High Molecular Weight Polyethylene Particles Research Articles

An in vivo murine model of continuous intramedullary infusion of polyethylene particles

Wear debris affects both initial osseointegration and subsequent bone remodeling of total joint replacements (TJRs). To study the complex cascade associated with the continuous generation of particles, a robust animal model is essential. To date, an animal model that incorporates continuously delivered particles to an intramedullary orthopaedic implant has not been available. In this study, we successfully infused clinically relevant ultra high molecular weight polyethylene particles, previously isolated from joint simulator tests, to the intramedullary space of the mouse femur for 4 weeks using a subcutaneous osmotic pump. Reduction of bone volume following the 4-week infusion of UHMWPE was detected by microCT. UHMWPE particles also changed the level of Alkaline Phosphatase expression in the infused femurs. Continuous infusion of particles to the murine bone–implant interface simulated the clinical scenario of local polymer wear particle generation and delivery in humans and can be used to further study the biological processes associated with wear debris particles.

The influence of molecular weight, crosslinking and counterface roughness on TNF-alpha production by macrophages in response to ultra high molecular weight polyethylene particles

The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated. Clinically relevant ultra high molecular weight polyethylene (UHMWPE) wear debris was generated in vitro in a lubricant of RPMI 1640 supplemented with 25% (v/v) foetal calf serum using a multi-directional pin-on-plate wear rig under sterile conditions. Wear debris was cultured with C3H murine peritoneal macrophages at various particle volume (μm 3): cell number ratios. The secretion of TNF-α was determined by ELISA. Initially the effect of molecular weight of UHMWPE was considered. Higher molecular weight GUR415HP was shown to have a lower wear rate than the lower molecular weight GUR1120, however a greater volume of the wear debris produced by the high molecular weight GUR415HP was in the 0.1–1.0 μm size range. Wear debris from GUR415HP produced significant levels of TNF-α at a concentration of 1 μm 3/cell while at least 10 μm 3/cell of GUR1120 wear debris per cell was needed to produce significant levels of TNF-α. Secondly the effects of crosslinking GUR1050 was examined when worn against a scratched counterface. The wear rate of the material was shown to decrease as the level of crosslinking increased. However the materials crosslinked with 5 and 10 Mrad of gamma irradiation produced higher percentages of 0.1–1.0 μm size wear particles than the non-crosslinked material. While the crosslinked material was able to stimulate cells to produce significantly elevated TNF-α levels at a particle concentration of just 0.1 μm 3/cell only concentrations of 10 μm 3/cell and above of the non-crosslinked wear debris were stimulatory. When the counterface was changed from scratched to smooth the wear rate for all three GUR1050 materials was further reduced. For the first time nanometre size wear particles were observed from polyethylene which reduced the percentage mass of debris in the 0.1–1.0 μm size range. For all three materials on the smooth counterface only concentrations of 50 μm 3/cell and above were stimulatory. This study has demonstrated that molecular weight, crosslinking and counterface roughness are important factors in determining the biological activity of polyethylene.

Flow cytometric technique for the detection of phagocytosed wear particles in patients with total joint arthroplasty

Wear particles from prosthetic implants have been shown to cause inflammatory synovitis and periprosthetic osteolysis. These particle-induced pathologies are manifestations of adverse cellular responses to phagocytosed particles. In this study, phagocytosis of polyethylene particles was analyzed using flow cytometry (FCM), and the clinical utility of FCM in diagnosing particle-induced synovitis was examined. Ultra high molecular weight polyethylene particles exhibited natural autofluorescence at fluorescein isothiocyanate wavelengths when determined by FCM. Using this autofluorescent property of the particles, peripheral blood monocytes (PBMs) phagocytosing the particles could be detected by autofluorescence emission from intracellular particles. This autofluorescence from PBMs increased with particles/cell ratio in a dose-dependent manner. Particle phagocytosis was also detectable in joint fluid cells obtained from the patients with particle-induced synovitis following total joint arthroplasty (TJA). Phenotypic analysis indicated that phagocytes were typically CD14 +CD16 − macrophages, with occasional CD14 +CD16 + macrophages. Interestingly, decreased autofluorescence intensity of CD14 + cells was observed after arthroscopic drainage, suggesting that FCM was useful in examining whether the treatment was successful. In summary, these results indicate that FCM analysis offers a simple and useful method of detecting phagocytosis of polyethylene particles and estimating the severity of particle-induced synovitis in post-TJA patients.

Synergistic effect of particles and cyclic pressure on cytokine production in human monocyte/macrophages: proposed role in periprosthetic osteolysis

Macrophages, activated by particulate wear debris, are important in the process of osteolysis, which occurs during joint implant loosening. We previously found increased levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α in cultured macrophages subjected to cyclical pressure of 0.138 MPa, suggesting that cyclic pressure may be another relevant cause of macrophage activation. The current study first investigated the effects of a range of cyclic pressures on cultured macrophages, including an investigation of the time course of cytokine expression. At 0.138 MPa, supernatant levels of TNF-α were maximal at 12 h, whereas IL-6 and IL-1β were maximal at 24 h. All four cyclic pressure levels tested (without particles) resulted in increased production of all three cytokines relative to control. These increases were most marked at 0.069 and 0.035 MPa, and the increase in cytokine production at 0.017 MPa was not statistically significant. Further studies demonstrated that conditioned media from cyclically pressurized macrophages stimulated bone resorption in a neonatal mouse calvarial assay system. There were increased levels of calcium released from calvaria cultured in conditioned media from pressurised monocytes, and an increase in tartate-resistant acid phosphatase–positive osteoclasts was observed microscopically. As particulate wear debris is important in implant loosening, ultra high molecular weight polyethylene particles were also added to the pressurized cell cultures. The experiments compared the effect of atmospheric pressure, cyclic pressure alone, particles alone, and particles and cyclic pressure combined. A combination of ultra high molecular weight polyethylene particles and cyclic pressure at 0.017 MPa resulted in a dramatic synergistic elevation of levels of all three cytokines compared with the levels found with either pressure or particles alone. We propose that monocyte/macrophage activation by cyclic pressure plays a major role in the osteolysis seen in aseptic loosening of implants. The synergistic effect observed between particles and pressure could accelerate implant loosening, and implies that reduction in either cyclic pressure (by improving implant fixation) or wear debris load would reduce osteolysis.

Effect of size and dose on bone resorption activity of macrophages by in vitro clinically relevant ultra high molecular weight polyethylene particles.

Polyethylene wear debris generated at the bearing surfaces of total artificial hip joints is thought to play an important role in the periprosthetic osteolysis and ultimately the aseptic loosening of these prostheses. The macrophage is believed to be central to this process by releasing various cytokines and other mediators of osteolysis upon phagocytosis of the polyethylene wear debris. This study evaluated the in vitro bone resorption response of C3H murine peritoneal macrophages to clinically relevant GUR 1120 polyethylene particles. Macrophages were co-cultured in vitro with GUR 1120 particles with a mean size of 0.24, 0.45, 1.71, and 7.62, and GUR 1120 polyethylene resin with a mean size of 88 microm at various particle volume (microm)(3): macrophage ratios (0.1:1; 1:1; 10:1; and 100:1). The conditioned supernatants were incubated with (45)calcium radio-labeled mouse calvariae, and bone resorption was measured as (45)calcium release. The results showed that the 0.24 microm particles stimulated the macrophages to generate bone resorbing activity at a ratio of 10(microm)(3) per macrophage. The 0.45 and 1.71 microm particles were active at a ratio of 100( microm)(3) per macrophage, and the 7.62 and 88 microm particles were inactive at all the doses tested. The co-culture supernatants were also assayed for TNF-alpha, IL-1beta, IL-6, and PGE(2). The results followed the same trend for particle size and volume dose to that observed for the bone resorbing activity. This study has demonstrated, for the first time, the importance of size and dose of clinically relevant polyethylene particles on the osteolytic response of macrophages in vitro.

Technique for generating submicrometer ultra high molecular weight polyethylene particles.

Ultra high molecular weight polyethylene wear debris is believed to have a major role in aseptic loosening of prosthetic joints. In order to study the cellular and host response to this and other such particulate debris, a source of fine ultra high molecular weight polyethylene debris is needed. We have described a technique to fracture the GUR 4150 primary ultra high molecular weight polyethylene grain, which reproducibly generated particles less than 1 micron in size. Furthermore, the particle morphology was similar to that of ultra high molecular weight polyethylene particles generated in vivo and retrieved from interfacial tissues. The fabricated polyethylene particles ranged from 0.1 to 33 microns in diameter, with a mean of 2.3 +/- 0.2 micron. Sixty percent of the particles were smaller than 1 micron and 90% were smaller than 7 microns. Using filtration and sedimentation, it is possible to acquire finer particle fractions. These particles are currently being used for biological response studies.