3D Printing of MgAl2O4 Spinel Mesh and Densification Through Pressure-Less Sintering and Hot Isostatic Pressing

MgAl2O4 spinel mesh with micro-features of 410 and 250 μm unit cell length and rib thickness, respectively, was three-dimensional (3D) printed and sintered followed by Hot Isostatic Pressing (HIPing). A stable colloidal dispersion of spinel in polymer-water solution was prepared and 3D-printed using a 30-gauge needle (∼100 μm inner diameter) on a regenHU 3D-Discovery bioprinter. Samples were characterized for their density and microstructure. Samples with near theoretical density after HIPing was subjected to mechanical property evaluation such as hardness by Vickers indentation and elastic modulus using nanoindentation technique. Microstructure of sintered samples across the ribs have shown graded grain structure with finer grains near the edges (0.7 μm average) with occasional porosity and coarser grains toward the center of the rib (5.2 μm average). HIPing resulted in substantial grain growth and the average grain size was found to be 10.9 μm (with a variation in the grain size of 2.2 μm along the edges and 13.1 μm at the center of the rib) exhibiting close packed and dense microstructure. Finer grains toward the edges may probably be due to the flow behavior during printing process and lower distribution of the powder loading along the edges resulting in low green density. This relatively higher porosity pining the grain growth under the extremely low heating rate employed for the controlled shrinkage to maintain the integrity of the sample. 3D printed samples after HIPing exhibited a density of 3.57 g/cc and hardness of 12.95 GPa, which are at par with the samples processed through conventional ceramic processing techniques. Nanoindentation studies employing maximum load of 45 mN with depth have shown an elastic modulus of 238 ± 15 GPa. MgAl2O4 spinel mesh 3D printed in this study is a potential prospective candidate that can be explored for cranioplasty procedures and other biomedical applications.

Changes in the practice of angioaccess surgery: impact of dialysis outcome and quality initiative recommendations

PURPOSE

Recommendations recently published by the National Kidney Foundation-Dialysis Outcome and Quality Initiative (DOQI) included an appeal for increased use of native arteriovenous fistulas (NAVFs) to improve overall patency and contain angioaccess costs. We evaluated the impact of the DOQI recommendations on angioaccess surgery and its outcome at our institution.

METHODS

From June 1996 to April 1999, 483 angioaccess procedures were performed on 247 patients. There were 133 men and 114 women, with an average age ranging from 28 to 95 years (mean age, 69 +/- 0.59 years). Risk factors included smoking in 143 patients (58%), diabetes mellitus in 135 patients (55%), hypertension in 150 patients (61%), and coronary artery disease in 98 patients (40%). The patients were divided in two groups. Group I (pre-DOQI) included patients who had angioaccess procedures between June 1996 and November 1997, and group II (post-DOQI) included patients who had angioaccess procedures between December 1997 and April 1999. The types of procedures performed included placement of arteriovenous grafts (AVGs) in 122 patients (25%), creation of NAVFs in 99 patients (20%), revision of AVGs in 123 patients (25%), and temporary access procedures in 135 patients (28%). Forty-seven of the NAVF procedures were radial-cephalic fistulas (47%), 22 were brachial-cephalic fistulas (23%), and 30 were brachial-basilic fistulas (30%). Patients underwent serial ultrasonography scanning and physical examinations; the mean follow-up period was 9 months. Choice of angioaccess procedures and patency rates before and after implementation of the DOQI recommendations were compared.

RESULTS

There was a significant increase in the use of NAVFs after implementing DOQI recommendations (5% vs 68%, P <.001). The 1-year primary patency rate of AVGs was less than that of arteriovenous fistulas (54% vs 85%, P <.001). During the study period, the percentage of AVGs placed at our institution that required revision (59%; 72 of 123) was higher than that of NAVFs that required revision (4%; 4 of 99; P <.001). There was no significant difference in the maturation rates of radial-cephalic fistulas (75%), brachial-cephalic fistulas (91%), and brachial-basilic fistulas (87%).

CONCLUSION

By adopting the DOQI recommendations, we used NAVFs more often. This resulted in superior patency rates, compared with synthetic grafts. The liberal use of preoperative duplex venous mapping further increased NAVF use, surpassing the DOQI expectations for primary arteriovenous fistulas. Additionally, fewer revisions were required.

P53 gene transfer to the injured rat carotid artery promotes apoptosis

BACKGROUND

In a previous study we have demonstrated significant reduction of intimal hyperplasia after adenovirus-mediated gene transfer of p53 protein to the injured rat carotid artery. The purpose of this study was to elucidate whether apoptosis is one of the mechanisms responsible for this reduction. Apoptosis, a physiologic cell death process that stabilizes cell numbers in tissues, can be independently induced by p53.

METHODS

In vivo gene transfer was used in isolated segments of balloon-injured rat carotid arteries. Genetically modified adenovirus encoding for wild-type p53 protein (AdWTp53) was applied at 8 x 10(10) plaque-forming units/mL. Control rats received either adenovirus null at the same concentration or balloon injury alone. Arteries were harvested at 24 and 48 hours after the procedure. Apoptosis was detected in tissue sections by in situ terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay. Specimens were graded either negative or positive less than 10%, 10% to 20%, 20% to 30%, or greater than 30% according to the number of apoptotic cells in the medial or intimal layer per high power field. Specimens were also subjected to DNA agarose gel electrophoresis and transmission electron microscopy.

RESULTS

With the TUNEL assay no apoptosis was visualized at 24 and 48 hours in the controls (n = 5 in each group), whereas in the AdWTp53 groups (n = 5 in each) all specimens presented apoptosis (P < .05, AdWTp53 vs controls). The average grade of apoptotic cells detected in the medial layer in the AdWTp53 groups was less than 10% to 20% at 24 hours and 20% to 30% at 48 hours. The DNA agarose gel electrophoresis failed to detect a DNA laddering pattern, characteristic of apoptosis. Electron microscopy revealed morphologic changes typical of apoptosis in the treated group, whereas specimens from control group did not reveal any apoptotic features.

CONCLUSIONS

At 48 hours after balloon injury alone, no apoptosis was observed in the vessel wall. However, when p53 gene was transferred, apoptosis was visualized in all specimens with greater intensity at 48 hours after injury. Promotion of apoptosis may play a key role in the mechanism by which p53 gene decreases intimal hyperplasia.

Clinical experience with superior vena caval Greenfield filters

PURPOSE

To evaluate the results of superior vena caval (SVC) Greenfield filters in patients at risk for pulmonary embolism (PE) secondary to upper extremity deep venous thrombosis (UEDVT).

METHODS

Over a 46-month period, 26 patients (10 men, mean age 67 years, range 25 to 89) with UEDVT in whom anticoagulation was contraindicated (n = 22) or ineffective in preventing recurrent PE or extension of the thrombus (n = 4) were treated with placement of SVC Greenfield filters.

RESULTS

One SVC filter was misplaced into the innominate vein but left in place; this vein remains patent after 2 months without evidence of filter migration. Follow-up ranged from 10 days to 46 months (mean 7.8 months). Fifteen (58%) patients died inhospital of causes unrelated to the SVC filter or recurrent thromboembolism (mean time to death 36 days). Of the 11 survivors, follow-up ranged from 1 to 38 months (mean 22). Sequential chest roentgenograms in 9 (82%) patients revealed no filter migration or displacement. No evidence of PE was found in any of the survivors over the course of follow-up.

CONCLUSIONS

Insertion of SVC Greenfield filters is a safe and feasible therapy to prevent recurrent thromboembolism in patients with UEDVT who are refractory to or inappropriate for anticoagulation therapy.

The use of duplex ultrasound arterial mapping as an alternative to conventional arteriography for primary and secondary infrapopliteal bypasses

BACKGROUND

For more than 1 decade, duplex ultrasonography has been investigated as a potential replacement for invasive contrast arteriography (CA) prior to lower extremity revascularization. While some authors advocate the reliability of this methodology for infrainguinal imaging, revascularizations based on duplex ultrasonography alone are seldom reported. Our initial experience with duplex ultrasound arterial mapping (DUAM) for primary and secondary infrapopliteal bypasses performed without preoperative CA is reported in this series.

METHODS

Twenty-eight infrapopliteal bypasses based on DUAM alone (26) and combined DUAM and CA (2) were performed. Indications for surgery were tissue loss in 22 cases and rest pain in 6. Eight patients (29%) had at least 1 previous ipsilateral revascularization. A schematic anatomical drawing based on DUAM helped the selection of optimal inflow and outflow bypass sites. Bypasses originated from the femoral arteries in 17 cases, external iliac in 3, and popliteal in 4, and from a previous graft in 4. The distal anastomosis was to the dorsalis pedis in 12 cases, posterior tibial in 7, anterior tibial in 6, and peroneal in 3.

RESULTS

DUAM revealed unobstructed inflow in 24 cases, significant iliac stenosis in 1, and in 3 cases imaging was not possible owing to obesity. A pressure gradient of 15 mm Hg between donor and radial artery confirmed the stenosis diagnosed by DUAM, and was successfully treated with balloon angioplasty and stent placement. A single infrapopliteal runoff artery was identified by DUAM in 22 cases, 2 in 4 cases, and 3 in 2 cases. Preoperative CA was performed in 2 instances because of severe arterial calcification. Completion arteriography matched the run-off status predicted by DUAM in 25 out of 26 cases (96%). DUAM missed a significant anterior tibial artery stenosis that required a distal graft extension. One-, 3-, and 6-month patency rates were 96%, 85%, and 62%, respectively. Limb salvage rate was 86%.

CONCLUSIONS

This early experience shows that DUAM may be a safe alternative to invasive conventional arteriography for the majority of patients (89%) presenting with critical ischemia and in need of infrapopliteal bypasses.

Values and limitations of duplex ultrasonography as the sole imaging method of preoperative evaluation for popliteal and infrapopliteal bypasses

The purpose of this study was to evaluate whether duplex ultrasound arterial mapping (DAM) can reliably replace standard arteriography (SA) in the preoperative assessment of candidates for popliteal and infrapopliteal bypasses. This is the report of a two-phase study undertaken at our institution from July 1997 to May 1998. Carefully performed DAM averted the need for preoperative SA (51 of 58 procedures). The results of this study can be used as an impetus to initiate larger, multicenter protocols to further evaluate this newer noninvasive approach for patients presenting with severe lower-limb ischemia.

Hemodynamic instability following carotid endarterectomy does not affect early discharge

Over the last few years, there has been increased emphasis on early discharge of patients following carotid endarterectomy in the United States. Recent studies have shown that short-stay hospitalization for carotid endarterectomy may be safe and cost-effective. However, this is not always possible because of reasons that are not clearly delineated. In order to optimize the early discharge of patients following carotid endarterectomy, an analysis of the causes of delayed discharges was performed in the present series. Since hemodynamic instability has been shown to be the most frequent complication following carotid endarterectomy, the authors investigated whether it was an important factor preventing early postoperative discharge. This study reviewed the data of 100 consecutive patients admitted for elective carotid endarterectomy. The incidence of post-carotid endarterectomy hemodynamic instability was 37% (n = 37), with hypertension occurring in 25 patients (68%) and hypotension occurring in 12 patients (32%). Hemodynamic instability tended to occur with the use of general anesthesia as compared with regional anesthesia. Hemodynamic instability did not correlate with pre-existent history of hypertension, nor with the type of drug used when general anesthesia was applied. All the patients were successfully treated either in the recovery room or in a monitored area. The average total length of stay was 1.65 days with 79% of the patients being discharged on the first postoperative day and 21% having delayed discharge ranging from 2 to 15 days (mean 4 days). The main reasons for delayed discharges were cardiac and urinary tract complications. Blood pressure instability accounted for only 2% of cases. Thus, these data show that hemodynamic instability does not significantly affect early discharge.