Tugba Endogan

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.

Blood compatibility of polymers derived from natural materials

Several polymers derived from natural materials are effective for tissue engineering or drug delivery applications, due to specific properties, such as biocompatibility, biodegradability, and structural activity. Their blood compatibility needs to be carefully evaluated to avoid thrombosis and other material-related adverse events in the hematic environment. We compared the surface properties and blood compatibility of protein and polysaccharide polymers, including fibroin, gelatin, and chitosan. Both fibroin and chitosan showed good hemocompatibility, with low platelet adhesion and spreading. Chitosan induced strong interactions with plasma proteins, especially with albumin. It was hypothesized that surface passivation by albumin inhibited the adsorption of other procoagulant and proadhesive proteins on chitosan and fibroin films, which limited platelet spreading. However, the significant and rapid polymer swelling encouraged protein entrapment within the soft, gelatin films, inducing higher platelet adhesion and activation. Thrombin generation assay confirmed the higher blood compatibility of chitosan and fibroin with regard to clotting.

Microfabrication of PDLLA scaffolds

This study aimed to comprehend the potentialities of the microfabrication to produce tissue‐engineering scaffolds. Structures presenting homogeneously distributed pores of size 100 and 200 µm were fabricated through layer‐by‐layer deposition of filaments of poly(D,L‐lactic acid) (PDLLA) prepared from dichloromethane/dimethylformamide solutions. Rheological tests on the solution and molecular weight distributions of PDLLA, solvent cast films and microfabricated scaffolds were performed to determine which material conditions are optimal for the microfabricated system and to identify any possible material modification induced by the process. In vitro qualitative preliminary cell culture studies were conducted using MG63 osteoblast cell lines after assuring the non‐cytotoxicity of the scaffold material by the lactate dehydrogenase in vitro toxicology assay; biological evaluations were initially performed using scaffolds with the smaller (100 µm) pore size. Scanning electron microscopy imaging was used to determine cell morphology distribution. A second cell culture test was performed, using the scaffold with the higher (200 µm) porosity. Confocal laser microscopy (CLM) was utilized to examine cell morphology and growth behaviour. Cellular metabolic activity and viability were also examined using Alamar Blue assay and further verifications were performed using CLM. Cell culture studies indicated homogeneous distribution, high viability and metabolic activity. Pore dimension affects cell distribution: pores < 100 µm acted as barrier structures for the MG63 osteoblast cell line; penetration inside the matrix was hindered and cells grew on the outer part. Increasing pore size resulted in a more homogeneous cell distribution and penetration of cells inside the structure was achieved. Copyright

Polymer Fundamentals: Polymer Synthesis

Polymers can be of biological and synthetic origin, and are very important in our daily lives. They are used in all the major industries including textile, automotive, household goods, medical devices and products, etc. The significant difference between the requirements of these applications necessitates the availability of a large variety of polymers to choose from. Synthetic polymers can be prepared by addition and condensation polymerization using a variety of polymerization processes to yield polymers with differences in their stereoregularity, organization of their constituents, molecular weight, and crystallinity. All these differences yield polymers with different mechanical properties. Since the number of monomers available is very high, the variety of the polymers theoretically possible is also high. Some become viscoelastic and some are just plastic. Polymers are not always linear like noodles but can be made to have branches either of the same monomer or by adding other monomers to change the chemistry and the crystallinity of the product. They can be further branched or cross-linked so that the polymer becomes insoluble, and just swells in its linear polymers solvents creating the gels. Or, a number of monomers can be used simultaneously to prepare macromolecules with properties that can be tailored to the needs of the application. All these play a deciding role on whether a polymer is suitable for load-bearing applications or in replacing the soft tissues in the human body. In this chapter, the main approaches to polymer synthesis and the parameters influencing the properties of the final product are discussed.

Effects of Local and Sustained Release of FGF, IGF, and GH on Germ Cells in Unilateral Undescended Testis in Rats

OBJECTIVES To evaluate the effects of the local release of fibroblast growth factor (FGF), insulin-like growth factor (IGF), and growth hormone (GH) on a germ cell population of ipsilateral undescended and contralateral descended testes of rats with a surgically created unilateral abdominal testis for 12 weeks and after the application of growth factors after orchidopexy. METHODS Forty 4-week old male Wistar albino rats were divided into 5 groups as follows: group 1, sham; group 2, gelatin; group 3, FGF; group 4, IGF; and group 5, GH. In the sham group, the right testis was exposed and sutured with 5-0 silk sutures. In groups 2-5, a right intra-abdominal testis was surgically created. After 12 weeks, orchidopexy was performed, and 1 cm(2) gelatin films were sutured to the right testes, either unloaded (group 2), or containing 2.5 microg FGF (group 3), 5 microg IGF (group 4), or 5 microg GH (group 5). After 30 days, both testes were removed for histopathologic investigation and DNA flow cytometry. The mean seminiferous tubular diameters (MSTDs), mean testicular biopsy scores (MTBSs), and percentages of haploid (1n) cells were calculated. RESULTS Ipsilateral MSTD and MTBS significantly decreased in the gelatin and FGF groups compared with the sham, IGF, and GH groups. Contralateral MSTDs and MTBSs did not differ among groups. The haploid cell percentage significantly decreased in the ipsilateral and contralateral testes of the gelatin group compared with the sham, FGF, IGF, and GH groups. CONCLUSIONS Local release of IGF and GH resulted in the preservation of germ cell histology in the ipsilateral testes of rats with a surgically created unilateral undescended testis for 12 weeks and after orchidopexy. The administration of IGF, GH, and FGF increased the haploid germ cell population in both ipsilateral undescended and contralateral descended testes.

1.121 – Polymer Fundamentals: Polymer Synthesis

Polymers can be of biological and synthetic origin, and are very important in our daily lives. They are used in all the major industries including textile, automotive, household goods, medical devices and products, etc. The significant difference between the requirements of these applications necessitates the availability of a large variety of polymers to choose from. Synthetic polymers can be prepared by addition and condensation polymerization using a variety of polymerization processes to yield polymers with differences in their stereoregularity, organization of their constituents, molecular weight, and crystallinity. All these differences yield polymers with different mechanical properties. Since the number of monomers available is very high, the variety of the polymers theoretically possible is also high. Some become viscoelastic and some are just plastic. Polymers are not always linear like noodles but can be made to have branches either of the same monomer or by adding other monomers to change the chemistry and the crystallinity of the product. They can be further branched or cross-linked so that the polymer becomes insoluble, and just swells in its linear polymers solvents creating the gels. Or, a number of monomers can be used simultaneously to prepare macromolecules with properties that can be tailored to the needs of the application. All these play a deciding role on whether a polymer is suitable for load-bearing applications or in replacing the soft tissues in the human body. In this chapter, the main approaches to polymer synthesis and the parameters influencing the properties of the final product are discussed.

Preparation and characterization of natural polymer-based composite films for hard tissue engineering approaches

Hard tissue engineering has emerged to compensate for the losses in the properties of damaged bones by using scaffolds and cells. In this study, natural polymers chitosan and gelatin were used as scaffold materials because of their great resemblance to extracellular matrix elements. To enhance the mechanical properties and osteoconductivity of structures hydroxyapatite was added. This study is about the characterization of physico-chemical properties and cell behavior on scaffolds to optimize chitosan-gelatin ratio and aims to assess the effects of hydroxyapatite addition into polymeric matrix. According to thermal test results, decomposition temperatures decreased with non-sintered hydroxyapatite (nsHA) addition. Mechanical test results of composite structures were similar to that of cortical bone. Chitosan-gelatin films prepared with same amount of polymers showed the highest swelling degree. While nsHA added pure chitoan films showed higher cell number with respect to chitosan films; on the contrry, chitosan-gelatin polymeric blends indicated an opposite trend after nsHA addition.

Preparation and characterization of chitosan containing acrylic bone cement formulations

Bone cements are used in orthopaedic surgery and dentistry, and the commonly used commercial ones are prepared from poly (methylmethacrylate) (PMMA). In orthopaedic surgery bone cements are used as filling agents for the treatment of damaged tissues and they are used to stabilize the prosthesis by providing the mechanical interlock between bone and metal during the use of metal prothesis and to provide the homogeneous distribution of applied load. In this study, bone cements compositions were prepared by using two different PMMA (microspheres prepared by suspension polymerization and ground and sieved PMMA particles). Compositions were prepared by addition of hydroxyapatite (HA) as inorganic load carrying substance, and barium sulphate (BaSO4) as opacifier. To increase biocompatibility of the prepared bone cements, natural polymer chitosan was added. It was observed that addition of chitosan had a positive effect on mechanical properties.