Longer Implantation Time Research Articles

Biocompatibility, Degradation Behavior, and Mechanical Properties of Magnesium Alloy Plates In Vivo

The magnesium alloy was made into orthopedic steel plates to repair tibial fractures of New Zealand white rabbits and to explore the biocompatibility, degradation behavior, and mechanical properties of the magnesium alloy plates in repairing fractures in vivo. Fifty-four rabbits were randomly divided into experimental, control, and sham-operated groups. Tibial fractures in the experimental and the control groups were fixed with magnesium alloy and titanium alloy plates, respectively, and only bone tunnels were established without any implants in the sham-operated group. The concentrations of serum alanine transaminase, creatinine (CREA), creatine kinase (CK), and magnesium ion were measured before and 1 day, 1, 2, 4, 8, and 16 weeks after operation, respectively, to evaluate the biocompatibility of magnesium alloy plates. The corrosion products and components were observed using a scanning electron microscope with an energy-dispersive spectroscopy system, and the corrosion rate was observed by weight loss testing. Then the degradation behavior of magnesium alloy plate was analyzed. Analysis of mechanical properties of magnesium alloy plates was done by four-point bending tests. There were no statistically significant differences in serum alanine transaminase, CREA, or CK at each time point among the three groups ( P > 0.05 ). The degradation behavior of the magnesium alloy plates increased with the longer implantation time. The four-point bending test results indicated that the mechanical properties of magnesium alloy plates decreased gradually during the degradation. The results showed that magnesium alloy plates implanted into rabbit tibias degrade gradually with the implantation time, and the mechanical properties of the magnesium alloy weaken gradually during the degradation. Meanwhile, the magnesium alloy plate had excellent biocompatibility and biosafety in the process of degradation in vivo.

Explant Analysis of Utah Electrode Arrays Implanted in Human Cortex for Brain-Computer-Interfaces.

Brain-computer interfaces are being developed to restore movement for people living with paralysis due to injury or disease. Although the therapeutic potential is great, long-term stability of the interface is critical for widespread clinical implementation. While many factors can affect recording and stimulation performance including electrode material stability and host tissue reaction, these factors have not been investigated in human implants. In this clinical study, we sought to characterize the material integrity and biological tissue encapsulation via explant analysis in an effort to identify factors that influence electrophysiological performance. We examined a total of six Utah arrays explanted from two human participants involved in intracortical BCI studies. Two platinum (Pt) arrays were implanted for 980 days in one participant (P1) and two Pt and two iridium oxide (IrOx) arrays were implanted for 182 days in the second participant (P2). We observed that the recording quality followed a similar trend in all six arrays with an initial increase in peak-to-peak voltage during the first 30–40 days and gradual decline thereafter in P1. Using optical and two-photon microscopy we observed a higher degree of tissue encapsulation on both arrays implanted for longer durations in participant P1. We then used scanning electron microscopy and energy dispersive X-ray spectroscopy to assess material degradation. All measures of material degradation for the Pt arrays were found to be more prominent in the participant with a longer implantation time. Two IrOx arrays were subjected to brief survey stimulations, and one of these arrays showed loss of iridium from most of the stimulated sites. Recording performance appeared to be unaffected by this loss of iridium, suggesting that the adhesion of IrOx coating may have been compromised by the stimulation, but the metal layer did not detach until or after array removal. In summary, both tissue encapsulation and material degradation were more pronounced in the arrays that were implanted for a longer duration. Additionally, these arrays also had lower signal amplitude and impedance. New biomaterial strategies that minimize fibrotic encapsulation and enhance material stability should be developed to achieve high quality recording and stimulation for longer implantation periods.

Implantation Warm Ischemia Time in Kidney Transplant Recipients: Defining Its Limits and Impact on Early Graft Function.

BackgroundProlonged cold ischemia is an established risk factor for poor early graft function (EGF). However, warm ischemia incurring during graft implantation has received little attention regarding its possible detrimental effect on EGF. The aim of our study was to examine the impact of recipient warm ischemia time on EGF.Material/MethodsThe data of 102 consecutive kidney transplants were analyzed to determine the association between duration of graft implantation time (IT) and EGF. Recipient IT groups were (GI) up to 45 min, (GII) 45–60 min, and (GIII) >60 min. EGF was categorized as immediate (IGF), slow (SGF), or delayed graft function (DGF). In recipients with IGF, graft function was further assessed by time needed for reduction in serum creatinine by 50% (SC50) of pre-transplant value, and serum creatinine on day 7 (SCD7).ResultsOf a total of 102 recipients, 55 (55%) were in GI, 33 (32%) were in GII, and 14 (13%) were in GIII. Factors prolonging IT were recipient body mass index (BMI) (p=0.02) and multiple arteries in donor kidneys (p<0.01). No recipients in GI had DGF or SGF, while 2 in GII had DGF, and 5 patients in GIII had poor EGF. SC50 was significantly longer in GIII and GII versus GI (40.8±42.4 and 32.8±20.4 vs. 22.2±17.2 [p=.02, p≤.01]), respectively. Mean SCD7 was also significantly higher in GIII and GII versus GI. The mean last serum creatinine was comparable among all groups.ConclusionsIT of more than 45 min was a risk factor for poor EGF, but achieved statistical significance only when it exceeded 60 min. Longer IT also significantly slowed the fall in SC50, and led to a higher SCD7. However, poor EGF and suboptimal early SC trends had little long-term effect on serum creatinine.

Does Taper Size Have an Effect on Taper Damage in Retrieved Metal-on-Polyethylene Total Hip Devices?

BackgroundTaper design has been identified as a possible contributor to fretting corrosion damage at modular connections in total hip arthroplasty systems, but variations in as-manufactured taper interfaces may confound this analysis. This study characterized taper damage in retrievals with 2 different taper sizes but comparable taper surface finishes and investigated if fretting and corrosion damage is related to taper size in the context of a multivariable analysis for metal-on-polyethylene bearings. MethodsA total of 252 cobalt chromium femoral heads were identified in a collection of retrievals: 77 with taper A and 175 with taper B. Implantation time averaged 5.4 ± 6.0 years (range, 0-26 years). Explants were cleaned and analyzed using a 4-point semiquantitative method. Clinical and device factors related to head taper fretting corrosion damage were assessed using ordinal logistic regression with forward stepwise control. Components were then selected to create 2 balanced cohorts, matched on significant variables from the multivariable analysis. ResultsIncreased head offset (P < .001), longer implantation time (P = .002), heavier patients (P < .001), and more flexible tapers (P < .001) were associated with increased taper fretting and corrosion damage. When damage scores were compared between the balanced groups, no significant differences were found. ConclusionThese results suggest that fretting and corrosion damage is insensitive to differences in taper size. The final model derived explains almost half of the fretting corrosion damage observed and identifies contributing factors that are consistent with other in vitro and retrieval studies.

Estoques de carbono e nitrogênio em solo sob florestas nativas e pastagens no bioma Pantanal

O objetivo deste trabalho foi avaliar o impacto da conversão da floresta nativa em pastagem cultivada, e exposição da pastagem nativa ao sistema de pastejo contínuo, sobre os estoques de C e N no solo, em ecossistemas naturais do Pantanal. Foram avaliados três remanescentes de floresta nativa, três áreas de pastagens de Urochloa decumbens com diferentes idades de formação, e uma pastagem nativa submetida ao sistema de pastejo contínuo e sem pastejo, por 3 e 19 anos. Amostras de solo foram coletadas nas profundidades de 0-10, 10-20 e 20-40 cm, com três repetições. A conversão de florestas em pastagens promoveu redução nos estoques de carbono orgânico e carbono microbiano no solo, principalmente nas pastagens cultivadas há mais tempo. Contudo, não houve alteração nos estoques de nitrogênio total. As perdas nos estoques de carbono ocorreram nas três frações húmicas, mas, proporcionalmente, as maiores perdas ocorreram nas frações ácidos húmicos e fúlvicos. As pastagens cultivadas e nativas, sob pastejo contínuo, não são capazes de acumular mais carbono no solo do que os ecossistemas naturais.

Abstract 6016: Pathology Of Hypersensitivity In Late Drug Eluting Stent Thrombosis

Background: Localized hypersensitivity (HS) has been reported as a pathologic risk factor for late DES thrombosis (DES-LST). The objectives of the study were to examine the pathologic features of HS in DES-LST and correlate with stent characteristics, underlying plaque morphologies and patient risk factors. Materials and methods: From a registry of 153 DES patients, 33 patients with DES-LST were identified. LST was defined as platelet-rich thrombus in a coronary stent implanted &gt; 30 days. Stented arteries were serially sectioned at 2–3 mm intervals and stained with H&amp;E, Movat stain, Luna stain (eosinophils), and UCHL (T-lymphocytes). Localized HS was defined as an inflammatory cell infiltrate composed predominantly of eosinophils and T-lymphocytes limited to the arterial wall surrounding the stent. Patient data, risk factors, stent characteristics, and underlying plaque morphology were compared between two groups: hypersensitivity (HS), and non-hypersensitivity LST (NHS). Results: Of the 33 DES-LST cases with occlusive thrombus, 6 (4 men, 2 women) demonstrated HS histologically (18%). The mean age was 54 years (range 40 – 62 years). All 6 had Cypher stents (mean stent length=24 mm), 4 had &gt;1 stent, 2 with overlapping stents. The mean stent duration was 624 days (range 112 to 990 days). Three patients were on ASA and clopidogrel, 2 ASA only, 1 discontinued ASA/clopidogrel prior to non-cardiac surgery. Patient risk factors included hyperlipidemia (n=6), hypertension (n=5) and smoking (n=4). All demonstrated underlying fibroatheroma with stent struts penetrating necrotic core in 3 and 2 with previous rupture sites. Stent malapposition was present in 5 (83%). Twenty-seven patients demonstrated NHS-LST (Cypher=7, Taxus=20). Mean stent duration was 326 days (range 31–1200 days). Malapposition was identified in 10 (37%). Compared to NHS, the HS LST group was more likely to demonstrate stent malapposition (p=0.04) and longer implant times (p=0.049). Conclusions: DES-LST is related to HS in 18% of cases, is associated with Cypher stents, malapposition and longer implantation time. Localized HS with stent thrombosis is a clinically important problem that may occur late after stenting and warrants further pathologic study.

In vivo biocompatibility of gelatin-based hydrogels and interpenetrating networks

The in vivo host response to two gelatin-based hydrogel systems of varying crosslinking modalities and loaded with the anti-inflammatory agent dexamethasone sodium phosphate was investigated. Either gelatin was chemically crosslinked with glutaraldehyde, or polyethyleneglycol diacrylate was photopolymerized around gelatin to form interpenetrating networks. The subcutaneous cage implant system was utilized to determine differential leukocyte concentrations in the inflammatory exudate surrounding the materials as indices for biocompatibility and drug efficacy in vivo. Most of the crosslinked gelatin-based materials, either via glutaraldehyde fixation or interpenetrating network formation, elicited stronger inflammatory responses than either of the starting materials, gelatin and polyethyleneglycol diacrylate. In general, dexamethasone delayed and intensified the inflammatory response. The loss of material mass did not correlate directly with the degree of cellular inflammatory response, but increased with longer implantation time and decreased with more extensive fixation.

Tensile bond between bone and titanium: a reappraisal of osseointegration.

When Branemark in the 1970s established the term osseointegration, this implied a direct chemical bond between a titanium implant and bone. However, ultrastructural studies seemed not to support this idea, and osseointegration came to be defined as the absence of interfering fibrous tissue. Titanium was therefore described as bioinert rather than bioactive. We now demonstrate mechanically a chemical bond between bone and titanium, using unloaded cp titanium plates, similar to those used in previous studies on prosthetic loosening. Tensile force can be transmitted only by chemical bonds. Bone-bonding was therefore evaluated by a detachment test. The plates were developed so that a flat titanium surface touched traumatized bone and the rest of the detachable part had no contact with surrounding tissue. The titanium plates were either polished and sterilized in an autoclave or treated in 4 M NaOH and then heated to 600 degrees C according to Yan et al. (1996). After 4 weeks, the plates were separated from the bone by a perpendicular traction force. The detaching load of the untreated titanium plates never exceeded 0.03 MPa, whereas with treatment it increased to median 0.8 MPa, with bone remaining attached to parts of the plates after detachment. Our findings confirm that a chemical bond can be obtained within 4 weeks with the described pretreatment. It may occur also without treatment, after a longer implantation time.

Enhanced rate of kindling after prolonged electrode implantation into the amygdala of rats

A comparison was made between the rate of amygdaloid kindling in rats which had been implanted with electrodes either 6–8 days or 28–33 days before the start of a series of kindling stimulations. Using both stainless-steel and platinum/iridium electrodes the rate of kindling was significantly reduced after the longer implantation time. Possible mechanisms by which the presence of an electrode in the amygdala may influence the rate of subsequent kindling, and the implications for studies on kindling, are discussed.