Fundamentals of tissue engineering: carrier materials and an application.
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Animals↗
Biomedical subjects
V Hasirci
Publications and source records attributed to V Hasirci.
Fundamentals of tissue engineering: tissues and applications.
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Biocompatible Materials↗
Versatility of biodegradable biopolymers: degradability and an in vivo application.
Biodegradable materials have various important applications in the biomedical field. There are basically two groups of polyesters which have significant importance in this field. These are polylactides and polyhydroxybutyrates. Both groups degrade via hydrolysis with the rates of degradation depending on medium properties such as pH, temperature, solvent and presence of biocatalysts, as well as on chemical compositions. In order for these biomaterials to be suitable for use in load bearing applications without deformation or warping their strengths and their capability to maintain their form must be improved. To insure dimensional stability during degradation and to match modulus and strength to that of bone, introduction of a reinforcing structure for those applications to plate fixation through the creation of an interpenetrating network might be a feasible approach. In this study, poly(lactide-co-glycolide) (PLGA), was the major structural element to be strengthened by a three-dimensional network or "scaffold" of another biodegradable polymer, poly(propylene fumarate) (PPF). PPF would be crosslinked with a biocompatible vinyl monomer, vinylpyrrolidone (VP). Three different approaches were tested to create dimensionally stable bone plates. First, via in situ crosslinking of PPF in the presence of PLGA. Secondly, by blending of precrosslinked PPF with PLGA. Finally, by simultaneous crosslinking and molding of the PLGA, PPF and VP. These were compared against extruded or compression molded PLGA controls. Results showed that compression molding at room temperature followed by crosslinking under pressure at elevated temperature and subsequently by gamma-irradiation appeared to yield the most favorable product as judged by swelling, hardness and flexural strength data. The composition of the implant material, PLGA(3):PPF(1):VP(0.7), appeared to be suitable and formed the compositional and procedural basis for in vivo biocompatibility studies.
Absorbable Implants↗
In vivo application of biodegradable controlled antibiotic release systems for the treatment of implant-related osteomyelitis.
In this study the construction and in vivo testing of antibiotic-loaded polyhydroxyalkanoate rods were planned for use in the treatment of implant-related osteomyelitis. The rods were constructed of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), carrying 50% (w/w) Sulperazone or Duocid. They were implanted in rabbit tibia in which implant-related osteomyelitis (IRO) had been induced with Staphylococcus aureus. The effectiveness of the antibiotics in the treatment of IRO was determined. The establishment of IRO with bacterial inoculation was complete after 3 weeks with 100% infection rate in all groups. There was no contamination or super-infection. Both antibiotics were found to be highly effective against the bacteria. Following the application of Sulperazone-P(3-HB-co-4-HB) rods, no infective agents could be isolated from the infection site within the 6-week test period, indicating complete treatment of the infection. Macroscopical evaluation at follow-up revealed no drainage, minimal swelling and increase in local warmth, most probably due to the surgery rather than to a reaction towards the implant. The overall scores for radiological findings by the end of 6 weeks were 0.8/5 for the antibiotic-loaded rod implanted in the right limb, and 1.1/5 for the antibiotic-free rod implanted in the left limb. There was no statistical difference between the antibiotic-loaded and antibiotic-free polymeric rods. In vivo drug release was almost complete within the first week. One interesting observation, however, was that the therapy was still very effective even when the release rate was very high. In the SEM of in vitro tested rods, the polymeric component was unchanged in 2 weeks while the drug leached out, leaving voids behind. In vivo, however, the morphology of the implant was significantly modified within 6 weeks post-implantation. Since a substantial degree of the in vivo drug release was complete within 1 week, we believe that dissolution of the drug must be the predominant mechanism through which the drug release is controlled.
Absorbable Implants↗
Expression of liver-specific functions by rat hepatocytes seeded in treated poly(lactic-co-glycolic) acid biodegradable foams.
Techniques of liver replacement would benefit patients awaiting donor livers and may be a substitute for transplantation in patients whose livers can regenerate. Poly(lactic-co-glycolic acid) (PLGA) copolymers are biodegradable and have been shown to be useful as scaffolds for seeding and culturing various types of cells. In this study, foam disks were prepared from PLGA (lactic-to-glycolic mole ratio of 85:15) by lyophilization of benzene (5% w/v) solutions. These disks were then used as scaffolds for rat hepatocyte culture. Foams were coated with either a type I collagen gel (0.1% w/v), coated with gelatin (5% w/v), or treated with oxygen plasma (25 W, 90 s) to modify their surface chemistry and wettability. The disks were then seeded with rat hepatocytes (10(6)/mL) and cultured for a period of 2 weeks. All surface treatments resulted in increased hydrophilicity, the greatest being obtained by collagen treatment (contact angle < 10 degrees ), and a minimal decrease in void fraction (5%). DNA content after a 2-week culture period increased proportionally with the wettability of the treated foam surface. Urea synthesis in untreated foams averaged 15.3 +/- 2.3 microg/h/microg DNA, which was significantly higher than that for controls, whereas gelatin and collagen treated foams exhibited urea synthetic rates below the control levels at all times. The DNA content decreased significantly by about 50% between days 1 and 12. PLGA foams, treated and untreated, represent a promising scaffold for scaling up hepatocyte cultures.
Animals↗
Biodegradable polyhydroxyalkanoate implants for osteomyelitis therapy: in vitro antibiotic release.
Various random copolyesters of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV) and 3-hydroxybutyrate and 4-hydroxybutyrate P(3HB-4HB) were used in the construction of biodegradable, implantable rods for the local delivery of antibiotics (Sulperazone and Duocid) in chronic osteomyelitis therapy. Drug loading, type of active agent, and additional coating of the implant surface all have significant contributions to the in vitro release profile. The rate and duration of Sulperazone release from P(3HB-4HB) rods were controlled by the polymer/drug ratio (drug loading). The rate of drug dissolution was substantially higher than that of polymer degradation. Therefore, the release phenomenon was more dependent on drug dissolution rather than on polymer degradation or diffusion. Coating rods with the same type of polymer substantially reduced the initial burst effect observed with the uncoated rods, and significantly decreased the release rate so that the release kinetics became almost zero order. Antibiotic release from coated rods was sustained for over a period of 2 weeks at a constant rate, whereas uncoated rods released their contents in less than a week. Impregnation of Duocid into the hydrophobic polymer matrix yielded a rod with a smoother surface topography. The release from these rods was significantly higher than for rods loaded with Sulperazone and a zero order release could not be obtained with these samples.
Ampicillin↗
Immobilization of acetylcholinesterase and choline oxidase in/on pHEMA membrane for biosensor construction.
In this study, acetylcholinesterase (AChE) and choline oxidase (ChO) were co-immobilized on poly(2-hydroxyethyl methacrylate) (pHEMA) membranes with the aim of using them in biosensor construction. pHEMA membranes were prepared with the addition of different salts in different HEMA: aqueous solution ratios and characterized in terms of porosity, thickness. permeability, and mechanical properties. Membranes prepared in the presence of SnCl4 were found to be superior in terms of porosity and permeability and were chosen as the immobilization matrix. Immobilization of the enzymes was achieved both by entrapment and surface attachment via epichlorohydrin (Epi) and Cibacron Blue F36A (CB) activation. The effect of immobilization on enzyme activity was evaluated by the comparison of Km and Vmax values for the free and immobilized bi-enzyme systems. The increase in Km was negligible (1.08-fold) for the bi-enzyme system upon immobilization on surface but was 2.12-fold upon entrapment. Specific activity of the free enzyme system was found to be 0.306 mV s(-1) microg(-1) ChO while it was 0.069 (4.43-fold decrease) for entrapped and 0.198 (1.54 fold decrease) for CB-Epi immobilized enzymes. The performance of immobilized enzymes in different buffer types, pH, and temperature conditions were evaluated. The best enzyme activity was obtained at pH 9.0. Activity of the enzymes was found to increase with increasing temperature (in the range 25-40 degrees C).
Acetylcholinesterase↗
In vivo response to biodegradable controlled antibiotic release systems.
In this study, the major goal was to evaluate in vitro and in vivo findings by macroscopy, radiology, and histology to determine the effectiveness of therapy of experimental implant-related osteomyelitis with antibiotic carrier rods constructed of microbial polyesters. The polymers used were poly(3-hydroxybutyrate-co-4-hydroxyvalerate) [P(3-HB-co-4-HB)] and poly(3-hydroxybutyrate-co-3-hydroxy- valerate) [P(3-HB-co-3-HV)]. Both the Sulperazone and the Duocid-P(3-HB-co-4-HB) rods with a drug to polymer ratio of 1:1 (w/w) were effective in treating the bone infection that was experimentally initiated by inoculation of a hemolytic strain of Staphylococcus aureus (coagulase positive; phage type 52/52b) together with metal implants into the medullary area of rabbit tibia. Macroscopical data revealed that the effectiveness of therapy was apparent at week 6 for all categories tested. Radiological findings with Duocid- and Sulperazone-loaded P(3-HB-co-4-HB) rods improved significantly when judged by changes in periosteal elevation, widening of bone shaft, new bone formation, and soft-tissue deformation after 6 weeks of implantation. Histologically the signs of infection were found to subside by weeks 3 and 6. Inflammatory cells were replaced with bone-forming cells upon treatment with Sulperazone-P(3-HB-co-4-HB) and Duocid-P(3-HB-co-4-HB). Osteoblastic activity was prominent. Intramedullary inflammation, although still present, started to be replaced by fibrous or bony tissue. Histological findings presented the subsidence of infection. In summary, the antibiotic-loaded biopolymeric rods appeared to have potential as a new controlled-release system for the treatment of implant related osteomyelitis and chronic osteomyelitis.
Animals↗
Biodegradable foam coating of cortical allografts.
Clinical outcomes of bone allograft procedures may be improved by modifying the surface of the graft with an osteoconductive biopolymeric coating. In this comparative in vitro study, we evaluated the dimensional stability, mechanical strength, hydrophilicity, and water uptake of biodegradable foams of poly(propylene fumarate) (PPF) and poly(d,l-lactic-co glycolic acid) (PLGA) when applied as surface coatings to cortical bone. Cortical bone samples were divided into four groups: Type I, untreated bone; Type II, laser-perforated bone; Type III, partially demineralized bone; and Type IV, laser-perforated and partially demineralized bone. Results show that PPF wets easily, achieving 12.5% wt/wt in 30 min. Compressive tests on the PPF foam material showed that the compressive strength was 6.8 MPa prior to in vitro incubation but then gradually reduced to 1.9 MPa at 8 weeks. Push-out and pulloff strength tests showed that initially both PPF and PLGA foam coatings had comparable adherence strengths to the cortical bone samples (100-150 N). When additional geometrical surface alteration by perforation and demineralization of the bony substrate was employed, in vitro adherence of the PPF foam coating was further increased to 120 N, demonstrating a statistically significant improvement of push-out strength throughout the entire 8-week observation period (p<0.0002 for all four data points). The pore geometry of PPF-foam coatings changed little over the 2-month evaluation period. In comparison, PLGA foam coating around the cortical bone samples rapidly lost structure with a decrease of 67% in strength seen after 1-week in vitro incubation. These new types of bone allografts may be particularly useful where the use of other replacement materials is not feasible or practical.
Bone Remodeling↗
Tissue responses to molecularly reinforced polylactide-co-glycolide implants.
Plates for internal fixation fabricated from biodegradable polymers degrade via an autocatalytic route. When they are used in bone implants of significant size and thickness, hollowing of the implant may occur while the overall dimensions appear unchanged. We hypothesized that incorporation of a cross-linked polypropylene fumarate matrix into polylactide-co-glycolide bone plates may provide an internal molecular network which prevents implant collapse. Cross-linking reagents of varying hydrophilicity including N-vinylpyrrolidone (VP), hydroxyethylmethacrylate (HEMA), and ethyleneglycol dimethacrylate (EGDMA) were employed. With the objective of determining the most biocompatible and structurally sound composition for molecular reinforcement, we investigated tissue responses in both subcutaneous and orthotopic rodent implantation models in relation to maintenance of implant integrity by histologic, histomorphometric, and stereomicroscopic analysis. Results showed that tissue responses were correlated with dimensional stability of the implants. The most favorable results were seen with the hydrophobic cross-linker EGDMA; this may have been related to the initial reduction of the water uptake by the implant. Cross-linking of polypropylene fumarate with EGDMA within a polylactide-co-glycolide bone plate may offer a means to maintain excellent biocompatibility while improving dimensional stability of biodegradable bone plates.
Animals↗
High strength bioresorbable bone plates: preparation, mechanical properties and in vitro analysis.
Biodegradable bone plates were prepared as semi-interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide-co-glycolide)-85:15 (PLGA) or poly(1-lactide-co-d,l-lactide)-70:30 (PLA) using N-vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100-140 degrees C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50-67 MPa, (3) flexural modulus of 7-13 GPa, and (4) manufacturability stiffness of 300-600 N/m. HAP-loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF-SIPN did not show any additional improvement of mechanical properties.
Absorbable Implants↗
Sulbactam-cefoperazone polyhydroxybutyrate-co-hydroxyvalerate (PHBV) local antibiotic delivery system: in vivo effectiveness and biocompatibility in the treatment of implant-related experimental osteomyelitis.
In this study, a novel antibiotic carrier system for use in the treatment of implant-related and chronic osteomyelitis was developed. Sulbactam-cefoperazone was introduced to rods of polyhydroxybutyrate-co-hydroxyvalerate (22 mol % HV, w/w), a member of a family of microbial-origin polymer that is biodegradable, biocompatible, and osteoconductive due to its piezoelectric property. The antibiotic-loaded carrier was implanted into the infection site that was induced by Staphylococcus aureus inoculation into the rabbit tibia. The effectiveness of this was assessed macroscopically, radiographically, bacteriologically, and histopathologically. Findings of infection subsided on day 15 and almost complete remission was observed on day 30. The control side that contained antibiotic-free rods, however, worsened. These findings prompted us to conclude that the novel biodegradable antibiotic carrier developed in the present study seems to be a promising candidate for use in the treatment of severe bone infection.
Animals↗
Antibiotic release from biodegradable PHBV microparticles.
For the treatment of periodontal diseases, design of a controlled release system seemed very appropriate for an effective, long term result. In this study a novel, biodegradable microbial polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV of various valerate contents containing a well established antibiotic, tetracycline, known to be effective against many of the periodontal disease related microorganisms, was used in the construction of a controlled release system. Tetracycline was loaded in the PHBV microspheres and microcapsules both in its acidic (TC) and in neutral form (TCN). Microcapsules of PHBV were prepared under different conditions using w/o/w double emulsion and their properties such as encapsulation efficiency, loading, release characteristics, and morphological properties were investigated. It was found that concentration of emulsifiers polyvinyl alcohol (PVA) and gelatin (varied between 0-4%) influenced the encapsulation efficiency appreciably. In order to increase encapsulation efficiency (from the obtained range of 18.1-30.1%) and slow down the release of the highly soluble tetracycline.HCl, it was neutralized with NaOH. Encapsulation efficiency of neutralized tetracycline was much higher (51.9-65.3%) due to the insoluble form of the drug used during encapsulation. The release behaviour of neither of the drugs was found to be of zero order. Rather the trends fitted reasonably well to Higuchi's approach for release from spherical micropheres. Biodegradability was not an appreciable parameter in the release from microcapsules because release was complete before any signs of degradation were observed.
Bacteria↗
Development of a calcium phosphate-gelatin composite as a bone substitute and its use in drug release.
This study was carried out to develop a calcium phosphate-gelatin composite implant that would mimic the structure and function of bone for use in filling voids or gaps and to release bioactive compounds like drugs, growth hormones into the implant site to assist healing. XDS analysis of the synthesized calcium phosphate revealed a calcium to phosphorus molar ratio of ca. 2.30, implying a less erodible material than hydroxyapatite (1.67). Release of the antibiotic gentamicin from the implant was with a burst, whether in situ or in vivo, followed by an almost constant release for about three months. It was found that the release rate could be decreased by increasing the density of the gelatin membrane. Upon implantation into rabbit tibia the release duration was substantially shortened (to about 4 weeks) with respect to the in situ tests basically due to the degradation of gelatin. In vivo studies with rabbits confirmed this degradation. The composite was perfectly biocompatible as shown by the histological studies. It, thus, has a great potential as a bone substitute material.
Animals↗
A novel osteochondral implant.
A novel implant for the use as an osteochondral graft was designed. This implant was prepared by stepwise formation of calcium phosphate crystals within the matrix of a lyophilised collagen sponge. Chondrocytes were then grown on this material to create the osteochondral implant. The implant was characterized with light microscopy, scanning electron microscopy (SEM), electron diffraction crystallography (EDX), and IR. It was observed with IR that the implant had a peak, that was not found so distinctly in its components, at 1400 cm(-1), implying a strong interaction of the two main ingredients of the implant, calcium phosphate and collagen. This strong interaction was also shown in the graft degradation test while the untreated collagen sponge degraded rapidly (in one day) the mineral loaded implant was able to maintain its integrity for two weeks. In the chondrocyte culture medium degradation of the implant was shown by a decrease of the calcium content and calcium to phosphorous ratio. Also, EDX revealed the presence of sulfur one and two weeks after incubation, an element not found among the components of the implant, possibly due to the development of an extracellular matrix. SEM showed that the form of the crystals of calcium phosphate differed depending on whether they were prepared on the template, collagen, or in the absence of a template. The chondrocytes appeared to be growing in number on the implant and their shapes were morphologically normal. The chondrocyte loaded collagen-calcium phosphate composite could thus be considered a potential tissue engineered osteochondral implant.
Biocompatible Materials↗
An overview of the role of mineral solubility in silicosis and asbestosis.
Asbestosis and silicosis are fibrotic diseases initiated by the inhalation of silica-containing dusts, asbestos and quartz. There are various approaches for explaining the causes of these diseases. At present, our knowledge on the matter indicates that silicic acid dissolved from these minerals, contact between macrophages and minerals, highly reactive and oxidative species formed on the mineral surface, and lysosomal enzymes released upon engulfment of particulate mineral of appropriate size all contribute to various extents to the initiation of fibrosis. Among these mineral solubility seems to have a substantial contribution as a causative factor.
Asbestosis↗
Synthesis and mechanical properties of interpenetrating networks of polyhydroxybutyrate-co-hydroxyvalerate and polyhydroxyethyl methacrylate.
Naturally occurring, biocompatible, and biodegradable polyhydroxybutyrate-co-hydroxyvalerate (PHBV), and synthetic, non-degrading polyhydroxyethylmethacrylate (PHEMA) membranes were prepared and their mechanical properties were studied. Their performances were compared with the interpenetrating networks (IPN) prepared by photopolymerization of HEMA in the presence of PHBV. The modulus of elasticity, failure stress and failure strain indicated that the IPNs are viscoelastic with properties closer to PHEMA but much stronger than PHEMA homopolymers. Incorporation of PHBV (7, 14 and 22% HV) affected the mechanical properties positively. Increasing the PHBV content increased the modulus of elasticity and failure stress nearly in all samples tested. PHBV (7, 14, and 22% HV, 300 mg) samples showed an approximately 17-30 fold increase in terms of modulus of elasticity and 7-10 fold increase in terms of failure stress. The scanning electron micrographs of the membranes showed that the PHEMA membranes are more porous than the PHBV membranes but the IPN structure displayed channels on the membrane surface indicating that HEMA polymerization was achieved by using the PHBV as a scaffold. With the use of the present technique, it is possible to synthesize supramolecular structures from molecules that are not compatible and miscible with each other.
Biocompatible Materials↗
Imaging of liposomes by scanning tunneling microscopy.
In this study, unilamellar and multilamellar liposomes consisting of dipalmitoylphosphatidylcholine, cholesterol and dicetylphosphate were prepared. Scanning tunneling microscopy images of these liposomes on highly oriented pyrolytic graphite surfaces were obtained. It was observed that scanning tunnelling microscopy can be successfully used for high-resolution, three-dimensional structure analysis of liposomes under very mild conditions.
1,2-Dipalmitoylphosphatidylcholine↗