M. Michelle Evancho-Chapman

Drug-eluting stent coatings.

This paper reviews the development of coronary stents from a polymer scientists view point, and presents the first results of an interdisciplinary team assembled for the development of new stent systems. Poly(styrene-b-isobutylene-b-styrene) block copolymer (SIBS), a nanostructured thermoplastic elastomer, is used in clinical practice as the drug-eluting polymeric coating on the Taxus coronary stent (trademark of Boston Scientific Co.). Our group has been developing new architectures comprising of arborescent (dendritic) polyisobutylene cores (D_SIBS), which were shown to be as biocompatible as SIBS. ElectroNanospray (Nanocopoeia Inc.) was used to coat test coupons and coronary stents with selected D(S)IBS polymers loaded with dexamethasone, a model drug. The surface topology varied from smooth to nanosized particulate coating. This paper will demonstrate how drug release profiles were influenced by both the molecular weight of the polyisobutylene core and spraying conditions of the polymer-drug mixture.

A nanostructured carbon-reinforced polyisobutylene-based thermoplastic elastomer

This paper presents the synthesis and characterization of a polyisobutylene (PIB)-based nanostructured carbon-reinforced thermoplastic elastomer. This thermoplastic elastomer is based on a self-assembling block copolymer having a branched PIB core carrying -OH functional groups at each branch point, flanked by blocks of poly(isobutylene-co-para-methylstyrene). The block copolymer has thermolabile physical crosslinks and can be processed as a plastic, yet retains its rubbery properties at room temperature. The carbon-reinforced thermoplastic elastomer had more than twice the tensile strength of the neat polymer, exceeding the strength of medical grade silicone rubber, while remaining significantly softer. The carbon-reinforced thermoplastic elastomer displayed a high T(g) of 126 degrees C, rendering the material steam-sterilizable. The carbon also acted as a free radical trap, increasing the onset temperature of thermal decomposition in the neat polymer from 256.6 degrees C to 327.7 degrees C. The carbon-reinforced thermoplastic elastomer had the lowest water contact angle at 82 degrees and surface nano-topography. After 180 days of implantation into rabbit soft tissues, the carbon-reinforced thermoplastic elastomer had the thinnest tissue capsule around the microdumbbell specimens, with no eosinophiles present. The material also showed excellent integration into bones.

Effects of sterilization on poly(ethylene glycol) hydrogels

The past few decades have witnessed a dramatic increase in the development of polymeric biomaterials. These biomaterials have to undergo a sterilization procedure before implantation. However, many sterilization procedures have been shown to profoundly affect polymer properties. Poly(ethylene glycol) hydrogels have gained increasing importance in the controlled delivery of therapeutics and in tissue engineering. We evaluated the effect of ethylene oxide (EtO), hydrogen peroxide (H(2)O(2)), and gamma sterilization of poly(ethylene glycol) hydrogels on properties relevant to controlled drug delivery and tissue engineering. We observed that the release of cyclosporine (CyA) (an immunosuppressive drug that is effective in combating tissue rejection following organ transplantation) was significantly affected by the type of sterilization. However, that was not the case with rhodamine B, a dye. Hence, the drug release characteristics were observed to be dependent not only on the sterilization procedure but also on the type of agent that needs to be delivered. In addition, differences in the swelling ratios for the sterilized and unsterilized hydrogels were statistically significant for 1:1 crosslinked hydrogels derived from the 8000 MW polymer. Significant differences were also observed for gamma sterilization for 1:1 crosslinked hydrogels derived from the 3350 MW polymer and also the 2:1 crosslinked hydrogels derived from the 8000 MW polymer. Atomic force microscopy (AFM) studies revealed that the roughness parameter for the unsterilized and EtO-sterilized PEG hydrogels remained similar. However, a statistically significant reduction of the roughness parameter was observed for the H(2)O(2) and gamma-sterilized samples. Electron spin resonance (ESR) studies on the unsterilized and the sterilized samples revealed the presence of the peroxy and the triphenyl methyl carbon radical in the samples. The gamma and the H(2)O(2)-sterilized samples were observed to have a much higher concentration of the radical pecies when compared with the EtO and the unsterilized samples.

Immunologic function in the elderly after injury--the neutrophil and innate immunity.

BACKGROUND Aging is associated with a decline in immune function. This may contribute to decreased ability of an elderly patient to mount an appropriate innate inflammatory response when injured. This study examined elderly trauma patients to determine whether there was a difference in neutrophil response to injury when compared with controls. METHODS This prospective, observational, cohort study compared neutrophil function in 24 injured elderly (older than 65 years) patients admitted to our trauma center to control groups of noninjured individuals (11 elderly and 17 young). Blood samples were also taken from the injured elderly group within 48 hours of trauma and subsequently at two periods during their hospital stay. A single blood sample was obtained from the noninjured control groups. Neutrophils were analyzed for CD18 expression, stimulated oxidative burst, apoptosis, and IL-10. Results were compared using one-way analysis of variance (alpha 0.05). This study was approved by the Institutional Review Board. RESULTS Twenty-four injured elderly subjects were enrolled: mean injury severity score 15.3, average age 74.6 years, 92% survival, 100% blunt trauma. CD18 levels in the elderly injured subjects for all three time periods were significantly higher than both control groups. When evaluated between controls, CD18 for the noninjured elderly (NIE) was also significantly higher than the noninjured young (NIY). The neutrophil stimulated oxidative burst in the injured elderly subjects at time periods 1, 2, and 3 was not significantly different from the NIY controls. However, the injured elderly had a significantly higher oxidative burst at time period 3 than the NIE controls. Apoptosis in the injured elderly subjects was significantly lower in all three time periods than the NIY. There was no difference in apoptosis between the injured elderly subjects when compared with the NIE controls. There was no significant difference in IL-10 expression among groups. CONCLUSION Injury results in differences in innate immune function in the elderly when compared with controls. The clinical significance of this is uncertain and warrants further investigation.

In vitro evaluation of anti-oxidant and anti inflammatory properties of Genistein Modified Hemodialysis Membranes

Genistein-modified poly(amide):poly(vinyl pyrrolidone) (PA:PVP/G) hemodialysis membranes have been fabricated by coagulation via solvent (dimethyl sulfoxide, DMSO)/nonsolvent (water) exchange. The antioxidant and anti-inflammatory properties of the unmodified PA:PVP membranes were evaluated in vitro using human blood. It was found that these unmodified PA:PVP membranes were noncytotoxic to peripheral blood mononuclear cells (PBMC) but raised intracellular reactive oxygen species (ROS) levels. Pure genistein (in DMSO solution) was not only nontoxic to PBMC, but also suppressed the ROS levels in a manner dependent on genistein dosage. A similar dose-dependent suppression of ROS was found in genistein-modified PA (i.e., PA/G) membranes. However, the PVP addition had little or no effect in the suppression of ROS levels for the ternary PA:PVP/G system; the membrane ROS suppression was largely controlled by the genistein dosage. The levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin (IL-6) in whole blood were measured by ex vivo stimulation with lipopolysaccharide (LPS). The unmodified PA:PVP membranes drastically increased the level of TNF-α; however, the concentration of IL-1β and IL-6 remained almost the same. The PA/G membranes reduced the concentration of IL-1β and TNF-α even at very low genistein loadings, but it required a higher genistein loading to realize a similar effect in the case of IL-6. Of particular importance is that the genistein-modified blend membranes (PA:PVP/G) showed greater suppression of the concentrations of all three cytokines (TNF-α, IL-1β, and IL-6) in comparison with those of the PA/G membranes, signifying the role of PVP in the enhanced anti-inflammatory properties of these genistein-modified membranes. Ultraviolet-visible (UV-vis) spectroscopy was employed to quantify any genistein leaching during the in vitro testing.

Endoluminal reconstruction of the canine common biliary duct

PURPOSE Extrahepatic biliary duct injuries such as transections, stenoses, and biliary leaks are well-known complications of upper abdominal surgeries. The popularization of laparoscopic cholecystectomies in the early 1990s resulted in an increase in the numbers of these reported injuries. The surgical repair of these injuries may be challenging. In this feasibility study, we were presented with the opportunity to evaluate a novel polytetrafluoroethylene (PTFE) covered stent graft that could be useful in common bile duct reconstructions. The long-term goal of this research is to offer the surgeon a new technique for reconstructing the biliary duct or repairing biliary strictures.John G. Zografakis MD, was the first place winner in the Basic Sciences Resident Competition at the Ohio American College of Surgeons meeting. METHODS Seven dogs were originally enrolled in the study. After general endotracheal anesthesia and open cholecystectomy, the common bile duct was identified in each dog. A guide wire was then passed through the neck of the cystic duct, anterograde into the common bile duct, through the Ampulla of Vater and into the duodenum. A stent graft delivery system was placed over the wire, and the covered stent graft was deployed within the lumen of the common bile duct. Study outcomes included graft patency and assessment of the bio-incorporation of the graft and the effectiveness of the graft to drain the biliary system as determined by liver enzyme tests. RESULTS Three implants were harvested at 1 month, and 2 grafts were harvested each at 3 months and 6 months postoperatively. All of the stent grafts were patent. Liver enzyme tests revealed that all dogs had increased serum levels of alkaline phosphatase, alanine aminotransferase (ALT) serum glutamate pyruvate transaminase (SGPT) and aspartate aminotransferase (AST) serum glutamic oxaloacetic transaminase (SGOT). Four dogs had increased total bilirubin. These increases were all measured in the immediate postoperative period. Peak levels for each measure were reached between 4 and 10 days and then gradually trended toward baselines by 1 month postoperatively. We did not observe meaningful changes in serum albumin or total protein. One dog suffered a tear in the common bile duct due to balloon overinflation. This tear was suture repaired when the graft was implanted. However, bile leakage was found when the graft was harvested at 1 month postoperatively. There appeared to be minimal bio-incorporation of the stent-grafts into the biliary duct wall, and there was no pronounced inflammatory response found in the duct wall or surrounding tissues. CONCLUSIONS We are encouraged by these early results. Additional studies are planned to evaluate a self-expanding PTFE covered stent graft and a percutaneous delivery system.

Feasibility of a novel veno–veno circuit as a central rewarming method in a severely hypothermic canine model

PURPOSE Many victims of accidental hypothermia are successfully resuscitated, but questions remain regarding the optimum rewarming techniques. Most of the invasive warming techniques such as closed thoracic lavage, hemodialysis, peritoneal dialysis, and cardiopulmonary bypass require specialized personnel, equipment, and procedures that are not readily available in all facilities. The objective of this study was to investigate the technical feasibility of utilizing a novel veno-veno rewarming circuit to resuscitate severely hypothermic subjects. If this alternative invasive warming technique is successful, it could be available to treat hypothermic patients in virtually any emergency department setting. METHODS The rewarming system consisted of a Baxter ThermaCyl warmer (Baxter Co., McGaw Park, IL), a roller pump, hemodialysis tubing, connectors, and 2 venous catheters. Blood was pumped from the body via the femoral vein, through the roller pump, into the warmer, and then returned to the body via the right jugular vein. Seven adult mongrel hounds of similar weights (20 to 25 kg) were anesthetized and instrumented for data collection. Temperature probes were placed in the rectum, the peritoneal cavity, and the esophagus to record core temperatures. Each animal was cooled by ice packing to a central core temperature of 29 degrees C and then rewarmed using the described veno-veno circuit. Vital signs, pulse oximetry, cardiac rhythm, and laboratory values were obtained prior to cooling the animals, and were repeated for every degree Celsius change once warming began. Christopher Haughn, MD, was the second place winner in the Basic Sciences Resident Competition at the Ohio American College of Surgeons meeting. RESULTS Because of technical difficulties, data from 1 dog were not included in the results. Of the remaining 6 dogs, all were rewarmed from 29 degrees C to 37 degrees C. Adverse side effects included gross hematuria, acidemia (median pH decrease was 0.088), and decreases in haptoglobin (median decrease 13.5 g/dl), hemoglobin (median decrease 1.35 g/dl), and arterial pO(2) level (median decrease 167 mm Hg). Decreases in blood pressure and heart rate were also noted during the cooling process, but reversed upon rewarming. CONCLUSIONS From this pilot study, we conclude that our novel veno-veno circuit rewarming is a feasible method of rewarming hypothermic subjects and warrants further investigation and comparison with other active warming methods.

Current challenges in dedifferentiated fat cells research

ABSTRACT Dedifferentiated fat cells show great promises as a novel cell source for stem cell research. It has many advantages when used for cell–based therapeutics including abundance, pluripotency, and safety. However, there are many obstacles researchers need to overcome to make the next big move in DFAT cells research. In this review, we summarize the current main challenges in DFAT cells research including cell culture purity, phenotypic properties, and dedifferentiation mechanisms. The common methods to produce DFAT cells as well as the cell purity issue during DFAT cell production have been introduced. Current approaches to improve DFAT cell purity have been discussed. The phenotypic profile of DFAT cells have been listed and compared with other stem cells. Further studies on elucidating the underlying dedifferentiation mechanisms will dramatically advance DFAT cell research.

Fluorinated methacrylamide chitosan hydrogel dressings enhance healing in an acute porcine wound model

Wound healing involves multiple interrelated processes required to lead to successful healing outcomes. Phagocytosis, inflammation, cell proliferation, angiogenesis, energy production, and collagen synthesis are all directly or indirectly dependent on oxygen. Along with other critical factors, such as nutrition and comorbidities, availability of oxygen is a key determinant of healing success. Previously, we have presented a novel oxygenated hydrogel material that can be made into dressings for continuous localized oxygen delivery to wounds. In this study, an acute porcine wound model was used to test the healing benefits of these oxygenated MACF (MACF + O2) hydrogel dressings compared to controls, which included commercial Derma-GelTM hydrogel dressings. Wound closure and histological analyses were performed to assess re-epithelialization, collagen synthesis, angiogenesis, and keratinocyte maturation. Results from these assays revealed that wounds treated with MACF + O2 hydrogel dressings closed faster as compared to Derma-Gel (p<0.05). Targeted metabolomics via liquid chromatography separation and mass spectrometric detection (LC-MS/MS) and a biochemical assay determined the concentration of hydroxyproline in wound samples at days 14 and 21, showing that MACF + O2 hydrogel dressings improved wound healing via an upregulated collagen synthesis pathway as compared to Derma-Gel (p<0.05). Histological evidence showed that MACF + O2 hydrogel dressings improve new blood vessel formation and keratinocyte maturation over all other treatments.