Biocompatibility of total joint replacements: A review

A review on manufacturing processes of cobalt-chromium alloy implants and its impact on corrosion resistance and biocompatibility

Cobalt-Chromium (CoCr) alloys are currently used for various cardiovascular, orthopedic, fracture fixation, and dental implants. A variety of processes such as casting, forging, wrought processing, hot isostatic pressing, metal injection molding, milling, selective laser melting, and electron beam melting are used in the manufacture of CoCr alloy implants. The microstructure and precipitates (carbides, nitrides, carbonitrides, and intermetallic compounds) formed within the alloy are primarily determined by the type of manufacturing process employed. Although the effects of microstructure and precipitates on the physical and mechanical properties of CoCr alloys are well reviewed and documented in the literature, the effects on corrosion resistance and biocompatibility are not comprehensively reviewed. This article reviews the various processes used to manufacture CoCr alloy implants and discusses the effects of manufacturing processes on corrosion resistance and biocompatibility. This review concludes that the microstructure and precipitates formed in the alloy are unique to the manufacturing process employed and have a significant impact on the corrosion resistance and biocompatibility of CoCr alloys. Additionally, a historical and scientific overview of corrosion and biocompatibility for metallic implants is included in this review. Specifically, the failure of CoCr alloys when used in metal-on-metal bearing surfaces of total hip replacements is highlighted. It is recommended that the type of implant/application (orthopedic, dental, cardiovascular, etc.) should be the first and foremost factor to be considered when selecting biomaterials for medical device development.

Compliant Intramedullary Stems for Joint Reconstruction

The longevity of current joint replacements is limited by aseptic loosening, which is the primary cause of non-infectious failure for hip, knee, and ankle arthroplasty. Aseptic loosening is typically caused either by osteolysis from particulate wear, or by high shear stresses at the bone-implant interface from over-constraint. Our objective was to demonstrate feasibility of a compliant intramedullary stem that eliminates over-constraint without generating particulate wear. The compliant stem is built around a compliant mechanism that permits rotation about a single axis. We first established several models to understand the relationship between mechanism geometry and implant performance under a given angular displacement and compressive load. We then used a neural network to identify a design space of geometries that would support an expected 100-year fatigue life inside the body. We additively manufactured one representative mechanism for each of three anatomic locations, and evaluated these prototypes on a KR-210 robot. The neural network predicts maximum stress and torsional stiffness with 2.69% and 4.08% error respectively, relative to finite element analysis data. We identified feasible design spaces for all three of the anatomic locations. Simulated peak stresses for the three stem prototypes were below the fatigue limit. Benchtop performance of all three prototypes was within design specifications. Our results demonstrate the feasibility of designing patient- and joint-specific compliant stems that address the root causes of aseptic loosening. Guided by these results, we expect the use of compliant intramedullary stems in joint reconstruction technology to increase implant lifetime.

Survivability of Titanium Implant Materials: In Vitro Simulated Inflammatory and Infectious Environment

Titanium-based implants utilized in total joint arthroplasties could restore primary musculoskeletal function to patients suffering from osteoarthritis and other conditions. Implants are susceptible to failure stemming from aseptic loosening and infection at the joint site, eventually requiring revision surgery. We hypothesized that there might be a feedback loop by which metal degradation particles and ions released from the implant decrease cell viability and increase immune response, thereby creating biochemical conditions that increase the corrosion rate and release more metal ions. This study focused on the synergistic process through cell viability assays and electrochemical tests. From the results, inflammatory conditions from ion release resulting in cell death would further increase the corrosion rate at the metal implant site. The synergistic interaction in the implant surroundings in which infectious conditions produce Ti ions that contribute to more infection, creating a potential cycle of accelerating corrosion.

Green synthesized nano-cellulose polyethylene imine-based biological membrane

In hemodialysis process, membrane serves as a barrier between blood and the dialysate. The barrier when contacted by blood accompanied activation of coagulation, immunity, and cellular passageways. In the recent years, hemodialysis membrane's biocompatibility has become a issue which leads to reduce the performance during the separation process. In previous work, we developed and evaluated a cellulose-based membrane blended with polyaziridine or polyetyleneimine in formic acid for hydrophilicity, pure water flux, surface morphology, and permeation efficiency. Biocompatibility was accessed, by conducting cellular viability and cellular attachments tests. In this study, the membrane compared to a non-treated control, and cell viability revealed active and growing cell cultures after 14 days. During the cellular attachment experiment, cell cultures attached to the fabricated membrane simulated the formation of cell junctions, proving that the membrane is non-toxic and biocompatible. CA + PEI + FA membrane tested with a blood mimic fluid having density identical to renal patient's blood. The BSA concentration in the feed solution was the same as that in the blood of the renal patient. The results revealed that the CA + PEI + FA membrane was able to reject 99% bovine serum albumin (BSA) and 69.6% urea. Therefore, from biocompatibility and blood mimic fluid testing, it is confirmed that the CA + PEI + FA membrane is the finest implant for dialysis applications.

Path Planning for Laser Cladding Robot on Artificial Joint Surface Based on Topology Reconstruction

Artificial joint surface coating is a hot issue in the interdisciplinary fields of manufacturing, materials and biomedicine. Due to the complex surface characteristics of artificial joints, there are some problems with efficiency and precision in automatic cladding path planning for coating fabrication. In this study, a path planning method for a laser cladding robot for artificial joints surface was proposed. The key of this method was the topological reconstruction of the artificial joint surface. On the basis of the topological relation, a set of parallel planes were used to intersect the CAD model to generate a set of continuous, directed and equidistant surface transversals on the artificial joint surface. The arch height error method was used to extract robot interpolation points from surface transversal lines according to machining accuracy requirements. The coordinates and normal vectors of interpolation points were used to calculate the position and pose of the robot tool center point (TCP). To ensure that the laser beam was always perpendicular to the artificial joint surface, a novel laser cladding set-up with a robot was designed, of which the joint part clamped by a six-axis robot moved while the laser head was fixed on the workbench. The proposed methodology was validated with the planned path on the surface of an artificial acetabular cup using simulation and experimentation via an industrial NACHI robot. The results indicated that the path planning method based on topological reconstruction was feasible and more efficient than the traditional robot teaching method.

A Vibrational Technique for In Vitro Intraoperative Prosthesis Fixation Monitoring

OBJECTIVE

In this paper, a new vibrational modal analysis technique was developed for intraoperative cementless prosthesis fixation evaluation upon hammering.

METHODS

An artificial bone (Sawbones)-prosthesis system was excited by sweeping of a sine signal over a wide frequency range. The exponential sine sweep technique was implemented to the response signal in order to determine the linear impulse response. Recursive Fourier transform enhancement (RFTE) technique was applied to the linear impulse response signal in order to enhance the frequency spectrum with sharp and distinguishable peak values indicating distinct high natural frequencies of the system (ranging from 15 kHz to 90 kHz). The experiment was repeated with 5 Sawbones-prosthesis samples. Upon successive hammering during the prosthesis insertion, variation of each natural frequency was traced.

RESULTS

Compared to classical Fast Fourier Transform, RFTE provided a better tracing and enhancement of frequency components during insertion. Three different types of frequency evolving trends (monotonically increasing, insensitive, and plateau-like) were observed for all samples, as confirmed by a new finite element simulation of the prosthesis dynamic insertion. Two main mechanical phenomena (i.e., geometrical compaction and compressive stress) were shown to govern these trends in opposite ways. Follow-up of the plateau-like trend upon hammering showed that the frequency shift is a good indicator of fixation.

CONCLUSION

Alongside the individual follow-up of frequency shifts, combinatorial frequency analysis provides new objective information on the mechanical stability of Sawbone-prosthesis fixation.

SIGNIFICANCE

The proposed vibrational technique based on RTFE can provide the surgeon with a new assistive diagnostic technique during the surgery by indicating when the bone-prosthesis fixation is acceptable, and beyond of which further hammering should be done cautiously to avoid bone fracture.

In vivo osseointegration of a randomized trabecular titanium structure obtained by an additive manufacturing technique

The additive manufacturing techniques (AM) are able to realize three-dimensional trabecular structures that mimic the trabecular structure of the bone. An in vivo study in sheep was carried out with the aim of assessing the bone response and the trend of osteointegration of a randomized trabecular titanium structure produced by the AM technique. In 6 sheep were implanted 84 specimens with a trabecular titanium structure (4 implants in the femur distal epiphysis; 4 implants in the tibial plate; 6 implants in the tibial shaft). Sheep were sacrificed at 3 postoperative time-points: 6 weeks, 10 weeks, 14 weeks. Histomorphometric analysis was performed for the evaluation of Bone Implant Contact, and Bone Ingrowth. A standard push-out test was used to analyze the mechanical characteristics of the bone-implant interface. The histomorphometric data and biomechanical tests showed a fast osseointegration of the specimens both in the cancellous and in the cortical bone. The quantitative analysis of osseointegration data in cancellous bone showed the percentage of the surface of the implant in direct contact with the regenerated bone matrix significantly improved from 28% at 6 weeks to 54% at 14 weeks. An early osseointegration occurred in cortical bone showing that 75% of surface of implant was in direct contact with regenerated bone after 6 weeks; this value increased to 85% after 14 weeks. Mechanical tests revealed an early improvement of mean peak load of implants at 10 weeks (4486 N ± 528 N) compared to values at 6 weeks (2516 N ± 910 N) confirming the high rate of progression of osseointegration in the cortical bone. The non-mineralized matrix followed an increasing process of mineralization almost completely after 14 weeks. The results of this study have showed a rapid osseointegration and excellent biocompatibility for a randomized trabecular titanium structure that should be confirmed by clinical investigations.

Diagnosis and management of implant debris-associated inflammation

Introduction: Total joint replacement is one of the most common, safe, and efficacious operations in all of surgery. However, one major long-standing and unresolved issue is the adverse biological reaction to byproducts of wear from the bearing surfaces and modular articulations. These inflammatory reactions are mediated by the innate and adaptive immune systems.Areas covered: We review the etiology and pathophysiology of implant debris-associated inflammation, the clinical presentation and detailed work-up of these cases, and the principles and outcomes of non-operative and operative management. Furthermore, we suggest future strategies for prevention and novel treatments of implant-related adverse biological reactions.Expert opinion: The generation of byproducts from joint replacements is inevitable, due to repetitive loading of the implants. A clear understanding of the relevant biological principles, clinical presentations, investigative measures and treatments for implant-associated inflammatory reactions and periprosthetic osteolysis will help identify and treat patients with this issue earlier and more effectively. Although progressive implant-associated osteolysis is currently a condition that is treated surgically, with further research, it is hoped that non-operative biological interventions could prolong the lifetime of joint replacements that are otherwise functional and still salvageable.

Inflammation and Bone Repair: From Particle Disease to Tissue Regeneration

When presented with an adverse stimulus, organisms evoke an immediate, pre-programmed, non-specific innate immune response. The purpose of this reaction is to maintain the organism's biological integrity and function, mitigate or eradicate the injurious source, and re-establish tissue homeostasis. The initial stage of this protective reaction is acute inflammation, which normally reduces or terminates the offending stimulus. As the inflammatory reaction recedes, the stage of tissue repair and regeneration follows. If the above sequence of events is perturbed, reconstitution of normal biological form and function will not be achieved. Dysregulation of these activities may result in incomplete healing, fibrosis, or chronic inflammation. Our laboratory has studied the reaction to wear particles from joint replacements as a paradigm for understanding the biological pathways of acute and chronic inflammation, and potential translational treatments to reconstitute lost bone. As inflammation is the cornerstone for healing in all anatomical locations, the concepts developed have relevance to tissue engineering and regenerative medicine in all organ systems. To accomplish our goal, we developed novel in vitro and in vivo models (including the murine femoral continuous intramedullary particle infusion model), translational strategies including modulation of macrophage chemotaxis and polarization, and methods to interfere with key transcription factors NFκB and MyD88. We purposefully modified MSCs to facilitate bone healing in inflammatory scenarios: by preconditioning the MSCs, and by genetically modifying MSCs to first sense NFκB activation and then overexpress the anti-inflammatory pro-regenerative cytokine IL-4. These advancements provide significant translational opportunities to enhance healing in bone and other organs.

Use of Materials Based on Polymeric Silica as Bone-Targeted Drug Delivery Systems for Metronidazole

Mesostructured ordered silica-based materials are the promising candidates for local drug delivery systems in bone disease due to their uniform pore size and distribution, and high surface area which affect their excellent adsorption properties, good biocompatibility and bioactivity, and versatile functionalization so that their properties can be controlled. Ordered mesoporous silica (MCM-41 type) was synthesized by a surfactant-assisted sol-gel process using tetraethoxysilane as a silica precursor and hexadecyltrimethylammonium bromide as the structure-directing agent. Functionalized silica materials containing various types of organic groups (3-aminopropyl, 3-mercaptopropyl, or 3-glycidyloxypropyl groups) were synthesized by the post-grafting method onto pre-made mesoporous silica. Comparative studies of their structural characteristics, the surface mineralization activity and release properties for the model drug Metronidazole (MT) were then conducted. It has been found that porosity parameters, mineralization activity and adsorption/release of metronidazole from mesoporous channels of silica can be regulated using functional groups which are chemically bounded with an outer silica surface. The preferential mineral nucleation was found on negatively charged surfaces-MCM-41, and mercaptopropyl and glycidyloxypropyl functionalized silica (MCM-SH and MCM-epoxy, respectively) in simulated body fluid (SBF solution), as well as a sustained release of MT. In contrast to them, aminopropyl-functionalized samples (MCM-NH₂) achieved a high MT release rate. These results confirm the potential of silica-based materials for local therapeutic applications (as drug carriers and bone substitutes) in bone disease.

Effects of metal ions on caspase-1 activation and interleukin-1β release in murine bone marrow-derived macrophages

Ions released from metal implants have been associated with adverse tissue reactions and are therefore a major concern. Studies with macrophages have shown that cobalt, chromium, and nickel ions can activate the NLRP3 inflammasome, a multiprotein complex responsible for the activation of caspase-1 (a proteolytic enzyme converting pro-interleukin [IL]-1β to mature IL-1β). However, the mechanism(s) of inflammasome activation by metal ions remain largely unknown. The objectives of the present study were to determine if, in macrophages: 1. caspase-1 activation and IL-1β release induced by metal ions are oxidative stress-dependent; and 2. IL-1β release induced by metal ions is NF-κB signaling pathway-dependent. Lipopolysaccharide (LPS)-primed murine bone marrow-derived macrophages (BMDM) were exposed to Co2+ (6-48 ppm), Cr3+ (100-500 ppm), or Ni2+ (12-96 ppm), in the presence or absence of a caspase-1 inhibitor (Z-WEHD-FMK), an antioxidant (L-ascorbic acid [L-AA]), or an NF-κB inhibitor (JSH-23). Culture supernatants were analyzed for caspase-1 by western blotting and/or IL-1β release by ELISA. Immunoblotting revealed the presence of caspase-1 (p20 subunit) in supernatants of BMDM incubated with Cr3+, but not with Ni2+ or Co2+. When L-AA (2 mM) was present with Cr3+, the caspase-1 p20 subunit was undetectable and IL-1β release decreased down to the level of the negative control, thereby demonstrating that caspase-1 activation and IL-1β release induced by Cr3+ was oxidative stress-dependent. ELISA demonstrated that Cr3+ induced the highest release of IL-1β, while Co2+ had no or limited effects. In the presence of Ni2+, the addition of L-AA (2 mM) also decreased IL-1β release, below the level of the negative control, suggesting that IL-1β release induced by Ni2+ was also oxidative stress-dependent. Finally, when present during both priming with LPS and activation with Cr3+, JSH-23 blocked IL-1β release, demonstrating NF-κB involvement. Overall, this study showed that while both Cr3+ and Ni2+ may be inducing inflammasome activation, Cr3+ is likely a more potent activator, acting through oxidative stress and the NF-κB signaling pathway.

Investigation of nano-sized debris released from CoCrMo secondary interfaces in total hip replacements: Digestion of the flakes

The in vivo release of wear debris and corrosion products from the metallic interfaces of total hip replacements is associated with a wide spectrum of adverse body reactions and systemic manifestations. The origin of debris and the electrochemical conditions at the sites of material loss both play a role in determining the physicochemical characteristics of the particles, and thus influence their in vivo reactivity. Debris retrieved from revised CoCrMo tapers and cement-stem interfaces consists of heterogeneous flakes that comprise mechanically mixed metal particles, corrosion products and organic material. Detailed investigation of the size and composition of the metal debris contained within these composites requires the digestion of the flakes to release the small metal particles. Here, we compare alkaline and enzymatic digestion methods that both aim to fragment the flakes and reveal their smallest building blocks. The characterization of debris cleaned with both methods revealed crystalline Cr oxide nanoparticles and clusters. Comparison between the treatments showed that the alkaline method is more efficient in fragmenting the flakes and provided cleaner and generally smaller nanoparticles than exhibited in debris released with the enzymatic treatment. The provision of cleaner nanoparticles from the alkaline method also allows the physicochemical properties of the particles to be more clearly identified. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 424-434, 2019.

Suppression of osteogenic activity by regulation of WNT and BMP signaling during titanium particle induced osteolysis

Periprosthetic osteolysis remains the leading obstacle for total joint replacements. Primarily, it was thought that aseptic loosening is mainly caused by macrophage mediated inflammatory process arising from production of wear debris. The role of osteoclasts and its sequential bone resorption ability has been extensively studied, but little is known about impaired osteogenesis during osteolysis. In the current study, we have tried to delineate the regulatory mechanism of osteogenic signals by Ti particles in osteoprogenitor cells as well its participatory role in wear debris induced osteolysis. Implantation of Ti particles on mice calvaria induced pro-inflammatory response, elevated expression of COX2 and reduced the expression of Osterix. Treatment of Ti particles to MC3T3 E-1 cells displayed decreased osteogenic activity including ALP activity, mineralization and mRNA levels several osteogenic genes. Moreover, the basal activity of WNT and BMP signaling pathways was suppressed in MC3T3 E-1 cells treated with Ti particles. As an early response to Ti particles, MC3T3 E-1 cells showed activation of ERK and JNK. Co-inhibition of ERK and JNK with their specific inhibitors resulted in partial recovery of WNT and BMP signaling activity as well as ALP activity and collagen synthesis. Finally, LiCl mediated activation of WNT signaling pathway demonstrated rescue of Ti particle facilitated suppression of Osterix expression in mice calvaria. Our results provide evidences that WNT signaling pathway is regulated by ERK, JNK, and BMP signaling pathway during wear debris induced inflammatory osteolysis and may be considered as suitable therapeutic targets for the treatment. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 912-926, 2017.

Study on critical-sized ultra-high molecular weight polyethylene wear particles loaded with alendronate sodium: in vitro release and cell response

The aim of this study was to investigate the in vitro release and the effect of RAW 264.7 macrophages of critical-sized wear particles of ultra-high molecular weight polyethylene (UHMWPE) loaded with alendronate sodium (ALN), one of the most effective drugs to treat osteoporosis in clinic. The critical-sized UHMWPE-ALN 0.5 wt.% wear particles were prepared by vacuum gradient filtration combined with Pluronic F-68. In vitro release of ALN from critical-sized UHMWPE-ALN wear particles was investigated in phosphate buffered saline (PBS) at 37 °C with a shaker. Cell morphology, proliferation, lactate dehydrogenase (LDH) leakage and secretions of cytokines were evaluated after co-cultured with critical-sized UHMWPE-ALN wear particles in vitro. Results showed that ALN released from critical-sized UHMWPE-ALN wear particles included burst release and slow release in vitro. Macrophages would be chemotaxis and aggregated around the critical-sized UHMWPE-ALN or UHMWPE wear particle, which was phagocytosed with time. The proliferation of macrophages co-cultured with critical-sized UHMWPE-ALN wear particles was significantly decreased compared with that of critical-sized UHMWPE group. Meanwhile, the critical-sized UHMWPE-ALN wear particles significantly induced the LDH leakage of macrophages, which indicated the cell death. The death of macrophages induced by ALN was one of pathways to inhibit their proliferation. The secretions of cytokines (interleukin-6 and tumor necrosis factor-alpha) in critical-sized UHMWPE-ALN group were significantly lower than those in critical-sized UHMWPE group due to the released ALN. The present results suggested that UHMWPE-ALN had the potential application in clinic to treat osteolysis induced by wear particles.

Ion-Doped Silicate Bioceramic Coating of Ti-Based Implant

Titanium and its alloy are known as important load-bearing biomaterials. The major drawbacks of these metals are fibrous formation and low corrosion rate after implantation. The surface modification of biomedical implants through various methods such as plasma spray improves their osseointegration and clinical lifetime. Different materials have been already used as coatings on biomedical implant, including calcium phosphates and bioglass. However, these materials have been reported to have limited clinical success. The excellent bioactivity of calcium silicate (Ca-Si) has been also regarded as coating material. However, their high degradation rate and low mechanical strength limit their further coating application. Trace element modification of (Ca-Si) bioceramics is a promising method, which improves their mechanical strength and chemical stability. In this review, the potential of trace element-modified silicate coatings on better bone formation of titanium implant is investigated.

The biological response to orthopaedic implants for joint replacement: Part I: Metals

Joint replacement is a commonly performed, highly successful orthopaedic procedure, for which surgeons have a large choice of different materials and implant designs. The materials used for joint replacement must be both biologically acceptable to minimize adverse local tissue reactions, and robust enough to support weight bearing during common activities of daily living. Modern joint replacements are made from metals and their alloys, polymers, ceramics, and composites. This review focuses on the biological response to the different biomaterials used for joint replacement. In general, modern materials for joint replacement are well tolerated by the body as long as they are in bulk (rather than in particulate or ionic) form, are mechanically stable and noninfected. If the latter conditions are not met, the prosthesis will be associated with an acute/chronic inflammatory reaction, peri-prosthetic osteolysis, loosening and failure. This article (Part 1 of 2) is dedicated to the use of metallic devices in orthopaedic surgery including the associated biological response to metallic byproducts is a review of the basic science literature regarding this topic. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2162-2173, 2017.

The biological response to orthopedic implants for joint replacement. II: Polyethylene, ceramics, PMMA, and the foreign body reaction

Novel evidence-based prosthetic designs and biomaterials facilitate the performance of highly successful joint replacement (JR) procedures. To achieve this goal, constructs must be durable, biomechanically sound, and avoid adverse local tissue reactions. Different biomaterials such as metals and their alloys, polymers, ceramics, and composites are currently used for JR implants. This review focuses on (1) the biological response to the different biomaterials used for TJR and (2) the chronic inflammatory and foreign-body response induced by byproducts of these biomaterials. A homeostatic state of bone and surrounding soft tissue with current biomaterials for JR can be achieved with mechanically stable, infection free and intact (as opposed to the release of particulate or ionic byproducts) implants. Adverse local tissue reactions (an acute/chronic inflammatory reaction, periprosthetic osteolysis, loosening and subsequent mechanical failure) may evolve when the latter conditions are not met. This article (Part 2 of 2) summarizes the biological response to the non-metallic materials commonly used for joint replacement including polyethylene, ceramics, and polymethylmethacrylate (PMMA), as well as the foreign body reaction to byproducts of these materials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1685-1691, 2017.

Material Science in Cervical Total Disc Replacement

Current cervical total disc replacement (TDR) designs incorporate a variety of different biomaterials including polyethylene, stainless steel, titanium (Ti), and cobalt-chrome (CoCr). These materials are most important in their utilization as bearing surfaces which allow for articular motion at the disc space. Long-term biological effects of implanted materials include wear debris, host inflammatory immune reactions, and osteolysis resulting in implant failure. We review here the most common materials used in cervical TDR prosthetic devices, examine their bearing surfaces, describe the construction of the seven current cervical TDR devices that are approved for use in the United States, and discuss known adverse biological effects associated with long-term implantation of these materials. It is important to appreciate and understand the variety of biomaterials available in the design and construction of these prosthetics and the considerations which guide their implementation.

Immunomodulatory properties of stem cells and bioactive molecules for tissue engineering

The immune system plays a crucial role in the success of tissue engineering strategies. Failure to consider the interactions between implantable scaffolds, usually containing cells and/or bioactive molecules, and the immune system can result in rejection of the implant and devastating clinical consequences. However, recent research into mesenchymal stem cells, which are commonly used in many tissue engineering applications, indicates that they may play a beneficial role modulating the immune system. Likewise, direct delivery of bioactive molecules involved in the inflammatory process can promote the success of tissue engineering constructs. In this article, we will review the various mechanisms in which modulation of the immune system is achieved through delivered bioactive molecules and cells and contextualize this information for future strategies in tissue engineering.

MicroRNA-mediated immune modulation as a therapeutic strategy in host-implant integration

The concept of implanting an artificial device into the human body was once the preserve of science fiction, yet this approach is now often used to replace lost or damaged biological structures in human patients. However, assimilation of medical devices into host tissues is a complex process, and successful implant integration into patients is far from certain. The body's immediate response to a foreign object is immune-mediated reaction, hence there has been extensive research into biomaterials that can reduce or even ablate anti-implant immune responses. There have also been attempts to embed or coat anti-inflammatory drugs and pro-regulatory molecules onto medical devices with the aim of preventing implant rejection by the host. In this review, we summarize the key immune mediators of medical implant reaction, and we evaluate the potential of microRNAs to regulate these processes to promote wound healing, and prolong host-implant integration.

Novel artificial hip joint: A layer of alumina on Ti-6Al-4V alloy formed by micro-arc oxidation

In many hip replacement surgeries, monolithic alumina is used as a femoral head due to its high wear resistance. However, it is liable to fracture under load bearing operations in artificial joints. We propose a promising way to overcome this limitation by forming a dense alumina layer onto a relatively tough substrate such as Ti-6Al-4V alloy to obtain high wear resistance on a material that can sustain relatively high toughness. For this purpose, Al metal powders were deposited onto Ti-6Al-4V alloy by cold spraying in N2 atmosphere. Interfacial adhesion between Al and the Ti alloy was improved by the formation of a reaction layer of Al3Ti between them by heating at 640 °C for 1h in air. Subsequently, micro-arc oxidation treatment was performed to oxidize Al. The oxidized layer was composed of an outer porous layer of γ-alumina and inner-most dense layer of α-alumina. The α-alumina layer was almost fully densified and exhibited high Vickers hardness almost equal to that of alumina ceramics used as the femoral head. Thus, the newly developed dense alumina/Ti alloy can be potentially used to produce the reliable bearing surfaces of artificial hip joint.

Genetic susceptibility of early aseptic loosening after total hip arthroplasty: the influence of TIMP-1 gene polymorphism on Chinese Han population

Objective

Genetic factor plays an important role in early failure of total hip arthroplasty (aseptic loosening) etiology, and TIMP-1 gene may be involved. The present study was conducted to reveal possible association between TIMP-1 polymorphisms with the risk of early failure of total hip arthroplasty (THA) (aseptic loosening).

Methods

The TIMP-1 single nucleotide polymorphisms (SNPs) rs4898, rs6609533, and rs2070584 were genotyped in 59 subjects who were diagnosed as aseptic loosening after total hip arthroplasty and in 100 controls.

Results

The TIMP-1 SNP rs4898 T allele in the case group was found to be 1.32 fold (P = 0.0013, 95% CI = 1.16 to 1.58) than the control group. Similarly, the G allele of rs6609533 was found to be associated with increased risk of aseptic loosening (OR = 1.78, 95% CI = 1.52 to 2.17, P < 0.0001). For SNP rs2070584, no statistical association was found (A vs. G, OR = 1.14, 95% CI = 0.97 to 1.40, P = 0.2028).

Conclusion

The results showed that the TIMP-1 SNPs rs4898 and rs6609533 were associated with the increased risk of early aseptic loosening susceptibility.

Interaction of Materials and Biology in Total Joint Replacement - Successes, Challenges and Future Directions

Total joint replacement (TJR) has revolutionized the treatment of end-stage arthritic disorders. This success is due, in large part, to a clear understanding of the important interaction between the artificial implant and the biology of the host. All surgical procedures in which implants are placed in the body evoke an initial inflammatory reaction, which generally subsides over several weeks. Thereafter, a series of homeostatic events occur leading to progressive integration of the implant within bone and the surrounding musculoskeletal tissues. The eventual outcome of the operation is dependent on the characteristics of the implant, the precision of the surgical technique and operative environment, and the biological milieu of the host. If these factors and events are not optimal, adverse events can occur such as the development of chronic inflammation, progressive bone loss due to increased production of degradation products from the implant (periprosthetic osteolysis), implant loosening or infection. These complications can lead to chronic pain and poor function of the joint reconstruction, and may necessitate revision surgery or removal of the prosthesis entirely. Recent advances in engineering, materials science, and the immunological aspects associated with orthopaedic implants have fostered intense research with the hope that joint replacements will last a lifetime, and facilitate pain-free, normal function.

Genetic susceptibility to total hip arthroplasty failure: a case-control study on the influence of MMP 1 gene polymorphism

Background

Genetic factors plays an important role in early failure of total hip arthroplasty (THA) etiology and MMP-1 gene polymorphism rs5854 may be involved. The present study was conducted to reveal the possible association between MMP-1 rs5854 C/T polymorphism and the risk of early failure of THA (aseptic loosening).

Methods

The rs5854 single nucleotide polymorphism (SNP) in MMP-1 gene was genotyped in 63 subjects who were diagnosed as aseptic loosening after total hip arthroplasty within 10 years and in 81 age and gender matched controls.

Results

The genotype frequencies of the MMP-1 rs5854 C/T polymorphism were 57.1% (CC), 28.6% (CT), and 14.3% (TT) in patients with failure of THA, and 79.0% (CC), 17.3% (CT), and 3.7% (TT) in the controls (P = 0.0099). Rs5854 polymorphism was found to be significantly associated with increased risk of aseptic loosening.

Conclusion

The results showed the rs5854 SNP was associated with increased risk of the early aseptic loosening susceptibility.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_177

Novel biological strategies for treatment of wear particle-induced periprosthetic osteolysis of orthopaedic implants for joint replacement

Wear particles and by-products from joint replacements and other orthopaedic implants may result in a local chronic inflammatory and foreign body reaction. This may lead to persistent synovitis resulting in joint pain and swelling, periprosthetic osteolysis, implant loosening and pathologic fracture. Strategies to modulate the adverse effects of wear debris may improve the function and longevity of joint replacements and other orthopaedic implants, potentially delaying or avoiding complex revision surgical procedures. Three novel biological strategies to mitigate the chronic inflammatory reaction to orthopaedic wear particles are reported. These include (i) interference with systemic macrophage trafficking to the local implant site, (ii) modulation of macrophages from an M1 (pro-inflammatory) to an M2 (anti-inflammatory, pro-tissue healing) phenotype in the periprosthetic tissues, and (iii) local inhibition of the transcription factor nuclear factor kappa B (NF-κB) by delivery of an NF-κB decoy oligodeoxynucleotide, thereby interfering with the production of pro-inflammatory mediators. These three approaches have been shown to be viable strategies for mitigating the undesirable effects of wear particles in preclinical studies. Targeted local delivery of specific biologics may potentially extend the lifetime of orthopaedic implants.

Macrophages-Key cells in the response to wear debris from joint replacements

The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening, and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of proinflammatory and pro-osteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

Septic failure is not a septic loosening: A case report of a failed shoulder prosthesis

Septic failure of a shoulder arthroplasty due to a low-grade infection is generally called septic loosening. However, it is often not investigated if a prosthesis is genuinely loose. We present a case of a failed resurfacing prosthesis in a 70-year-old woman. This prosthesis failed due to a low-grade infection and a revision procedure was mandatory. All intraoperative cultures were positive and revealed a combination of bacteria. Nevertheless, histology revealed a macroscopic and a microscopic stable prosthesis with full osseointegration beneath the prosthesis. The general conception is that an infection leads to interface formation (with neutrophils) and loosening of the prosthesis. We debate this with the presentation of this case of a failed shoulder prosthesis and we think that periprosthetic infection and septic prosthetic loosening are two different entities.

Endotoxins-the invisible companion in biomaterials research

Metal implants and polymeric devices for the application in the clinical treatment of orthopedic tissue injuries are increasingly coated with bioactive biomaterials derived from natural substances to induce desirable biological effects. Many metals and polymers used in biomaterials research show high affinity for endotoxins, which are abundant in the environment. Endotoxin contamination is indicated in the pathology of periodontitis and aseptic implant loosening, but may also affect the evaluation of a biomaterial's bioactivity by inducing strong inflammatory reactions. In this review, we discuss the high affinity of three commonly used implant biomaterials for endotoxins and how the contamination can affect the outcome of the orthopedic fixation. The chemical nature of bacterial endotoxins and some of the clinical health implications are described, as this knowledge is critically important to tackle the issues associated with the measurement and removal of endotoxins from medical devices. Commonly used methods for endotoxin testing and removal from natural substances are examined and the lack of standard guidelines for the in vitro evaluation of biomaterials is discussed.

Endotoxins affect bioactivity of chitosan derivatives in cultures of bone marrow-derived human mesenchymal stem cells

Biomaterials research has been expanding over the last decade, in part to provide improved medical devices for the treatment of orthopedic tissue injuries. In the quest to provide the best performance combined with low cost for medical implants, an increasing number of non-chemists have entered the field of biomaterials research without the profound knowledge of chemistry needed to understand the complex interaction mechanisms and characteristics of natural substances. Likewise, non-biologists often lack understanding when it comes to the presence of the contaminating biota frequently found in natural substances. This lack of knowledge by researchers in the field, combined with sensitive in vitro cell-based assays, can lead to inaccurate evaluation of biomaterials. Hence, there should be both an active effort to assemble multi-disciplinary teams and a genuine concern for the possible effects of contamination on in vitro assays. Here, we show that the presence of bacterial endotoxins in chitosan derivatives can result in false-positive results, profoundly altering product performance in in vitro assays. False-positive results through uncritical use of natural substances in vitro can be avoided by proper endotoxin testing and careful evaluation of cytokine secretion patterns.

Inhibiting wear particles-induced osteolysis with naringin

PURPOSE

The purpose of this study was to determine the effects of naringin on osteoclastogenesis and osteolysis both in vitro and in vivo.

METHODS

In this research osteoclasts were generated from mouse bone marrow monocytes with the receptor activator of NF-КB ligand and the macrophage colony stimulating factor. Naringin, at a concentration of 1, 10, 50, and 100 μg/mL, was respectively added to the medium. Seven days later, the osteoclasts were determined through tartrate-resistant acid phosphatase (TRAP) staining. Mature osteoclasts were isolated from newborn rabbits and cultured for three days on bone slices. Naringin at a concentration of 1, 10, 50, and 100 μg/mL was respectively added to the medium. The resorption bone slices were quantified, and the area was calculated after toluidine blue and Mayer-hematoxylin staining. Polymethyl methacrylate (PMMA) particles were implanted on the calvariae of C57BL/J6 mice. Naringin, at a dose of 50 μg/kg and 100 μg/kg, was respectively given intraperitoneally for seven. Seven days later, the calvariae were removed and processed for pathological analysis.

RESULTS

The result indicated that naringin treatment effectively inhibited in vitro osteoclastogenesis and inhibited mature osteoclasts. In vivo data indicated that naringin strongly inhibited PMMA-induced osteolysis.

CONCLUSION

Naringin can effectively inhibit osteoclastogenesis and suppress wear particles-induced osteolysis and might be useful in the treatment or prevention of wear particles-induced osteolysis and aseptic loosening for its effect on osteoclast generation and function.

RANKL in the osteolysis of AES total ankle replacement implants

Peri-implant tissue reactions in failed total ankle replacement (TAR) are characterized by early developing peri-implant osteolysis. The hypothesis of the study was that this reaction is mediated by receptor activator of nuclear factor kappa B ligand (RANKL). Samples of peri-prosthetic tissues from failed TAR implants were stained for macrophages, RANKL, its receptor RANK and osteoprotegerin (OPG), and compared to control samples. The failed TAR implants were surrounded by implant capsule, synovial lining-like interface membrane or necrotic tissues. Infiltrating scavenger receptor I positive CD163(+) macrophages were frequent, in particular around necrotic soft tissues or bone sequestrate, and possibly in part formed due to ischemia and mechanical factors. In contrast, implant-derived wear debris was scanty. Still many RANK(+) macrophages were often seen in close contact with RANKL(+) mesenchymal cells, whereas OPG was mostly located at a distance in vascular endothelial cells. Foreign body giant cells were frequent. RANKL seems to stimulate locally accumulated CD163(+) RANK-expressing cells to fusion, which leads to the local formation of multinuclear foreign body giant cells (and probably of osteoclasts). Therefore, peri-implant osteolysis in early TAR implant failure seems to be caused by the RANKL-driven chronic foreign body inflammation directed against, not implant-derived particles, but against necrotic autologous tissues.

Bearing surfaces for total disc arthroplasty: metal-on-metal versus metal-on-polyethylene and other biomaterials

BACKGROUND CONTEXT

Concerns about the effect of metallic wear debris from metal-on-metal bearing surfaces in total hip arthroplasty have increased. Some spinal arthroplasty devices include metal-on-metal bearing surfaces.

PURPOSE

To review the literature for clinical reports of complications because of wear debris from metal-on-metal spinal arthroplasty devices. To review the biology of wear debris from metal-on-metal bearing surfaces drawn from the hip arthroplasty literature and place it in the context of global regulatory actions and clinical and laboratory studies.

STUDY DESIGN

Literature review.

METHODS

To identify clinical reports, the PubMed database from the United States National Library of Medicine was queried using Medical Subject Headings terms and additional keyword terms. In addition, experts from academia and regulatory agencies were questioned regarding their knowledge of reports, including experts who attended the US Food and Drug Administration roundtable in September 2010.

RESULTS

Three case reports and one case series including seven total cases were identified in which abnormal inflammatory reactions and soft-tissue masses after metal-on-metal disc replacements were consistent with pseudotumor and metal hypersensitivity. Spinal cases are present as pain and neurologic symptoms. On plain radiography, there is no clear periprosthetic osteolysis or loosening. On magnetic resonance imaging, there is increased magnetic susceptibility artifact because of metallic debris that renders images inadequate. Computed tomography myelography demonstrates a soft-tissue mass, which exhibits epidural extension surgically. Histologically, large areas of necrotic debris and exudates are interspersed with chronic inflammatory cells. Lymphocyte or macrophage predominance is determined by the rate of wear and the presence of gross, microscopic, or submicron metallic wear debris. The metallurgy of the involved devices is cobalt-chromium-molybdenum (CoCrMo) alloy, and the bearing surface is CoCrMo-on-CoCrMo.

CONCLUSIONS

Metal-on-metal spinal arthroplasty devices are subject to postoperative complications because of metallic wear debris with similar clinical, radiographic, histologic, gross anatomic, and device-related features to those found in metal-on-metal bearing surfaces in total hip arthroplasty.

Biomaterials-based electronics: polymers and interfaces for biology and medicine

Advanced polymeric biomaterials continue to serve as a cornerstone for new medical technologies and therapies. The vast majority of these materials, both natural and synthetic, interact with biological matter in the absence of direct electronic communication. However, biological systems have evolved to synthesize and utilize naturally-derived materials for the generation and modulation of electrical potentials, voltage gradients, and ion flows. Bioelectric phenomena can be translated into potent signaling cues for intra- and inter-cellular communication. These cues can serve as a gateway to link synthetic devices with biological systems. This progress report will provide an update on advances in the application of electronically active biomaterials for use in organic electronics and bio-interfaces. Specific focus will be granted to covering technologies where natural and synthetic biological materials serve as integral components such as thin film electronics, in vitro cell culture models, and implantable medical devices. Future perspectives and emerging challenges will also be highlighted.

Low-intensity pulsed ultrasound (LIPUS) may prevent polyethylene induced periprosthetic osteolysis in vivo

We investigated the effect of local low-intensity pulsed ultrasound (LIPUS) on polyethylene debris induced periprosthetic osteolysis. The periprosthetic osteolysis model was made by injecting endotoxin-free pure polyethylene particles into the distal part of the femur canal and inserting a stainless steel plug into this femur. The effects of polyethylene and LIPUS were assessed histologically and by the shear strength test and periprosthetic bone mineral density (BMD) test. Sixteen rabbits received a stainless steel plug on one side and both polyethylene and a stainless steel plug on the other side. Three months later, the side that received polyethylene showed periprosthetic osteolysis. Subsequently, another 16 rabbits received polyethylene plus local LIPUS (200 mW/cm(2) for 20 min daily) on one side and polyethylene alone on the other side. Three months later, LIPUS effectively prevented the periprosthetic osteolysis caused by polyethylene in this rabbit model.

Functional variants of the P2RX7 gene, aseptic osteolysis, and revision of the total hip arthroplasty: a preliminary study

Periprosthetic osteolysis (OL) is a major long-term complication of the total hip arthroplasty (THA), which can result in aseptic loosening and revision surgery. Purinergic receptor P2X, ligand-gated ion channel 7 (P2RX7) is an important regulator of inflammation and bone turnover. We were therefore interested in whether functional variants of the P2RX7 gene may be associated with OL and risk of THA failure. A total of 205 unrelated Czech patients with cementless-type THA were stratified according to the severity of acetabular OL and revision of THA. Four "loss-of-function" P2RX7 single nucleotide polymorphisms (SNPs), namely Glu496Ala, Ile568Asn, Arg307Gln, and null allele (rs35933842), were genotyped by polymerase chain reaction with sequence-specific primers (PCR-SSP). No significant association of P2RX7 variants with severity of OL was observed. The carriers of rare variants P2RX7 568Asn, 307Gln and null allele, all causing complete loss of P2RX7 function, tended to be overrepresented among patients with THA revision (9.6%) by comparison with those with unrevised functional prosthesis (2.1%, p = 0.09). Furthermore, the carriage of the P2RX7 307Gln allele was associated with greater cumulative hazard of THA revision (p = 0.02). In this preliminary study, we could nominate but not clearly demonstrate rare P2RX7 loss-of-function variants being associated with THA failure. Investigation in large THA cohorts is therefore warranted.

Cement removal and bone bed preparation of the femoral medullary canal assisted by flexible endoscope in total hip revision arthroplasty

PURPOSE

The flexible endoscope was applied to cemented femoral medullary canal to obtain better visual field and assist surgical procedures in total hip revision arthroplasty.

METHODS

Fifteen cases of failed cemented total hip joints were analyzed. Efficacy of cement removal was assessed, combined with degree of implant loosening and bone defect, postoperative radiographic findings, and perioperative status of the patients and complications. Status of the bone bed between bone and cement and that of bone grafting were also evaluated.

RESULTS

The cement mantle was efficiently extractable in all cases under good exposure and with maintenance of efficient working space. Endoscopic time for cement removal was dependent on the status of the cement-bone interface and bone defect. Rigid and less loosened interfaces, as well as cases of minimal bone defect, required a longer time. However, it was effective to confirm the status of the bone bed during the procedure. Occult foreign-body reaction was detectable in three cases of unloosened interface under endoscopic inspection. Impaction bone grafting was performed in eight cases. The scope was also helpful to confirm the status of a grafted bone bed. Three fractures occurred, of which two cases revealed minor cement leakage and one required additional osteosynthesis with extensive approach. JOA Hip Score was improved, and the implants were stable at latest follow-up. Dislocation was found in two cases. Neither thromboembolic events nor infection was found.

CONCLUSIONS

Cement removal in the femoral medullar canal was effectively performed not only in the cases of loose interface but also those of rigid and less-loosened interface under flexible endoscopic inspection. The scope could support cement removal in femoral revisions under good exposure and maintenance of working space, as well as confirmation of bone bed state. Although one case required an additional approach, application of the flexible endoscope has potential merit to contribute to less invasive total hip revision arthroplasty, possibly combined with other refined devices of cement extraction.