Halil Murat Aydin

Improving pore interconnectivity in polymeric scaffolds for tissue engineering

A new scaffold fabrication technique aiming to enhance pore interconnectivity for tissue engineering has been developed. Medical grade poly(lactic acid) was utilized to generate scaffolds by a solvent‐evaporating/particulate‐leaching technique, using a new dual‐porogen system. Water‐soluble sodium chloride particles were used to control macro‐pore size in the range 106–255 µm, while organic naphthalene was utilized as a porogen to increase pore interconnections. The three‐dimensional (3D) morphology of the scaffolds manufactured with and without naphthalene was examined by optical coherence tomography and scanning electron microscopy. The mechanical properties of the scaffolds were characterized by compression tests. MG63 osteoblast cells were seeded in the scaffolds to study the cell attachment and viability evaluated by confocal microscopy. It was revealed that introducing naphthalene as the second porogen in the solvent‐evaporating/particulate‐leaching process resulted in improvement of the pore interconnectivity. Cells grew in both scaffolds fabricated with and without naphthalene. They exhibited strong green fluorescence when using a live/dead fluorescent dye kit, indicating that the naphthalene in the scaffold process did not affect cell viability. Copyright

A 6-month in vivo study of polymer/mesenchymal stem cell constructs for cranial defects

Two biodegradable polymers, poly(L-lactide) and poly(ε-caprolactone) were blended (50/50) and used to produce polymeric scaffolds by the dual porogen approach using a salt leaching technique to create pores within the matrix, while supercritical-CO 2 treatment was used to enhance the interconnectivity and to remove impurities from synthesis steps. The scaffolds were highly porous (porosity >90%) with interconnected pore morphologies. These biodegradable scaffolds were evaluated in Sprague Dawley rats for osteoconductive properties over a 6-month period. Bone specimens were analyzed after 1, 3, and 6 months, for bone healing and tissue response. The cortical bone remodeling by controlled osteoblastic and osteoclastic activities as well as the bone marrow elements recovery were semi-quantitatively examined for each group. Excellent integration and biocompatibility behavior was observed in all groups. No adverse tissue responses were observed.

Microwave-assisted rapid synthesis of poly(glycerol-sebacate) elastomers

Poly(glycerol-sebacate) (PGS) was introduced a decade ago as a potential material for soft tissue repair. All of the proposed copolymerization reactions in the literature include a two-stage (prepolymerization and curing) synthesis where the reaction times can take as long as several days. This study, on the other hand, proposes a new route that eliminates these disadvantages and enables a rapid synthesis of PGS elastomers via microwave-assisted prepolymerization in minutes instead of days. No purge gas, catalyst or vacuum is needed in the first prepolymerization step. The curing stage was carried out at 150 °C for 4, 8, 16, and 24 hours. The glass transition temperature (Tg) and melting temperatures for the glycerol and sebacic acid fragments (Tm1 and Tm2 ) of these PGS elastomers were found as -35.61 °C, -15.82 °C, and 61.70 °C, respectively. The Youngs modulus and tensile strength values were found as 0.50 ± 0.02 MPa and 0.27 ± 0.06 MPa, respectively.

Aminated poly(vinyl chloride) solid state adsorbents with hydrophobic function for post-combustion CO2 capture

In this paper, we show a novel sustainable route for the production of sorption materials for carbon capture technologies by utilizing a general plastic waste. By supporting aminated poly(vinyl chloride) on mesoporous silicas, a family of polymer/silica composites was synthesized, characterized and tested gravimetrically for adsorption of CO2 from the 1 : 1 v/v CO2–N2 mixture. The composites show good adsorption capacity for CO2 peaking at 12 cm3 g−1 for ethylenediamine-treated PVC products on SBA-15 support. The adsorption efficiency (CO2 : N ratio) is comparable to those observed for other nanoporous materials, such as amine-grafted mesoporous silicas. Ethylenediamine was found to be the best aminating reagent for PVC as the composite prepared from EDA–PVC gave the highest CO2 adsorption efficiency. Moreover, contact angle measurements suggested a significant improvement in hydrophobicity of the selected composites when they were compared with the unfunctionalized silica supports. This very useful development could make the composites suitable for applications in elevated moisture content environments found in flue vapours of gas-fired power plants.

Synthesis and characterization of poly(glycerol-co-sebacate-co-ε-caprolactone) elastomers

In this study, poly(glycerol‐co‐sebacate‐co‐ε‐caprolactone) (PGSCL) elastomers were synthesized for the first time from the respective monomers. The structural analysis of PGSCL elastomers by nuclear magnetic resonance (1H‐NMR) and Fourier transform infrared spectroscopy (FTIR) revealed that the elastomers have a high number of hydrogen bonds and crosslinks. X‐ray diffraction (XRD) and thermal analysis indicated an amorphous state. Differential scanning calorimetry (DSC) analysis showed that the elastomers has a glass transition temperature (Tg) of –36.96°C. The Youngs modulus and compression strength values were calculated as 46.08 MPa and 3.192 MPa, respectively. Calculations based on acid number and end groups analysis revealed a number average molecular weight of 148.15 kDa. Even though the foaming studies conducted by using supercritical CO2 resulted in a porous structure; the obtained morphology tended to disappear after 48 h, leaving small cracks on the surface. This phenomenon was interpreted as an indication of self‐healing due to the high number of hydrogen bonds. The PGSCL elastomers synthesized in this study are flexible, robust to compression forces and have self‐healing capacity. Thanks to good biocompatibility and poor cell‐adhesion properties, the elastomers may find diverse applications where a postoperative adhesion barrier is required. Copyright

Supercritical Carbon Dioxide (sc-CO2) Assisted Decellularization of Aorta and Cornea.

Tissue engineering approaches utilize both natural and synthetic materials in the repair and regeneration processes. A naturally sourced material for this purpose is required to be free from any antigenic matter such as cells or cellular components. Decellularization of tissues may be achieved through chemical or physical removal agents. Supercritical carbon dioxide (sc-CO2) has been used on the purpose of removing bioburden from tissues and offers an alternative to the traditionally used treatment methods. In addition to many advantages it offers with regard to the successful decellularization of tissues, it is known to have a sterilization effect. This study provides an insight into sc-CO2-assisted decellularization trials of corneal and aortic tissues. Results showed that high pressure of the fluid bursts the cells during the treatment and rapid depressurization was found to be effective in the removal of the cells from the tissues. sc-CO2 decellularization offers significantly reduced treatment times, complete decellularization, and preserved extracellular matrix structure.

Bi-layered constructs of poly(glycerol-sebacate)-β-tricalcium phosphate for bone-soft tissue interface applications

This study aims to establish a facile protocol for the preparation of a bi-layered poly(glycerol-sebacate) (PGS)/β-tricalcium phosphate (β-TCP) construct and to investigate its potential for bone-soft tissue engineering applications. The layered structure was prepared by distributing the ceramic particles within a prepolymer synthesized in a microwave reactor followed by a cross-linking of the final construct in vacuum (<10mbar). The vacuum stage led to the separation of cross-linked elastomer (top) and ceramic (bottom) phases. Results showed that addition of β-TCP particles to the elastomer matrix after the polymerization led to an increase in compression strength (up to 14±2.3MPa). Tensile strength (σ), Youngs modulus (E), and elongation at break (%) values were calculated as 0.29±0.03MPa and 0.21±0.03; 0.38±0.02 and 1.95±0.4; and 240±50% and 24±2% for PGS and PGS/β-TCP bi-layered constructs, respectively. Morphology was characterized by using Scanning Electron Microscopy (SEM) and micro-computed tomography (μ-CT). Tomography data revealed an open porosity of 35% for the construct, mostly contributed from the ceramic phase since the elastomer side has no pore. Homogeneous β-TCP distribution within the elastomeric structure was observed. Cell culture studies confirmed biocompatibility with poor elastomer-side and good bone-side cell attachment. In a further study to investigate the osteogenic properties, the construct were loaded with BMP-2 and/or TGF-β1. The PGS/β-TCP bi-layered constructs with improved mechanical and biological properties have the potential to be used in bone-soft tissue interface applications where soft tissue penetration is a problem.

Tri-layered composite plug for the repair of osteochondral defects: in vivo study in sheep:

Cartilage defects are a source of pain, immobility, and reduced quality of life for patients who have acquired these defects through injury, wear, or disease. The avascular nature of cartilage tissue adds to the complexity of cartilage tissue repair or regeneration efforts. The known limitations of using autografts, allografts, or xenografts further add to this complexity. Autologous chondrocyte implantation or matrix-assisted chondrocyte implantation techniques attempt to introduce cultured cartilage cells to defect areas in the patient, but clinical success with these are impeded by the avascularity of cartilage tissue. Biodegradable, synthetic scaffolds capable of supporting local cells and overcoming the issue of poor vascularization would bypass the issues of current cartilage treatment options. In this study, we propose a biodegradable, tri-layered (poly(glycolic acid) mesh/poly(l-lactic acid)-colorant tidemark layer/collagen Type I and ceramic microparticle-coated poly(l-lactic acid)-poly(ϵ-caprolactone) monolith) osteochondral plug indicated for the repair of cartilage defects. The porous plug allows the continual transport of bone marrow constituents from the subchondral layer to the cartilage defect site for a more effective repair of the area. Assessment of the in vivo performance of the implant was conducted in an ovine model (n = 13). In addition to a control group (no implant), one group received the implant alone (Group A), while another group was supplemented with hyaluronic acid (0.8 mL at 10 mg/mL solution; Group B). Analyses performed on specimens from the in vivo study revealed that the implant achieves cartilage formation within 6 months. No adverse tissue reactions or other complications were reported. Our findings indicate that the porous biocompatible implant seems to be a promising treatment option for the cartilage repair.

Characterization of scaffold architecture by optical coherence tomography

Cells, scaffold and culture environment are the three essential elements in engineering tissue constructs. Among these elements, the scaffold plays a critical role in converting cells into tissue since it provides a template and space for cells to grow and produce the desired matrix. Scaffolds are usually fabricated into three-dimensional blocks from biodegradable polymers with different internal architectures, for instance they are with fibrous or porous structures. The mechanical properties and nutrient diffusion ability of scaffolds are highly dependent on their internal structure. The biodegradable feature of scaffolds leads to a dramatic change in their microstructure during in vitro culture or after implantation. In this study, we explore optical coherence tomography (OCT) as a potential tool to characterize architecture of scaffolds including porosity, pore distribution and interconnectivity. This instrument is a fibre based time domain OCT equipped with a 1300 nm superluminescent diode, with a bandwidth of 52 nm and a free space resolution of 16x16x14 μm. Two model scaffold systems have been investigated. One was porous poly(lactide) scaffold fabricated by solvent-evaporation and salt leaching technique with dual poregens. Another was fibrous chitosan scaffold produced by wet spinning. Variations of scaffolds architecture, in term of porosity and interconnectivity, with different fabrication conditions could be quantified with the help of a commercial software (Volocity, Improvision). This study demonstrated that OCT can be used as a tool to guide scaffold fabrication and optimise their internal structure. Moreover, it can be used as on-line monitoring for scaffold degradation in various culture conditions.

Evaluation of collagen foam, poly(l-lactic acid) nanofiber mesh, and decellularized matrices for corneal regeneration: EVALUATION OF COLLAGEN FOAM, PLLA, AND DECELLULARIZED MATRICES

Corneal tissue engineering efforts to obtain corneal tissue matrices through various types of materials for the replacement of damaged tissues. In this study, three different corneal constructs were prepared and evaluated in terms of morphological, optical, and biological characteristics. Type-I collagen was used to obtain collagen foam scaffolds through dehydrothermal crosslinking, while poly(l-lactic acid) (PLLA) was used to produce both random and aligned oriented electrospun corneal constructs. Bovine corneas were decellularized as third matrix. Software analyses showed that average pore size of collagen scaffolds was 88.207 ± 29.7 µm, while the average fiber diameter of aligned and random PLLA scaffolds were 0.69 ± 0.03 and 0.65 ± 0.03 μm, respectively. Degradation profiles revealed that collagen foam exhibits high degradation (20% mass loss) while electrospun PLLA scaffolds hold low degradation (9% mass loss) rates at day-28. Transmittance values of the obtained scaffolds were calculated as 92, 80, and 70% for collagen, PLLA, and decellularized cornea constructs, respectively. The evaluation of stromal keratocyte behavior on the constructs revealed that the cells exhibited their own morphology mostly on the aligned PLLA constructs, while they were mostly active on random PLLA electrospun corneal scaffolds.