The role of microneedles in the healing of chronic wounds.

Chronic wounds occur for several reasons, such as trauma, accidents, and diseases. Diabetes has been one of the primary causes of non-healing wounds, and the number of people with diabetes is increasing in most countries. Wounds in diabetic people have a complex and prolonged treatment process, with high treatment costs to both healthcare providers and patients. They often have severe consequences, such as pain, wound infection, tissue necrosis, and even limb amputation. Various methods have been used to treat chronic wounds, but clinical success has been limited due to inefficient delivery to the wound bed. Microneedles (MNs), as new platforms, can offer an effective treatment, easy to use and non-invasive with less tissue damage, capable of delivering a wide range of drugs to accelerate the wound healing process. Different methods and materials can be used for this technique, and there are different geometric parameters such as needle length, tip angle, shape and radius, together with needle array density to optimize for the most effective treatment. This review paper will investigate the role of MNs in healing chronic wounds and discuss the most recent development in MN-based devices in the field and their effectiveness. The manuscript will also discuss the various types of MNs and their potential applications for delivering therapeutic agents. Finally, the challenges associated with using MNs to heal chronic wounds and future directions in this field are discussed.

Fabrication and testing of polymer microneedles for transdermal drug delivery.

Microneedle (MN) patches have considerable potential for medical applications such as transdermal drug delivery, point-of-care diagnostics, and vaccination. These miniature microdevices should successfully pierce the skin tissues while having enough stiffness to withstand the forces imposed by penetration. Developing low-cost and simple manufacturing processes for MNs is of considerable interest. This study reports a simple fabrication process for thermoplastic MNs from cycloolefin polymers (COP) using hot embossing on polydimethylsiloxane (PDMS) soft molds. COP has gained interest due to its high molding performance and low cost. The resin master MN arrays (9 × 9) were fabricated using two-photon polymerization (TPP). A previous gap in the detailed characterization of the embossing process was investigated, showing an average of 4.99 ± 0.35% longitudinal shrinkage and 2.15 ± 0.96% lateral enlargement in the molded MN replicas. The effects of bending, buckling, and tip blunting were then examined using compression tests and also theoretically. MN array insertion performance was studied in vitro on porcine back skin using both a prototype custom-made applicator and a commercial device. An adjustable skin stretcher mechanism was designed and manufactured to address current limitations for mimicking skin in vivo conditions. Finite element analysis (FEA) was developed to simulate single MN insertion into a multilayered skin model and validated experimentally using a commercial Pen Needle as a model for the thermoplastic MNs. Margins of safety for the current MN design demonstrated its potential for transdermal drug delivery and fluid sampling. Experimental results indicated significant penetration improvements using the prototype applicator, which produced array penetration efficiencies as high as >92%, depending on the impact velocity setting.

An overview of microneedle applications, materials, and fabrication methods.

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics - so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

High-resolution two-photon polymerization: the most versatile technique for the fabrication of microneedle arrays.

Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.

Effects of neuropeptide Y on coronary artery vasomotion in patients with microvascular angina.

BACKGROUND: Patients with microvascular angina (exertional angina, positive exercise tests and normal coronary arteriograms) usually have a reduced coronary blood flow reserve. Neuropeptide Y (NPY) is a potent endogenous vasoconstrictor involved in modulation of coronary vasomotor tone and may play a role in microvascular angina. METHODS: We compared the effects of NPY (0.2-1.0pmol/kg, intracoronary) on the vasomotor response of proximal and distal segments of the coronary arteries in 7 patients with microvascular angina, 9 with chronic stable angina, and 9 control individuals. The coronary response to the administration of ergonovine was also assessed in 9 other patients with microvascular angina. Computerized coronary artery diameter measurements were carried out before (baseline) and after the administration of the vasoactive agents. RESULTS: Mean baseline coronary lumen diameters were similar in control, microvascular angina, and coronary artery disease patients. NPY constricted proximal coronary segments by 8±2%, 5±2% and 6±3% and distal segments by 14±2%, 11±2% and 10±2% in control, microvascular angina, and coronary artery disease patients, respectively (p=NS between groups). In patients with microvascular angina, ergonovine constricted proximal coronary segments by 7±1.5% and distal segments by 12.5±3% (p=NS vs. NPY). During NPY administration four microvascular angina patients developed chest pain, ST segment depression, and a marked lengthening of the contrast medium run off, in the absence of epicardial coronary artery spasm. Control individuals and coronary artery disease patients did not experience chest pain, ST segment shifts, or lengthening of the run off during NPY administration. Ergonovine administration caused chest pain and lengthening of the contrast run-off, in the absence of epicardial coronary artery spasm, in one microvascular angina patient. CONCLUSIONS: Exogenous NPY causes mild epicardial coronary artery constriction which is similar in patients with non-cardiac chest pain, microvascular angina and coronary artery disease. Myocardial ischemia and marked lengthening of the contrast run off in response to NPY occurred in microvascular angina patients but not in control or coronary artery disease patients. An abnormal constrictor response to NPY at the microcirculation level could be the mechanism underlying the ischemic manifestations observed in patients with microvascular angina. CONDENSED ABSTRACT (TABLE OF CONTENTS): The vasomotor response of proximal and distal coronary artery segments was studied in twenty five patients: 7 microvascular angina, 9 chronic stable angina, and 9 control subjects. Computerized measurements of coronary diameters were carried out before and after the intracoronary administration of neuropeptide Y (NPY) and ergonovine. Constriction of epicardial arteries in response to NPY was mild and not significantly different in control, microvascular angina and coronary artery disease patients. Ergonovine-induced epicardial coronary artery constriction was similar to that of NPY. However, NPY caused transient myocardial ischemia in patients with microvascular angina (probably through constriction of the small intramyocardial vessels), but not in control subjects or coronary artery disease patients.

High-fidelity replication of thermoplastic microneedles with open microfluidic channels.

Development of microneedles for unskilled and painless collection of blood or drug delivery addresses the quality of healthcare through early intervention at point-of-care. Microneedles with submicron to millimeter features have been fabricated from materials such as metals, silicon, and polymers by subtractive machining or etching. However, to date, large-scale manufacture of hollow microneedles has been limited by the cost and complexity of microfabrication techniques. This paper reports a novel manufacturing method that may overcome the complexity of hollow microneedle fabrication. Prototype microneedles with open microfluidic channels are fabricated by laser stereolithography. Thermoplastic replicas are manufactured from these templates by soft-embossing with high fidelity at submicron resolution. The manufacturing advantages are (a) direct printing from computer-aided design (CAD) drawing without the constraints imposed by subtractive machining or etching processes, (b) high-fidelity replication of prototype geometries with multiple reuses of elastomeric molds, (c) shorter manufacturing time compared to three-dimensional stereolithography, and (d) integration of microneedles with open-channel microfluidics. Future work will address development of open-channel microfluidics for drug delivery, fluid sampling and analysis.

Plasma salicylate level and aspirin resistance in survivors of myocardial infarction.

To investigate the effect of aspirin on the platelets of survivors of myocardial infarction we correlated plasma salicylate level with platelet reactivity in ten patients and ten normal controls. The patients and controls were tested at the end of 2 week periods on 75, 150 and 300 mg aspirin daily by mouth. Platelet reactivity was measured, under high shear stress conditions, using cartridges containing adrenaline and adenosine diphosphate in a PFA-100 platelet function analyser. The time taken by the developing platelet aggregate to close an aperture in the collagen membrane of the cartridge, the closure time, was taken as an index of platelet reactivity. There was no difference in baseline haematocrit, platelet count or plasma vWF antigen level between the groups. There was a dose-dependent increase in closure time of the adrenaline containing cartridge in the controls (P < 0.001), but not in the patients (P = 0.08), compatible with a reduced anti-platelet effect of aspirin in the patients. Furthermore, plasma salicylate level was higher in the patient group (P < 0.05).

Plasminogen activator inhibitor-1 removal using dextran sulphate columns. Evidence of PAI-1 homeostasis.

Patients with high plasma plasminogen activator inhibitor-1 (PAI-1) antigen levels are prone to develop thrombosis. Lowering PAI-1 levels may offer a therapeutic option and help to better understand PAI-1 metabolism. We examined the effect on plasma PAI-1 levels of LDL-apheresis using dextran sulphate (DS) columns in 12 patients (9 male, 3 female, 49 +/- 10 years) with heterozygous familial hypercholesterolaemia and coronary artery disease. One plasma volume equivalent (2.3-4.0 l) was treated during each procedure (at flow rates of 23 +/- 2 ml/min). Lipids and PAI-1 antigen levels were measured in plasma before and immediately after 19 aphereses (once in 7 patients, twice in 3 patients and three times in 2 patients) and also at 3 and 7 days post apheresis in five of these patients and in the column eluates from 8 of these patients. DS-apheresis reduced plasma cholesterol (50 +/- 8%), triglyceride (45 +/- 27%), apolipoprotein B (59 +/- 10%) and PAI-1 antigen levels from 10.2 +/- 5.2 to 6.0 +/- 3.1 ng/ml (P = 0.005). The PAI-I changes were independent of circadian variation. PAI-I bound to the DS-columns (3.51 +/- 1.03 ng/ml filtered plasma) and the percent of filtered PAI-1 that was bound correlated inversely (r = -0.81, P < 0.02) with basal PAI-1 levels indicating a high affinity saturable binding process. In four patients, plasma PAI-1 levels post-apheresis were higher than expected based on the amount of PAI-removed by the DS columns. The difference between the expected and actual PAI-1 level post apheresis, reflecting PAI-1 secretion or extracellular redistribution, correlated inversely with basal PAI-1 levels (r = -0.83, P = 0.01). PAI-1 levels returned to baseline pre-apheresis values 7 days post apheresis. PAI-1 antigen may be removed from plasma without adverse effect, resulting temporarily in its extracellular redistribution and restoration to baseline levels over one week. PAI-1 redistribution particularly when baseline pre-apheresis values were low may reflect a homeostatic mechanism to maintain sufficient PAI-1 levels. Procedures that could selectively remove PAI-1 from plasma may offer a treatment option for those with very high plasma PAI-1 levels and thrombosis.

Elevated plasma lipid peroxide levels in angina pectoris and myocardial infarction.

BACKGROUND: The concept that oxidised low-density lipoprotein (LDL), not native LDL, plays a major role in atherogenesis is gaining support. Lipid hydroperoxides in plasma are carried almost exclusively in LDL and reflect oxidised LDL. Previously, elevated plasma lipid hydroperoxides were reported in coronary artery disease (CAD) patients following bypass surgery. To determine whether the increased lipid hydroperoxide was related to bypass or reflected ongoing atherosclerosis, plasma lipid hydroperoxide was measured in acute myocardial infarction (AMI) and stable angina. METHODS: Patients with AMI (n=39) and stable angina (n=40) were compared with matched controls. Lipids and lipoproteins were selectively removed from plasma by absorption to Liposorb gel. Lipid hydroperoxide concentration in the gel was measured by a sensitive triiodide spectrophotometric technique. RESULTS: Lipid hydroperoxide levels in AMI and stable angina were elevated (3.47+/-0.21 micromol/l, P<.001 and 3.76+/-0.24 micromol/l, P<.001) compared to controls (2.18+/-0.13 micromol/l). Previously, a concentration >3 mol/l was considered pathological. Using this criterion, we detected pathological lipid hydroperoxide concentrations in 10.3% of controls, 57.5% of AMI and 61.5% of angina patients. CONCLUSION: Plasma lipid hydroperoxide levels are significantly elevated in AMI and angina. This is not attributable to previous cardiopulmonary bypass but to the presence of atherosclerotic disease and is likely to play a role in atherogenesis.