reviewed. There are two main types of curable osteoplastic materials: bone cements and hydrogels. Compared to hydrogels, bone cements have high strength features, but their biological properties are not ideal and must be improved. Hydrogels are biocompatible and closely mimic the extracellular matrix. They can be used as cytocompatible scaffolds for tissue engineering, as can protein- and nucleic acid-activated structures. Hydrogels may be impregnated with osteoinductors such as proteins and genetic vectors without conformational changes. However, the mechanical properties of hydrogels limit their use for load-bearing bone defects. Thus, improving the strength properties of hydrogels is one of the possible strategies to achieve the basis for an ideal osteoplastic material.

The Effects of Cyclic Loading and Motion on the Implant-Cement Interface and Cement Mantle of PEEK and Cobalt-Chromium Femoral Total Knee Arthroplasty Implants: A Preliminary Study

This study investigated the fixation of a cemented PEEK femoral TKA component. PEEK and CoCr implants were subjected to a walking gait cycle for 10 million cycles (MC), 100,000 cycles or 0 cycles (unloaded control). A method was developed to assess the fixation at the cement-implant interface, which exposed the implants to a fluorescent penetrant dye solution. The lateral condyles of the implants were then sectioned and viewed under fluorescence to investigate bonding at the cement-implant interface and cracking of the cement mantle. When tested for 100,000 cycles, debonding of the cement-implant interface occurred in both PEEK (61%) and CoCr (13%) implants. When the duration of testing was extended (10 MC), the percentage debonding was further increased for both materials to 88% and 61% for PEEK and CoCr, respectively. The unloaded PEEK specimens were 79% debonded, which suggests that, when PEEK femoral components are cemented, complete bonding may never occur. Analysis of cracks in the cement mantle showed an absence of full-thickness cracks in the unloaded control group. For the 100,000-cycle samples, on average, 1.3 and 0.7 cracks were observed for PEEK and CoCr specimens, respectively. After 10 MC, these increased to 24 for PEEK and 19 for CoCr. This was a preliminary study with a limited number of samples investigated, but shows that, after 10 MC under a walking gait, substantial debonding was visible for both PEEK and CoCr implants at the cement-implant interface and no significant difference in the number of cement cracks was found between the two materials.

Factors affecting aseptic loosening in primary total knee replacements: an in vitro study

Background

Implant surface integrity and cement bonding are assumed to be sufficient in primary total knee replacements to stabilize implants for extended wear without concerns over delamination and loosening. Yet there exists a significant rate of aseptic loosening where failure at implant cement interface occurs. The aim of this study is to look at specific aspects leading to aseptic loosening of the total knee replacement, where cement adhesion to the implant results in the lowest pull off strength.

Methods

Virgin ceramic coated and uncoated chrome cobalt tibial trays were used in a pull off study using differing viscosities of cement at varied time intervals to compare which combination is strongest compared to which is least resistant to pull off testing.

Results

Low viscosity cement had a 44% (5.9 kg verses 3.3 kg, p < 0.001) higher pull-off strength compared to high viscosity cement. Coated implants had a 30% (3.9 kg verses 5.5 kg, p = 0.037) lower pull-off strength compared to non-coated. Testing measures were limited to cement utilization less than 5 minutes due to the poor adhesion of the dowels beyond this time. Finally, there was a significant difference in adhesion properties between brand names when utilizing low viscosity cement on the non-coated trays (10.34 kg for Simplex verses 4.87 for Palacos, p = 0.021).

Conclusion

There are differences in adhesion properties between cement vendors, prompting significant concerns over the use of coated implants with particular cement types. Use of low viscosity cement on non-coated surfaces in the early liquid phase of cement curing was found to produce the best chance for adequate adhesion. This study demonstrates that there is variation in the adhesive properties of implants utilized in total knee replacements, and that the orthopedic community should consider not only the implant, cement, and curing time individually, but the overall integrity conferred from the combination of all of these variables.

Surface fluorination of polylactide as a path to improve platelet associated hemocompatibility

Surface-induced thrombosis is still a significant clinical concern for many types of blood-contacting medical devices. In particular, protein adsorption and platelet adhesion are important events due to their ability to trigger the coagulation cascade and initiate thrombosis. Poly(lactic acid) (PLA) has been the predominant polymer used for making bioresorbable stents. Despite long-term advantages, these stents are associated with higher rates of early thrombosis compared with permanent metallic stents. To address this issue, we modified the surface of PLA with a perfluoro compound facilitated by surface activation using radio frequency (RF) plasma. Fluoropolymers have been extensively used in blood contacting materials, such as blood vessel replacements due to their reduced thrombogenicity and reduced platelet reactivity. The compositions of plasma-treated surfaces were determined by electron spectroscopy for chemical analysis (ESCA). Also, contact angle measurements, cell cytotoxicity and the degradation profile of the treated polymers are presented. Finally, relevant blood compatibility parameters, including plasma protein adsorption, platelet adhesion and morphology, were evaluated. We hypothesized that tight binding of adsorbed albumin by fluoropolymers enhances its potential for blood-contacting applications.

STATEMENT OF SIGNIFICANCE

Although bioresorbable stents made from poly(lactic acid) (PLA) may have long-term clinical advantages, they have shown higher rates of early thrombosis as compared with permanent metallic stents. To improve the thromboresistance of PLA, we developed a novel method for surface fluorination of this polymer with a perfluoro compound. Fluoropolymers (e.g., expanded polytetrafluoroethylene) have long been used in blood-contacting applications due to their satisfactory clinical performance. This is the first report of PLA surface fluorination which might be applied to the fabrication of a new generation of fluorinated PLA stents with improved platelet interaction, tunable degradability and drug release capabilities. Also, we describe a general strategy for improving the platelet interactions with biomaterials based on albumin retention.

Bioinspired Mineral-Organic Bioresorbable Bone Adhesive

Bioresorbable bone adhesives have potential to revolutionize the clinical treatment of the human skeletal system, ranging from the fixation and osteointegration of permanent implants to the direct healing and fusion of bones without permanent fixation hardware. Despite an unmet need, there are currently no bone adhesives in clinical use that provide a strong enough bond to wet bone while possessing good osteointegration and bioresorbability. Inspired by the sandcastle worm that creates a protective tubular shell around its body using a proteinaceous adhesive, a novel bone adhesive is introduced, based on tetracalcium phosphate and phosphoserine, that cures in minutes in an aqueous environment and provides high bone-to-bone adhesive strength. The new material is measured to be 10 times more adhesive than bioresorbable calcium phosphate cement and 7.5 times more adhesive than non-resorbable poly(methyl methacrylate) bone cement, both of which are standard of care in the clinic today. The bone adhesive also demonstrates chemical adhesion to titanium approximately twice that of its adhesion to bone, unlocking the potential for adherence to metallic implants during surrounding bony incorporation. Finally, the bone adhesive is shown to demonstrate osteointegration and bioresorbability over a 52-week period in a critically sized distal femur defect in rabbits.

First step towards a model system of the drug delivery network based on amide-POSS nanocarriers

We present the synthetic and release aspects of a novel drug delivery system (DDS) based on amido-functionalized POSS. DDS after drug release hydrolyses at pH = 7.40 to non-toxic products such as carboxylic acid salts and aminopropyl-POSS.

Blood compatibility assessment of polymers used in drug eluting stent coatings

Differences in thrombosis rates have been observed clinically between different drug eluting stents. Such differences have been attributed to numerous factors, including stent design, injury created by the catheter delivery system, coating application technologies, and the degree of thrombogenicity of the polymer. The relative contributions of these factors are generally unknown. This work focuses on understanding the thrombogenicity of the polymer by examining mechanistic interactions with proteins, human platelets, and human monocytes of a number of polymers used in drug eluting stent coatings, in vitro. The importance for blood interactions of adsorbed albumin and the retention of albumin was suggested by the data. Microscopic imaging and immunostaining enhanced the interpretation of results from the lactate dehydrogenase cell counting assay and provided insight into platelet interactions, total quantification, and morphometry. In particular, highly spread platelets may be surface-passivating, possibly inhibiting ongoing thrombotic events. In many of the assays used here, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) showed a differentiated protein deposition pattern that may contribute to the explanation of the consistently thromboresistant blood-materials interaction for fluororpolymers cited in literature. These results are supportive of one of several possible factors contributing to the good thromboresistant clinical safety performance of PVDF-HFP coated drug eluting stents.

Reduction of bacterial adhesion on dental composite resins by silicon-oxygen thin film coatings

Adhesion of bacteria on dental materials can be reduced by modifying the physical and chemical characteristics of their surfaces, either through the application of specific surface treatments or by the deposition of thin film coatings. Since this approach does not rely on the use of drugs or antimicrobial agents embedded in the materials, its duration is not limited by their possible depletion. Moreover it avoids the risks related to possible cytotoxic effects elicited by antibacterial substances released from the surface and diffused in the surrounding tissues. In this work, the adhesion of Streptococcus mutans and Streptococcus mitis was studied on four composite resins, commonly used for manufacturing dental prostheses. The surfaces of dental materials were modified through the deposition of a-SiO(x) thin films by plasma enhanced chemical vapor deposition. The chemical bonding structure of the coatings was analyzed by Fourier-transform infrared spectroscopy. The morphology of the dental materials before and after the coating deposition was assessed by means of optical microscopy and high-resolution mechanical profilometry, while their wettability was investigated by contact angle measurements. The sample roughness was not altered after coating deposition, while a noticeable increase of wettability was detected for all the samples. Also, the adhesion of S. mitis decreased in a statistically significant way on the coated samples, when compared to the uncoated ones, which did not occur for S. mutans. Within the limitations of this study, a-SiO(x) coatings may affect the adhesion of bacteria such as S. mitis, possibly by changing the wettability of the composite resins investigated.

Effects of Alendronate Sodium Content on the Interface Strengths of Composite Acrylic Bone Cement

Objective. Aim to study how the content of alendronate affected shear strengths at bone-bone cement-metal interfaces. Methods. All samples were divided into 6 groups, G0-G5. On the 1st and 60th day after surgery, bone-bone cement interface shear strengths and bone densities were examined. Interface strengths of metal-bone cement specimens were studied before immersion and 4 weeks after immersion. Results. On the 60th day, bone-bone cement interface shear strengths and bone densities showed significant differences (P < 0.05), and compared with G0, G2-G5 values increased significantly (P < 0.05), and the peak value was met in G3. Compared with the 1st day, on the 60th postoperative day both factors decreased significantly in G0 and G1 (P < 0.05). Four weeks after immersion, with the increasing dose of alendronate, the shear strengths decreased gradually and in G5 decreased significantly (P < 0.05). Compared with before immersion, the metal-bone cement interface strengths decreased significantly 4 weeks after immersion (P < 0.05). Conclusions. 50-500 mg alendronate in 50 g cement powders could prevent the decrease of shear strengths at bone-bone cement interfaces and had no effect on metal-bone cement interface strengths. While the addition dose was 100 mg, bone cement showed the best strengths.

Effect of fabrication process on the bond strength between silicone elastomer and acrylic resin for maxillofacial prosthesis

This study evaluated the effects of the fabrication process on tensile bond strength between maxillofacial silicone elastomer and acrylic resin. A common maxillofacial silicone elastomer (VST-50), two primers (Sofreliner primer and R-SI-LINE Plasticbond), and two acrylic resins (Unifast III and Palapress Vario) were selected. Silicone elastomer between primed acrylic resin plates were polymerized using a metal flask mold or a flaskless stone mold. Bond strength of the specimens was measured by a tensile test and analyzed using two-way analysis of variance (ANOVA) with Tukey's honest significant difference test. All fracture surfaces showed interfacial fracture. Both the fabrication process and the primer-acrylic resin combination affected bond strength, and two-way ANOVA indicated a significant interaction. Bond strength was generally greater when silicone elastomer was polymerized using a flaskless stone mold.

Preliminary Study of the Application of PET Knitted Fabrics in Artificial Bone Scaffold

Having good mechanical strength, biocompatibility, and workability, polyethylene terephthalate (PET) is often used as a biomaterial. In this study, PET filaments with various deniers are made into plied yarn with various coefficients of twist. The plied yarn is then made into PET knitted fabrics. Mechanical property tests are performed to determine the differences among the various PET knitted fabrics. Finally, by using cell culture, the PET knitted fabrics are analyzed and evaluated with their cell attachment.

[What can be done when hip prostheses fail? : New trends in revision endoprosthetics]

Revision surgery after total hip arthroplasty is increasing steadily in numbers. These procedures demand high performance from both the treating surgeon as well as the implants used. Novel developments from basic research and industrial partners extend the possibilities for treating affected patients. This article gives an overview of the state of the art in revision hip arthroplasty: new techniques and trends are outlined and presented.

Antimicrobial activity of gentamicin palmitate against high concentrations of Staphylococcus aureus

The reduction of implant related infections plays a pivotal role in orthopaedic surgery as an increasing number of people require implants (up to 200,000 per year in the United States (source: Joint Implant Surgery & Research Foundation 2010)). The aim of the current study is to prevent and thus decrease the number of bacterial infections. Both pre and post operative systemic antibiotic treatment and gentamicin containing bone cements (polymethylmethacrylate, PMMA) are commonly used strategies to overcome infections. In this study, the antimicrobial efficacy of gentamicin sulfate loaded bone cement was compared with titan discs coated with a new form of gentamicin, gentamicin palmitate. Adherence prevention, killing rates and killing kinetics were compared in an in vitro model, using Staphylococcus aureus (S. aureus), which together with Staphylococcus epidermidis (S. epidermidis) represents 60% of bacteria found responsible for hip implant infections (An and Friedman, 1996, J Hosp Infect 33(2):93-108). In our experiments gentamicin, which was applied as gentamicin palmitate on the surface of the implants, showed a high efficacy in eliminating bacteria. In contrast to gentamicin sulfate containing bone cements, gentamicin palmitate is released over a shorter period of time thus not inducing antibiotic resistance. Another benefit for clinical application is that it achieves high local levels of active ingredient which fight early infections and minimize toxic side effects. Furthermore, the short term hydrophobic effect of gentamicin palmitate can successfully impede biofilm formation. Thus, the use of self-adhesive antibiotic fatty acid complexes like gentamicin palmitate represents a new option for the anti-infective coating of cementless titan implants.

Effect of titania-based surface modification of polyethylene terephthalate on bone-implant bonding and peri-implant tissue reaction

Organic polymers can be uniformly surface-modified with bioactive TiO(2) by using a sol-gel method. Titania-based surface-modified polyethylene terephthalate (TiPET) plates and fabric have shown apatite-forming ability in simulated body fluid. Here, we first investigated the bone-bonding ability and mechanical bonding strength between the surface-modified layer and the base material (PET) of TiPET plates in vivo. For clinical applicability, we also examined the bone-bonding ability of TiPET fabric and the effect of titania-based surface modification on peri-implant tissue reactions (e.g. connective tissue capsule formation) in bone in vivo. Solid PET plates and PET fabric were prepared. Test plates and fabric were surface-modified with titania solution by using a sol-gel method. Histological examinations of the plates implanted into rabbit tibiae revealed direct contact between the TiPET plate and the bone. After the detaching test, a considerable amount of bone residue was observed on the surface of the TiPET plate. This result suggests that the mechanical bond strength between surface-modified layer and the base material is stronger than that between newly generated bone and tibia, and indirectly ensures the mechanical stability of the surface-modified layer. Pulling tests and histological examinations of the TiPET fabric revealed its excellent bone-bonding ability and micro-computed tomographic images showed excellent osteoconductive ability of TiPET fabric. The connective tissue capsule was much thinner, with less inflammatory tissue around the TiPET implants than around the control samples. These results indicate that TiPET fabric possesses a mechanically stable surface-modified layer, excellent bone-bonding ability, osteoconductive ability, and biocompatibility in bone.

Silicon, silica and its surface patterning/activation with alkoxy- and amino-silanes for nanomedical applications

Silica and silicates are widely used in nanomedicine with applications as diverse as medical device coatings to replacement materials in tissue engineering. Although much is known about silica and its synthesis, relatively few biomedical scientists fully appreciate the link that exists between its formulation and its resultant structure and function. This article attempts to provide insight into relevant issues in that context, as well as highlighting their importance in the material’s eventual surface patterning/activation with alkoxy- and organo-silanes. The use of aminosilanes in that context is discussed at some length to permit an understanding of the specific variables that are important in the reproducible and robust aminoactivation of surfaces using such molecules. Recent investigative work is cited to underline the fact that although aminosilanization is a historically accepted mechanism for surface activation, there is still much to be explained about how and why the process works in the way it does. In the last section of this article, there is a detailed discussion of two classical approaches for the use of aminosilanized materials in the covalent immobilization of bioligands, amino-aldehyde and amino-carboxyl coupling. In the former case, the use of the homobifunctional coupler glutaraldehyde is explored, and in the latter, carbodiimides. Although these chemistries have long been employed in bioconjugations, it is apparent that there are still variables to be explored in the processes (as witnessed by continuing investigations into the chemistries concerned). Aspects regarding optimization, standardization and reproducibility of the fabrication of amino functionalized surfaces are discussed in detail and illustrated with practical examples to aid the reader in their own studies, in terms of considerations to be taken into account when producing such materials. Finally, the article attempts to remind readers that although the chemistry and materials involved are ‘old hat’, there is still much to be learnt about the methods involved. The article also reminds readers that although many highly specific and costly conjugation chemistries now exist for bioligands, there still remains a place for these relatively simple and cost-effective approaches in bioligand conjugate fabrication.

Initial adhesion of glass-fiber-reinforced composite to the surface of porcine calvarial bone

The aim of this preliminary study was to compare the initial bond strength of the glass-fiber-reinforced composite veil to the surface of the porcine calvarial compact bone using different adhesives. Fiber-reinforced composite (FRC) made of E-glass fiber veil with the BisGMA-PMMA resin system was used in the study. For the shear bond strength test, porcine calvarial bone cubes were mounted into resin matrix. FRC-veil discs were bonded to compact bone with different types of adhesives: (A) BisGMA-HEMA based (3M-ESPE Scotchbond Multi-Purpose Adhesive), (B) 4-META/UDMA/BisGMA based (Unifil Bond Bonding Agent) and MDP based (Clearfil Se Bond adhesive), (C) UDMA/BisGMA/PMMA-based experimental adhesive, and (D) silane-based (APS, ICS, MPS) experimental adhesives. The surface of the bone was mechanically roughened and was either used as such, treated with dental primers (Unifil Bond Self-etching Primer, Clearfil Se Bond Primer), or treated with an experimental silane mixture (APS, ICS, MPS), or with a mixture of the experimental silane liquid and Clearfil Se Bond Primer. The 3M-ESPE Scotchbond Multi-Purpose Adhesive and UDMA/BisGMA/PMMA experimental adhesive gave poor results in the shear bond test (0.58 and 0.40 MPa, respectively). Unifil Bond Bonding Agent and Clearfil Se Bond adhesive with respective primers markedly improved the shear bond strength; with Unifil the result was 3.40 MPa, and with Clearfil it was 6.19 MPa. When the bone surface was primed with a mixture of Clearfil Se Bond Primer and Clearfil Porcelain Bond Activator, the Clearfil Se Bond adhesive-impregnated FRC veil gave the best adhesion to the bone surface in this test: 9.50 MPa. The addition of bioactive glass granules between the veil and the bone lowered the shear bond strength in the test system described above to 6.72 MPa. The test systems with the silane mixture were also promising. In the SEM study, it was found that the mechanical treatment reveals the pores of the bone surface. Chemical treatments of the bone surface improved the adhesion of the FRC veil to the bone. The results showed that the adhesion of the FRC to the surface of the bone can be significantly improved with mechanical roughening and with special chemical treatments of the bone surface.

Amphiphilic bonder improves adhesion at the acrylic bone cement-bone interface of cemented acetabular components in total hip arthroplasty: in vivo tests in an ovine model

INTRODUCTION

Even following the introduction of the "third generation" cementing technique, an improvement of the fixation of the acetabular component similar to that of the femoral has not been shown in clinical studies. The goal of the present study was to achieve a better stability with the use of an amphiphilic bonder while preserving the mechanically important subchondral sclerosis.

MATERIALS AND METHODS

In a total of 20 sheep, a cemented total hip replacement was implanted. In the treatment group (n = 10), the implantation was carried out following surface conditioning of the acetabular bed with an amphiphilic bonder. All the sheep were followed for 9 months. To assess the biocompatibility, the osseous ingrowth at the cement-bone interface was depicted with the help of an in vivo fluorescent marking of the osteoblasts. Additionally, conventional radiographs were obtained over the course of treatment. Finally, the ovine pelvic regions were split following a standardized technique allowing for histological evaluation of the cement-bone interfaces.

RESULTS

The acetabular components of the treatment group revealed a stable cement-bone compound. In the control group, the implants were easily dislodged from their beds. This finding was consistent with the radiological and histological results, which had revealed increased, progressive lytic radiolucent lines and the interposition of fibrous tissue at the cement-bone interface in the control group compared to the treatment group. The bonder was biocompatible.

CONCLUSION

Following the application of the bonder, the cemented acetabular components revealed an improved stability without signs of inflammation or neoplasia in a viable acetabular osseous bed. With the help of this technique, the in vivo longevities of cemented acetabular components can be increased in the clinical setting without sacrificing the biomechanical relevant subchondral sclerosis.

A new adhesive technique for internal fixation in midfacial surgery

Background

The current surgical therapy of midfacial fractures involves internal fixation in which bone fragments are fixed in their anatomical positions with osteosynthesis plates and corresponding screws until bone healing is complete. This often causes new fractures to fragile bones while drilling pilot holes or trying to insert screws. The adhesive fixation of osteosynthesis plates using PMMA bone cement could offer a viable alternative for fixing the plates without screws. In order to achieve the adhesive bonding of bone cement to cortical bone in the viscerocranium, an amphiphilic bone bonding agent was created, analogous to the dentin bonding agents currently on the market.

Methods

The adhesive bonding strengths were measured using tension tests. For this, metal plates with 2.0 mm diameter screw holes were cemented with PMMA bone cement to cortical bovine bone samples from the femur diaphysis. The bone was conditioned with an amphiphilic bone bonding agent prior to cementing. The samples were stored for 1 to 42 days at 37 degrees C, either moist or completely submerged in an isotonic NaCl-solution, and then subjected to the tension tests.

Results

Without the bone bonding agent, the bonding strength was close to zero (0.2 MPa). Primary stability with bone bonding agent is considered to be at ca. 8 MPa. Moist storage over 42 days resulted in decreased adhesion forces of ca. 6 MPa. Wet storage resulted in relatively constant bonding strengths of ca. 8 MPa.

Conclusion

A new amphiphilic bone bonding agent was developed, which builds an optimizied interlayer between the hydrophilic bone surface and the hydrophobic PMMA bone cement and thus leads to adhesive bonding between them. Our in vitro investigations demonstrated the adhesive bonding of PMMA bone cement to cortical bone, which was also stable against hydrolysis. The newly developed adhesive fixing technique could be applied clinically when the fixation of osteosynthesis plates with screws is impossible. With the detected adhesion forces of ca. 6 to 8 MPa, it is assumed that the adhesive fixation system is able to secure bone fragments from the non-load bearing midfacial regions in their orthotopic positions until fracture consolidation is complete.

[ Improvement of femoral bone-cement adhesion in cemented revision hip arthroplasty by application of an amphiphilic bonder in a dynamic femur expulsion testing in vitro ]

Cemented femoral stems have shown decreased longevity compared to cementless implants in hip revision arthroplasty. The aim of this study was to evaluate the effect of an amphiphilic bonder on bone cement stability in a biomechanical femur expulsion test. A simplified hip simulator test setup with idealised femur stem specimens was carried out. The stems were implanted into bovine femurs (group 1: no bonder, n=10; group 2: bonder including glutaraldehyde, n=10; group 3: bonder without glutaraldehyde, n=10). A dynamic loading (maximum load: 800 N; minimum load: 100 N; frequency: 3 Hz; 105 cycles) was performed. Subsequently, the stem specimens were expulsed axially out of their implant beds and maximum load at failure was recorded. The static controls showed a mean maximum load to failure of 4123 N in group 1, 8357.5 N in group 2 and 5830.8 N in group 3. After dynamic loading, the specimens of group 2 reached the highest load to failure (8191.5 N), followed by group 3 (5649.5 N) and group 1 (3462 N), respectively. In group 2, we observed nine periprosthetic fractures at a load of 8400 N without signs of interface loosening. Application of an amphiphilic bonder led to a significant improvement of bonding stability, especially when glutaraldehyde was added to the bonder. This technique might offer an increased longevity of cemented femur revision stems in total hip replacement.

Hydrolytic stability of composite repair bond

The hydrolytic stability of composite repairs is a desirable property. In the present study, the composite repair microtensile bond strength, failure mode distribution, and nanoleakage occurrence before and after thermocycling were evaluated. Standardized, 1-month-old composite substrates were roughened, cleaned, and randomly assigned to seven groups according to the intermediate agent applied. Resin-based, silane-based, and combined silane/adhesive coupling agents were investigated. The same resin composite as the substrate was used for repair. For each group, repaired samples were wet stored for 24 h (37 degrees C) or thermocycled (5,000 cycles, 5-55 degrees C). Failure mode and silver nitrate penetration were examined by stereomicroscopy. Intermediate agent, experimental condition, and their interaction were significant factors. Hydrophobic flowable composites resulted in statistically higher repair strengths, lower occurrence of adhesive failures, and good quality interfacial coupling without any silver uptake in both conditions. Light-curing, hydrophilic resin monomer-based intermediate agents, although not affected by thermocycling, showed a more pronounced silver penetration. The composite repair strength of a self-curing silane/adhesive agent was significantly affected by thermal stresses, despite the absence of silver uptake. A prehydrolized silane agent recorded the lowest repair strength, with minimal or no evidence of interfacial silver impregnation after thermocycling. In conclusion, flowability and hydrophobic nature can be considered important properties when selecting intermediate agents for composite repair.

Improvement of the long-term adhesive strength between bone cement and bone in cemented cup arthroplasty: ex-vivo study

INTRODUCTION

One of the main causes of cup loosening in cemented total hip replacement is the lack of a hydrolysis stable compound between the hydrophobic bone cement and the hydrophilic acetabular bone stock. Thus, the long-term adhesive strength between bone and bone cement is decreased resulting in premature aseptic loosening. Accordingly, an amphiphilic bonding system was developed to prevent hydrolytic debonding in the interface bone-to-bone cement.

MATERIALS AND METHODS

Polyethylene cups were cemented in cadaver sheep hips. The hips were prepared with (n = 10) a multilayer bonding system as well as with an improved monolayer bonding system with (n = 10) and without (n = 10) UV-light hardening. The hips were dynamically loaded (10(6) cycles; 3 Hz; upper/lower load 1,500/200 N) and afterwards turned out with a defined strength to determine the interface compound strength. Dynamically loaded cemented cups without using the bonding system (n = 10) function as a control group.

RESULTS

The interface adhesive strength improved significantly by a factor of 1.9 (using the multilayer bonding system) compared to the unconditioned ones (P < or = 0.05); for the monolayer bonding system without (with) UV-light hardening the compound strength was 11.9-fold (> or =22.2-fold) higher (P < or = 0.001).

CONCLUSION

The bonding system significantly improves the adhesive strength between bone and bone cement in cemented cup arthroplasty.

Influence of gradual introduction of hydrophobic groups (stearic acid) in denatured atelocollagen on fibroblasts behaviorin vitro

To prepare new biocompatible hydrophobic collagen films for medical devices, innovative collagen derivatives were synthesized by reaction of the lysyl amino groups of the alpha-chains with activated stearic acid. Different collagens having different substitution degrees were obtained and used to prepare films crosslinked with oxidized glycogen. Their physicochemical surface properties were evaluated, and in vitro assays were performed to analyze the behavior of fibroblasts in contact with the materials. The assays were performed with cells in adhesion and growth phases. The hydrophobic properties increased with the number of stearic acid introduced in the collagen but only in the range of 1-12 stearic acids per molecule. For higher modifications a decrease of hydrophoby was observed. All the films induced a decrease of cells growth and adhesion but without cytotoxicity. These effects were more pronounced for the collagen containing about eight stearic acid residues. Cells behavior on modified collagens films seems to be related to the chemical groups exposed on the surface of the films. Indeed, the surface chemistry directly influences the adsorption of adhesion proteins and modulates their conformation therefore modifying the cell adhesion.

Mechanical bond strength of the cement-tibial component interface in total knee arthroplasty

The purpose of this study was to mechanically test the cement-tibial component interface using titanium and cobalt-chrome sample prostheses with several commercially available surface textures. The results of this study indicate that the type of metal substrate and surface preparation of contemporary tibial baseplates may influence the strength of the metal-cement interface and as such influence tibial component survival. The results indicate that, in general, metal-cement interface strength increases with increasing surface roughness and common surface treatments such as AlO2 grit-blasting (Ra = 6.76 microm) produce interface strengths similar to plasma-spray, porous-coated specimens. Macrosurfaced tibial components, although comparable in tension, may be vulnerable to metal-cement interface failure with rotational loading.

Oberflächenkonditionierung für eine verbesserte Überlebenswahrscheinlichkeit von Knieprothesen: Komplett- vs. Oberflächenzementiertechnik der Tibiakomponente / Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique

Aseptic loosening of tibial components due to degradation of the interface between bone cement and metallic tibial shaft component is still a persistent problem, particularly for surface-cemented tibial components. The surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by SiOx-PVD layering to avoid crack formation. A biomechanical model for a vibration fatigue test was done to prove that crack formation can be significantly reduced in the case of coated surfaces. It was found that coated tibial components showed a highly significant reduction of cement cracking near the metal/bone cement interface (p < 0.01) and a significant reduction of gap formation in the metal-to-bone cement interface (p < 0.05). Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis metal/bone cement interface. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the metal/bone cement/bone interfaces. With surface coating of the tibial component it should become possible that surface-cemented TKAs reveal similar loosening rates as TKAs both surface- and stem-cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in the case of revision and stress shielding for a better bone health.

Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique

Background

One of few persisting problems of cemented total knee arthroplasty (TKA) is aseptic loosening of tibial component due to degradation of the interface between bone cement and metallic tibial shaft component, particularly for surface cemented tibial components. Surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. Degradation of the interface between bone cement and bone may be a secondary effect due to excessive crack formation in bone cement starting at the opposite metallic surface.

Methods

This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by PVD layering with SiO_x to avoid that crack formation in the bone cement. A biomechanical model for vibration fatigue test was done to simulate the physiological and biomechanical conditions of the human knee joint and to prove excessive crack formation.

Results

It was found that coated tibial components showed a highly significant reduction of cement cracking near the interface metal/bone cement (p < 0.01) and a significant reduction of gap formation in the interface metal-to-bone cement (p < 0.05).

Conclusion

Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis interface metal/bone cement. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the interfaces metal/bone cement/bone. With surface coating of the tibial component it should become possible that surface cemented TKAs reveal similar loosening rates as TKAs both surface and stem cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in case of revision and stress shielding for better bone health.