Smart releasing electrospun nanofibers—poly: L.lactide fibers as dual drug delivery system for biomedical application

Nanotechnology in development of next generation of stent and related medical devices: Current and future aspects

Coronary stents have saved millions of lives in the last three decades by treating atherosclerosis especially, by preventing plaque protrusion and subsequent aneurysms. They attenuate the vascular SMC proliferation and promote reconstruction of the endothelial bed to ensure superior revascularization. With the evolution of modern stent types, nanotechnology has become an integral part of stent technology. Nanocoating and nanosurface fabrication on metallic and polymeric stents have improved their drug loading capacity as well as other mechanical, physico-chemical, and biological properties. Nanofeatures can mimic the natural nanofeatures of vascular tissue and control drug-delivery. This review will highlight the role of nanotechnology in addressing the challenges of coronary stents and the recent advancements in the field of related medical devices. Different generations of stents carrying nanoparticle-based formulations like liposomes, lipid-polymer hybrid NPs, polymeric micelles, and dendrimers are discussed highlighting their roles in local drug delivery and anti-restenotic properties. Drug nanoparticles like Paclitaxel embedded in metal stents are discussed as a feature of first-generation drug-eluting stents. Customized precision stents ensure safe delivery of nanoparticle-mediated genes or concerted transfer of gene, drug, and/or bioactive molecules like antibodies, gene mimics via nanofabricated stents. Nanotechnology can aid such therapies for drug delivery successfully due to its easy scale-up possibilities. However, limitations of this technology such as their potential cytotoxic effects associated with nanoparticle delivery that can trigger hypersensitivity reactions have also been discussed in this review. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

The engineering, drug release, and in vitro evaluations of the PLLA/HPC/Calendula Officinalis electrospun nanofibers optimized by Response Surface Methodology

A system based on poly(l-lactic acid) (PLLA) and hydroxypropyl cellulose (HPC) was considered in this study to achieve electrospun mats with outstanding properties and applicability in biomedical engineering. A novel binary solvent system of chloroform/N,N-dimethylformamide (CF/DMF:70/30) was utilized to minimize the probable phase separation between the polymeric components. Moreover, Response Surface Methodology (RSM) was employed to model/optimize the process. Finally, to scrutinize the ability of the complex in terms of drug delivery, Calendula Officinalis (Marigold) extract was added to the solution of the optimal sample (Opt.PH), and then the set was electrospun (PHM). As a result, the presence of Marigold led to higher values of fiber diameter (262 ± 34 nm), pore size (483 ± 102 nm), and surface porosity (81.0 ± 7.3 %). As this drug could also prohibit the micro-scale phase separation, the PHM touched superior tensile strength and Young modulus of 11.3 ± 1.1 and 91.2 ± 4.2 MPa, respectively. Additionally, the cumulative release data demonstrated non-Fickian diffusion with the Korsmeyer-Peppas exponent and diffusion coefficient of n = 0.69 and D = 2.073 × 10-14 cm2/s, respectively. At the end stage, both the Opt.PH and PHM mats manifested satisfactory results regarding the hydrophilicity and cell viability/proliferation assessments, reflecting their high potential to be used in regenerative medicine applications.

Detection of acoustic emission from nanofiber nonwovens under tensile strain - An ultrasonic test setup for critical medical device components

In the biomedical field, nanofiber materials are gaining increasing application. For material characterization of nanofiber fabrics, tensile testing and scanning electron microscopy (SEM) are established standards. However, tensile tests provide information about the entire sample without information about single fibers. Conversely, SEM images examine individual fibers, but cover only a small section near the surface of the sample. To gain information on failure at the fiber level under tensile stress, recording of acoustic emission (AE) is a promising method, but challenging due to weak signal intensity. Using AE recording, beneficial findings can be obtained even on "invisible" material failure without affecting tensile tests. In this work, a technology for recording weak ultrasonic AE of tearing nanofiber nonwovens is presented, which uses a highly sensitive sensor. Functional proof of the method using biodegradable PLLA nonwoven fabrics is provided. The potential benefit is demonstrated by unmasking significant AE intensity in an almost imperceptible bend in the stress-strain curve of a nonwoven fabric. AE recording has not yet been performed on standard tensile tests of unembedded nanofiber material intended for safety-related medical applications. The technology has the potential to enrich the spectrum of testing methods, even those not confined to medical field.

Local biocompatibility and biochemical profile of hepatic cytolysis in subcutaneous implantation of polylactide matrices

The aim of the study was to investigate local biocompatibility and systemic effects of nonwoven polylactide (PLA) matrices on blood and liver parameters after their subcutaneous implantation in Wistar rats.

Materials and methods. Bioabsorbable fibrous PLA matrices were produced by electrospinning and had dimensions (10 × 10 mm², thickness of no more than 0.5 mm; fiber diameter in the matrix ~1 μm) appropriate for subcutaneous implantation in white laboratory rats. Polymer implants were sterilized in ethylene oxide vapor. Thirty days after the implantation of PLA matrices, local biocompatibility according to GOST ISO 10993-6-2011, cellular parameters (total leukocyte count, hemogram, erythrocyte count, hemoglobin concentration), and biochemical blood parameters (lactate concentration, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels) were studied, and a standard histologic evaluation of the liver was performed.

Results. PLA matrix samples were mild local irritants on a scale of 1–1.9 points according to GOST ISO 10993-6-2011 criteria 30 days after the subcutaneous implantation. The median density of distribution of multinucleated giant cells (MNGCs) in the connective tissue around and in PLA matrices was 1,500 (1,350; 1,550) per 1 mm² of a slice. Pronounced leukocytic reaction due to lymphocytosis was noted (an increase by 1.7 times compared with a sham-operated (SO) control group, р < 0.02). The absence of a significant neutrophil count in the blood revealed sterile inflammation proceeding in the subcutaneous tissue around the PLA materials. Normalization of hepatic cytolysis markers (ALT and AST activity) in the blood without pronounced changes in the structure of the liver and the number of binuclear hepatocytes was noted. These markers were increased in SO controls (ALT up to 123% and AST up to 142%, p < 0.001 compared with values in the intact group).

Conclusion. Nonwoven PLA matrices are biocompatible with subcutaneous tissue, undergo bioresorption by MNGCs, and have a distant protective effect on the functional state of the liver in laboratory animals. Hypotheses on the detected systemic effect during subcutaneous implantation of PLA matrices were discussed; however, specific mechanisms require further study.

A Review of the Release Profiles and Efficacies of Chemotherapy Drug-Loaded Electrospun Membranes

Electrospun fibrous membranes loaded with chemotherapy drugs have been broadly studied, many of which have had promising data demonstrating therapeutic effects on cancer cell inhibition, tumor size reduction, the life extension of tumor-bearing animals, and more. Nevertheless, their drug release profiles are difficult to predict since their degradation pattern varies with crystalline polymers. In addition, there is room for improving their release performances, optimizing the release patterns, and achieving better therapeutic outcomes. In this review, the key factors affecting electrospun membrane drug release profiles have been systematically reviewed. Case studies of the release profiles of typical chemotherapy drugs are carried out to determine the preferred polymer choices and techniques to achieve the expected prolonged or enhanced release profiles. The therapeutic effects of these electrospun, chemo-drug-loaded membranes are also discussed. This review aims to assist in the design of future drug-loaded electrospun materials to achieve preferred release profiles with enhanced therapeutic efficacies.

Stretchable, breathable, and highly sensitive capacitive and self-powered electronic skin based on core-shell nanofibers

Fiber-based nanostructures are greatly desired for the improvement of wearable/flexible electronics, which are expected to be stretchable, conformable, flexible, and long-term. Herein, an ultra-stretchable, breathable, and highly sensitive flexible capacitive tactile sensor and triboelectric effect core-shell nanofibers are proposed. In particular, core-shell ionic TPU/PVDF-HFP nanofibers are effectively prepared by an electrospinning approach. The core-shell ionic TPU/PVDF-HFP nanofibers exhibit high performance as a capacitive flexible sensor with high sensitivity (0.718 kPa^-1) in a low linear pressure range (0-1.2 kPa), an ultralow detection limit (7 Pa), a rapid response and recovery time, and excellent stability. Moreover, we assembled a self-powered pressure sensor, which has a sensitivity of 0.071 V kPa^-1 in the high linear pressure range of 90 kPa to 400 kPa. The increase in the inductive charges of the nanofiber layer allows it to work as an energy harvester with a high power density (1.6 W m^-2) that can light up 100 LEDs instantly. These remarkable results allow the capacitive flexible devices to be applied in various applications, such as spatial pressure mapping, bending angle detection, soft grabbing, and physiological signal monitoring.

PLLA Coating of Active Implants for Dual Drug Release

Cochlear implants, like other active implants, rely on precise and effective electrical stimulation of the target tissue but become encapsulated by different amounts of fibrous tissue. The current study aimed at the development of a dual drug release from a PLLA coating and from the bulk material to address short-term and long-lasting release of anti-inflammatory drugs. Inner-ear cytocompatibility of drugs was studied in vitro. A PLLA coating (containing diclofenac) of medical-grade silicone (containing 5% dexamethasone) was developed and release profiles were determined. The influence of different coating thicknesses (2.5, 5 and 10 µm) and loadings (10% and 20% diclofenac) on impedances of electrical contacts were measured with and without pulsatile electrical stimulation. Diclofenac can be applied to the inner ear at concentrations of or below 4 × 10⁻⁵ mol/L. Release of dexamethasone from the silicone is diminished by surface coating but not blocked. Addition of 20% diclofenac enhances the dexamethasone release again. All PLLA coatings serve as insulator. This can be overcome by using removable masking on the contacts during the coating process. Dual drug release with different kinetics can be realized by adding drug-loaded coatings to drug-loaded silicone arrays without compromising electrical stimulation.

Recent applications of electrical, centrifugal, and pressurised emerging technologies for fibrous structure engineering in drug delivery, regenerative medicine and theranostics

Advancements in technology and material development in recent years has led to significant breakthroughs in the remit of fiber engineering. Conventional methods such as wet spinning, melt spinning, phase separation and template synthesis have been reported to develop fibrous structures for an array of applications. However, these methods have limitations with respect to processing conditions (e.g. high processing temperatures, shear stresses) and production (e.g. non-continuous fibers). The materials that can be processed using these methods are also limited, deterring their use in practical applications. Producing fibrous structures on a nanometer scale, in sync with the advancements in nanotechnology is another challenge met by these conventional methods. In this review we aim to present a brief overview of conventional methods of fiber fabrication and focus on the emerging fiber engineering techniques namely electrospinning, centrifugal spinning and pressurised gyration. This review will discuss the fundamental principles and factors governing each fabrication method and converge on the applications of the resulting spun fibers; specifically, in the drug delivery remit and in regenerative medicine.

Insight into levofloxacin loaded biocompatible electrospun scaffolds for their potential as conjunctival substitutes

The rehabilitation of visual acuity with severe conjunctival fibrosis depends on ocular reconstruction with suitable conjunctival substitutes. In this study, we have developed poly(lactic acid) (PLA) electrospun nanofibrous membranes (EFMs) surface coated by cellulose nanofibrils (CNF) and/or silk peptide (SP). The CNF coating improved the hydrophilicity and the SP coating proliferated conjunctival epithelial cells (CjECs). To prevent post-operative infections, the composite scaffolds were loaded with levofloxacin (LF), constantly exerting efficient bactericidal effects. In in vivo evaluations, the PLA EFMs presented excellent therapeutic effects by promoting structural and functional restoration of conjunctiva after transplant. Even with reduced topical administration of antibiotics, the coloboma treated with LF loaded scaffolds presented no infections. It could be deduced that the potent bacterial inhibition feature could save troubles for patients by minimizing the application of antibiotics post-surgery. Hence, the developed PLA EFMs loaded with LF could be promising conjunctival substitutes.

Influence of Drug Incorporation on the Physico-Chemical Properties of Poly(l-Lactide) Implant Coating Matrices-A Systematic Study

Local drug delivery has become indispensable in biomedical engineering with stents being ideal carrier platforms. While local drug release is superior to systemic administration in many fields, the incorporation of drugs into polymers may influence the physico-chemical properties of said matrix. This is of particular relevance as minimally invasive implantation is frequently accompanied by mechanical stresses on the implant and coating. Thus, drug incorporation into polymers may result in a susceptibility to potentially life-threatening implant failure. We investigated spray-coated poly-l-lactide (PLLA)/drug blends using thermal measurements (DSC) and tensile tests to determine the influence of selected drugs, namely sirolimus, paclitaxel, dexamethasone, and cyclosporine A, on the physico-chemical properties of the polymer. For all drugs and PLLA/drug ratios, an increase in tensile strength was observed. As for sirolimus and dexamethasone, PLLA/drug mixed phase systems were identified by shifted drug melting peaks at 200 °C and 240 °C, respectively, whereas paclitaxel and dexamethasone led to cold crystallization. Cyclosporine A did not affect matrix thermal properties. Altogether, our data provide a contribution towards an understanding of the complex interaction between PLLA and different drugs. Our results hold implications regarding the necessity of target-oriented thermal treatment to ensure the shelf life and performance of stent coatings.