Mechanoresponsive materials for drug delivery: Harnessing forces for controlled release

Mechanically-activated delivery systems harness existing physiological and/or externally-applied forces to provide spatiotemporal control over the release of active agents. Current strategies to deliver therapeutic proteins and drugs use three types of mechanical stimuli: compression, tension, and shear. Based on the intended application, each stimulus requires specific material selection, in terms of substrate composition and size (e.g., macrostructured materials and nanomaterials), for optimal in vitro and in vivo performance. For example, compressive systems typically utilize hydrogels or elastomeric substrates that respond to and withstand cyclic compressive loading, whereas, tension-responsive systems use composites to compartmentalize payloads. Finally, shear-activated systems are based on nanoassemblies or microaggregates that respond to physiological or externally-applied shear stresses. In order to provide a comprehensive assessment of current research on mechanoresponsive drug delivery, the mechanical stimuli intrinsically present in the human body are first discussed, along with the mechanical forces typically applied during medical device interventions, followed by in-depth descriptions of compression, tension, and shear-mediated drug delivery devices. We conclude by summarizing the progress of current research aimed at integrating mechanoresponsive elements within these devices, identifying additional clinical opportunities for mechanically-activated systems, and discussing future prospects.

Self-assembled nanofiber hydrogels for mechanoresponsive therapeutic anti-TNFα antibody delivery

Low molecular weight hydrogels, prepared from glycosyl-nucleoside-lipid amphiphiles, exhibit shear-thinning behaviour and reversible thermally- and mechanically-triggered sol-gel transitions. Using mechanical shear stimulation, the release of entrapped anti-TNFα increases and the released anti-TNFα demonstrates efficacy in in vitro neutralization bioassays. Delivery of anti-TNFα is of general interest and broad medicinal utility for treating autoimmune diseases such as rheumatoid arthritis.

Self-assembly of a 5-fluorouracil-dipeptide hydrogel

The self-assembly of 5-fluorouracil dilysine conjugates into self-supporting hydrogels, comprised of entangled nanofibers or rigid nanotubes with diameters of 10 and 16 nm, respectively, is reported. The rate of release of 5-Fu from the conjugates was highly dependent on concentration in solution, whereas, release from the fully formed hydrogels was significantly slower. The 5-Fu conjugate also exhibited promising in vitro cytotoxicity against human tumor cell lines A549, H460 and H23.

Stretch-Induced Drug Delivery from Superhydrophobic Polymer Composites: Use of Crack Propagation Failure Modes for Controlling Release Rates

The concept of using crack propagation in polymeric materials to control drug release and its first demonstration are reported. The composite drug delivery system consists of highly-textured superhydrophobic electrosprayed microparticle coatings, composed of biodegradable and biocompatible polymers poly(caprolactone) and poly(glycerol monostearate carbonate-co-caprolactone), and a cellulose/polyester core. The release of entrapped agents is controlled by the magnitude of applied strain, resulting in a graded response from water infiltration through the propagating patterned cracks in the coating. Strain-dependent delivery of the anticancer agents cisplatin and 7-ethyl-10-hydroxycamptothecin to esophageal cancer cells (OE33) in vitro is observed. Finally the device is integrated with an esophageal stent to demonstrate delivery of fluorescein diacetate, using applied tension, to an ex vivo esophagus.

Prevention of lung cancer recurrence using cisplatin-loaded superhydrophobic nanofiber meshes

For early stage lung cancer patients, local cancer recurrence after surgical resection is a significant concern and stems from microscopic disease left behind after surgery. Here we apply a local drug delivery strategy to combat local lung cancer recurrence after resection using non-woven, biodegradable nanofiber meshes loaded with cisplatin. The meshes are fabricated using a scalable electrospinning process from two biocompatible polymers--polycaprolactone and poly(glycerol monostearate-co-caprolactone)--to afford favorable mechanical properties for use in a dynamic tissue such as the lung. Owing to their rough nanostructure and hydrophobic polymer composition, these meshes exhibit superhydrophobicity, and it is this non-wetting nature that sustains the release of cisplatin in a linear fashion over ∼90 days, with anti-cancer efficacy demonstrated using an in vitro Lewis Lung carcinoma (LLC) cell assay. The in vivo evaluation of cisplatin-loaded superhydrophobic meshes in the prevention of local cancer recurrence in a murine model of LLC surgical resection demonstrated a statistically significant increase (p = 0.0006) in median recurrence-free survival to >23 days, compared to standard intraperitoneal cisplatin therapy of equivalent dose. These results emphasize the importance of supplementing cytoreductive surgery with local drug delivery strategies to improve prognosis for lung cancer patients undergoing tumor resection.

Photo-crosslinking of a self-assembled coumarin-dipeptide hydrogel

The photo-crosslinking of a coumarin-functionalized dipeptide hydrogel enhances the stability of the self-assembled nanofibers that comprise the hydrogel.

The self-assembly of anticancer camptothecin-dipeptide nanotubes: a minimalistic and high drug loading approach to increased efficacy

20-(S)-Camptothecin (CPT)-conjugated dipeptides are reported that preassemble into nanotubes with diameters ranging from 80-120 nm. These nanoassemblies maintain a high (∼47 %) drug loading and exhibit greater drug stability (i.e., resistance to lactone hydrolysis), and consequently greater efficacy against several human cancer cells (HT-29, A549, H460, and H23) in vitro compared with the clinically used prodrug irinotecan. A key and defining feature of this system is the use of the CPT-conjugated dipeptide as both the drug and precursor to the nanostructured carrier, which simplifies the overall fabrication process.

Evidence of active nerve cell degeneration in the substantia nigra of humans years after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine exposure

This report provides the first detailed neuropathological study of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in humans. All 3 subjects self-administered the drug under the impression it was "synthetic heroin" and subsequently developed severe and unremitting parkinsonism, which was L-dopa responsive, at least in the earlier stages of illness. Survival times ranged from 3 to 16 years. Neuropathological examination revealed moderate to severe depletion of pigmented nerve cells in the substantia nigra in each case. Lewy bodies were not present. In Patients 1 and 2, there was gliosis and clustering of microglia around nerve cells. Patient 3 had a similar picture and also showed large amounts of extraneuronal melanin. These findings are indicative of active, ongoing nerve cell loss, suggesting that a time-limited insult to the nigrostriatal system can set in motion a self-perpetuating process of neurodegeneration. Although the mechanism by which this occurs is far from clear, the precedent set by the cases could have broad implications for human neurodegenerative disease.

Fatal hypernatremic dehydration in exclusively breast-fed newborn infants due to maternal lactation failure

Infants who die of hypernatremic dehydration usually demonstrate at autopsy an underlying condition or disease process that predisposes to increased water loss. In the absence of such findings, forensic concerns may focus sharply on parental or caretaker neglect as an underlying cause of death. In this case report, we describe unrecognized fatal hypernatremic dehydration in two exclusively breast-fed neonates due solely to failure of maternal lactation. We further describe epidemiologic and etiologic features of such deaths and discuss forensic difficulties encountered in their certification.

Quinolones for the treatment and prophylaxis of tuberculosis

Quinolones possess enormous potential as antimycobacterial agents, and have been proven to have excellent in vitro activity against M. tuberculosis, as well as limited in vivo efficacy. These drugs appear to be safe and well tolerated even when taken for an extended period. This is important considering that one of the most significant factors contributing to resistance is compliance. Quinolones exhibit great promise for initial treatment and retreatment of MDRTB, a rapidly growing problem, as well as for prevention. They have shown to be as effective as some of the first-line agents currently used in treating TB. There appears to be overwhelming need to further study these agents and determine their role in the treatment of TB. In the future, quinolones may emerge as first-line therapy for TB.

"Hyperacute" subdural hematoma: CT mimic of recurrent episodes of bleeding in the setting of child abuse

Mixed density extraaxial hematomae on computed tomography (CT) scanning generally represent recurrent episodes of bleeding (chronic subdural hematoma with rebleeding). Hyperacute hemorrhages in which the patient is actively bleeding or has a coagulopathy have also been described as mixed density. We report a case of child abuse in a fourteen month old child who presented with a CT scan showing a mixed density subdural hematoma which was originally interpreted as recurrent episodes of hemorrhage, but who had evidence of only acute, active bleeding at surgery and by histologic examination. There is a proportionally high incidence of subdural hematoma in cases of child abuse, due in part to the increased susceptibility of the immature brain to trauma. Because the mechanism of injury is different for hemorrhage due to hyperacute subdural hematoma (SDH) and that of acute bleeding within a chronic SDH, the distinction between these entities has potentially important legal implications in cases of suspected child abuse. This potential pitfall in interpretation of the CT scan has not to our knowledge been reported in the forensic literature.

Blunt impact to the chest leading to sudden death from cardiac arrest during sports activities

BACKGROUND

Sudden death from cardiac arrest in a young person may occur during sports play after a blunt blow to the chest in the absence of structural cardiovascular disease or traumatic injury (cardiac concussion or commotio cordis). We studied the clinical features of this apparently uncommon but important phenomenon.

METHODS

We identified cases from the registries of relevant agencies and organizations, as well as newsmedia accounts, and developed a clinical profile of 25 children and young adults, 3 to 19 years of age.

RESULTS

Each victim collapsed with cardiac arrest immediately after an unexpected blow to the chest, which was usually inflicted by a projectile (such as a baseball or hockey puck). Incidents took place during organized competitive sports in 16 cases and in recreational settings at home, at school, or on the playground in 9. In each instance, the impact to the chest was not judged to be extraordinary for the sport involved and did not appear to have sufficient force to cause death. Twelve victims collapsed virtually instantaneously on impact, whereas 13 remained conscious and physically active for a brief time before cardiac arrest. Cardiopulmonary resuscitation was administered within about three minutes to 19 victims, but normal cardiac rhythm could be restored in only 2 (both incurred irreversible brain damage and died shortly thereafter). Seven victims (28 percent) were wearing some form of protective chest padding.

CONCLUSIONS

We speculate that most sudden deaths related to impact to the chest (not associated with traumatic injury) are due to ventricular dysrhythmia induced by an abrupt, blunt precordial blow, presumably delivered at an electrically vulnerable phase of ventricular excitability. This profile of blunt chest impact leading to cardiac arrest adds to our understanding of the range of causes of sudden death on the athletic field and may help in the development of preventive measures.

Patterns of facial resuscitation injury in infancy

Cardiopulmonary resuscitation (CPR)-related artifacts in pediatric rescue that have the potential for serious complications in surviving patients have been well described in the medical literature. Medically trivial soft-tissue injuries, especially of the face and neck, carry predominantly forensic significance and have received less attention. We describe such injuries in nine of 25 consecutive cases of infants who received CPR, and correlate those injuries with specific rescue maneuvers. Techniques for effective investigation and interpretation of such injuries are suggested.

Delayed fatal hemothorax due to traumatic carotid dissection: a case report of a previously unreported cause of death

A unique case of delayed fatal hemothorax in a 12-year-old girl resulting from atypical dissection of a traumatic carotid aneurysm is reported, due to occult neck trauma received in a sledding accident which occurred one week prior to death. Aspects of traumatic carotid dissection and forensic implications of delayed presentation of such findings in the setting of occult trauma are discussed.

Commotio cordis in two amateur ice hockey players despite the use of commercial chest protectors: case reports

We describe two recent deaths in 15-year-old male ice hockey players. Both adolescents died of commotio cordis from chest impacts by ice hockey pucks despite their use of commercially designed and manufactured chest protectors. Commotio cordis is discussed as a preventable sports-related injury in the adolescent age group, and the need for improved chest protective equipment in preventing such injuries is also examined.

An unusual entrance wound associated with rimfire rifles

In many cases of self-inflicted contact wounds of the head with rimfire rifles, we have noted that the entrance wound appears unusual: in 50% of cases studied, a pencil-like extension or zone of blackened and seared skin extends downward from the entrance. The most probable cause for the appearance of this wound is a momentary break in contact between the muzzle and skin as the victim reaches for the trigger with resultant escape of a jet of hot sooty gas. Whereas not unique for rimfire rifles, such a wound from a handgun is uncommon.

Clinical considerations for the use of intravenous nicardipine in the treatment of postoperative hypertension

The incidence of postoperative hypertension after both cardiac and noncardiac surgery is a major concern. alpha-Adrenergic-blocking drugs, such as phentolamine, and direct-acting vasodilators, such as nitroglycerin and nitroprusside, are commonly used to treat hypertension. Nifedipine, a calcium channel blocker, may also be used, but because no intravenous preparation is available, its effects are not titratable. A new short-acting calcium channel blocker, nicardipine, is a potent vasodilator and produces more selective responses in the coronary versus the systemic vascular circulation. It is an effective cerebral vasodilator, increasing cerebral blood flow and oxygen delivery. Nicardipine can be administered as an intravenous loading infusion of 10 to 15 mg/hr for 25 minutes, followed by a maintenance infusion of 3 to 5 mg/hr. Nicardipine has a short duration factor, is easily titratable and is as effective as nitroglycerin or nitroprusside in the control of hypertension. In summary, nicardipine has many properties of an ideal drug for the treatment of postoperative hypertension.

Effects of doxacurium chloride on biventricular cardiac function in patients with cardiac disease

The effects of doxacurium chloride, a new long-acting non-depolarizing neuromuscular blocking drug, on cardiac performance were studied in 45 patients undergoing high-dose fentanyl-diazepam-oxygen anaesthesia for cardiac surgery. Data were collected at baseline (10 min after tracheal intubation), and at 2, 5 and 10 min after an i.v. bolus of doxacurium with a rapid-response thermistor pulmonary arterial catheter, using two-dimensional transoesophageal echocardiography, and direct arterial pressure measurement. The patients were allocated to four groups based on the type of surgery and dose of doxacurium (0.05 or 0.08 mg kg-1). No changes in left or right ventricular dimensions or contractility were detected in any group. Although significant changes (P less than 0.05) occurred in several groups, all these changes were clinically insignificant (less than 10% change from baseline values), and were similar to those seen in unstimulated anaesthetized patients. Doxacurium appears to be a safe drug for use in patients undergoing cardiac surgery, and is devoid of significant cardiovascular side effects in the doses tested.

Hemodynamic effects of verapamil during fentanyl-nitrous oxide anesthesia

The hemodynamic effects of a verapamil infusion were investigated in six dogs given fentanyl-nitrous oxide anesthesia. Verapamil, 0.2 mg/kg, was given followed by an infusion of 3, 6, and 9 micrograms/kg per minute, which produced plasma verapamil concentrations ranging from 98 to 204 ng/ml. Verapamil significantly reduced the systemic vascular resistance index and mean arterial pressure. The decrease in afterload led to an increase in cardiac index, since there was little change in myocardial contractility (LV dP/dt). Administration of calcium chloride, 20 mg/kg, did not reverse the hemodynamic effects of verapamil. The data indicate that in dogs verapamil can be given, even in high concentrations, during fentanyl-nitrous oxide anesthesia without serious adverse electrophysiologic or hemodynamic consequences.

Cardiovascular effects of a nifedipine infusion during fentanyl-nitrous oxide anesthesia in dogs

The hemodynamic effects of a nifedipine infusion were investigated in eight dogs given fentanyl/pancuronium/nitrous oxide/oxygen anesthesia. Nifedipine (20 micrograms/kg) was given intravenously over two minutes immediately prior to each 30-minute infusion at 2 micrograms/kg/min, 4 micrograms/kg/min, and 6 micrograms/kg/min. The range of plasma nifedipine levels obtained was 52.1 to 113.7 ng/mL. The predominant hemodynamic effects were significant reductions in systemic vascular resistance (SVR) and mean aortic pressure (MAP), accompanied by a rise in cardiac index and heart rate (HR). Administration of calcium chloride (20 mg/kg) after the nifedipine infusion had no effect on SVR or MAP, but HR was significantly reduced. Serum epinephrine and norepinephrine levels increased after the infusion of nifedipine and suggested that fentanyl did not completely overcome the sympathetic response to the profound vasodilatation. The resulting tachycardia in combination with diastolic hypotension from nifedipine could have a detrimental effect on the myocardial oxygen balance.

Comparative hemodynamic effects of labetalol and hydralazine in the treatment of postoperative hypertension

The antihypertensive efficacy and safety of IV labetalol were evaluated and compared with the efficacy and safety of IV hydralazine in the treatment of postoperative hypertension. Twenty patients undergoing major noncardiac surgery were entered into the study. Patients were randomized and treated for postoperative hypertension with either labetalol (n = 10) or hydralazine (n = 10). Labetalol and hydralazine both produced significant reductions in arterial blood pressure (p less than 0.001) within 10 minutes, which lasted at least 2 hours. In addition, labetalol produced a significant reduction in the heart rate and rate-pressure product without creating any adverse effects. In contrast, hydralazine produced significant sinus tachycardia requiring IV propranolol in three patients, two of whom developed transient ST segment depression. These results indicate that labetalol is safe and effective for the control of postoperative hypertension, especially in those patients who are least able to tolerate tachycardia.

Comparison of propofol and thiamylal for induction and maintenance of anaesthesia for outpatient surgery

In an open, randomized study we have compared the safety and efficacy of propofol with thiamylal for induction and maintenance of anaesthesia supplemented by nitrous oxide in elective termination of pregnancy. Induction of anaesthesia was achieved with either propofol 2.5 mg kg-1 or thiamylal 4.0 mg kg-1 followed by maintenance with 70% nitrous oxide in oxygen and repeat boluses of 25% of the induction dose i.v. as indicated clinically. Both drugs induced and maintained anaesthesia reliably, with some minor differences. Recovery from propofol was significantly more rapid. The patients in the propofol group were alert and orientated early in the postoperative period, with less nausea or vomiting. Propofol has properties that are of particular benefit in anaesthesia for ambulatory surgery.

Open heart surgery in patients in the eighth and ninth decades of life

One hundred fifty-one patients aged 70-89 years underwent a variety of open heart surgical procedures during a period of 1 year. We divided these patients into two groups: Group A was comprised of 127 patients between 70 and 79 years of age. In group B, 24 patients were between 80 and 89 years of age. These patients underwent elective open heart surgery. Information was retrieved retrospectively from the computerized data pool of the cardiothoracic registry in our institution. Statistical analysis in these two groups revealed no significant differences in any of the evaluated factors. We concluded that age should not be a contraindication for cardiac operations.

Response of lower esophageal contractility to changing concentrations of halothane or isoflurane: a multicenter study

A multiple-center study was performed to determine the relationship between lower esophageal contractility, clinical signs, and anesthetic concentration as expressed by minimum alveolar concentration (MAC). One hundred four American Society of Anesthesiologists Class I through III patients were exposed to isoflurane (with and without nitrous oxide) or halothane in concentrations of 0.5, 1.0, and 1.5 MAC. Heart rate and systolic blood pressure were continuously monitored. Both the amplitude and frequency of spontaneous and provoked lower esophageal contractions were measured in situ by using a 24-F probe equipped with provoking and measuring balloons. Combined results demonstrated statistically significant correlations (P less than 0.001) between lower esophageal contractility and MAC. Spontaneous lower esophageal contractions decreased from 1.10 +/- 0.12 (SEM) contractions per minute (0.5 MAC) to 0.42 +/- 0.05 (1 MAC) to 0.18 +/- 0.05 (1.5 MAC). Provoked lower esophageal contractility values decreased from 45 +/- 4 mm Hg (0.5 MAC) to 29 +/- 3 (1 MAC) to 19 +/- 2 (1.5 MAC). Heart rate changes did not correlate with MAC, and systolic blood pressure correlated in only one of three centers. Intracenter and intercenter analyses failed to demonstrate a significant relationship between lower esophageal contractility and heart rate or systolic blood pressure. No intracenter differences in either amplitude or frequency of lower esophageal contractions were observed, despite differences in volatile agents, induction techniques and agents, patient populations, and durations of anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Dupont critical care lecture: Role of ultrashort-acting β-blockers in the perioperative period

beta-blockade can result in extreme bradycardia, significant conduction problems, bronchospasm, or left ventricular dysfunction. For this reason, the use of long-acting beta-blockers is of limited value in the perioperative period. Esmolol, due to its ultrashort action and cardioselective properties, has been shown to be safe and effective for use in treatment of tachycardia and hypertension. Doses of up to 300 microg/kg/min for up to seven hours have been used with a return to baseline parameters within 30 minutes of discontinuation of the infusion. It can also be safely used in treatment of the asthmatic patient with tachycardia or hypertension with no clinically significant increases in airway resistance. Studies using esmolol during general anesthesia have also demonstrated that it appears to have no significant interaction with various anesthetic agents.

Reversal of the adverse cardiovascular effects of intravenous diltiazem in anesthetized dogs

Intravenous diltiazem can be used to treat myocardial ischemia, hypertension, and supraventricular dysrhythmias, but significant adverse effects including atrioventricular block and hypotension have been reported. At the present time, there is controversy as to which drug is most effective in reversing these sequelae. This study was designed to assess the effectiveness of calcium chloride v epinephrine in reversing these side effects. The hemodynamic and electrophysiologic effects of diltiazem infusion were investigated in eight dogs anesthetized with fentanyl and nitrous oxide/oxygen. This study confirmed that diltiazem infusions in high concentrations produced predominantly atrioventricular conduction depression followed by profound hypotension. Epinephrine infusion proved to be most effective in attenuating and eliminating each of these deleterious side effects. In contrast, calcium chloride did not significantly increase heart rate or blood pressure or reverse atrioventricular block. In two instances calcium chloride produced further depression of atrioventricular conduction, leading to severe bradycardia and sinus arrest. Although calcium chloride increased left ventricular contractile force (LV dP/ dt) and cardiac index (CI), mean arterial pressure was not affected and SVR was further decreased. This study indicates that calcium chloride should not be given to reverse the side effects of diltiazem in the presence of atrioventricular conduction block or profound hypotension. Calcium chloride is indicated only when isolated myocardial depression is present and after the calcium channels have been reopened by epinephrine.

The effects of metabolic acidosis and alkalosis on the response to sympathomimetic drugs in dogs

Sympathomimetic drugs are commonly used in many circumstances to increase cardiac output, blood pressure, and myocardial contractility. However, factors such as acidosis or alkalosis are known to influence the action of these drugs. This study looked at the response to the administration of epinephrine, norepinephrine, dopamine, dobutamine, isoproterenol, and glucagon at normal pH and under acidotic (pH 7.2 +/- 0.01) and alkalotic (pH 7.59 +/- 0.01) conditions in 17 dogs. Acidosis was produced with an infusion of hydrochloric acid and alkalosis by infusion of sodium bicarbonate. The infusions were given over one hour followed by a 15- to 30-minute stabilization period. With the administration of each sympathomimetic drug at each pH level, hemodynamic parameters and measurements of myocardia; contractility were recorded. Epinephrine increased cardiac output at normal pH, but decreased cardiac output under conditions of both acidosis and alkalosis; the net change from values at pH 7.40 was nearly 3 L/min. The only other drug to demonstrate this reversal of cardiac output, though to a lesser degree, was dopamine, 10 microg/kg/min, and only in the alkalotic state. Dobutamine was the only drug that decreased contractility under acidotic conditions, while all other drugs caused an increase. In sum, epinephrine was the only drug markedly affected by metabolic acidosis and alkalosis. Isoproterenol's hemodynamic effects were altered the least by changes in acid-base balance. Alkalosis had an equally adverse effect on the cardiovascular system as compared with acidosis.