Aysel Kiziltay

Epidermal growth factor-containing wound closure enhances wound healing in non-diabetic and diabetic rats

Background: This study was designed to elucidate the in vivo efficacy of epidermal growth factor (EGF) on wound healing in non diabetic and diabetic rats.

Effect of oxygen plasma on surface properties and biocompatibility of PLGA films

Chemical structure, roughness, hydrophilicity, distribution of charged groups, etc. are the examples of factors that affect the cell attachment and cell proliferation in tissue engineering applications. Plasma glow discharge is one technique which is used to modify the surfaces without affecting the bulk properties. In this study, poly(D, L-lactide-co-glycolide) (PLGA) films were prepared by solvent casting in chemistry, topography and surface free energy (SFE) with oxygen plasma treatment were investigated by electron spectroscopy for chemical analysis (ESCA), atomic force microscopy (AFM) and goniometer, respectively. The cellmaterial interactions of the samples were evaluated by cell culture tests using 3T3 fibroblast cell line. As the applied power of the RF generator was increased from 20 watts to 300 watts, the surface oxygen content (examined by ESCA) first increased up to 100 watts, and then decreased mostly because of crosslink formation by elimination of oxygen. Surface roughness was examined by AFM and hydrophilicity was examined by water contact angle measurement. SFE values of PLGA films increased in agreement with the applied power according to harmonic mean, geometric mean and acid base approaches. In vitro material-cell interaction studies showed that, oxygen plasma modification enhanced cell attachment and cell proliferation on PLGA films.

PCL and PCL-based materials in biomedical applications

Abstract Biodegradable polymers have met with an increasing demand in medical usage over the last decades. One of such polymers is poly(ε-caprolactone) (PCL), which is a polyester that has been widely used in tissue engineering field for its availability, relatively inexpensive price and suitability for modification. Its chemical and biological properties, physicochemical state, degradability and mechanical strength can be adjusted, and therefore, it can be used under harsh mechanical, physical and chemical conditions without significant loss of its properties. Degradation time of PCL is quite long, thus it is used mainly in the replacement of hard tissues in the body where healing also takes an extended period of time. It is also used at load-bearing tissues of the body by enhancing its stiffness. However, due to its tailorability, use of PCL is not restricted to one type of tissue and it can be extended to engineering of soft tissues by decreasing its molecular weight and degradation time. This review outlines the basic properties of PCL, its composites, blends and copolymers. We report on various techniques for the production of different forms, and provide examples of medical applications such as tissue engineering and drug delivery systems covering the studies performed in the last decades.

Poly(ester-urethane) scaffolds: effect of structure on properties and osteogenic activity of stem cells

The present study aimed to investigate the effect of structure (design and porosity) on the matrix stiffness and osteogenic activity of stem cells cultured on poly(ester‐urethane) (PEU) scaffolds. Different three‐dimensional (3D) forms of scaffold were prepared from lysine‐based PEU using traditional salt‐leaching and advanced bioplotting techniques. The resulting scaffolds were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), mercury porosimetry and mechanical testing. The scaffolds had various pore sizes with different designs, and all were thermally stable up to 300 °C. In vitro tests, carried out using rat bone marrow stem cells (BMSCs) for bone tissue engineering, demonstrated better viability and higher cell proliferation on bioplotted scaffolds compared to salt‐leached ones, most probably due to their larger and interconnected pores and stiffer nature, as shown by higher compressive moduli, which were measured by compression testing. Similarly, SEM, von Kossa staining and EDX analyses indicated higher amounts of calcium deposition on bioplotted scaffolds during cell culture. It was concluded that the design with larger interconnected porosity and stiffness has an effect on the osteogenic activity of the stem cells. Copyright

Construction and in vitro testing of a multilayered, tissue-engineered meniscus

A novel three-dimensional construct was designed to serve as a substitute for the natural meniscus tissue, and tested in vitro. The design consisted of mats of aligned collagen micro/nanofibers, entrapped within a macroporous poly(l-lactic acid)/poly(lactic acid-co-glycolic acid) foam coated with Ca+2-cross-linked alginic acid. Fibrochondrocytes derived from human meniscus were tested in vitro to study cell attachment and proliferation. After a 21-day culture, the cells populating the constructs were shown to produce extracellular matrix components specific for fibrocartilages, such as collagen Types I and II and aggrecan. Coating the foam with alginate increased the compressive modulus of the collagen-containing constructs (from 320 to 381 kPa, after 21 days of incubation with fibrochondrocytes) but decreased cell attachment and proliferation, as well as aggrecan production. Collagen fibers substantially increased the tensile modulus of the cell-seeded constructs (from 0.98 to 1.71 MPa for uncoated and from 0.67 to 1.32 MPa for coated samples). All constructs produced extracellular matrix components specific for fibrocartilages. These findings indicate that these constructs have potential for use as meniscus substitutes.

Desferrioxamine release from gelatin-based systems

The conventional treatment with regular red‐blood‐cell transfusions and simultaneous chelation of excess iron with DFO (desferrioxamine) improves quality of life of thalassaemic patients while increasing their rate of survival considerably. Although DFO is the main iron‐ chelating drug currently utilized, it has various drawbacks, including high cost, poor oral effectiveness, toxicity and short plasma half‐life. It has to be administered by slow, subcutaneous infusion during blood transfusion for 8–12 h at night, 5–7 nights a week, and this leads to a very poor patient compliance. In order to avoid frequent and uncomfortable infusions of DFO, application of controlled‐release systems might be alternative routes in the supportive treatment of thalassaemia. In the present study, GMs (gelatin microspheres) and GFs (gelatin films) were prepared by coacervation and casting methods respectively to develop controlled DFO‐release systems. Cross‐linking by glutaraldehyde and carbodi‐imide were performed to increase the stability of gelatin matrices. Microspheres and films prepared without the addition of cross‐linker degraded completely in 4 h. On the other hand, addition of cross‐linker extended this time from hours to weeks depending on the added amount. Therefore the amount of DFO released from microspheres in 7 days was found to be in the range 12–82%, whereas the amount permeated through the films in 5.0 h was found to be in the range 34–67%. GFs were elastic and demonstrated good mechanical properties. Films achieved 0.14–0.69 MPa tensile strength, with 0.12–1.29 MPa elastic modulus and 26.49–109.38% strain values at break point. These studies showed that gelatin‐based controlled‐release systems could be improved and could be good candidates for the production of long‐term DFO‐carrying systems.

Evaluation of neointimal hyperplasia on tranilast-coated synthetic vascular grafts: an experimental study.

Tranilast is an antiallergic drug that interferes with proliferation and migration of vascular smooth muscle cell induced by platelet-derived growth factor (PDGF) and transforming growth factor-β1 (TGF-β1). We investigated the local effect of tranilast on neointimal hyperplasia using tranilast-coated prosthetic grafts. The inner sides of the thin-walled polytetrafluoroethylene (PTFE) grafts were coated with chitosan and tranilast containing chitosan solution. Wistar albino rats (32) were used in the study. Patches (1 × 2 mm) for vascular grafts were prepared. Three groups were tested: group 1 (n = 12; tranilast coated), group 2 (n = 10; adhesive-only film-layer–coated), and group 3 (n = 10; normal ePTFE patch grafts sutured to the carotid arteries of the rats). Recipient sites of the carotid arteries were excised 4 weeks after surgery. All sections were examined histologically for graft patency, thrombus formation, and neointimal thickness. Expression of PDGF, fibroblast growth factor, and TGF-β1 on cross-sections of the neointima were evaluated by immunohistochemistry. No significant differences were found regarding mean neointimal thicknesses. PDGF and TGF-β-1 expressions were significantly lower in group 1. Although a decrease in local effect of tranilast was observed for growth factor expressions at a drug concentration of 0.05 mg/cm2, a significant reduction in neointimal hyperplasia was not achieved. The coating concentration of 0.05 mg/cm2 may have been too low to produce an antiproliferative effect. Given our promising results, further studies are recommended and planned using different drug concentrations and time intervals.

How safe is the use of prosthetic materials in the repair of abdominal-wall defects in malnourished subjects?

Incisional hernias and abdominal-wall defects consume large amounts of healthcare resources. Use of mesh is effective in treatment of these disorders and can decrease the rate of recurrence. This experimental study focused on the safety of mesh use in the setting of malnutrition, a condition that impairs wound healing. Rats were divided into two groups: normally fed and food-restricted. An abdominal-wall defect, 2 by 2 cm, was covered with polypropylene mesh, 2.5 by 2.5 cm. After sacrifice of the rats at the 21st and 60th days, tissue samples were sent for tensiometric and histopathological studies. No significant difference in infectious complications was observed between the two groups. Tensiometry revealed no significant differences between the groups. On histopathological examination, the only difference noted was in the vascularization scores of normally fed rats. For malnourished subjects that survived after surgery, the use of polypropylene mesh appeared safe in the closure of abdominal-wall defects, with no increase in infection rate and satisfactory wound healing.

PCL-TCP wet spun scaffolds carrying antibiotic-loaded microspheres for bone tissue engineering

Abstract Scaffolds produced for tissue engineering applications are proven to be promising alternatives to be used in healing and regeneration of injured tissues and organs. In this study, porous and fibrous poly(ε-caprolactone) (PCL) scaffolds were prepared by wet spinning technique and modified by addition of tricalcium phosphate (TCP) and by immobilizing gelatin onto fibers. Meanwhile, gelatin microspheres carrying Ceftriaxone sodium (CS), a model antibiotic, were added onto the scaffolds and antimicrobial activity of CS was investigated against Escherichia coli (E. coli), a model gram-negative bacterium. TCP and gelatin were added to enhance mechanical properties while directing the scaffold towards osteogenic infrastructure and to increase hydrophilicity by activating cell attachment via protein molecules, respectively. Modifications with TCP and gelatin enhanced the compression modulus by about 70%, and attachment of Saos-2 cells by 60%, respectively. Release of the antibiotic demonstrated effective antimicrobial activity against E. coli. The bioactive scaffolds were shown to be good candidates for bone tissue engineering applications.

Synthesis, characterization and biocompatibility of biodegradable poly(ester-urethane) for tissue engineering applications

Polyurethanes (PUs) are able to degrade into harmless molecules upon implantation and have received a significant level of attention as a biomaterial. PUs based on polycaprolactone (PCL) and amino acid derivatives are examples of these polymers. As a potential biomaterial, their biocompatibility coupled with biodegradability attracted attention in tissue engineering applications. In this study, a biodegradable thermoplastic, poly(ester-urethane) based on L-lysine diisocyanate (LDI) and PCL was synthesized. The resulting polymer was fully characterized with nuclear magnetic resonance spectroscopy (NMR), FTIR-ATR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mechanical test. The surface properties were studied by goniometer and biocompatibility was evaluated using L929 mouse fibroblast cell line. The FTIR-ATR, and NMR results together provide a proof for the synthesis of the polyurethane polymer. According to thermal analysis results, melting temperature and weight loss were found to be around 48°C and between 300°C–450°C, respectively. Cell culture studies showed that the cells attached and proliferated well and had proper morphology on PU films.