Antiproliferative coatings for the treatment of coronary heart disease:. what are the targets and which are the tools?

Progress in drug-delivery systems in cardiovascular applications: stents, balloons and nanoencapsulation

Drug-delivery systems in cardiovascular applications regularly include the use of drug-eluting stents and drug-coated balloons to ensure sufficient drug transfer and efficacy in the treatment of cardiovascular diseases. In addition to the delivery of antiproliferative drugs, the use of growth factors, genetic materials, hormones and signaling molecules has led to the development of different nanoencapsulation techniques for targeted drug delivery. The review will cover drug delivery and coating mechanisms in current drug-eluting stents and drug-coated balloons, novel innovations in drug-eluting stent technologies and drug encapsulation in nanocarriers for delivery in vascular diseases. Newer technologies and advances in nanoencapsulation techniques, such as the use of liposomes, nanogels and layer-by-layer coating to deliver therapeutics in the cardiovascular space, will be highlighted.

Protective effect and mechanism of rat recombinant S100 calcium-binding protein A4 on oxidative stress injury of rat vascular endothelial cells

The aim of the present study was to examine the protective effects and mechanisms of S100 calcium-binding protein A4 (S100A4) on endothelial cell apoptosis induced by oxidative stress injury. Endothelial cells were cultured and divided into control and oxidative stress injury groups, with the latter state induced by H₂O₂. Endothelial cells in every group were incubated with or without 50 or 100 µM S100A4. The cell viability and amounts of malondialdehyde, nitric oxide and lactate dehydrogenase in the culture medium were measured. The apoptotic index was detected by TUNEL staining. Western blot and immunoprecipitation analyses were used to detect the expression levels and the association between S100A4 and P53. H₂O₂ treatment led to oxidative stress injury in the cultured vascular endothelial cells, a decrease in the cell viability and an increase in the rate of apoptosis of vascular endothelial cells compared with the negative control group. Exogenous S100A4 serves a significant function against oxidative stress injury (P<0.05), increasing the viability and attenuating the apoptotic rate of endothelial cells. Western blotting results suggested that the protein levels of S100A4 and P53 increased subsequent to oxidative stress injury and that exogenous S100A4 increased the expression of P53 in the cytoplasm and decreased the expression of P53 in nucleus. The immunoprecipitation assay results revealed a protein-protein interaction between S100A4 and P53. These results suggested that rat recombinant S100A4 serves an anti-apoptotic function in oxidative stress injury. This effect of S100A4 is mediated, at least in part, via the inhibition of the translocation of P53 to the nucleus.

Mechanisms Underlying Drug Delivery to Peripheral Arteries

Delivery of drugs onto arterial targets via endovascular devices commands several principles: dissolution, diffusion, convection, drug binding, barriers to absorption, and interaction between the drug, delivery vehicle, and accepting arterial wall. The understanding of drug delivery in the coronary vasculature is vast; there is ongoing work needed in the peripheral arteries. There are differences that account for some failures of application of coronary technology into the peripheral vascular space. Breakthroughs in peripheral vascular interventional techniques building on current technologies require investigators willing to acknowledge the similarities and differences between these different vascular territories, while developing technologies adapted for peripheral arteries.

Organ transplantation and drug eluting stents: Perioperative challenges

Patients listed for organ transplant frequently have severe coronary artery disease (CAD), which may be treated with drug eluting stents (DES). Everolimus and zotarolimus eluting stents are commonly used. Newer generation biolimus and novolimus eluting biodegradable stents are becoming increasingly popular. Patients undergoing transplant surgery soon after the placement of DES are at increased risk of stent thrombosis (ST) in the perioperative period. Dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor such as clopidogrel, prasugrel and ticagrelor is instated post stenting to decrease the incident of ST. Cangrelor has recently been approved by Food and Drug Administration and can be used as a bridging antiplatelet drug. The risk of ischemia vs bleeding must be considered when discontinuing or continuing DAPT for surgery. Though living donor transplant surgery is an elective procedure and can be optimally timed, cadaveric organ availability is unpredictable, therefore, discontinuation of antiplatelet medication cannot be optimally timed. The type of stent and timing of transplant surgery can be of utmost importance. Many platelet function point of care tests such as Light Transmittance Aggregrometry, Thromboelastography Platelet Mapping, VerifyNow, Multiple Electrode Aggregrometry are used to assess bleeding risk and guide perioperative platelet transfusion. Response to allogenic platelet transfusion to control severe intraoperative bleeding may differ with the antiplatelet drug. In stent thrombosis is an emergency where management with either a drug eluting balloon or a DES has shown superior outcomes. Post-transplant complications often involved stenosis of an important vessel that may need revascularization. DES are now used for endovascular interventions for transplant orthotropic heart CAD, hepatic artery stenosis post liver transplantation, transplant renal artery stenosis following kidney transplantation, etc. Several antiproliferative drugs used in the DES are inhibitors of mammalian target of rapamycin. Thus they are used for post-transplant immunosuppression to prevent acute rejection in recipients with heart, liver, lung and kidney transplantation. This article describes in detail the various perioperative challenges encountered in organ transplantation surgery and patients with drug eluting stents.

Activation of Protein Kinase G (PKG) Reduces Neointimal Hyperplasia, Inhibits Platelet Aggregation, and Facilitates Re-endothelialization

In spite of its great success in reducing restenosis, drug-eluting stent (DES) has unfavorable aspects such as stent thrombosis and delayed re-endothelialization. We examined the effects of PKG activation by Exisulind on neointimal formation, platelet aggregation, and re-endothelialization. Exisulind significantly reduced VSMCs viability, cell cycle progression, migration, and neointimal hyperplasia after vascular injury in rat carotid arteries. Interestingly, in contrast to the effect on VSMC viability, Exisulind did not reduce the viability of endothelial cells. Increased PKG activity by Exisulind inhibited PDGF-stimulated phenotype change of VSMCs from a contractile to a synthetic form. Conversely, the use of PKG inhibitor or gene transfer of dominant-negative PKG reversed the effects of Exisulind, resulting in the increased viability of VSMCs and neointimal formation. In addition, Exisulind facilitated the differentiation of peripheral blood mononuclear cells to endothelial lineage via PKG pathway, while inhibiting to VSMCs lineage, which was correlated with the enhanced re-endothelialization in vivo. Finally, Exisulind reduced platelet aggregation, which was mediated via PKG activation. This study demonstrated that Exisulind inhibits neointimal formation and platelet aggregation while increasing re-endothelialization via PKG pathway. These findings suggest that Exisulind could be a promising candidate drug of DES for the prevention of restenosis without other complications.

Secreted Matrix Metalloproteinase-9 of Proliferating Smooth Muscle Cells as a Trigger for Drug Release from Stent Surface Polymers in Coronary Arteries

Cardiovascular diseases are the leading causes of death in industrialized countries. Atherosclerotic coronary arteries are commonly treated with percutaneous transluminal coronary intervention followed by stent deployment. This treatment has significantly improved the clinical outcome. However, triggered vascular smooth muscle cell (SMC) proliferation leads to in-stent restenosis in bare metal stents. In addition, stent thrombosis is a severe side effect of drug eluting stents due to inhibition of endothelialization. The aim of this study was to develop and test a stent surface polymer, where cytotoxic drugs are covalently conjugated to the surface and released by proteases selectively secreted by proliferating smooth muscle cells. Resting and proliferating human coronary artery smooth muscle cells (HCASMC) and endothelial cells (HCAEC) were screened to identify an enzyme exclusively released by proliferating HCASMC. Expression analyses and enzyme activity assays verified selective and exclusive activity of the matrix metalloproteinase-9 (MMP-9) in proliferating HCASMC. The principle of drug release exclusively triggered by proliferating HCASMC was tested using the biodegradable stent surface polymer poly-l-lactic acid (PLLA) and the MMP-9 cleavable peptide linkers named SRL and AVR. The specific peptide cleavage by MMP-9 was verified by attachment of the model compound fluorescein. Fluorescein release was observed in the presence of MMP-9 secreting HCASMC but not of proliferating HCAEC. Our findings suggest that cytotoxic drug conjugated polymers can be designed to selectively release the attached compound triggered by MMP-9 secreting smooth muscle cells. This novel concept may be beneficial for stent endothelialization thereby reducing the risk of restenosis and thrombosis.

Concentration-dependent differential effects of udenafil on viability, proliferation, and apoptosis in vascular endothelial and smooth muscle cells

OBJECTIVES

Local strategies directed against vascular smooth muscle cell (VSMC) proliferation, such as drug-eluting stents (DES), reduce the occurrence of restenosis. However, these approaches may also inhibit vascular endothelial cell (VEC) proliferation and impair reendothelialization, and hence, increase susceptibility to late thrombosis. In this study we examined the differential effects of various concentrations of the type 5 phosphodiesterase (PDE-5) inhibitor, udenafil, on viability, proliferation, and apoptosis of VEC and VSMC, in order to identify the optimal concentration of udenafil that minimizes inhibition of VEC survival and growth, and maximizes inhibition of VSMC survival and growth.

MATERIALS AND METHODS

VEC from human umbilical veins and VSMC from human aorta were exposed to various concentrations of udenafil (1, 10, and 100 μmol/l and 1 mmol/l) for 24 h, and its effects on cell viability, proliferation, and apoptosis were studied using 5-bromo-2'- deoxyuridine (BrdU), methylthiazoletetrazolium (MTT) assay, trypan blue dye exclusion, and flow cytometry.

RESULTS

Udenafil inhibited the survival and growth of VEC and VSMC in a concentration-dependent manner over a range of concentrations. At 100 μmol/l, udenafil, inhibited VEC proliferation significantly less than VSMC proliferation (P < 0.05), and could significantly induce VEC apoptosis less than VSMC apoptosis (P < 0.05).

CONCLUSIONS

Udenafil has a differential effect on survival and growth in VEC and VSMC. The maximal differential effect, with minimal inhibition of VEC and maximal inhibition of VSMC, occurs at 100 μmol/l. This characteristic suggests that udenafil is a promising agent for use in DES.

Preclinical evaluation of sorafenib-eluting stent for suppression of human cholangiocarcinoma cells

Background

Cholangiocarcinoma is a malignant tumor arising from the epithelium of the bile ducts. In this study, we prepared sorafenib-loaded biliary stents for potential application as drug-delivery systems for localized treatment of extrahepatic cholangiocarcinoma.

Methods

A sorafenib-coated metal stent was prepared using an electrospray system with the aid of poly(ɛ-caprolactone) (PCL), and then its anticancer activity was investigated using human cholangiocellular carcinoma (HuCC)-T1 cells in vitro and a mouse tumor xenograft model in vivo. Anticancer activity of sorafenib against HuCC-T1 cells was evaluated by the proliferation test, matrix metalloproteinase (MMP) activity, cancer cell invasion, and angiogenesis assay in vitro and in vivo.

Results

The drug-release study showed that the increased drug content on the PCL film induced a faster drug-release rate. The growth of cancer cells on the sorafenib-loaded PCL film surfaces decreased in a dose-dependent manner. MMP-2 expression of HuCC-T1 cells gradually decreased according to sorafenib concentration. Furthermore, cancer cell invasion and tube formation of human umbilical vein endothelial cells significantly decreased at sorafenib concentrations higher than 10 mM. In the mouse tumor xenograft model with HuCC-T1 cells, sorafenib-eluting PCL films significantly inhibited the growth of tumor mass and induced apoptosis of tumor cells. Various molecular signals, such as B-cell lymphoma (Bcl)-2, Bcl-2-associated death promoter, Bcl-x, caspase-3, cleaved caspase-3, Fas, signal transducer and activator of transcription 5, extracellular signal-regulated kinases, MMP-9 and pan-janus kinase/stress-activated protein kinase 1, indicated that apoptosis, inhibition of growth and invasion was cleared on sorafenib-eluting PCL films.

Conclusion

These sorafenib-loaded PCL films are effective in inhibiting angiogenesis, proliferation and invasion of cancer cells. We suggest that sorafenib-loaded PCL film is a promising candidate for the local treatment of cholangiocarcinoma.

Comparison of 5-year clinical outcomes between sirolimus-versus paclitaxel-eluting stent: Korean multicenter network analysis of 9000-patient cohort

BACKGROUND

The paclitaxel-eluting stent (PES) and sirolimus-eluting stent (SES) are first-generation drug-eluting stents (DES) that have been the most widely used; however, it is unclear whether there are differences in the long-term safety and efficacy between the 2 stents. The long-term effectiveness of DES in unselected people with diabetes is also currently unclear. Moreover, the possibility of late catch-up is suggested in the DES population.

METHODS AND RESULTS

This study is an 8-center collaborative network analysis of all comers who received SES and PES. All patients who received SES and PES from February 2003 to October 2006 were enrolled. We analyzed 9315 patients (33.3% with diabetes) treated with SES or PES in the major 8 centers representing whole area of Korea. The primary end point was a major adverse cardiac event (MACE) composite of overall death, myocardial infarction, and target lesion revascularization. All analyses were performed using multivariable, adjusted models and propensity score-matching methods. Long-term MACE for 5 years were significantly lower in the SES than the PES group (13.3% versus 15.6%; hazard ratio, 0.82; 95% confidence interval, 0.71 to 0.96; P=0.01), which was mainly driven by the difference of MACE within the first year (hazard ratio, 0.73; 95% CI, 0.59 to 0.90; P=0.003), but the rate of MACE between 1 and 5 years in the landmark analysis was not different between the 2 stents (1.9 versus 2.0%/yr). In the subpopulation of people with diabetes, in contrast to the whole population, PES was comparable to SES in terms of any clinical outcome, both within the first year and from 1 to 5 years (MACE for 5 years, 20.3 versus 17.9%; MACE within the first year, 9.6 versus 8.2%; MACE 1 to 5 years, 2.9 versus 2.6%/yr).

CONCLUSIONS

The PES was inferior to the SES in the clinical follow-up of more than 9000 patients' cohort for 5 years, which was mainly driven by the difference in the first year. In the subpopulation of people with diabetes that showed higher MACE than people without diabetes, however, PES was comparable to SES in any clinical outcome for 5 years. Although these 2 stents are not frequently used as before, the data would be useful to expect the long-term clinical course of the current DES.

The Management of Antiplatelet Therapy in Patients With Coronary Stents Undergoing Noncardiac Surgery

Whereas the development of coronary stents has been a major breakthrough in the treatment of coronary artery disease, stent thrombosis, associated with myocardial infarction and death, has introduced a new challenge in the care of patients with coronary stents undergoing noncardiac surgery. This review presents the authors’ recommendations regarding the optimal management of such patients. Elective surgery should be postponed for at least 6 weeks and optimally 3 months for a bare-metal stent and at least 1 year for a drug-eluting stent. On the other hand, managing a patient undergoing non-elective surgery is more difficult and necessitates a case-by-case assessment of bleeding risk versus thrombotic risk based on patient comorbidities, type of stents present, details of the coronary intervention, and type of surgical procedure. Patients with a risk of bleeding that outweighs the risk of stent thrombosis should discontinue at least clopidogrel, whereas all other patients should continue dual antiplatelet therapy throughout the perioperative period.

A link between stent radial forces and vascular wall remodeling: the discovery of an optimal stent radial force for minimal vessel restenosis

Coronary and peripheral artery disease (PAD) continue to be primary causes of morbidity and mortality in western nations; percutaneous transluminal angioplasty (PTA) with stenting has become a popular treatment. Unfortunately, restenosis is a significant problem following intravascular stent placement. This study considers the contribution of stent forces in vascular stenosis and remodeling to develop an equation for identifying the optimal stent force. z-Type stents of three radial forces [low (3.4 N), high (16.4 N), and ultrahigh (19.4 N)] were deployed into the iliac arteries of a juvenile porcine model. Vessel diameters were measured before, after deployment, and again at 30 days. At 30 days animals were killed and the vessels fixed in situ. After implantation, there was a significant increase in total thickness and neointimal hyperplasia with increasing stent force. The model for vessel radius and experimental data was in agreement. The model shows that maximum late-term radius is achieved with a stent deployment stress of 480 kPa, which occurs at the end of the stress-strain curve nonlinear domain and beginning of the high-strain collagen domain. The results and calculations suggest that an optimal stent force exists that is subject to the geometry, structure, and mechanics of the target vessel. To achieve maximum late-term dilatation, stents should not produce stress in the vessel wall greater than the end of the transitional domain of the vessel's stress-strain curve. This finding is extremely important for vascular stent development and will be expanded to preliminary vessel wall injury and atherosclerotic models.

Sculptured drug-eluting stent for the on-site delivery of tacrolimus

This work aimed to evaluate the flexibility of a novel pyrolytic carbon coated drug-eluting stent platform, which presents the peculiarity of deep sculptures realized on the stent's outer surface (reservoirs). Tacrolimus (TCR) or TCR/excipient mixtures were loaded into the reservoirs, and their permanence into stent's reservoirs was verified by an in vitro short-time release test in human blood. Moreover, the impact of the excipients on the TCR physical state and surface morphology of the reservoirs and the release kinetics were studied. The reservoirs resulted homogeneously filled. Upon exposure to blood, no loss of materials from reservoirs was observed, and the drug release after 15 min was negligible in all cases. The loading procedure caused the drug amorphization and, AFM revealed that the surfaces were smooth and homogeneous with the exception of the TCR/poloxamer 188 mixture where spatial oriented crystals were evident. Poly(N-vinyl pyrrolidone) improved the in vitro TCR release rate constants (K). Poly(methylmethacrylate) (PMM) significantly reduced the K value both in vitro and in vivo. Indeed, the in vivo drug concentrations in rabbit artery wall significantly decreased, decreasing the TCR/PMM ratio. The characteristics of the stent strut resulted suitable to load material with different physicochemical characteristics.

Acrylic Copolymers as Candidates for Drug-Eluting Coating of Vascular Stents

The aim of the present work is the synthesis and characterization of polymer materials showing good adhesion, drug loading, and delivery properties, for potential cardiovascular application. In particular, poly(methylmethacrylate-co-acrylic acid) copolymers are prepared in different compositions by a radical polymerization and investigated as potential materials to coat metallic stents and to carry out a local drug release. Films obtained by dissolving the copolymer in an appropriate organic solvent (also loaded with an anti-restenosis drug, such as tacrolimus) are investigated: physicochemical properties, adhesiveness to metallic stent material, and kinetics of drug release in physiological environment are studied.

Nanoscale architectural tuning of parylene patch devices to control therapeutic release rates

The advent of therapeutic functionalized implant coatings has significantly impacted the medical device field by enabling prolonged device functionality for enhanced patient treatment. Incorporation of drug release from a stable, biocompatible surface is instrumental in decreasing systemic application of toxic therapeutics and increasing the lifespan of implants by the incorporation of antibiotics and anti-inflammatories. In this study, we have developed a parylene C-based device for controlled release of Doxorubicin, an anti-cancer chemotherapy and definitive read-out for preserved drug functionality, and further characterized the parylene deposition condition-dependent tunability of drug release. Drug release is controlled by the deposition of a layer of 20-200 nm thick parylene over the drug layer. This places a porous layer above the Doxorubicin, limiting drug elution based on drug accessibility to solvent and the solvent used. An increase in the thickness of the porous top layer prolongs the elution of active drug from the device from, in the conditions tested, the order of 10 min to the order of 2 d in water and from the order of 10 min to no elution in PBS. Thus, the controlled release of an anti-cancer therapeutic has been achieved via scalably fabricated, parylene C-encapsulated drug delivery devices.

Endothelial injury induces vascular smooth muscle cell proliferation in highly localized regions of a direct contact co-culture system

Though previous studies have indicated a relationship between the proliferation of endothelial cells and vascular smooth muscle cells (VSMCs) in co-culture, the results have been contradictory and the signaling mechanism poorly understood. In this transmembrane co-culture study, VSMCs and endothelial cells were grown to confluence on opposite sides of a microporous membrane to mimic the intima/media border of vessels. The endothelial layer was injured, and then cultured for 3 days, resulting in partial re-endothelialization. VSMC proliferation across from the injured/partially recovered endothelial region was significantly higher than across from the de-endothelialized region (a sevenfold increase) and the uninjured region (a threefold increase). ELISA indicated that PDGF, which was undetectable in uninjured co-culture and homotypic controls, increased after injury and the addition of a piperazinyl-quinazoline carboxamide PDGF receptor inhibitor blocked VSMC proliferation across from the injured/partially recovered region. We conclude that co-culture signaling initiated by endothelial cell injury locally stimulates VSMC proliferation and that this signaling could be mediated by PDGF-BB.

Intravascular ultrasound findings in patients with restenosis of sirolimus- and paclitaxel-eluting stents

OBJECTIVE

We used intravascular ultrasound (IVUS) to compare restenotic sirolimus-eluting (SES) vs paclitaxel-eluting (PES) stents.

BACKGROUND

Little is known about the IVUS pattern and mechanisms of restenosis, in the two widely available drug-eluting stent (DES) platforms.

METHODS

Volumetric IVUS analysis was performed in patients with clinical restenosis in DES (n=29 SES and 11 PES respectively).

RESULTS

Despite similar vessel volumes (347.5+/-155.6 vs 356.5+/-164.1 mm(3), p=0.84) and stent volumes (175.6+/-74.57 vs 179.7+/-84.24 mm(3), p=1.0), IVUS analysis showed that neointimal hyperplasia volume was significantly greater in PES restenoses than in SES restenoses (40.0+/-44.2 vs 19.3+/-11.4 mm(3), p=0.02) without any significant difference in distribution over the stent length. This leads to a higher percent of volume obstruction (intimal hyperplasia volume divided by stent volume: 18.5+/-13.7% vs 11.8+/-7.7%, p=0.045). Minimal stent area was smaller in SES than in PES (4.3+/-1.2 vs 5.6+/-1.2 mm(2), p=0.06) and stent underexpansion was more frequently observed in SES stents: minimal stent area <4.5 mm(2) (65% in SES vs 27% in PES, p=0.04). Stent edge restenosis occurred in 1/29 SES (3%) vs 3/11 PES (27%) stents, p=0.056.

CONCLUSION

The magnitude of neointimal hyperplasia was greater in PES than in SES while stent underexpansion appeared to be more common in SES.

Poly(ethylene carbonate): A thermoelastic and biodegradable biomaterial for drug eluting stent coatings?

A first feasibility study exploring the utility of poly(ethylene carbonate) (PEC) as coating material for drug eluting stents under in vitro conditions is reported. PEC (Mw 242 kDa, Mw/Mn=1.90) was found to be an amorphous polymer with thermoelastic properties. Tensile testing revealed a stress to strain failure of more than 600%. These properties are thought to be advantageous for expanding coated stents. In vitro cytotoxicity tests showed excellent cytocompatibility of PEC. Based on these findings, a new stenting concept was suggested, pre-coating a bare-metal stent with PPX-N as non-biodegradable basis and applying a secondary PEC coating using an airbrush method. After manual expansion, no delamination or destruction of the coating could be observed using scanning electron microscopy. The surface degradation-controlled release mechanism of PEC may provide the basis for "on demand" drug eluting stent coatings, releasing an incorporated drug predominantly at an inflamed implantation site upon direct contact with superoxide-releasing macrophages. As a release model, metal plates of a defined size and area were coated under the same conditions as the stents with PEC containing radiolabelled paclitaxel. An alkaline KO(2-) solution served as a superoxide source. Within 12 h, 100% of the incorporated paclitaxel was released, while only 20% of the drug was released in non-superoxide releasing control buffer within 3 weeks.

Brief review: Coronary drug-eluting stents and anesthesia

PURPOSE

Anesthesiologists managing patients with drug-eluting stents (DES) face the challenge of balancing the risks of bleeding vs perioperative stent thrombosis (ST). This article reviews DES and the influence of antiplatelet medications related to their use. A perioperative management algorithm is suggested. Novel P2Y12 antagonists currently under investigation, including cangrelor and prasugrel are considered, as well as their potential role in modification of perioperative cardiovascular risks and management of patients with DES.

SOURCE

A PubMed search of the relevant literature over the period 1985-2005 was undertaken using the terms "drug-eluting stent", "coronary artery stent", "bare metal stent", "antiplatelet medication", "aspirin", "clopidogrel."

PRINCIPAL FINDINGS

Delayed re-endothelialization may render both sirolimus-eluting and paclitaxel-eluting stents susceptible to thrombosis for a longer duration than bare metal stents. Stent thrombosis may be associated with resistance to antiplatelet medication. In patients with a DES, a preoperative cardiology consultation is essential. Elective surgery should be postponed if the duration between DES placement and noncardiac surgery is less than six months. For semi-emergent procedures, both aspirin and clopidogrel should be continued during surgery unless clearly contraindicated by the nature of the surgery. If the risk of bleeding is high, then modification of antiplatelet medications should be considered on a case-by-case basis.

CONCLUSION

A profound increase in the number of patients with DES requires anesthesiologists to be familiar with their associated antiplatelet medications, and strategies for risk modification of ST and possible hemorrhagic complications in the perioperative setting.

Mechanisms of controlled drug release from drug-eluting stents

The clinical importance of drug-eluting stents (DESs) has been demonstrated by their unparalleled success in preventing restenosis after stenting procedures. The magnitude of success is historic despite their short history. The current DESs deliver a single drug aiming to prevent or minimize proliferation of smooth muscle cells. Since the restenosis process involves several different biological responses, the ability to deliver the right drugs at the right times is critical for further development of the second generation of DESs. As the type of drugs that can be delivered from DESs varies, it is imperative to understand the drug delivery mechanisms and the approaches available for drug coating on the stents. The drug delivery mechanisms of current DESs that have been used clinically and under clinical trials are explained.

The significance of infection related to orthopedic devices and issues of antibiotic resistance

Over the last 15 years, with the advent of modern standards in the control of sterility within the operating room environment and adequate protocols of peri-operative antibiotic prophylaxis, the incidence of infections associated to orthopedic implants has become very low. Nevertheless, the event of infection still represents one of the most serious and devastating complications which may involve prosthetic devices. It leads to complex revision procedures and, often, to the failure of the implant and the need for its complete removal. In orthopedics, for the enormous number of surgical procedures involving invasive implant materials, even if nowadays rare, infections have a huge impact in terms of morbidity, mortality, and medical costs. The difficult battle to prevent and fight bacterial infections associated to prosthetic materials must be played on different grounds. A winning strategy requires a clear view of the pathogenesis and the epidemiology of implant-related infections, with a special attention on the alarming phenomenon of antibiotic resistance. In this regard staphylococci are the prevalent and most important causative pathogens involved in orthopedic implant-related infections, and, thus, the main enemy to defeat. In this paper, we offer an overview of the complexity of this battleground and of the current and new, in our opinion most promising, strategies in the field of biomaterials to reduce the risks and counteract the establishment of implant infections.