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PubMed2001

Biomimetic apatite formation on polyethylene photografted with vinyltrimethoxysilane and hydrolyzed.

A photografting technique to produce functional groups of silanol able to induce apatite nucleation was attempted on polyethylene substrate for biomimetic formation of bone-mineral-like apatite layer on its surface. The polyethylene surface was subjected to vapor-phase photografting of vinyltrimethoxysilane and subsequently to hydrolysis. The photografting formed methoxysilyl groups on the polyethylene substrate, which was changed into silanol groups successively by the hydrolysis in a hydrochloric solution. The polyethylene modified in this way formed a dense and homogeneous bone-mineral-like apatite layer in a solution with ion concentrations 1.5 times that of human blood plasma. This result indicates that the biomimetic process in combination with a polymeric grafting technique might provide a homogeneous bone-mineral-like apatite coating even on polymer fibers to be woven into an apatite-polymer composite with three-dimensional structure analogous to that of natural bone.

Apatites↗
PubMed1998

Polyethylene particles of a 'critical size' are necessary for the induction of cytokines by macrophages in vitro.

Particulate wear debris from total hip prosthetic components can stimulate macrophages to produce mediators of osteolysis which may cause aseptic implant loosening. This study evaluated the in vitro response of murine peritoneal macrophages to polyethylene particles of definitive size distributions at varying volume doses. Ceridust 3615 polyethylene particles with a mean size of 0.21, 0.49, 4.3 and 7.2 microm and GUR 120 polyethylene resin with a mean size of 88 microm were co-cultured with C3H murine peritoneal macrophages at volume (microm)3 to cell number ratios of 100:1, 10:1, 1:1 and 0.1: 1. The secretion of IL-6, IL-1beta and TNF-alpha was determined by ELISA. Significantly elevated levels of TNF-alpha and IL-1beta were determined at 100:1 ratios when the macrophages were challenged with particles with a mean size of 0.49, 4.3 and 7.2 microm, and at 10:1 ratios for particles with a mean size of 0.49 and 4.3 microm. IL-6 production was significantly elevated at 100:1 ratios for mean particle sizes of 0.49 and 4.3 microm. Particles outside this range produced considerably less cytokine suggesting that both the size and volume (or number) of polyethylene particles are critical factors in macrophage activation. Therefore particles in the phagocytosable size range of 0.3-10 microm appear to be the most biologically active.

Animals↗
PubMed2000

Postcontrast magnetic resonance imaging assessment of porous polyethylene orbital implant (Medpor).

OBJECTIVE: To evaluate the fibrovascular ingrowth progression within the porous polyethylene orbital implant (Medpor) with serial magnetic resonance imaging (MRI). DESIGN: Prospective, nonrandomized, comparative (self-controlled) trial. PARTICIPANTS: Ten patients who underwent enucleation and implantation of a 20-mm porous polyethylene implant wrapped with heterologous sclera. METHODS: Serial precontrast and postcontrast T1-weighted MRI were obtained at 1.5, 3, 6, and 12 months after implantation. The percentage area of enhancement was calculated by use of manual planimetric contouring unenhanced areas at the equator of each sphere on axial and coronal planes. RESULTS: All the implants showed enhancing areas as early as 1.5 months after enucleation. In 8 of the 10 patients, the areas of enhancement at the equator of the implant consistently showed similar centripetal progression primarily during the first 6 months after enucleation. The presence of fibrovascular tissue at the equator was associated in all cases with enhancing zones at the anterior portion of the implant. None of the implants showed diffuse complete enhancement after 12 months. Two patients failed to demonstrate further enhancement progression 1.5 months after implantation. No histopathologic study to equate with the MRI findings was performed in this series. CONCLUSIONS: Postcontrast magnetic resonance studies seem to be the best-suited imaging modality for assessing the fibrovascular tissue progression into porous polyethylene spheres after enucleation and for identifying patients in whom failure of vascularization occurs. Incomplete vascularization at the equator of the porous polyethylene sphere does not prove an absence of fibrovascular ingrowth in the anterior region. Prior ocular surgery and coexisting arterial hypertension may slow the progression of fibrovascular ingrowth.

Adolescent↗
PubMed1994

Orbital reconstruction using porous polyethylene sheets.

BACKGROUND: There has been growing interest in using porous alloplastic implants for reconstructive orbital surgery because of their perceived increased biocompatibility. One commercially available porous implant is high-density porous polyethylene (Medpor). It is made of pure particles of polyethylene that form interconnecting pores and have excellent handling characteristics. METHODS: The authors performed 37 orbital reconstructions using 0.85-, 1.5-, or 3-mm porous polyethylene sheets to reconstruct internal orbital defects. Mean postoperative follow-up was 18.5 months. Four patients were treated for anophthalmic enophthalmos; there was one patient with spontaneous enophthalmos. In selected patients, other implants also were used, including miniplates or microplates, silastic sheets, autologous bone, or nasal septal cartilage. In patients with enophthalmos, the implants were stacked to reverse the malposition evident at surgery. RESULTS: Preoperatively, 27 patients had symptomatic diplopia. Postoperatively, the diplopia resolved in 15 patients and decreased in 7. No patients had induced diplopia or exacerbation of preoperative diplopia. Enophthalmos resolved in 9 of 18 patients. Hypoglobus was normalized in nine of nine patients. There was one major complication of orbital infection requiring explantation 1 week postoperatively. Minor complications included undercorrection, a symptomatically palpable implant, and transient postoperative chemosis. CONCLUSION: Porous polyethylene sheets offer several distinct advantages when used for orbital reconstruction. They are easy to handle, shape, contour, position, fixate, and use with other autogenous and alloplastic implants. In this series, these sheets permitted predictable, stable results with few complications.

Adolescent↗
PubMed2000

Immobilized soy-sauce yeasts: development and characterization of a new polyethylene-oxide support.

Entrapment of cells in alginate gel is a widely used mild immobilization procedure. However, alginate gel is not very suitable for use in long-term continuous soy-sauce processes because alginate is sensitive to abrasion and chemically unstable towards the high salt content of soy-sauce medium. Therefore, a chemically crosslinked polyethylene-oxide gel was used instead. The disadvantage of this gel was that due to the crosslinking reaction, the viability of the cells after immobilization was poor. For this reason, a new mild procedure for immobilizing soy-sauce yeasts in polyethylene-oxide gel was developed, resulting in high survival percentages of the soy-sauce yeasts Zygosaccharomyces rouxii and Candida versatilis. This newly developed polyethylene-oxide gel, unlike alginate gel, appeared not to be sensitive to abrasion, even in the presence of high salt concentrations. Therefore, we concluded that this newly developed polyethylene-oxide gel is more suitable than alginate gel for use as immobilization material in long-term processes with a high salt content, like soy-sauce processes.

Candida↗
PubMed2002

Mechanism of increased dissolution of diazepam and temazepam from polyethylene glycol 6000 solid dispersions.

Solid dispersion literature, describing the mechanism of dissolution of drug-polyethylene glycol dispersions, still shows some gaps; (A). only few studies include experiments evaluating solid solution formation and the particle size of the drug in the dispersion particles, two factors that can have a profound effect on the dissolution. (B). Solid dispersion preparation involves a recrystallisation process (which is known to be highly sensitive to the recrystallisation conditions) of polyethylene glycol and possibly also of the drug. Therefore, it is of extreme importance that all experiments are performed on dispersion aliquots, which can be believed to be physico-chemical identical. This is not always the case. (C). Polyethylene glycol 6000 (PEG6000) crystallises forming lamellae with chains either fully extended or folded once or twice depending on the crystallisation conditions. Recently, a high resolution differential scanning calorimetry (DSC)-method, capable of evaluating qualitatively and quantitatively the polymorphic behaviour of PEG6000, has been reported. Unraveling the relationship between the polymorphic behavior of PEG6000 in a solid dispersion and the dissolution characteristics of that dispersion, is a real gain to our knowledge of solid dispersions, since this has never been thoroughly investigated. The aim of the present study was to fill up the three above mentioned gaps in solid dispersion literature. Therefore, physical mixtures and solid dispersions were prepared and in order to unravel the relationship between their physico-chemical properties and dissolution characteristics, pure drugs (diazepam, temazepam), polymer (PEG6000), solid dispersions and physical mixtures were characterised by DSC, X-ray powder diffraction (Guinier and Bragg-Brentano method), FT-IR spectroscopy, dissolution and solubility experiments and the particle size of the drug in the dispersion particles was estimated using a newly developed method. Addition of PEG6000 improves the dissolution rate of both drugs. Mechanisms involved are solubilisation and improved wetting of the drug in the polyethylene glycol rich micro-environment formed at the surface of drug crystals after dissolution of the polymer. Formulation of solid dispersions did not further improve the dissolution rate compared with physical mixtures. X-ray spectra show that both drugs are in a highly crystalline state in the solid dispersions, while no significant changes in the lattice spacings of PEG6000 indicate the absence of solid solution formation. IR spectra show the absence of a hydrogen bonding interaction between the benzodiazepines and PEG6000. Furthermore, it was concluded that the reduction of the mean drug particle size by preparing solid dispersions with PEG6000 is limited and that the influence of the polymorphic behavior of PEG6000 (as observed by DSC) on the dissolution was negligible.

Chemistry, Pharmaceutical↗
PubMed2000

Migration of polyethylene wear debris in one type of uncemented femoral component with circumferential porous coating: an autopsy study of 5 femurs.

This autopsy study analyzed the migration of polyethylene wear debris adjacent to uncemented femoral components with circumferential porous coating. Five femoral specimens retrieved at autopsy from 3 patients were investigated. Two stems were 40% porous coated, 2 were 80% porous coated, and 1 was 100% porous coated. The implants' time in situ ranged from 53 to 132 months (average, 94.8 months). All patients were followed clinically and radiographically until death. Radiographically, 3 of the stems were bone ingrown with proximal bone loss, 1 stem was mainly fibrous encapsulated, and 1 stem was completely fibrous encapsulated. Histologic examination of bone adjacent to the middle and distal sections of the femoral implant revealed no polyethylene wear debris or granulation tissue in any of the specimens. In 2 bone-ingrown cases, a small number of polyethylene particles and small areas of granulation tissue were present at the proximal level. This granulation tissue, however, did not cause major osteolysis. The findings in this study imply that circumferential porous coating of cementless femoral components could prevent distal migration of polyethylene wear debris along the bone-implant interface in both bone-ingrown and fibrous-encapsulated femoral implants.

Aged↗
PubMed2003

"Backside" polyethylene deformation in total knee arthroplasty.

The clinical importance of polyethylene deformation between the tibial insert and base plate ("backside") is unclear. We used a semiquantitative scoring system to compare clinical and radiographic factors with articular and backside deformation of 106 retrieved polyethylene tibial inserts. Backside deformation was associated with polyethylene thickness and type of locking mechanism. Deformation of the articular surface correlated with femoral osteolysis (P=.05). The mean backside deformation score was 33% greater for implants from patients with osteolysis than for implants from patients without osteolysis (P=.07). Our study may be biased based on the types of implants available for study, but for this group of implants, we cannot conclude with 95% certainty that backside polyethylene deformation was clinically important as a cause of periprosthetic osteolysis or implant loosening.

Adult↗
PubMed2003

Dislocation after polyethylene liner exchange in total hip arthroplasty.

Little has been published on the outcomes of polyethylene liner exchanges for wear or osteolysis. We assessed 24 patients from our clinic who had an isolated polyethylene liner exchange for wear or osteolysis with retention of the acetabular shell and femoral stem. At a mean 56-month follow-up time, 6 hips (25%) had dislocated. Of these, 2 underwent repeat surgery for recurrent dislocation; 1 had 3 dislocations; 1 had 2 dislocations; and 2 had single dislocations. Seventeen of the remaining patients answered our questionnaire: 13 recovered faster from the polyethylene liner exchange than from the primary arthroplasty; 4 believed that their hips were not as stable, 4 believed the hip did not function as well; and 1 underwent revision for cup loosening. We conclude that polyethylene liner exchanges, with or without femoral head exchange for wear or osteolysis, are associated with a high risk of dislocation and possible decrease in function.

Arthroplasty, Replacement, Hip↗
PubMed1996

Relationship between polyethylene wear, pelvic osteolysis, and clinical symptomatology in patients with cementless acetabular components. A framework for decision making.

The purpose of this study is to assess the relationship between acetabular component polyethylene wear, pelvic osteolysis, and clinical symptoms to determine when operative intervention should occur and to predict the degree of difficulty of the revision. Fifty-four revisions of failed cementless acetabular components were performed in 52 patients. All cases demonstrated polyethylene wear radiographically, and in 43 cases (80%), osteolysis of the pelvis was seen. Symptoms of groin or buttock pain were seen in 45 of 54 cases (83%). Preoperative staging of the disease process included one patient with wear radiographically but neither symptoms nor lysis (stage I), 10 patients with wear and pain (stage IIA), 8 patients with wear and lysis but no pain (stage IIB), and 35 patients with wear, lysis, and pain (stage III). Patients in stages I and IIA could be revised with cementless components without structural allograft. Patients in stages IIB and III required structural allograft in 79% and cemented components in 53%. Cemented components were used when there was less than 50% contact between host-bone and prosthesis. Polyethylene wear alone (stage I) is an indication of impending failure, and when symptoms develop (stage IIA), revision should be undertaken. The development of radiographic lysis is a critical event, and as soon as osteolysis develops (stage IIB or III), revision should be undertaken immediately. From the perspective of the revision surgeon, there is great value in the early intervention for polyethylene wear and pelvic osteolysis.

Acetabulum↗
PubMed1997

Absorption profiles for polyethylene glycols after regional jejunal perfusion and oral load in healthy humans.

The study aimed at applying closed segmental intestinal perfusion with a multichannel tube (Loc-I-Gut) for studies of regional small bowel permeability to different-sized polyethylene glycols and to compare jejunal absorption with absorption after oral load in healthy subjects. Intestinal perfusion was performed in 10 healthy volunteers and recovery of (14)C-labeled polyethylene glycol 4000 was used to detect leakage. Absorption of polyethylene glycols 546-942 was measured as urinary recovery after perfusion and oral load, and as disappearance from the lumen during steady-state perfusion. Steady-state conditions were obtained during the second hour of perfusion. Absorption of polyethylene glycols during perfusion was size-selective for molecular weights 546-766, but not for 810-942. After oral load, absorption was size-selective throughout 546-942. Segmental perfusion with Loc-I-Gut may be used to study regional jejunal permeability. Our data support the hypothesis of a dual pore system for absorption of hydrophilic molecules in the human jejunum.

Administration, Oral↗
PubMed1991

A phase I study including pharmacokinetics of polyethylene glycol conjugated interleukin-2.

A more soluble formulation of recombinant interleukin-2 with a prolonged half-life would allow alternate routes or schedules of administration and enhance patient comfort. The covalent attachment of polyethylene glycol to recombinant interleukin-2 provides an analog with preclinical data suggesting those desired characteristics while maintaining biologic activity. This is the report of a phase I study in which we sought to determine the maximum tolerated dose of polyethylene glycol interleukin-2, observe biologic activity, and confirm the prolonged half-life in vivo. Sixty-six patients were entered into the study during 19 months. Polyethylene glycol interleukin-2 was administered intravenously once a week over 15 minutes. The maximum tolerated dose was 20 x 10(6) U/M2. The pattern of toxicity was quite similar to that of the parent compound. Four patients had evidence of tumor regression (three partial remission; one minor response). The pharmacokinetic data confirmed a 10- to 20-fold prolongation in half-life compared with recombinant interleukin-2. No neutralizing antibodies were detected. This study provides sufficient impetus for the ongoing phase II studies of polyethylene glycol interleukin-2.

Adult↗
PubMed2001

Matched-pair analysis of all-polyethylene versus metal-backed tibial components.

Forty-eight matched pairs of osteoarthritic knees from patients who underwent primary total knee arthroplasty with a round-on-round, Apollo Knee System were studied to evaluate the outcome between all-polyethylene and metal-backed tibial components. Patients were matched for patient factors, preoperative deformities, cruciate salvage or sacrifice, and surgical technique. At the last follow-up (average, 38.4 months), there was no statistically significant difference in terms of knee scores, patient self-assessment, and radiographic outcomes. No component required revision, and no revisions were pending. Maintenance of these results over time would project into better long-term success for all-polyethylene tibial components because of the amount of wear and osteolysis with current modular metal-backed tibial components. We advocate the use of a more cost-effective all-polyethylene tibial component in elderly patients (>70 years old) who are not likely to need the versatility of exchange of a modular polyethylene insert because of wear.

Adult↗
PubMedDate not supplied

[Polyethylene liner dislocation in Harris Galante acetabular components].

AIM: Dislocation and subsequent dissociation of the polyethylene liner as a result of failure of the acetabular locking mechanism is a potential source of failure in the Harris-Galante acetabular component. The purposes of this study are to present seven cases with a liner dislocation due to failure of the liner locking mechanism. METHOD: Between March 1997 and December 2001, seven patients who had had a total hip arthroplasty presented with clinical and radiologic signs of liner dislocation and signs of polyethylene wear of the liner from a Harris Galante acetabular shell. In all cases the intraoperative findings showed evidence of failure of the liner locking mechanism and subsequent dislocation. The medical records, radiographs, operative notes and explanted retrieved components were reviewed. RESULTS: The components had been in situ for an average of 5.3 years (range 1-9 years). Two components were first generation, five were second generation. The symptoms developed spontaneously in five patients, the other two patients described a minor trauma. Radiographs showed eccentric position of the head in all cases. All acetabular components showed an excellent stability intraoperatively, nevertheless we had to remove the well fixed acetabular shell due to complete destruction of the liner locking mechanism in two cases. Treatment consisted of revision of the shell in two patients and exchange of the liner in five patients. All retrieved liners showed severe deformation and/or fracture of the rim. CONCLUSION: Harris Galante modular acetabular components have been used widely for primary and revision arthroplasty. The survival of this implant has been well documented in the literature. Failure of the liner locking mechanism and following dislocation or fracture of the polyethylene liner is a potential cause of failure which may possibly occur more often than the literature to date has documented. We report seven cases of liner dislocation, in which two acetabular components had to be removed completely due to destruction of the liner locking mechanism. In the other five cases exchange of the liner was possible thanks to well timed revision. We believe that, as the liner wears and becomes loose due to an inefficient locking mechanism, the load increases on the polyethylene rim until it deforms or fractures. As a consequence of the prosthetic design at that stage nothing can prevent the liner from rotating out of the shell.

Acetabulum↗
PubMedDate not supplied

[Size and shape of commercially available polyethylene particles for in-vitro and in-vivo-experiments].

AIM: The longevity of total hip arthroplasty is sometimes limited by osteolysis and aseptic loosening. Aseptic loosening may be caused by the biologic reaction to polyethylene wear particles. Particles of less than 1 micro m diameter are of particular importance. These particles are not easily available for experimental use. METHOD: We performed a morphologic analysis of commercially available, very small polyethylene particles (Ceridust(R)) in order to determine the specific size distribution. We measured 1 978 particles. Size analysis was performed using an electron microscope. Particle size was described as the equivalent circle diameter (ECD). Particle morphology was described as feret ratio. In addition, Ceridust(R) particles were compared to different particles stemming from a hip simulator experiment. RESULTS: More than 35 % of the particles were less than 1 micro m in size. The particle size was 1.75 micro m +/- 1.43 micro m (median 1.42 micro m). The minimum was 0.06 micro m, the maximum was 11.06 micro m. The feret ratio was 0.58 +/- 0.17 (median 0.63). The minimum was 0.07, the maximum was 0.93. The majority of Ceridust(R) particles had a rough surface. Compared to polyethylene particles stemming from a hip simulator experiment, Ceridust(R) particles had a rougher surface, were less longitudinal, and had a more even size distribution. CONCLUSIONS: The pure, commercially available polyethylene particles analyzed here are suitable for in vitro and in vivo experiments due to their easy availability, minor costs, and large fraction of very small particles.

Biocompatible Materials↗
PubMed2000

Loss of THCCOOH from urine specimens stored in polypropylene and polyethylene containers at different temperatures.

The loss of delta9-tetrahydrocannabinol (THCCOOH) from urine specimens stored in polypropylene and polyethylene containers at 4 degrees C and 25 degrees C was examined. All specimens were analyzed by GC-MS after sampling at various times over a one-week period. Data were analyzed by one-way analysis of variance and fitted with a first order kinetic equation. Rapid loss of THCCOOH was seen at 4 degrees C for both polypropylene (14% maximal loss, t(1/2) = 0.53 min) and polyethylene (17% maximal loss, t(1/2) = 5.77 min) bottles. At 25 degrees C, a small loss (< 5%) was observed in polypropylene and no significant loss was seen for urine in polyethylene. All losses stabilized within 1 h, and no further losses were seen over one week. The results indicate that THCCOOH binding may be due to decreased solubility of THCCOOH at lower temperatures and subsequent association of THCCOOH with the more lipophilic plastic. The results also indicate that polypropylene and polyethylene do not bind THCCOOH to such an extent as to compromise the integrity of specimens.

Dronabinol↗
PubMed1998

Comparison of the effects of enucleation and orbital reconstruction using free-fat grafts, dermis grafts, and porous polyethylene implants in infant rabbits.

Twenty-nine infant rabbits from four litters were randomly assigned to three groups. No surgery was performed on left eyes. All right eyes were enucleated. Group 1, the control group, had no right-socket reconstruction. Group 2 had reconstruction using free-fat and dermis grafts. Group 3 had reconstruction using porous polyethylene implants. On attaining adult size, rabbits were killed, decapitated, and prepared for measurements. Orbital volume measurements were performed twice and orbital entrance areas were determined once. No significant differences were noted between first and second measurements of orbital volumes. Right orbital volumes were significantly smaller than left orbits in all groups except for the second measurement of the polyethylene implant group. Right orbital entrance areas were significantly smaller than left areas in the control and the free-fat and dermis graft groups. Right orbital entrance areas of the polyethylene group were not significantly smaller than the corresponding left orbital entrance areas. The use of free-fat and dermis grafts for orbital reconstruction in anophthalmic infant rabbits did not significantly stimulate orbital bone growth. In one trial, the polyethylene implant group displayed right orbital volumes and orbital entrance areas that were not significantly smaller than controls.

Adipose Tissue↗
PubMed2000

Porous polyethylene implant fibrovascularization rate is affected by tissue wrapping, agarose coating, and insertion site.

PURPOSE: Often used in facial and ocular reconstruction, biointegratable materials, such as hydroxyapatite and high density porous polyethylene, can be associated with migration, exposure, and infection. Complications are less likely after implants become fibrovascularly integrated. A model was sought to study the influence of multiple factors on the rate of fibrovascular ingrowth into porous implants. METHODS: High density porous polyethylene cubes were implanted into paraspinous skeletal muscles in rabbits. The cubes were explanted at weekly intervals using survival surgery. The number of fibroblasts at the center of each cube was counted, generating a time-dependent standard curve of cell accumulation. Porous polyethylene cubes uncoated, coated with agarose (a plant-derived carbohydrate), or coated with nonperforated sclera (human or rabbit) were implanted into suprascapular adipose and paraspinous skeletal muscle in other rabbits. RESULTS: Fibrovascular ingrowth occurred more rapidly with cube implantation into skeletal muscle versus adipose, with increased surface area contact between implants and muscle, and with removal of muscle capsules. While the rate of fibroblast accumulation decreased in cubes coated with sclera, coating the cubes with agarose increased the fibrous capsule formation without altering the rate of biointegration. CONCLUSIONS: This study provides a novel approach for the study of fibrovascular ingrowth into implants treated under a variety of conditions. Modification of current surgical techniques may increase the rate of porous polyethylene implant biointegration.

Adipose Tissue↗