Comparison of the biological activities of high-density porous polyethylene implants and oxidized regenerated cellulose-wrapped diced cartilage grafts

The use of alloplastic materials in plastic surgery has become more extensive with advancement of autogenous-tissue reconstruction techniques for the repair of defects, tissue augmentation, and the stabilization of bones. An ideal alloplastic material should be nonallergenic, noncarcinogenic, sterilizable, and easy to shape and should not cause rejection. Alloplastic material used for tissue augmentation should have a low rate of resorption and distortion. High-density porous polyethylene implants (Medpor) have been used widely and successfully for tissue augmentation. The Turkish Delight is a material composed of diced cartilage grafts wrapped in oxidized regenerated cellulose (Surgicel). Its indications are similar to those of the Medpor implant, and an additional donor site is usually not needed. Both materials are used in the same anatomical locations, especially for augmentation. Therefore, the authors evaluated the long-term stability of and suitable anatomical sites for these materials. Medpor implants or Turkish Delights were placed subperiosteally or subfascially in 10 young rabbits, and the resultant changes were evaluated 16 weeks after the operation by macroscopy and histopathology. Changes in projections were measured with an ocular micrometer. Medpor implants were neither resorbed nor distorted when placed subperiosteally or subfascially, and were highly stabilized by the surrounding tissues. Turkish Delight also enabled tissue augmentation, but had a significantly higher rate of resorption compared with the Medpor implant and was loosely bound to the surrounding tissue. The Turkish Delight was less resorbed and better fixed to adjacent tissues when placed subperiosteally than when placed subfascially.     

Osteochondral reconstruction of a non-weight-bearing joint using a high-density porous polyethylene implant

Currently, there is no reliable reconstructive modality allowing anatomic resurfacing of traumatic digital osteochondral articular defects. The purpose of the present study is to demonstrate the utility of Medpor, a high-density porous polyethylene (HDPP) scaffold biomaterial that can (1) be readily contoured to fit any joint defect, (2) permit stable internal fixation, and (3) permit osteocyte and chondrocyte ingrowth and subsequent articular cartilage resurfacing necessary to restore joint congruity. HDPP has gained wide acceptance for use in craniofacial and skeletal reconstruction and augmentation. An avian non-weight-bearing joint model was designed to study the role of the HDPP implant in small joint reconstruction. An osteochondral defect was created with a 5-mm circular punch in the humeral articular surface of both glenohumeral joints of 32 adult White Leghorn chickens. In each animal, one defect was press-fitted with a correspondingly sized HDPP implant (HDPP implant group); the contralateral defect was filled with the original osteochondral plug (isograft group) or left unrepaired (control group). At 2 weeks, and 1, 3, and 6 months,joints from each group were harvested and evaluated. Over the 6-month study period, joints in the control group demonstrated healing with dense collagenous scar tissue leaving residual defects at the articular surfaces and significant degenerative disease of the glenohumeral joints radiographically. Joints in the isograft group demonstrated near-complete resorption with some preservation of the cartilaginous cap but overall depression of the articular surface and significant degenerative joint disease. Joints in the HDPP implant group demonstrated stable fixation by highly mineralized bony trabecular ingrowth, preservation of the articular contour of the humeral head, and no evidence of significant degenerative joint disease. These findings indicate a potential role for this high-density porous polyethylene implant in the reconstruction of small joint articular and osseous defects.     

Axial pattern composite prefabrication of high-density porous polyethylene: experimental and clinical research

Currently, various alloplastic materials are being used for reconstruction of three-dimensional structures, and high-density porous polyethylene is so far the best and the most commonly used material. Various indications for high-density porous polyethylene have been defined for closure of craniofacial defects, correction of congenital anomalies, and aesthetic augmentations. A common property of various studies published so far is that after being fixed to the bone or underlying structures, high-density porous polyethylene has been covered primarily or by skin flaps. For reconstruction of complex three-dimensional structures such as the ear and nose, the success of current methods is limited by the thinness and pliability of the skin flap. In this study, the authors' aim was to investigate the graftability of high-density porous polyethylene after prefabrication with an axial pedicle and to explore possible clinical applications in light of the new data obtained. In the experimental study, three-dimensional implants (rectangular prism) carved from high-density porous polyethylene were prefabricated using bilateral superficial epigastric arteries and veins of 25 New Zealand rabbits. After a waiting period of 2 to 6 weeks in five groups, control samples were obtained and the prefabricated implants that had been left in place were directly grafted. The results showed that high-density porous polyethylene was vascularized 75 percent after 4 weeks and 90 percent after 5 weeks, and 95 percent of the grafts had survived after 8 weeks. In the clinical study, three nose defects, three ear defects, and one hard palate defect in seven patients ranging in age from 21 to 72 years were reconstructed using the same method. High-density porous polyethylene has been prefabricated and directly grafted for the very first time on a clinical basis. No serious complications have been observed, except for minimal graft loss in two patients. It is obvious that full-thickness skin grafts that are thinner than flaps will adapt better to the fine details of high-density porous polyethylene and will highly increase the detail obtained in the reconstruction of three-dimensional defects.     

Facial skeletal reconstruction using porous polyethylene implants

A retrospective review of clinical outcomes was performed to determine the clinical utility and morbidity associated with the use of porous polyethylene facial implants. Three hundred seventy implants were placed in 162 consecutive patients, in 178 operations performed in 11 years. The number of patients, the number of implants used, and the average follow-up period were categorized according to the cause of the deformity. The resultant distribution was as follows: acquired (tumor-related), 17 patients, 39 implants, and 30 months; congenital, eight patients, 31 implants, and 92 months; aesthetic, 39 patients, 97 implants, and 24 months; secondary posttraumatic, 48 patients, 139 implants, and 37 months; and acute trauma (internal orbit reconstruction), 50 patients, 64 implants, and 9 months. The distribution of implants according to location was as follows: frontal, 21; temporal, 30; internal orbit, 145; infraorbital rim, 28; malar, 58; paranasal, 29; nasal, 13; mandible, 24; and chin, 22. The combined average follow-up period per patient was 27 months (range, immediate postoperative period to 11 years). All implants were placed in the subperiosteal plane, and the majority were fixed with titanium screws. Antibiotics were administered perioperatively. No implants were extruded or migrated, formed clinically apparent capsules, or caused symptoms attributable to bioincompatibility. The overall reoperation rate was 10 percent (n = 16), which included operations to remove implants because of acute infections (2 percent, n = 3) or a late infection (1 percent, n = 1), to remove implants causing displeasing contours (2 percent, n = 3), and to improve contours (6 percent, n = 9). Porous polyethylene implants have biomaterial properties favorable for facial skeletal augmentation. Screw application of the implants to the skeleton allows precise predictable contouring, thus limiting the need for revisional surgical procedures.     

Preparation of chitosan derivative with polyethylene glycol side chains for porous structure without specific processing technique

The graft copolymer, chitosan-g-polyethylene glycol (PEG), was prepared through graft polymerization of PEG chains to chitosan due to the esterification reaction between PEG and 6-O-succinate-N-phthaloyl-chitosan (PHCSSA). The graft copolymer with porous structure was observed from scanning electron micrographs. It is a potential method to combine chitosan with the hydrophilic synthetic polymers. The graft reaction was carried out in homogeneous system and yielded copolymers with high grafting content. FTIR, NMR, XRD, DSC, spectrofluorophotometer and SEM were detected to characterize the copolymer.     

Nasal augmentation with Surgicel-wrapped diced cartilage: a review of 67 consecutive cases

Cartilage grafting has been used extensively to correct both the functional and aesthetic aspects of the nasal framework. The technique described by Erol ( 105: 2229, 2000) uses Surgicel-wrapped diced cartilage grafts in rhinoplasties. The advantages include its ease of preparation, the large volume of graft substrate available for use, and the avoidance of contour irregularities in the areas of placement. A retrospective case review of 67 consecutive patients who were treated with a Surgicel-wrapped diced cartilage graft as part of an aesthetic and/or functional rhinoplasty, in a 5-year period between 1995 and 2000, was performed in this study. All cases of congenital nasal deformities or deformities caused by trauma or tumors in which the technique was used were excluded. The charts were reviewed to determine demographic variables, the surgical procedures performed, prior operations, the rhinoplasty approach used, and the graft donor and recipient sites. Preoperative and postoperative photographs were examined, and the results were assessed. Data on the donor and recipient sites, complications, and the necessity for revisionary procedures were tabulated. There were two complications, namely, an infection, which resolved with aspiration and oral antibiotic therapy, and a recurrence of a dorsal depression, which necessitated repeated augmentation within 6 months. The technique of using Surgicel-wrapped diced cartilage proved to be effective for the augmentation of various areas of the nose. The complication and revision rates were acceptable and comparable to those of other techniques. Patient satisfaction with the aesthetic results was rated highly, with no reports of graft extrusion or contour irregularities. This technique is recommended for nasal augmentation and contouring for selected rhinoplasty patients.     

Thyrotropin interaction with high-density lipoproteins

Human high-density lipoproteins (HDL), but not other lipoprotein classes, bind bovine thyrotropin (TSH) with moderately high affinity. Binding of 125I-labeled HDL to TSH has been measured in a solid-phase assay; it is saturable and can be displaced by unlabeled HDL but not by other lipoproteins or bovine serum albumin. The interaction of HDL with TSH has been studied by fluorescence spectroscopy: HDL specifically modifies the fluorescence properties of the biologically active dansyl derivative (DNS, (5-dimethyl-aminonaphtalene-1-sulfonyl) chloride) of TSH (DNS-TSH) causing a 12 nm shift to lower wavelength of the emission maximum, a two-fold increase of the quantum yield and a significant increase of fluorescence polarization. The primary site of TSH binding on the HDL particle is likely to be located on its protein moieties, since other lipoprotein classes, which share similar lipids with HDL, do not bind TSH. 125I-labeled apolipoprotein A-I binds TSH in the solid-phase assay and titration of DNS-TSH with apolipoprotein A-I causes perturbations nearly identical to those observed with intact HDL. One HDL particle has at least 12 binding sites for TSH with an association constant, K = 10(7) M-1 whereas one apolipoprotein A-I molecule binds one or two TSH molecules with an association constant slightly lower than that for HDL (K = 10(6) M-1). The lipid moieties of HDL also appears to be perturbed by the interaction with TSH.     

A chemiluminescence flow immunosensor based on a porous monolithic metacrylate and polyethylene composite disc modified with protein G

A generic, fast, sensitive and new type of flow immunosensor has been developed. The basis is a monolithic porous poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate) polymer disc modified with protein G, placed in a fountain type flow cell compartment, in close proximity to a photomultiplier tube (PMT). Analyte and HRP labelled analyte derivative (tracer) compete for anti-analyte antibody binding sites. The mixture is then injected into the flow immunosensor system where the formed analyte- and tracer-antibody complexes are trapped by the monolithic protein G disc. The amount of bound tracer, inversely related to the concentration of analyte in the sample, is determined in a second step by injection of luminol, p-iodophenol and H2O2, generating enhanced chemiluminescence (CL) with horseradish peroxidase (HRP). A third and final step is need for regeneration of the protein G disc so that a new analysis cycle can take place. The performance of the disc immunosensor system was compared with a one step continuous flow injection immunoassay (FIIA) system, using the same reagents and a protein G column, in terms of assay sensitivity and influence of matrix effects from various water samples (millipore-, tap- and surface water). The detection limit for the analyte atrazine in PBS and surface water (SW) was 0.208 +/- 0.004 microg l(-1) (PBS) and 0.59 +/- 0.120 microg l(-1) (SW) for the FIIA and 0.033 +/- 0.003 microg l(-1) (PBS) and 0.038+/-0.003 microg l(-1) (SW) for the disc immunosensor. Statistical comparison of the two systems shows that the disc immunosensor results were significantly less influenced by the sample matrix, which is explained by the fact that the sample in the FIIA arrives simultaneously with the matrix to the detector, whereas these are separated in time in the disc immunosensor system.     

Motor unit tracking with high-density surface EMG

Following (tracking) individual motor units over time can provide important new insights, both into the relationships among various motor unit (MU) morphological and functional properties and into how these properties are influenced by neuromuscular disorders or interventions. The present study aimed to determine whether high-density surface EMG (HD-sEMG) recordings, which use an array of surface electrodes over a muscle, can increase the yield of MU tracking studies in terms of the number of MUs that can be tracked. For that purpose, four HD-sEMG recording sessions were performed on the thenar muscles of ten healthy subjects. Decomposition of the recorded composite responses yielded a study total of 2849 motor unit action potentials (MUAPs). MUAPs that were found in both of the first two sessions, performed on the same day, were defined as trackable MUAPs. Our results show that 22 (median value; range, 13–34) MUAPs per nerve were trackable, which represented approximately 5% of the total MU population. Of these trackable MUAPs, 16 (11–26) could also be found in one or both of the third and fourth sessions, which were performed between 1 and 13 weeks after the initial studies. Nine (4–18) MUAPs were found in all four sessions. Many of the characteristic MUAP shapes matched well between sessions, even when these sessions were several weeks apart. However, some MUAPs seem very sensitive to changes in arm position or in the muscle’s morphology (e.g., to changes in muscle fiber length due to variable degrees of thumb flexion or extension), particularly those from larger and/or superficial MUs. Standardization is, therefore, essential to detect even small MUAP changes, as may occur with pathology or interventions. If this is accomplished, MU tracking with HD-sEMG may prove to be a powerful tool for a promising type of neurophysiological investigation.