Macrophage/particle interactions: effect of size, composition and surface area

BSA Adsorption on Titanium Dioxide Nanoparticle Surfaces for Controlling Their Cellular Uptake in Skin Cells

Nanoparticles (NPs) are continuously being developed for many applications including imaging, biomedicine, and everyday products. It is difficult to avoid contact with NPs such as titanium dioxide (TiO2) NPs, which are widely used in sunscreens. However, the safety of TiO2 NPs for skin contact and inhalation remains controversial. If NPs cannot penetrate the skin, they will be unable to circulate in the bloodstream, accumulate in the body, or cause side effects, ensuring their safety. Therefore, this study aimed to modify TiO2 NP surfaces to inhibit their uptake in skin cells. Inspired by protein corona studies, bovine serum albumin (BSA) was chosen to functionalize TiO2 NP surfaces via physical adsorption. The maximum BSA adsorption occurred at pH 5.0. The physicochemical properties (size, ζ-potential, morphology, ultraviolet (UV) absorption efficiency, and sun protection factor (SPF)) of TiO2-BSA NPs were comparable to those of TiO2 NPs, indicating that these properties did not affect cellular uptake. In the safety evaluation, TiO2 NPs and TiO2-BSA NPs exhibited high biocompatibility with skin cells and no phototoxicity after UVA and UVB irradiation. In the efficacy evaluation, both NPs possessed the same photoprotection abilities, reducing membrane damage and DNA breakage after UVA irradiation. Compared with TiO2 NPs, TiO2-BSA NPs showed substantially reduced skin penetration in Franz diffusion cells (91%) and human immortalized keratinocyte (HaCaT) cells (89%). A qualitative cellular uptake study using transmission electron microscopy and confocal laser scanning microscopy confirmed that TiO2 NPs were more abundant than TiO2-BSA NPs inside the HaCaT cells. These findings indicate that TiO2 surface functionalization with BSA inhibits cellular uptake in skin cells while maintaining safety and UV protection efficacy, which might be extended to other NP-based sunscreens.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Signaling-biophysical modeling unravels mechanistic control of red blood cell phagocytosis by macrophages in sickle cell disease

Red blood cell (RBC) aging manifests through progressive changes in cell morphology, rigidity, and expression of membrane proteins. To maintain the quality of circulating blood, splenic macrophages detect the biochemical signals and biophysical changes of RBCs and selectively clear them through erythrophagocytosis. In sickle cell disease (SCD), RBCs display alterations affecting their interaction with macrophages, leading to aberrant phagocytosis that may cause life-threatening spleen sequestration crises. To illuminate the mechanistic control of RBC engulfment by macrophages in SCD, we integrate a system biology model of RBC-macrophage signaling interactions with a biophysical model of macrophage engulfment, as well as in vitro phagocytosis experiments using the spleen-on-a-chip technology. Our modeling framework accurately predicts the phagocytosis dynamics of RBCs under different disease conditions, reveals patterns distinguishing normal and sickle RBCs, and identifies molecular targets including Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP1) and cluster of differentiation 47 (CD47)/signal regulatory protein α (SIRPα) as therapeutic targets to facilitate the controlled clearance of sickle RBCs in the spleen.

An overview of the tribological and mechanical properties of PEEK and CFR-PEEK for use in total joint replacements

Poly-ether-ether-ketone (PEEK) and PEEK composites are outstanding candidates for biomedical applications, such as orthopedic devices, where biocompatibility and modulus match with surrounding tissue are requisite for long-term success. The mechanical properties can be optimized by incorporating fillers such as continuous and chopped carbon fibers. While much is known about the mechanical and tribological behavior of PEEK composites, there are few articles that summarize the viability of using PEEK reinforced with carbon fibers in orthopedic implants. This paper reviews biocompatibility, tribological, and mechanical studies on PEEK and their composites with carbon fibers, notably PEEK reinforced with polyacrylonitrile (PAN)-based carbon fibers and PEEK reinforced with pitch-based carbon fibers, for application in orthopedics and total joint replacements (TJRs). The main objectives of this review are two-fold. Firstly, this paper aims to assist designers in making informed decisions on the suitability of using PEEK and PEEK composites in orthopedic applications; as it is not well understood how these materials perform on the whole in orthopedics and TJRs. Secondly, this paper aims to serve as a centralized paper in which researchers can gain information on the tribological and mechanical advancements of PEEK and PEEK composites.

Vitamin E-added Highly Cross-Linked Polyethylene Decreases the Risk of Osteolysis in an In Vivo Arthroplasty Model

Introduction Aseptic loosening is one of the most important complications of arthroplasty surgery. It is known that immune response against particles plays role in the pathogenesis of aseptic loosening. Polyethylene (PE) has an important place in these particles. There are limited in vivo studies examining aseptic loosening caused by PE residues. Objective The aim of the present study is to evaluate the aseptic loosening created by highly cross-linked PE (HXLPE) and vitamin E-added PE particles in an in vivo knee prosthesis model. Materials and methods Thirty-nine male Sprague-Dawley rats, which were randomized into three groups, were included in the study. After surgical exposure of knee joints of rats, femoral intramedullary canals were drilled and instilled with isolated saline solution and saline solution that contained standard PE or vitamin E-added PE particles according to their groups. Afterwards, a titanium implant was placed on the femoral articular surface of each animal. Rats received intraarticular injections weekly of the same solution, which was initially instilled into their femoral canal. The rats were sacrificed at the end of the third week and then underwent radiological and histopathological evaluations. Result In histopathological evaluation, periprosthetic membrane formation, inflammatory cell change, and cellular damage of cartilage and bone tissue around the implant were assessed. There was a statistically lesser amount of cellular damage and periprosthetic membrane formation in the vitamin-E/HXLPE group compared to the HXLPE group (p=0.04, p=0.001). No significant difference was found between the PE groups with respect to inflammatory cells (p=0.715). Conclusions HXLPE caused more significant osteolysis compared to VE-HXLPE. Antioxidants in PE could provide a reduction in osteolysis and aseptic loosening.

Antioxidant Defense in Primary Murine Lung Cells following Short- and Long-Term Exposure to Plastic Particles

Polystyrene nano- and micro-sized plastic particles (NMP) are one of the common plastic materials produced that dramatically pollute the environment, water, and oceanic habitats worldwide. NMP are continuously absorbed by the body through a number of routes, especially via intestinal ingestion, dermal uptake, and inhalation into the lung. Several studies provided evidence of NMP provoking oxidative stress and affecting cellular responses. Yet, the NMP effects on primary lung cells have not been studied. To this end, we isolated and cultured murine lung cells and exposed them short-term or long-term to polystyrene 0.2-6.0 µm-sized NMP. We studied cellular consequences regarding oxidative stress, morphology, and secretion profiling. Visualization, distribution, and expression analyses confirmed lung cells accumulating NMP and showed several significant correlations with particle size. Moreover, we found substantial evidence of biological consequences of small-scale NMP uptake in lung cells. Besides alterations of cytokine secretion profiles resulting in inflammatory responses, indicators of oxidative stress were identified that were accompanied by Nrf2 and β-catenin signaling changes. Our results serve as an important basis to point out the potential hazards of plastic contaminations and uptake in lung cells.

Short- and long-term polystyrene nano- and microplastic exposure promotes oxidative stress and divergently affects skin cell architecture and Wnt/beta-catenin signaling

Nano- and microplastic particles (NMP) are strong environmental contaminants affecting marine ecosystems and human health. The negligible use of biodegradable plastics and the lack of knowledge about plastic uptake, accumulation, and functional consequences led us to investigate the short- and long-term effects in freshly isolated skin cells from mice. Using fluorescent NMP of several sizes (200 nm to 6 µm), efficient cellular uptake was observed, causing, however, only minor acute toxicity as metabolic activity and apoptosis data suggested, albeit changes in intracellular reactive species and thiol levels were observed. The internalized NMP induced an altered expression of various targets of the nuclear factor-2-related transcription factor 2 pathway and were accompanied by changed antioxidant and oxidative stress signaling responses, as suggested by altered heme oxygenase 1 and glutathione peroxide 2 levels. A highly increased beta-catenin expression under acute but not chronic NMP exposure was concomitant with a strong translocation from membrane to the nucleus and subsequent transcription activation of Wnt signaling target genes after both single-dose and chronic long-term NMP exposure. Moreover, fibroblast-to-myofibroblast transdifferentiation accompanied by an increase of α smooth muscle actin and collagen expression was observed. Together with several NMP-induced changes in junctional and adherence protein expression, our study for the first time elucidates the acute and chronic effects of NMP of different sizes in primary skin cells' signaling and functional biology, contributing to a better understanding of nano- and microplastic to health risks in higher vertebrates.

The Role of the Innate Immune System in Wear Debris-Induced Inflammatory Peri-Implant Osteolysis in Total Joint Arthroplasty

Periprosthetic osteolysis remains a leading complication of total hip and knee arthroplasty, often resulting in aseptic loosening of the implant and necessitating revision surgery. Wear-induced particulate debris is the main cause initiating this destructive process. The purpose of this article is to review recent advances in understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. A strong activator of the peri-implant innate immune this debris-induced inflammatory cascade is dictated by macrophage secretion of TNF-α, IL-1, IL-6, and IL-8, and PGE2, leading to peri-implant bone resorption through activation of osteoclasts and inhibition of osteoblasts through several mechanisms, including the RANK/RANKL/OPG pathway. Therapeutic agents against proinflammatory mediators, such as those targeting tumor necrosis factor (TNF), osteoclasts, and sclerostin, have shown promise in reducing peri-implant osteolysis in vitro and in vivo; however, radiographic changes and clinical diagnosis often lag considerably behind the initiation of osteolysis, making timely treatment difficult. Considerable efforts are underway to develop such diagnostic tools, therapies, and identify novel targets for therapeutic intervention.

Designing a Biomaterial Approach to Control the Adaptive Response to a Skin Injury

The goal of this review is to explain how to design a biomaterial approach to control the adaptive response to injury, with an emphasis on skin wounds. The strategies will be selected based on whether they have a reasonable probability of meeting the desired clinical outcome vs. just comparing the pros and cons of different strategies. To do this, the review will look at the normal adaptive response in adults and why it does not meet the desired clinical outcome in most cases. In addition, the adaptive response will be looked at in cases where it does meet the clinical performance requirements including animals that regenerate and for fetal wound healing. This will lead to how biomaterials can be used to alter the overall adaptive response to allow it to meet the desired clinical outcome. The important message of the review is that you need to use the engineering design process, not the scientific method, to design a clinical treatment. Also, the clinical performance requirements are functional, not structural. The last section will give some specific examples of controlling the adaptive response for two skin injuries: burns and pressure ulcers. For burns, it will cover some preclinical studies used to justify a clinical study as well as discuss the results of a clinical study using this system. For pressure ulcers, it will cover some preclinical studies for two different approaches: electrical stimulation and degradable/regenerative scaffolds. For electrical stimulation, the results of a clinical study will be presented.

Pristine and artificially-aged polystyrene microplastic particles differ in regard to cellular response

Microplastic particles (MP), arising from the gradual decomposition of plastics in the environment, have been identified as a global problem. Most investigations of MP cytotoxicity use pristine spherical particles available from commercial sources when evaluating their impact on mammalian cells, while only limited data is available for the more relevant "weathered microplastic". In this study, we exposed murine macrophages to polystyrene MP either after up to 130 days of accelerated ageing or in pristine condition. Weathered and pristine MP were physicochemically characterized, and their cytotoxicity was investigated using biological assays, transcriptome analysis, and metabolic pathways prediction. Whereas the response to pristine MP is mainly dominated by a TNF-α release, sharp-edged weathered MP induce broader adverse cellular reactions. This study stresses the importance of including more realistic test particles (e.g., weathered particles) in combination with a broad range of biological assays when evaluating the potential risk of microplastic exposure.

Nanoporous membrane fabrication by nanoimprint lithography for nanoparticle sieving

An isoporous membrane with strictly controlled pore size, shape and distribution could provide an efficient, precise and mild sieving of particles in nanotechnology and biomedical applications. However there is a lack of highly porous polymeric membranes combining isoporosity and high permeance in the range below 500 nm. Track-etched membranes are practically the only commercial option. Membranes prepared by phase inversion typically have a broad pore size distribution. Most nanofabrication methods have limited the preparation of membranes with pores in the micrometer range. In this work, we present a nanotechnology-based fabrication methodology to manufacture a stable and flexible nanoporous polymeric membrane with 300 nm isopores using UV nanoimprint lithography. The highly porous membrane has a pore density of 4 × 10⁹ pores per cm² and stable permeance of 108 000 L m^-2 h^-1 bar^-1. Uniform ZIF-8 nanoparticles were synthesized and the isoporous membrane successfully demonstrated as high as 100% rejection and size-based sieving performance of nanoparticles.

A novel hip joint prosthesis with uni-directional articulations for reduced wear

A novel polymer-on-metal hip joint prosthesis design that makes use of uni-directional articulations was developed and tested in this work. The new implant was tested using two polymer variants, virgin ultra-high molecular weight polyethylene (UHMWPE), and Vitamin E-infused highly crosslinked polyethylene (VEHXPE). The degrees of freedom of the ball-and-socket are reproduced by three cylindrical orthogonally-aligned articulations. This unconventional design leverages on the molecular orientation hardening mechanisms of the polyethylene and increased contact area to minimize wear. An experimental hip joint simulator was used to compare the gravimetric wear of the conventional ball-on-socket and the new implant. The new prosthesis including UHMWPE components produced a 78% reduction in wear, whereas the new prosthesis with VEHXPE components produced a 100% reduction in wear, as no measurable wear was detected. Machining marks on the acetabular cups of the new prosthesis were retained for both polyethylene variants, further demonstrating the low levels of wear exhibited by the new implants. Both polyethylene materials produced particles in the range of 0.1-1.0 μm, which are the most biologically active. Nonetheless, the extremely low wear rates are likely to induce minimal osteolysis effects. Furthermore, the novel design also offers an increase of more than 24% in the range of motion in flexion/extension when compared to a dual-mobility hip implant. A prototype of the prosthesis was implanted into a Thiel-embalmed human cadaver during a mock-surgery, which demonstrated high resistance to dislocation and the possibility of performing a figure of four position.

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage-biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and immunohistochemical methods (CD68⁺). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasorb^© material. The increased macrophage number, registered around the Ag/PVA/Gr implant on 60th p.o.d. indicates that the addition of graphene can, in a specific way, modulate different biological responses of tissues in the process of wound healing, regeneration, and integration.

The Effect of Size of Materials Formed or Implanted In Vivo on the Macrophage Response and the Resultant Influence on Clinical Outcome

Both the chemistry and size of a material formed in vivo, or an implanted biomaterial, can alter the in vivo host response. Within the size range covered within this review, over 1 μm, chemistry is only important if the solid material is unstable and leeching small molecules. The macrophage activity and the resultant inflammatory response, however, are related to the size of the solid material. The premise of this review is that differences in size of the solid material, in different cases, can be the reason why there is some individual-to-individual variation in response. Specifically, the inflammatory response is enhanced when the size is between 1-50 μm. This will be looked at for three configurations: spherical particulate (silicone oil or gel from breast implants), elongated particulate (monosodium urate [MSU] crystals in gout or in kidney stones), and fibers (e.g., polyester used in fabric implants). These specific examples were selected because many still believe that the clinical outcome for each is controlled by the surface chemistry, when in fact it is the size. In each case, specific studies will be highlighted to either show a mechanism for creating different sizes and therefore a differential biological response (first three) or how changing the size and shape (diameter and spacing of fibers, in this example) can affect the response and can help explain the different responses to fabric implants found in vivo within the 1-50 μm size range. It was found that polyester fibers under 70 μm had a significant increase in macrophage response. Further, it was found that compounds found in synovial fluid could limit MSU crystal size. In addition, it was shown that plasma with low triglyceride levels emulsifies silicone oils to a greater extent than plasma with higher triglyceride levels. Therefore, in three cases it appears that differences in the inflammatory response between individuals and between different implants could be explained just by the size of the material formed or implanted.

Replacement Process of Carbonate Apatite by Alveolar Bone in a Rat Extraction Socket

The objective of this study was to investigate a bone graft substitute containing carbonate apatite (CO₃Ap) to analyze bone replacement and the state of bone formation in vitro and in vivo compared with autogenous bone (AB) or control. An osteoclast precursor cell line was cultured with AB or CO₃Ap, and morphological analysis using scanning electron microscopy and a tartrate-resistant acid phosphatase activity assay were performed. The right maxillary first and second molars of Wistar rats were extracted and compensated by AB or CO₃Ap granules. Following implantation, the bone formation state was evaluated after 3, 5, 7, 14, and 28 days of surgery by micro-computed tomography and immunohistostaining. The osteoclast-like cell morphology was typical with many cell protrusions in the AB and CO₃Ap groups. Additionally, the number of osteoclast-like cells formed in the culture increased in each group; however, there was no significant difference between the AB and CO₃Ap groups. Five days after tooth extraction, osteoclasts were observed near CO₃Ap. The bone thickness in the CO₃Ap group was significantly increased than that in the control group and the bone formation in the CO₃Ap group increased by the same level as that in the AB group. CO₃Ap is gradually absorbed by osteoclasts in the extraction socket and is easily replaced by alveolar bone. The process of bone replacement by osteoclasts is similar to that of autologous bone. By observing the process of bone replacement in more detail, it may be possible to gain a better understanding of the bone formation and control the amount of bone after surgery.

Cytotoxic effects of submicron- and nano-scale titanium debris released from dental implants: an integrative review

OBJECTIVE

This integrative review aimed to report the toxic effect of submicron and nano-scale commercially pure titanium (cp Ti) debris on cells of peri-implant tissues.

MATERIALS AND METHODS

A systematic search was carried out on the PubMed electronic platform using the following key terms: Ti "OR" titanium "AND" dental implants "AND" nanoparticles "OR" nano-scale debris "OR" nanometric debris "AND" osteoblasts "OR "cytotoxicity" OR "macrophage" OR "mutagenic" OR "peri-implantitis". The inclusion criteria involved articles published in the English language, until December 26, 2020, reporting the effect of nano-scale titanium particles as released from dental implants on the toxicity and damage of osteoblasts.

RESULTS

Of 258 articles identified, 14 articles were selected for this integrative review. Submicron and nano-scale cp Ti particles altered the behavior of cells in culture medium. An inflammatory response was triggered by macrophages, fibroblasts, osteoblasts, mesenchymal cells, and odontoblasts as indicated by the detection of several inflammatory mediators such as IL-6, IL-1β, TNF-α, and PGE2. The formation of a bioactive complex composed of calcium and phosphorus on titanium nanoparticles allowed their binding to proteins leading to the cell internalization phenomenon. The nanoparticles induced mutagenic and carcinogenic effects into the cells.

CONCLUSIONS

The cytotoxic effect of debris released from dental implants depends on the size, concentration, and chemical composition of the particles. A high concentration of particles on nanometric scale intensifies the inflammatory responses with mutagenic potential of the surrounding cells.

CLINICAL RELEVANCE

Titanium ions and debris have been detected in peri-implant tissues with different size, concentration, and forms. The presence of metallic debris at peri-implant tissues also stimulates the migration of immune cells and inflammatory reactions. Cp Ti and TiO₂ micro- and nano-scale particles can reach the bloodstream, accumulating in lungs, liver, spleen, and bone marrow.

The Body's Cellular and Molecular Response to Protein-Coated Medical Device Implants: A Review Focused on Fibronectin and BMP Proteins

Recent years have seen a marked rise in implantation into the body of a great variety of devices: hip, knee, and shoulder replacements, pacemakers, meshes, glucose sensors, and many others. Cochlear and retinal implants are being developed to restore hearing and sight. After surgery to implant a device, adjacent cells interact with the implant and release molecular signals that result in attraction, infiltration of the tissue, and attachment to the implant of various cell types including monocytes, macrophages, and platelets. These cells release additional signaling molecules (chemokines and cytokines) that recruit tissue repair cells to the device site. Some implants fail and require additional revision surgery that is traumatic for the patient and expensive for the payer. This review examines the literature for evidence to support the possibility that fibronectins and BMPs could be coated on the implants as part of the manufacturing process so that the proteins could be released into the tissue surrounding the implant and improve the rate of successful implantation.

Trigger-responsive engineered-nanocarriers and image-guided theranostics for rheumatoid arthritis

Rheumatoid Arthritis (RA), one of the leading causes of disability due to progressive autoimmune destruction of synovial joints, affects ∼1% of the global population. Standard therapy helps in reducing inflammation and delaying the progression of RA but is limited by non-responsiveness on long-term use and several side-effects. The conventional nanocarriers (CNCs), to some extent, minimize toxicity associated with free drug administration while improving the therapeutic efficacy. However, the uncontrolled release of the encapsulated drug even at off-targeted organs limits the application of CNCs. To overcome these challenges, trigger-responsive engineered nanocarriers (ENCs) have been recently explored for RA treatment. Unlike CNCs, ENCs enable precise control over on-demand drug release due to endogenous triggers in arthritic paws like pH, enzyme level, oxidative stress, or exogenously applied triggers like near-infrared light, magnetic field, ultrasonic waves, etc. As the trigger is selectively applied to the inflamed joint, it potentially reduces toxicity at off-target locations. Moreover, ENCs have been strategically coupled with imaging probe(s) for simultaneous monitoring of ENCs inside the body and facilitate an 'image-guided-co-trigger' for site-specific action in arthritic paws. In this review, the progress made in recently emerging 'trigger-responsive' and 'image-guided theranostics' ENCs for RA treatment has been explored with emphasis on the design strategies, mechanism, current status, challenges, and translational perspectives.

Potential toxicity of polystyrene microplastic particles

Environmental pollution arising from plastic waste is a major global concern. Plastic macroparticles, microparticles, and nanoparticles have the potential to affect marine ecosystems and human health. It is generally accepted that microplastic particles are not harmful or at best minimal to human health. However direct contact with microplastic particles may have possible adverse effect in cellular level. Primary polystyrene (PS) particles were the focus of this study, and we investigated the potential impacts of these microplastics on human health at the cellular level. We determined that PS particles were potential immune stimulants that induced cytokine and chemokine production in a size-dependent and concentration-dependent manner.

Probing the Influence of γ-Sterilization on the Oxidation, Crystallization, Sliding Wear Resistance, and Cytocompatibility of Chemically Modified Graphene-Oxide-Reinforced HDPE/UHMWPE Nanocomposites and Wear Debris

Osteolysis and aseptic loosening due to wear at the articulating interfaces of prosthetic joints are considered to be the key concerns for implant failure in load-bearing orthopedic applications. In an effort to reduce the wear and processing difficulties of ultrahigh-molecular-weight polyethylene (UHMWPE), our research group recently developed high-density polyethylene (HDPE)/UHMWPE nanocomposites with chemically modified graphene oxide (mGO). Considering the importance of sterilization, this work explores the influence of γ-ray dosage of 25 kGy on the clinically relevant performance-limiting properties of these newly developed hybrid nanocomposites in vitro. Importantly, this work also probes into the cytotoxic effects of the wear debris of different compositions and sizes on MC3T3 murine osteoblasts and human mesenchymal stem cells (hMSCs). In particular, γ-ray-sterilized 1 wt % mGO-reinforced HDPE/UHMWPE nanocomposites exhibit an improvement in the oxidation index (16%), free energy of immersion (-12.1 mN/m), surface polarity (5.0%), and hardness (42%). Consequently, such enhancements result in better tribological properties, especially coefficient of friction (+13%) and wear resistance, when compared with UHMWPE. A spectrum of analyses using transmission electron microscopy (TEM) and in vitro cytocompatibility assessment demonstrate that phagocytosable (0.5-4.5 μm) sterilized 1 mGO wear particles, when present in culture media at 5 mg/mL concentration, induce neither significant reduction in MC3T3 murine osteoblast and hMSC growth nor cell morphology phenotype, during 24, 48, and 72 h of incubation. Taken together, this study suggests that γ-ray-sterilized HDPE/UHMWPE/mGO nanocomposites can be utilized as promising articulating surfaces for total joint replacements.

An assessment of the toxicity of polypropylene microplastics in human derived cells

Environmental pollution caused by plastic waste is a growing global problem. Discarded plastic products and debris (microplastic particles) in the oceans detrimentally affect marine ecosystems and may impact human. Humans are exposed to plastic debris via the consumption of seafood and drinking water, contact with food packaging, or inhalation of particles. The accumulation of microplastic particles in humans has potential health risks such as cytotoxicity, hypersensitivity, unwanted immune response, and acute response like hemolysis. We investigated the cellular responses of secondary polypropylene microplastics (PP particles) of approximately ~20 μm and 25-200 μm in different condition and size to normal cells, immune cells, blood cells, and murine immune cells by cytokine analysis, ROS assay, polarization assay and proliferation assay. We found that PP particles showed low cytotoxicity effect in size and concentration manner, however, a high concentration, small sized, DMSO method of PP particles stimulated the immune system and enhanced potential hypersensitivity to PP particles via an increase in the levels of cytokines and histamines in PBMCs, Raw 264.7 and HMC-1 cells.

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.

Conjugation of chitosan oligosaccharides enhances immune response to porcine circovirus vaccine by activating macrophages

Porcine circovirus type 2 (PCV2)-associated diseases have led to great economic losses to the pig industry. Our lab previously found that conjugation of chitosan oligosaccharides (COS) or via a carrier protein enhanced the immunogenicity of PCV2 vaccine against infectious pathogens. However, precise mechanisms and signal transduction pathways underlying the efficacy of COS conjugation remains poorly defined. In this study, to better understand the effects and mechanism of COS conjugates maintain the adjuvant potential in vivo, we investigated its augmentation of macrophage function, including cell activation, NO production, cytokine production and phagocytosis. Additionally, the role of Toll-like receptors (TLR) proteins in this process was also assessed. The results indicate that, as compared to the PCV and PCV/COS, conjugation of COS effectively enhanced the NO production, cytokines generation and phagocytosis activity of macrophages. Noticeably, the generation of NO and proinflammatory cytokines was closely related to the TLR2/4 signaling pathways, strongly suggesting that conjugation of COS regulates innate and adaptive immunity by activation of macrophages, resulting in immune enhancement. In summary, the present study provides a potential mechanism of COS conjugation as a novel adjuvant to improve immune responses against various diseases.

Systematic Overview of Solid Particles and Their Host Responses

Crystalline/particulate substances trigger a plethora of signaling events in host cells. The most prominent consequence is the inflammatory reactions that underlie crystal arthropathies, such as gout and pseudogout. However, their impact on our health was underestimated. Recent work on the role of cholesterol crystal in the development of atherosclerosis and the harm of environmental particulates has set up new frontiers in our defense against their detrimental effects. On the other hand, in the last 100 years, crystalline/particulate substances have been used with increasing frequencies in our daily lives as a part of new industrial manufacturing and engineering. Importantly, they have become a tool in modern medicine, used as vaccine adjuvants and drug delivery vehicles. Their biological effects are also being dissected in great detail, particularly with regard to their inflammatory signaling pathways. Solid structure interaction with host cells is far from being uniform, with outcomes dependent on cell types and chemical/physical properties of the particles involved. In this review, we offer a systematic and broad outlook of this landscape and a sage analysis of the complex nature of this topic.

Determination of "safe" and "critical" nanoparticles exposure to welders in a workshop

The present study examined consequences of "safe" versus "critical" exposure to nanoparticles (NP) released during welding operations. With this aim in mind, a set of measurements regarding NP emissions was undertaken in a workshop during welding by metal active gas of carbon steel using different mixtures of argon (Ar) and carbon dioxide (CO₂) as well as different process parameters which might influence emission of (NP). If these measurements were conducted in several locations away from the welding sources, the graphical representation of the obtained observations with time enabled definition of "safe" and "critical" regions within a welding workshop in terms of welder's exposure. This information may be combined with the results of risk analysis derived by control banding and helps to categorize the sites where regulatory measures such as operation containment or dedicated exhaust ventilation need to be implemented.

Microglia Endocytose Amyloid β Through the Binding of Transglutaminase 2 and Milk Fat Globule EGF Factor 8 Protein

Activation of glial cells has been observed in neurodegenerative diseases including Alzheimer's disease (AD). Aggregation of amyloid β (Aβ) is profusely observed as characteristic pathology in AD brain. In our previous study using microglial cell line BV-2, tissue-type transglutaminase (TG2) was found to be involved in phagocytosis (Kawabe et al., in Neuroimmunomodulation 22(4):243-249, 2015; Kawabe et al., Neurochem Res 2017). In the present study, we examined whether TG2 and milk fat globule EGF factor 8 protein (MFG-E8), an adaptor protein promotes macrophage to engulf apoptotic cells, were involved in Aβ endocytosis. When the neuronal/glial mixed culture was stimulated freshly prepared Aβ_1-42 for 3 days, the incorporation of Aβ was observed by immunofluorescence staining technique in Iba-1-positive microglia. Cystamine, a broad competitive inhibitor of TGs, suppressed it. When aggregated Aβ was added to the mixed culture, the immunoreactivity of MFG-E8 surrounding Aβ was observed, and then followed by microglial endocytosis. Using western blotting technique, MFG-E8 was detected in cell lysate of astrocyte culture, and was also detected in the medium. When microglia culture was incubated with astrocyte conditioned medium, MFG-E8 levels in microglia tended to increase. It is likely that microglia might utilize MFG-E8 released from astrocytes as well as that expressed in themselves in order to endocytose Aβ aggregation. Furthermore, we confirmed that MFG-E8 could bind with TG2 in microglia culture by immunoprecipitate technique. These results suggest that microglia might uptake Aβ as a complex of aggregated Aβ/MFG-E8/TG2.

Amphotericin B Increases Transglutaminase 2 Expression Associated with Upregulation of Endocytotic Activity in Mouse Microglial Cell Line BV-2

Amphotericin B (AmB), a polyene antibiotic, is reported to cause the microglial activation to induce nitric oxide (NO) production and proinflammatory cytokines expression, and change neurotrophic factors expression in cultured microglia (Motoyoshi et al. in Neurochem Int 52:1290-1296, 2008). On the other hand, tissue-type transglutaminase (TG2) is involved in connection to phagocytes with apoptotic cells. Engulfment of neurons by activated microglia is thought to cause neurodegenerative diseases but detail is unclear, and involvement of TG2 in phagocytosis has been reported in our previous study using lipopolysaccharide-stimulated BV-2 cells (Kawabe et al. in Neuroimmunomodulation 22(4):243-249, 2015). In the present study, we examined the changes of TG2 expression, phagocytosis and pinocytosis in BV-2 cells stimulated by AmB. AmB stimulation increased TG2 expression and TG activity. Phagocytosis of dead cells and pinocytosis of fluorescent microbeads were also up-regulated by AmB stimulation in BV-2 cells. Blockade of TG activity by cystamine, an inhibitor of TGs, suppressed AmB-enhanced TG2 expression, TG activity, NO production, phagocytosis and pinocytosis. Excessive NO production from microglia and/or facilitation of phagocytosis might be involved in neuronal death. To control TG activity might make possible to protect neurons and care for CNS diseases.

Macrophage integrins modulate response to ultra-high molecular weight polyethylene particles and direct particle-induced osteolysis

Aseptic loosening due to peri-prosthetic osteolysis is one of the primary causes for failure of artificial joint replacements. Implant-derived wear particles, often ultra-high molecular weight polyethylene (UHMWPE) microparticles, initiate an inflammatory cascade upon phagocytosis by macrophages, which leads to osteoclast recruitment and activation, ultimately resulting in osteolysis. Investigation into integrin receptors, involved in cellular interactions with biomaterial-adsorbed adhesive proteins, is of interest to understand and modulate inflammatory processes. In this work, we investigate the role of macrophage integrins Mac-1 and RGD-binding integrins in response to UHMWPE wear particles. Using integrin knockout mice as well as integrin blocking techniques, reduction in macrophage phagocytosis and inflammatory cytokine secretion is demonstrated when these receptors are either absent or blocked. Along this line, various opsonizing proteins are shown to differentially modulate microparticle uptake and macrophage secretion of inflammatory cytokines. Furthermore, using a calvarial osteolysis model it is demonstrated that both Mac-1 integrin and RGD-binding integrins modulate the particle induced osteolysis response to UHMWPE microparticles, with a 40% decrease in the area of osteolysis by the absence or blocking of these integrins, in vivo. Altogether, these findings indicate Mac-1 and RGD-binding integrins are involved in macrophage-directed inflammatory responses to UHMWPE and may serve as therapeutic targets to mitigate wear particle induced peri-prosthetic osteolysis for improved performance of implanted joints.

Histopathological Analysis of PEEK Wear Particle Effects on the Synovial Tissue of Patients

Introduction. Increasing interest developed in the use of carbon-fiber-reinforced-poly-ether-ether-ketones (CFR-PEEK) as an alternative bearing material in knee arthroplasty. The effects of CFR-PEEK wear in in vitro and animal studies are controversially discussed, as there are no data available concerning human tissue. The aim of this study was to analyze human tissue containing CFR-PEEK as well as UHMWPE wear debris. The authors hypothesized no difference between the used biomaterials. Methods and Materials. In 10 patients during knee revision surgery of a rotating-hinge-knee-implant-design, synovial tissue samples were achieved (tibial inserts: UHMWPE; bushings and flanges: CFR-PEEK). One additional patient received revision surgery without any PEEK components as a control. The tissue was paraffin-embedded, sliced into 2 μm thick sections, and stained with hematoxylin and eosin in a standard process. A modified panoptical staining was also done. Results. A “wear-type” reaction was seen in the testing and the control group. In all samples, the UHMWPE particles were scattered in the tissue or incorporated in giant cells. CFR-PEEK particles were seen as conglomerates and only could be found next to vessels. CFR-PEEK particles showed no giant-cell reactions. In conclusion, the hypothesis has to be rejected. UHMWPE and PEEK showed a different scatter-behavior in human synovial tissue.

Comparison of Tibial Insert Polyethylene Damage in Rotating Hinge and Highly Constrained Total Knee Arthroplasty: A Retrieval Analysis

This study compared the damage scores and damage patterns in 19 tibial inserts from rotating hinge (RH) implants with 19 inserts from highly constrained (HC) implants. Each insert was divided into 16 damage zones and each zone was subjectively graded from a scale of 0-3 for seven different damage modes. The overall damage scores were comparable for the two groups (RH: 64.1 ± 15.4; HC: 66.1 ± 29.0; P = 0.59). The HC group, however, had greater post damage (compared to the post-hole of RH) while the RH group had greater backside damage. The pattern of damage was also different, with burnishing and cold flow being more common in HC group while pitting, scratching and embedded debris were more common in the RH group.

Macrophages, Foreign Body Giant Cells and Their Response to Implantable Biomaterials

All biomaterials, when implanted in vivo, elicit cellular and tissue responses. These responses include the inflammatory and wound healing responses, foreign body reactions, and fibrous encapsulation of the implanted materials. Macrophages are myeloid immune cells that are tactically situated throughout the tissues, where they ingest and degrade dead cells and foreign materials in addition to orchestrating inflammatory processes. Macrophages and their fused morphologic variants, the multinucleated giant cells, which include the foreign body giant cells (FBGCs) are the dominant early responders to biomaterial implantation and remain at biomaterial-tissue interfaces for the lifetime of the device. An essential aspect of macrophage function in the body is to mediate degradation of bio-resorbable materials including bone through extracellular degradation and phagocytosis. Biomaterial surface properties play a crucial role in modulating the foreign body reaction in the first couple of weeks following implantation. The foreign body reaction may impact biocompatibility of implantation devices and may considerably impact short- and long-term success in tissue engineering and regenerative medicine, necessitating a clear understanding of the foreign body reaction to different implantation materials. The focus of this review article is on the interactions of macrophages and foreign body giant cells with biomaterial surfaces, and the physical, chemical and morphological characteristics of biomaterial surfaces that play a role in regulating the foreign body response. Events in the foreign body response include protein adsorption, adhesion of monocytes/macrophages, fusion to form FBGCs, and the consequent modification of the biomaterial surface. The effect of physico-chemical cues on macrophages is not well known and there is a complex interplay between biomaterial properties and those that result from interactions with the local environment. By having a better understanding of the role of macrophages in the tissue healing processes, especially in events that follow biomaterial implantation, we can design novel biomaterials-based tissue-engineered constructs that elicit a favorable immune response upon implantation and perform for their intended applications.

[Bone defect adjusted strategy in revision arthroplasty of the hip : Wich implant in wich situation? Innovations and approved methods]

BACKGROUND

Revision total hip arthroplasty is of rising importance, with 35,000 procedures a year in Germany.

OBJECTIVES

Primary stability of the revision implant, reconstruction of the anatomical hip center, reconstruction of bone stock, and permanent secondary integration are the main priorities.

METHODS

Current literature and examples from our own experience are presented.

RESULTS AND CONCLUSIONS

Novel developments from basic research and industrial partners extend the possibilities for treating affected patients. For an integrated therapy concept in implant selection criteria, such as situation and structure of the defect, combination with any remaining implants, causes of loosening and failure, implant allergy, and patient-specific parameters should be taken into consideration.

In vitro and in vivo evaluation of the inflammatory potential of various nanoporous hydroxyapatite biomaterials

Aim: To discriminate the most important physicochemical parameters for bone reconstruction, the inflammatory potential of seven nanoporous hydroxyapatite powders synthesized by hard or soft templating was evaluated both in vitro and in vivo. Materials & methods: After physical and chemical characterization of the powders, we studied the production of inflammatory mediators by human primary monocytes after 4 and 24 h in contact with powders, and the host response after 2 weeks implantation in a mouse critical size defect model. Results: In vitro results highlighted increases in the secretion of TNF-α, IL-1, -8, -10 and proMMP-2 and -9 and decreases in the secretion of IL-6 only for powders prepared by hard templating. In vivo observations confirmed an extensive inflammatory tissue reaction and a strong resorption for the most inflammatory powder in vitro. Conclusion: These findings highlight that the most critical physicochemical parameters for these nanoporous hydroxyapatite are, the crystallinity that controls dissolution potential, the specific surface area and the size and shape of crystallites.

Absence of systemic toxicity in mouse model towards BaTiO3 nanoparticulate based eluate treatment

One of the existing issues in implant failure of orthopedic biomaterials is the toxicity induced by the fine particles released during long term use in vivo, leading to acute inflammatory response. In developing a new class of piezobiocomposite to mimic the integrated electrical and mechanical properties of bone, bone-mimicking physical properties as well as in vitro cytocompatibility properties have been achieved with spark plasma sintered hydroxyapatite (HA)-barium titanate (BaTiO3) composites. However, the presence of BaTiO3 remains a concern towards the potential toxicity effect. To address this issue, present work reports the first result to conclusively confirm the non-toxic effect of HA-BaTiO3 piezobiocomposite nanoparticulates, in vivo. Twenty BALB/c mice were intra-articularly injected at their right knee joints with different concentrations of HA-BaTiO3 composite of up to 25 mg/ml. The histopathological examination confirmed the absence of any trace of injected particles or any sign of inflammatory reaction in the vital organs, such as heart, spleen, kidney and liver at 7 days post-exposure period. Rather, the injected nanoparticulates were found to be agglomerated in the vicinity of the knee joint, surrounded by macrophages. Importantly, the absence of any systemic toxicity response in any of the vital organs in the treated mouse model, other than a mild local response at the site of delivery, was recorded. The serum biochemical analyses using proinflammatory cytokines (TNF-α and IL-1β) also complimented to the non-immunogenic response to injected particulates. Altogether, the absence of any inflammatory/adverse reaction will open up myriad of opportunities for BaTiO3 based piezoelectric implantable devices in biomedical applications.

Characterization of airborne particles generated from metal active gas welding process

This study is focused on the characterization of particles emitted in the metal active gas welding of carbon steel using mixture of Ar + CO2, and intends to analyze which are the main process parameters that influence the emission itself. It was found that the amount of emitted particles (measured by particle number and alveolar deposited surface area) are clearly dependent on the distance to the welding front and also on the main welding parameters, namely the current intensity and heat input in the welding process. The emission of airborne fine particles seems to increase with the current intensity as fume-formation rate does. When comparing the tested gas mixtures, higher emissions are observed for more oxidant mixtures, that is, mixtures with higher CO2 content, which result in higher arc stability. These mixtures originate higher concentrations of fine particles (as measured by number of particles by cm(3) of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more severe worker's exposure.

Calcitonin gene-related peptide modulates the production of pro-inflammatory cytokines associated with periprosthetic osteolysis by THP-1 macrophage-like cells

OBJECTIVE

An anti-resorptive impact of the neuropeptide calcitonin gene-related peptide (CGRP) on periprosthetic osteolysis, the leading cause of early prosthesis loosening, has been shown previously. In this study, the impact of CGRP on pro-inflammatory cytokine production associated with periprosthetic osteolysis was analysed using THP-1 macrophage-like cells.

METHODS

Cells were stimulated with ultra-high-molecular-weight polyethylene (UHMWPE) particles (cell-to-particle ratios of 1:100 and 1:500) and lipopolysaccharides (LPS; 1 µg/ml) to establish osteolytic conditions, and simultaneously treated with CGRP (10(-8)M). Receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and tumour necrosis factor (TNF)-α mRNA expression were measured by quantitative RT-PCR. RANK protein was detected by Western blot. Secreted protein levels of TNF-α as well as interleukin (IL)-1β and IL-6 were quantified in cell culture supernatants by ELISA and Bio-Plex cytokine assay, respectively.

RESULTS

Activation of macrophage-like cells failed to enhance the production of RANK but led to a dose- and time-dependent increase of TNF-α mRNA and secreted protein levels of TNF-α, IL-1β and IL-6. Application of CGRP time-dependently suppressed TNF-α mRNA expression induced by low-particle concentrations and LPS, while both particle- and LPS-induced secretion of TNF-α was inhibited. A pronounced inhibitory effect of CGRP on LPS-induced cytokine production at 24 h of incubation was also observed with IL-1β and IL-6.

CONCLUSIONS

CGRP shows a time-dependent inhibitory effect on the secretion of osteolysis-associated pro-inflammatory cytokines, indicating an indirect anti-resorptive influence of the neuropeptide on both aseptic prosthesis loosening and bacterially induced bone resorption which might enhance the life time of total joint replacements.

Lipopolysaccharide-Stimulated Transglutaminase 2 Expression Enhances Endocytosis Activity in the Mouse Microglial Cell Line BV-2

OBJECTIVES

In peripheral macrophages, tissue-type transglutaminase (TG2) is reported to be involved in phagocytosis of apoptotic cells. However, the contribution of TG2 to microglial phagocytosis has not been investigated. In this study, using a microglial cell line, BV-2, we examined the changes in TG2 expression, phagocytosis and pinocytosis in cells stimulated by lipopolysaccharide (LPS).

METHODS

Cells of the mouse microglial cell line BV-2 were stimulated by LPS with or without cystamine, an inhibitor of TG enzyme activity, for 24 h. TG2 expression was measured by real-time RT-PCR and Western blotting. TG activity was evaluated using biotinylated pentylamine as a substrate. Pinocytosis was determined by uptake of 1-µm fluorescent microbeads. Phagocytosis was assessed by uptake of dead cells, human neuroblastoma SH-SY5Y cells, which were pretreated with H2O2 for 24 h.

RESULTS

Phagocytosis of dead cells and pinocytosis of fluorescent microbeads were up-regulated by LPS stimulation together with TG2 expression. Blockade of TG enzyme activity by cystamine suppressed TG2 expression, phagocytosis and pinocytosis.

CONCLUSIONS

These results suggested that LPS-induced TG2 was involved in the mechanism of pinocytosis and phagocytosis in microglia.

Alternative methods for assessing biocompatibility and function of implant materials

Biocompatibility testing is used to evaluate the host response to implantable materials and to assess their ability to perform in applications in which they are intended to interact with biological systems. In compliance with international and/or national standards, such assessment is based mainly on the results of experimental implantation into animal tissues. However, the development of in vitro experimental techniques creates new opportunities to observe and to understand the interaction of biomaterials with host tissue. The state-of-the-art application of alternative methods in biocompatibility testing is presented in this review article. It is discussed with respect to the Three Rs concept (reduction, refinement, replacement) of Russell & Burch. Perspectives on alternative methods in biocompatibility studies are discussed with regard to the possible role of biomaterials in tissue engineering.

Comparing velour versus silicone interfaces at the driveline exit site of HeartMate II devices: infection rates, histopathology, and ultrastructural aspects

BACKGROUND

Driveline exit site (DLES) infection is a major complication of ventricular assist devices (VADs). Differences in the sheath material interfacing with exit site tissue appear to affect healing time and infection risk more than site hygiene, but the mechanistic basis for this is not clear.

METHODS

Health record data from Utah Artificial Heart Program patients with HeartMate II (HMII) devices implanted from 2008 to 2012 were retrospectively reviewed, with particular attention to interface type, incorporation (healing) time, and infections. Tissue samples from the DLES were collected at the time of VAD removal in a small subset. These samples were examined by routine histology and environmental scanning electron microscopy (ESEM).

RESULTS

Among 57 patients with sufficient data, 15 had velour interfaces and 42 had silicone. Indications for and duration of support were similar between the groups. The silicone group had shorter incorporation time (45 ±22 vs. 56 ±34 days, P=.17) and fewer DLES infections (20% vs. 1.7%, P=.026, for patient infections and 0.0340 vs. 0.166, P=.16, for infections per patient-year). Tissues from five patients, three with velour, were examined. Velour interfaces demonstrated more hyperkeratosis, hypergranulosis, and dermal inflammation. By ESEM, the silicone driveline tracts appeared relatively smooth and flat, whereas the velour interface samples were irregular with deep fissures and globular material adhering to the surface.

CONCLUSIONS

Using the silicone portion of the HMII driveline at the DLES was associated with fewer infections and a trend toward faster healing in this small retrospective series. Whether the intriguing microscopic differences directly account for this needs further study on a larger scale.

Vertebral osteolytic defect due to cellulose particles derived from gauze fibers after posterior lumbar interbody fusion

Vertebral cystic lesions may be observed in pseudarthroses after lumbar fusion surgery. The authors report a rare case of pseudarthrosis after spinal fusion, accompanied by an expanding vertebral osteolytic defect induced by cellulose particles. A male patient originally presented at the age of 69 years with leg and low-back pain caused by a lumbar isthmic spondylolisthesis. He underwent a posterior lumbar interbody fusion, and his neurological symptoms and pain resolved within a year but recurred 14 months after surgery. Radiological imaging demonstrated a cystic lesion on the inferior endplate of L-5 and the superior endplate of S-1, which rapidly enlarged into a vertebral osteolytic defect. The patient underwent revision surgery, and his low-back pain resolved. A histopathological examination demonstrated foreign body-type multinucleated giant cells, containing 10-μm particles, in the sample collected just below the defect. Micro-Fourier transform infrared spectroscopy revealed that the foreign particles were cellulosic, presumably originating from cotton gauze fibers that had contaminated the interbody cages used during the initial surgery. Vertebral osteolytic defects that occur after interbody fusion are generally presumed to be the result of infection. This case suggests that some instances of vertebral osteolytic defects may be aseptically induced by foreign particles. Hence, this possibility should be carefully considered in such cases, to help prevent contamination of the morselized bone used for autologous grafts by foreign materials, such as gauze fibers.

Tribological characteristics of polyethylene glycol (PEG) as a lubricant for wear resistance of ultra-high-molecular-weight polyethylene (UHMWPE ) in artificial knee join

For the longevity of total knee joint prostheses, we have developed an artificial lubricant using polyethylene glycol (PEG) for the prevention of wear of ultra-high-molecular-weight polyethylene (UHMWPE). In the present study, the lubricative function of this PEG lubricant was evaluated by a wear test using Co-Cr alloy and UHMWPE counter surface samples. As a result, human synovial fluid including the PEG lubricant showed good result regarding the wear volume and a worn surface of UHMWPE. Considering its lubrication mechanism, it is suspected that interaction between the PEG molecules and the proteins in synovial fluid was involved. Since PE molecules are also organic compounds having a hydroxyl group at one or both ends, the albumin and PEG molecule complex would have bound more strongly to the metal oxide surface and UHMWPE surfaces might enhance and stabilize the lubricating film between the contact surfaces under the boundary lubrication. This study suggests that PEG lubricant as an intra-articular viscous supplement has the potential to prevent wear of UHMWPE by mixing with synovial fluid and to contribute to the longevity of knee joint prostheses.