E. Wintermantel

Inhibition of Neointima Formation by a Novel Drug-Eluting Stent System That Allows for Dose-Adjustable, Multiple, and On-Site Stent Coating

Objective—The risk of in-stent restenosis can be considerably reduced by stents eluting cytostatic compounds. We created a novel drug-eluting stent system that includes several new features in the rapidly evolving field of stent-based drug delivery. Methods and Results—The aim of the present study was the preclinical evaluation of a stent-coating system permitting individual, on-site coating of stents with a unique microporous surface allowing for individualizable, dose-adjustable, and multiple coatings with identical or various compounds, designated ISAR (individualizable drug-eluting stent system to abrogate restenosis). Stents were coated with 0.75% rapamycin solution, and high-performance liquid chromatography (HPLC)-based determination of drug release profile indicated drug release for >21 days. Rapamycin-eluting microporous (REMP) stents implanted in porcine coronary arteries were safe. To determine the efficacy of REMP stents, this novel drug-eluting stent platform was compared with the standard sirolimus-eluting stent. At 30 days, in-stent neointima formation in porcine coronary arteries was similar in both groups, yielding a significant decrease of neointimal area and injury-dependent neointimal thickness compared with bare-metal stents. Conclusion—The ISAR drug-eluting stent platform as a novel concept for stent coating allows for a safe, effective, on-site stent coating process, thus justifying further clinical evaluation to decrease in-stent restenosis in humans.

Future directions in biomaterials

Biomaterials have made a great impact on medicine. However, numerous challenges remain. This paper discusses three representative areas involving important medical problems. First, drug delivery systems; major considerations include drug-polymer interactions, drug transformation, diffusion properties of drugs and, if degradation occurs, of polymer degradation products through polymer matrices developing a more complete understanding of matrix degradation in the case of erodible polymers and developing new engineered polymers designed for specific purposes such as vaccination or pulsatile release. Second, cell-polymer interactions, including the fate of inert polymers, the use of polymers as templates for tissue regeneration and the study of polymers which aid cell transplantation. Third, orthopaedic biomaterials, including basic research in the behaviour of chondrocytes, osteocytes and connective tissue-free interfaces and applied research involving computer-aided design of biomaterials and the creation of orthopaedic biomaterials.

Ceramic TiO2-foams: characterisation of a potential scaffold

Abstract The Schwartzwalder process was chosen for the production of ceramic TiO 2 scaffolds and showed a fully open structure with a permeability for water of 39%. The window sizes were 445 μm (45 ppi foams) and 380 μm for the 60 ppi foams. The porosity of all foams was above 78% ( n =8). It was shown that scaffolds can be produced with defined pore sizes, shape and architecture, which is a requirement for scaffold production. The macro- and microarchitecture was reproducible. Hence a reproducible ceramic scaffold processing method has been established. The interconnectivity of the pores in the scaffold was tested with a novel method. For the tests a new device was constructed where the permeability was linked to the degree of interconnectivity. Results from the permeability measurements in the mercury intrusion meter and permeability tester show that increasing pore size increases the rate of permeability. The tortuosity, which was measured in the mercury intrusion meter, was several factors higher for 60 ppi foams compared to 45 ppi and therefore also understates the lower permeability. An initial cell culture test showed that fibroblasts adhere on the foams surface.

Direct Magnetic Tubular Cell Seeding: A Novel Approach for Vascular Tissue Engineering

Optimizing seeding efficiency, reducing delayed culture periods and mimicking native tissue architecture are crucial requirements for the development of seeding procedures in tissue engineering. In vascular applications, the tubular geometry of the grafts further hampers the efficient delivery of cells onto the scaffold. To overcome these limitations, a novel technology based upon the use of magnetic fields is presented in this study: a radial magnetic force drives the cells immediately onto the luminal surface of a tubular scaffold and immobilizes the cells on the substrate’s surface promoting cell attachment. Human smooth muscle cells (SMCs) labeled with CD44 magnetic Dynabeads® were successively seeded onto the luminal surface of a tubular shaped collagen membrane. After 5 h, one additional layer of human umbilical vein endothelial cells (HUVECs) labeled with CD31 magnetic Dynabeads® was seeded onto the luminal SMCs. The co-culture was incubated during 5 days prior to analysis. Cell viability and expression profiles were preserved during the entire seeding process. Histological examination of the constructs highlighted densely packed multilayers of SMCs covered by a monolayer of endothelial cells. SEM inspection confirmed a heterotypic multilayer assembly formed by multiple layers of elongated SMCs covered by a single layer of endothelial cells. Seeding kinetics of HUVECs and SMCs showed over 90% seeding efficiency after 20 and 40 min magnetic exposure respectively. Magnetically induced cell seeding provides a valuable tool for rapid seeding procedures of tubular scaffolds while complying with the histological architecture of tissue.

Effects of Weak Static Magnetic Fields on Endothelial Cells

Pulsed electromagnetic fields (PEMFs) have been used extensively in bone fracture repairs and wound healing. It is accepted that the induced electric field is the dose metric. The mechanisms of interaction between weak magnetic fields and biological systems present more ambiguity than that of PEMFs since weak electric currents induced by PEMFs are believed to mediate the healing process, which are absent in magnetic fields. The present study examines the response of human umbilical vein endothelial cells to weak static magnetic fields. We investigated proliferation, viability, and the expression of functional parameters such as eNOS, NO, and also gene expression of VEGF under the influence of different doses of weak magnetic fields. Applications of weak magnetic fields in tissue engineering are also discussed. Static magnetic fields may open new venues of research in the field of vascular therapies by promoting endothelial cell growth and by enhancing the healing response of the endothelium.

Grooves affect primary bone marrow but not osteoblastic MC3T3-E1 cell cultures

To elucidate the influence of microtextures on bone cell performance, primary adult rat bone marrow cells (RBMC) and osteoblastic MC3T3-E1 cells were cultured on tissue culture pretreated plates to which grooves at different density were applied. RBMC cells were found to be significantly affected by grooves in the substratum in contrast to osteoblastic MC3T3-E1 cells, taking culture morphology, total cell number, cell mass, and cell activity (MTT-dehydrogenase), parameter for differentiation of osteoblast progenitor cells into (pre-)osteoblasts (alkalinephosphatase activity, ALP) and tartrate-resistant acid phosphatase (TRAP) activity as indices. TRAP is located in lysosomes and secretory granules mainly although not solely in osteoclasts. By applying grooves to and/or by chemical treatment of unpretreated pure polysterene plates it could be concluded that the effects on RBMC cells were evoked not only by the presence of grooves but also by the surface chemistry of the grooved and ungrooved surface areas.

Mimicking Native Extracellular Matrix with Phytic Acid‐Crosslinked Protein Nanofibers for Cardiac Tissue Engineering

A functional scaffold fabricated is developed from natural polymers, favoring regeneration of the ischemic myocardium. Hemoglobin/gelatin/fibrinogen (Hb/gel/fib) nanofibers are fabricated by electrospinning and are characterized for morphology, scaffold composition, functional groups and hydrophilicity. It is hypothesized that ex vivo pretreatment of mesenchymal stem cells (MSCs) using 5-azacytidine and such a functional nanofibrous construct having a high oxygen-carrying potential could lead to enhanced cardiomyogenic differentiation of MSCs and result in superior biological and functional effects. The combination of a functional nanofibrous scaffold composed of natural polymers and crosslinked with a natural crosslinking agent, phytic acid, and stem cell biology may prove to be a novel therapeutic device for treatment of myocardial infarction.

Bio-inspired in situ crosslinking and mineralization of electrospun collagen scaffolds for bone tissue engineering.

Bone disorders are the most common cause of severe long term pain and physical disability, and affect millions of people around the world. In the present study, we report bio-inspired preparation of bone-like composite structures by electrospinning of collagen containing catecholamines and Ca(2+). The presence of divalent cation induces simultaneous partial oxidative polymerization of catecholamines and crosslinking of collagen nanofibers, thus producing mats that are mechanically robust and confer photoluminescence properties. Subsequent mineralization of the mats by ammonium carbonate leads to complete oxidative polymerization of catecholamines and precipitation of amorphous CaCO3. The collagen composite scaffolds display outstanding mechanical properties with Youngs modulus approaching the limits of cancellous bone. Biological studies demonstrate that human fetal osteoblasts seeded on to the composite scaffolds display enhanced cell adhesion, penetration, proliferation, differentiation and osteogenic expression of osteocalcin, osteopontin and bone matrix protein when compared to pristine collagen or tissue culture plates. Among the two catecholamines, mats containing norepinephrine displayed superior mechanical, photoluminescence and biological properties than mats loaded with dopamine. These smart multifunctional scaffolds could potentially be utilized to repair and regenerate bone defects and injuries.

Autosterilization of biodegradable implants by injection molding process

Sterilization of degradable implants by standard procedures may damage the parts due to the labile chemical nature of the polymers. This study examined whether the injection molding process used for the production of polymeric parts may itself sterilize the implant due to high temperature, pressure, and shear forces applied. Poly-D,L-lactic acid (PDLLA) and poly-L-lactic acid (PLLA) granules were contaminated with thermoresistant spores of Bacillus stearothermophilus (>10(5) spores/g). Sterile and contaminated granules of both polymers were injection molded and tested for sterility. All 27 samples produced with sterile PDLLA and processed at 120 degrees C and all 18 samples produced with sterile PLLA at 200 degrees C remained sterile after injection molding and handling. However, in five out of 28 PDLLA samples and in one out of 26 PLLA samples produced with contaminated material, spores had survived the process. In conclusion, the injection molding process could not reliably sterilize parts produced with polylactic acid granules that were heavily contaminated with thermoresistant organisms. However, the number of viable spores was significantly reduced by more than 99.99%. Thus, the injection molding process might allow the autosterilization of parts produced with raw material that is not heavily contaminated.

Impairment of pericardial leaflet structure from balloon-expanded valved stents

OBJECTIVE Malpositioning is one of the major problems in transcatheter aortic valve implantation. To evaluate the influence of mechanical balloon inflation on aortic valve stent positioning, the expansion process and the impact on the valve leaflets structure were investigated. METHODS Custom-made stents were laser cut from a 22-mm diameter stainless steel tube and mounted with a glutaraldehyde-treated bovine pericardial valve. The valved stents were crimped onto a standard balloon catheter and expanded by inflation of the balloon with 2 bar for 3 seconds. Expansion was studied using a high-speed camera, and the histology of the pericardial tissue was analyzed. RESULTS The valved stents were fully expanded within 3 seconds. Balloon inflation was observed to be asymmetric starting proximally. At the beginning of expansion, the valved stents were pulled proximally. During further inflation, the stents slipped distally on the balloon and experienced a total displacement of 13.5 mm. Macroscopic examination showed severe imprinting of the stent struts into the pericardial tissue. Histology revealed disrupted tissue layers and collagen fibers. CONCLUSIONS Analysis of valved stent expansion showed a displacement of the stent on the catheter during balloon inflation. Therefore, precise placement of the valved stent cannot be accomplished. Histologic analysis of the expanded pericardial tissue revealed disruption of collagen fibers. Disruption of pericardial tissue structures due to balloon expansion may result in early functional valve failure.