Mechanisms of polymer degradation in implantable devices. I. Poly(caprolactone)

Polymer-ceramic spiral structured scaffolds for bone tissue engineering: effect of hydroxyapatite composition on human fetal osteoblasts

For successful bone tissue engineering, a scaffold needs to be osteoconductive, porous, and biodegradable, thus able to support attachment and proliferation of bone cells and guide bone formation. Recently, hydroxyapatites (HA), a major inorganic component of natural bone, and biodegrade polymers have drawn much attention as bone scaffolds. The present study was designed to investigate whether the bone regenerative properties of nano-HA/polycaprolactone (PCL) spiral scaffolds are augmented in an HA dose dependent manner, thereby establishing a suitable composition as a bone formation material. Nano-HA/PCL spiral scaffolds were prepared with different weight ratios of HA and PCL, while porosity was introduced by a modified salt leaching technique. Human fetal osteoblasts (hFOBs) were cultured on the nano-HA/PCL spiral scaffolds up to 14 days. Cellular responses in terms of cell adhesion, viability, proliferation, differentiation, and the expression of bone-related genes were investigated. These scaffolds supported hFOBs adhesion, viability and proliferation. Cell proliferation trend was quite similar on polymer-ceramic and neat polymer spiral scaffolds on days 1, 7, and 14. However, the significantly increased amount of alkaline phosphatase (ALP) activity and mineralized matrix synthesis was evident on the nano-HA/PCL spiral scaffolds. The HA composition in the scaffolds showed a significant effect on ALP and mineralization. Bone phenotypic markers such as bone sialoprotein (BSP), osteonectin (ON), osteocalcin (OC), and type I collagen (Col-1) were semi-quantitatively estimated by reverse transcriptase polymerase chain reaction analysis. All of these results suggested the osteoconductive characteristics of HA/PCL nanocomposite and cell maturation were HA dose dependent. For instance, HA∶PCL = 1∶4 group showed significantly higher ALP mineralization and elevated levels of BSP, ON, OC and Col-I expression as compared other lower or higher ceramic ratios. Amongst the different nano-HA/PCL spiral scaffolds, the 1∶4 weight ratio of HA and PCL is shown to be the most optimal composition for bone tissue regeneration.

Surface-modified functionalized polycaprolactone scaffolds for bone repair: in vitro and in vivo experiments

A porcine calvaria defect study was carried out to investigate the bone repair potential of three-dimensional (3D)-printed poly-ε-caprolactone (PCL) scaffolds embedded with nanoporous PCL. A microscopic grid network was created by rapid prototyping making a 3D-fused deposition model (FDM-PCL). Afterward, the FDM-PCL scaffolds were infused with a mixture of PCL, water, and 1,4-dioxane and underwent a thermal-induced phase separation (TIPS) followed by lyophilization. The TIPS process lead to a nanoporous structure shielded by the printed microstructure (NSP-PCL). Sixteen Landrace pigs were divided into two groups with 8 and 12 weeks follow-up, respectively. A total of six nonpenetrating holes were drilled in the calvaria of each animal. The size of the cylindrical defects was h 10 mm and Ø 10 mm. The defects were distributed randomly using following groups: (a) NSP-PCL scaffold, (b) FDM-PCL scaffold, (c) autograft, (d) empty defect, (a1) NSP-PCL scaffold + autologous mononuclear cells, and (a2) NSP-PCL scaffold + bone morphogenetic protein 2. Bone volume to total volume was analyzed using microcomputed tomography (µCT) and histomorphometry. The µCT and histological data showed significantly less bone formation in the NSP-PCL scaffolds in all three variations after both 8 and 12 weeks compared to all other groups. The positive autograft control had significantly higher new bone formation compared to all other groups except the FDM-PCL when analyzed using histomorphometry. The NSP-PCL scaffolds were heavily infiltrated with foreign body giant cells suggesting an inflammatory response and perhaps active resorption of the scaffold material. The unmodified FDM-PCL scaffold showed good osteoconductivity and osseointegration after both 8 and 12 weeks.

Cenderitide-eluting film for potential cardiac patch applications

Cenderitide, also known as CD-NP, is a designer peptide developed by combining native mammalian c-type natriuretic peptide (CNP) and the C-terminus isolated from the dendroapis natriuretic peptide (DNP) of the venom from the green mamba. In early studies, intravenous and subcutaneous infusion of cenderitide was reported to reduce left ventricular (LV) mass and ameliorate cardiac remodelling. In this work, biodegradable polymeric films encapsulating CD-NP were developed and were investigated for their in vitro release and degradation characteristics. Subsequently, the bioactivity of released peptide and its effects on human cardiac fibroblast (HCF) were explored. We achieved sustained release from three films with low, intermediate and high release profiles for 30 days. Moreover, the bioactivity of released peptide was verified from the elevated production of cyclic guanosine monophospate (cGMP). The CD-NP released from films was able to inhibit the proliferation of hypertrophic HCF as well as suppress DNA synthesis in HCF. Furthermore, the sustained delivery from films showed comparable or superior suppressive actions on hypertrophic HCF compared to daily infusion of CD-NP. The results suggest that these films could be used to inhibit fibrosis and reduce cardiac remodelling via local delivery as cardiac patches.

Biocompatibility and biodegradation studies of PCL/β-TCP bone tissue scaffold fabricated by structural porogen method

Three-dimensional printer (3DP) (Z-Corp) is a solid freeform fabrication system capable of generating sub-millimeter physical features required for tissue engineering scaffolds. By using plaster composite materials, 3DP can fabricate a universal porogen which can be injected with a wide range of high melting temperature biomaterials. Here we report results toward the manufacture of either pure polycaprolactone (PCL) or homogeneous composites of 90/10 or 80/20 (w/w) PCL/beta-tricalcium phosphate (β-TCP) by injection molding into plaster composite porogens fabricated by 3DP. The resolution of printed plaster porogens and produced scaffolds was studied by scanning electron microscopy. Cytotoxicity test on scaffold extracts and biocompatibility test on the scaffolds as a matrix supporting murine osteoblast (7F2) and endothelial hybridoma (EAhy 926) cells growth for up to 4 days showed that the porogens removal process had only negligible effects on cell proliferation. The biodegradation tests of pure PCL and PCL/β-TCP composites were performed in DMEM with 10 % (v/v) FBS for up to 6 weeks. The PCL/β-TCP composites show faster degradation rate than that of pure PCL due to the addition of β-TCP, and the strength of 80/20 PCL/β-TCP composite is still suitable for human cancellous bone healing support after 6 weeks degradation. Combining precisely controlled porogen fabrication structure, good biocompatibility, and suitable mechanical properties after biodegradation, PCL/β-TCP scaffolds fabricated by 3DP porogen method provide essential capability for bone tissue engineering.

Development of perforated microthin poly(ε-caprolactone) films as matrices for membrane tissue engineering

The design and fabrication of thin films based on bioresorbable polymers such as poly(epsilon-caprolactone) (PCL) has been the focus of a part of current biomedical research, especially as matrices for membrane tissue engineering. We have successfully developed perforated microthin PCL membrane for this purpose. Two critical issues are the control of moisture permeability and understanding the degradation of PCL microthin film. In order to increase the moisture permeability. PCL films were biaxially stretched to a thickness of 10 +/- 3 microm and perforated with uniform array of holes (180-275 microm) using a Sony Robotic system. After perforation, the water vapour transmission rate was increased by 50% to a value of 47.6 +/- 2.7 g/h per m2. Accelerated hydrolytic degradations were performed in 5 M NaOH. The degraded samples were characterised for changes in weight, surface morphology, mechanical properties, crystallinity and molecular weight. Hydrolytic degradation commenced with random chain scission of backbone ester bonds on the film surface and followed by loss of material due to surface erosion. In general, the perforated films degraded faster than the unperforated microthin films. Scanning electron microscopic images showed that surface erosion led to extensive formation of micropores, microcracks and increased in surface roughness.

Changes in the surface of four calcium silicate-containing endodontic materials and an epoxy resin-based sealer after a solubility test

AIM

To compare the changes in the surface structure and elemental distribution, as well as the percentage of ion release, of four calcium silicate-containing endodontic materials with a well-established epoxy resin-based sealer, submitted to a solubility test.

METHODOLOGY

Solubility of AH Plus, iRoot SP, MTA Fillapex, Sealapex and MTA-Angelus (MTA-A) was tested according to ANSI/ADA Specification 57. The deionized water used in the solubility test was submitted to atomic absorption spectrophotometry to determine and quantify Ca(2+), Na(+), K(+), Zn(2+), Ni(2+) and Pb(2+) ions release. In addition, the outer and inner surfaces of nonsubmitted and submitted samples of each material to the solubility test were analysed by means of scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDX). Statistical analysis was performed by using one-way anova and Tukey's post hoc tests (α = 0.05).

RESULTS

Solubility results, in percentage, sorted in an increasing order were -1.24 ± 0.19 (MTA-A), 0.28 ± 0.08 (AH Plus), 5.65 ± 0.80 (Sealapex), 14.89 ± 0.73 (MTA Fillapex) and 20.64 ± 1.42 (iRoot SP). AH Plus and MTA-A were statistically similar (P > 0.05), but different from the other materials (P < 0.05). High levels of Ca(2+) ion release were observed in all groups except AH Plus sealer. MTA-A also had the highest release of Na(2+) and K(+) ions. Zn(+2) ion release was observed only with AH Plus and Sealapex sealers. After the solubility test, all surfaces had morphological changes. The loss of matrix was evident and the filler particles were more distinguishable. EDX analysis displayed high levels of calcium and carbon at the surface of Sealapex, MTA Fillapex and iRoot SP.

CONCLUSIONS

AH Plus and MTA-A were in accordance with ANSI/ADA's requirements regarding solubility whilst iRoot SP, MTA Fillapex and Sealapex did not fulfil ANSI/ADA's protocols. High levels of Ca(2+) ion release were observed in all materials except AH Plus. SEM/EDX analysis revealed that all samples had morphological changes in both outer and inner surfaces after the solubility test. High levels of calcium and carbon were also observed at the surface of all materials except AH Plus and MTA-A.

Cutinolytic esterase activity of bacteria isolated from mixed-plant compost and characterization of a cutinase gene fromPseudomonas pseudoalcaligenes

The objective of the current study was to examine cutinolytic esterase (i.e., cutinase) activity by pseudomonads and bacteria isolated from mixed-plant compost. Approximately 400 isolates representing 52 taxa recovered from mixed-plant compost using cuticle baits, along with 117 pseudomonad isolates obtained from a culture collection (i.e., non-compost habitats), were evaluated. The ability of isolates to degrade the synthetic cutin polycaprolactone (PCL) was initially measured. Isolates from 23 taxa recovered from the compost degraded PCL. As well, isolates from 13 taxa of pseudomonads cleared PCL. Secondary screening measured esterase activity induced by the presence of apple cuticle using the chromogenic substrate p-nitrophenyl butyrate. Eighteen isolates representing four taxa ( Alcaligenes faecalis , Bacillus licheniformis , Bacillus pumilus , and Pseudomonas pseudoalcaligenes ) recovered from compost exhibited substantial esterase activity when grown with cuticle. In contrast, none of the pseudomonad isolates from the culture collection produced appreciable esterase activity. Although degradation of PCL was not correlated with esterase activity, isolates that were unable to degrade PCL failed to produce measureable esterase activities. Zymogram analysis indicated that the esterases produced by bacteria from compost ranged in size from 29 to 47 kDa. A gene from P. pseudoalcaligenes (cutA) was found to code for a cutin-induced esterase consisting of 302 amino acids and a theoretical protein size of 32 kDa. The enzyme was unique and was most closely related to other bacterial lipases (≤48% similarity).

Through-thickness control of polymer bioresorption via electron beam irradiation

Predicable and controlled degradation is not only central to the accurate delivery of bioactive agents and drugs, it also plays a vital role in key aspects of bone tissue engineering. The work addressed in this paper investigates the utilisation of e-beam irradiation in order to achieve a controlled (surface) degradation profile. This study focuses on the modification of commercially and clinically relevant materials, namely poly(L-lactic acid) (PLLA), poly(L-lactide-hydroxyapatite) (PLLA-HA), poly(L-lactide-glycolide) co-polymer (PLG) and poly(L-lactide-DL-lactide) co-polymer (PLDL). Samples were subjected to irradiation treatments using a 0.5MeV electron beam with delivered surface doses of 150 and 500 kGy. In addition, an acrylic attenuation shield was used for selected samples to control the penetration of the e-beam. E-beam irradiation induced chain scission in all polymers, as characterized by reduced molecular weights and glass transition temperatures (T(g)). Irradiation not only produced changes in the physical properties of the polymers but also had associated effects on surface erosion of the materials during hydrolytic degradation. Moreover, the extent to which both mechanical and hydrolytic degradation was observed is synonymous with the estimated penetration of the beam (as controlled by the employment of an attenuation shield).

Release kinetics of polymer-bound bone morphogenetic protein-2 and its effects on the osteogenic expression of MC3T3-E1 osteoprecursor cells

BACKGROUND

In an effort to augment scaffold performance, additives such as growth factors are under investigation for their ability to optimize the "osteopotential" of synthetic polymer scaffolds. In parallel research, bone morphogenetic protein-2 (BMP-2), a growth factor that initiates bone formation, has been locally delivered to augment fracture healing and spinal fusion. The authors hypothesize that BMP-2 can be covalently bound to a polymer substrate, increasing its concentration and bioavailability over longer periods, thus improving the efficacy of the growth factor and subsequently the bony matrix production. It would remain bound longer when compared with published controls. This prolonged binding would then increase the bioavailability of the growth factor and thus increase bony matrix production over a longer interval.

METHODS

Mouse preosteoblast MC3T3-E1 cells were cultured on poly(lactic-co-glycolic acid) and polycaprolactone polymer disks covalently bound with BMP-2 to assess the progression and quality of osteogenesis. Covalent binding of BMP-2 to each polymer was visualized by immunohistochemical analysis of polymer-coated microscope slides. The quantity of covalently bound BMP-2 was determined using enzyme-linked immunosorbent assay.

RESULTS

Polymerase chain reaction results showed elevated expression levels for alkaline phosphatase and osteocalcin genes. BMP-2 was released from polycaprolactone over 2 weeks, with 86 percent remaining covalently bound, in contrast to 93 percent retained by poly(lactic-co-glycolic acid).

CONCLUSIONS

BMP-2, proven to alter polymer osteogenicity, remained bound to poly(lactic-co-glycolic acid), which may render poly(lactic-co-glycolic acid) an ideal choice as a polymer for scaffold-based bone tissue engineering using growth factor delivery.

Preparation and characterization of nano-hydroxyapatite/polymer composite scaffolds

Polycaprolactone/chitosan (PCL/CS) porous composite scaffolds were prepared by solution phase separation method, and the scaffolds were further enhanced by filling with nano-hydroxyapatite/polyvinyl alcohol (n-HA/PVA) composite slurry to prepare n-HA-PVA/PCL-CS composite porous scaffolds through slurry centrifugal filling technique. The morphology, microstructure, component, porosity and mechanical property of the scaffolds were characterized using scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscope, elemental analyzer and material test machine. The results show that PCL/CS scaffolds have mutual transfixion porous structure just like honeycombs. The porosity of the scaffolds can achieve 60-80%. As the content of CS increases, the porosity increases while the compressive strength decreases. After filled with HA/PVA composite slurry, the porosity of n-HA/PCL-CS composite scaffolds decreases, but still greater than 60%, while the compression modulus can increase to 25.7 MPa.

Physical characterization of polycaprolactone scaffolds

Films and sponges were prepared from a solution of Poly(epsilon-caprolactone) (PCL) in tetrahydrofuran (THF). The porosity, crystallinity, and mechanical properties of the samples were studied. Porosity of around 15% was obtained for the films produced by evaporation of THF at room temperature. A much more porous structure (50-70%) was found for the sponges obtained by cooling the solution at -30 degrees C and subsequently eliminating the solvent by freeze drying. The porosity of the samples was also observed by scanning electron microscopy (SEM). The crystallinity of the samples was studied by the calorimetric technique (DSC) before and after the compression scans. The mechanical properties of the different samples were determined by compression test, and were compared to those corresponding to the PCL in bulk. The compression scans did not affect the crystallinity of the samples. The variations observed in the results of the different scans were attributed to the differences in porosities and crystallinity.

Novel fabrication of a polymer scaffold with a dense bioactive ceramic coating layer

A novel method of coating a polymeric scaffold with a dense ceramic layer was developed. This method exploits the fact that only one of the two interlaced 3-D channels formed in a ceramic dual-scaffold can be infiltrated with a polymer. Firstly, a 3-D graphite network prepared by the rapid prototyping (RP) method was dip-coated with hydroxyapatite (HA) slurry, followed by heat-treatment at 1250 degrees C for 3 h in air. This created an additional 3-D channel through the removal of the graphite network, while preserving the pre-existing 3-D channel. Thereafter, only one channel was infiltrated with a molten poly(epsilon-caprolactone) (PCL) polymer at 140 degrees C for 12 h, producing a PCL scaffold with a dense, uniform HA coating layer. The sample showed high compressive strength with ductile behavior, due to the nature of the PCL polymer, and an excellent cellular response afforded by the bioactive HA coating layer. The results indicate that this novel technique provides a highly versatile method of coating various polymeric scaffolds with bioactive layers in order to endow them with advanced functionalities.

Modern biomaterials: a review - bulk properties and implications of surface modifications

This review concerns the importance of length and time on physicochemical interactions between living tissue and biomaterials that occur on implantation. The review provides information on material host interactions, materials for medical applications and cell surface interactions, and then details the extent of knowledge concerning the role(s) that surface chemistry and topography play during the first stage of implant integration, namely protein adsorption. The key points are illustrated by data from model in vitro studies. Host implant interactions begin nanoseconds after first contact and from then on are in a state of flux due to protein adsorption, cell adhesion and physical and chemical alteration of the implanted material. The many questions concerning the conformational form and control of bound proteins and how this may impact on cell adhesion in the first instance and later on cell signalling and implant integration can be answered by systematic investigations using model materials. Only then we will be in a more informed position to design new materials for use in the body.

Studies on alpha-amylase induced degradation of binary polymeric blends of crosslinked starch and pectin

A blend matrix of crosslinked starch and pectin was prepared and characterized by infra-red (IR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The prepared blends were investigated kinetically for water sorption studies and alpha-amylase induced degradation adopting a gravimetric procedure. Based on the experimental findings, a plausible mechanism including both diffusion and surface enhanced degradation was suggested and degradation profiles were interpreted. The influence of various factors such as chemical architecture of the blend, pH and temperature of alpha-amylase solution were examined for the swelling and degradation kinetics of crosslinked starch-pectin blends. The effect of concentration of enzyme solution was also studied on the degradation profile of the blends. A correlation was established between the extent of degradation and water imbibing capacity of the degrading blends.

Macrochanneled poly (epsilon-caprolactone)/ hydroxyapatite scaffold by combination of bi-axial machining and lamination

A combination of bi-axial machining and lamination was used to fabricate macrochanneled poly (epsilon-caprolactone) (PCL)/hydroxyapatite (HA) scaffolds. Thermoplastic PCL/HA sheets with a thickness of 1 mm, consisting of a 40 wt% PCL polymer and 60 wt% HA particles, were bi-axially machined. The thermoplastic PCL/HA exhibited an excellent surface finish with negligible tearing of the PCL polymer and pull-out of the HA particles. The bi-axially machined sheets were laminated with a solvent to give permanent bonding between the lamina. This novel process produced three-directionally connected macrochannels in the dense PCL/HA body. The macrochanneled PCL/HA scaffold exhibited excellent ductility and reasonably high strength. In addition, good cellular responses were observed due to the osteoconductive HA particles.

Alkaline-treated poly(ε-caprolactone) films: Degradation in the presence or absence of fibroblasts

In the first stage, we observed the study of the degradation behavior of alkaline-treated poly(epsilon-caprolactone) (PCL) in two biologically-related media: phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) for 18 months, finding a much accelerated degradation in the last one. As expected, the degradation in the presence of cells is much pronounced even considering that the study is limited to 6 months. The characterization of the degraded substrates by chemiluminescence (CL) allows to explain the modifications of the substrate and their relations with transitory oxidative stress phenomena described in the fibroblasts seeded onto the PCL membranes.

The in vivo degradation, absorption and excretion of PCL-based implant

The in vivo degradation of poly (epsilon-caprolactone)(PCL) was observed for 3 years in rats. The distribution, absorption and excretion of PCL were traced in rats by radioactive labeling. The results showed that PCL capsules with initial molecular weight (Mw) of 66000 remained intact in shape during 2-year implantation. It broke into low molecular weight (Mw=8000) pieces at the end of 30 months. The Mw of PCL deceased with time and followed a linear relationship between logMw and time. Tritium-labeled PCL (Mw 3000) was subcutaneous implanted in rats to investigate its absorption and excretion. The radioactive tracer was first detected in plasma 15 days after implantation. At the same time radioactive excreta was recovered from feces and urine. An accumulative 92% of the implanted radioactive tracer was excreted from feces and urine by 135 days after implantation. In the mean while, the plasma radioactivity dropped to the background level. Radioactivity in the organs was all close to the background level confirming that the material did not cumulate in body tissue and could be completely excreted.

Osteoblastic Phenotype Expression of MC3T3-E1 Cells Cultured on Polymer Surfaces

BACKGROUND

Current efforts in bone tissue engineering have as one focus the search for a scaffold material that will support osteoblast proliferation, matrix mineralization, and, ultimately, bone formation. The goal is to develop a bone substitute that is functionally equivalent to autograft bone. Previously published reports have shown that osteoblasts exhibit varying rates and degrees of proliferation and mineralization when grown on different surfaces.

METHODS

This study presents a histologic and biomolecular analysis of MC3T3-E1 murine preosteoblast cells grown on poly(lactide-co-glycolide) (PLGA) versus poly(-caprolactone) (PCL), two commonly studied scaffold polymers. MC3T3-E1 cells were cultured on slides coated with either PLGA or PCL, and on uncoated glass slides as control, with six slides in each group. After 6 weeks in culture, the cells were stained for osteocalcin, alkaline phosphatase activity, and matrix mineralization. In addition, to assess the effects of the surface material on phenotypic expression at the molecular level, MC3T3-E1 cells were cultured on polymer-coated 24-well plates for 4 days, and analyzed by reverse transcription polymerase chain reaction for the expression of osteocalcin and alkaline phosphatase.

RESULTS

The results showed that three groups of slides stained positively for osteocalcin at 6 weeks. However, markedly less alkaline phosphatase activity and mineralization were observed on the cells grown on PCL. Real-time polymerase chain reaction assays subsequently revealed decreased expression of both markers by cells cultured on PCL compared with PLGA.

CONCLUSIONS

These results suggest that PCL does not support the full expression of an osteoblastic phenotype by MC3T3-E1 cells. PCL, therefore, is less desirable as a scaffold polymer in bone tissue engineering in so far as supporting bone formation is concerned. However, because PCL has favorable handling characteristics and strength, modifications of PCL may prompt further investigation.

Polímeros bioreabsorvíveis na engenharia de tecidos

A Engenharia de Tecidos consiste em um conjunto de conhecimentos e técnicas para a reconstrução de novos órgãos e tecidos. Baseada em conhecimentos das áreas de ciência e engenharia de materiais, biológica e médica, a técnica envolve a expansão in vitro de células viáveis do paciente doador sobre suportes de polímeros bioreabsorvíveis. O suporte degrada enquanto um novo órgão ou tecido é formado. Os poli(alfa-hidróxi ácidos) representam a principal classe de polímeros sintéticos bioreabsorvíveis e biodegradáveis utilizados na engenharia de tecidos. No desenvolvimento e na seleção desses materiais, o tempo de degradação é fundamental para o sucesso do implante. Os estudos e os desafios atuais são normalmente direcionados ao entendimento das relações entre composição química, cristalinidade, morfologia do suporte, e o processamento desses materiais. Este artigo faz uma revisão dos trabalhos recentes sobre a utilização dos polímeros sintéticos bioreabsorvíveis como suportes na engenharia de tecidos.

Biocompatibility and biostability of a series of poly(carbonate)urethanes

In this work, we synthesized several MDI-based poly(carbonate)urethanes (PCU) by using four different soft segments, including two aliphatic macrodiols (poly(hexyl, ethyl)carbonate diols, MW 2017 and 865, respectively) and two aromatic macrodiols (MW approximately 2000 and 1000, respectively), in different molar ratios to MDI. We demonstrate that these polymers exhibited various degree of micro-phase separation that further influenced their surface protein adsorption, platelet activation as well as cellular attachment and growth. Polyurethanes based on poly(hexyl, ethyl)carbonate diol with MW 2017 in a molar ratio MDI/macrodiol/chain extender of either 3/2/1 or 4/3/1 resulted in greater micro-phase separation as well as superior biocompatibility and biostability.

Gravity spinning of polycaprolactone fibres for applications in tissue engineering

Poly(epsilon-caprolactone) (PCL) fibres have been produced by wet spinning from solutions in acetone under low shear (gravity flow) conditions. The tensile strength and stiffness of as-spun fibres were highly dependent on the concentration of the spinning solution. Use of a 6% w/v solution resulted in fibres having strength and stiffness of 1.8 MPa and 0.01 GPa, respectively, whereas these values increased to 9.9 MPa and 0.1 GPa when fibres were produced from 20% w/v solutions. Cold drawing to an extension of 500% resulted in further increases in fibre strength (up to 50 MPa) and stiffness (0.3 GPa). The surface morphology of as-spun fibres was modified, to yield a directional grooved pattern by drying in contact with a mandrel having a machined topography characterised by a peak-peak separation of 91 microm and a peak height of 30 microm. Limited in vitro studies of cell behaviour in contact with the fibres were performed using cell culture. The number of attached fibroblasts and myoblasts on as-spun PCL fibres after 5 days in cell culture was lower than on tissue culture plastic by a factor 2 and 1.5, respectively, but higher than on Dacron monofilament by a factor of 4 and 11, respectively. The high fibre compliance and the potential for controlling the fibre surface architecture to promote contact guidance effects together with the maintained proliferation of fibroblasts and myoblasts on as-spun PCL fibres in vitro recommends their use for 3-D scaffold production in soft tissue engineering.

Poly(ε-caprolactone) and Eudragit® microparticles containing fludrocortisone acetate

Substitutive hormonal therapies have to be administered for long periods. Thus, the development of sustained-release forms, as microparticle suspensions, is interesting in order to improve patient compliance by reducing dosing frequencies and side effects. The aim of this work was to compare different formulations of fludrocortisone microparticles for the treatment of mineralocorticoid insufficiency. The study was done with different polymers (poly(epsilon-caprolactone), Eudragit RS and Eudragit RL) and different processes (O/W solvent evaporation methods and S/O/W evaporation methods). The use of a suspension of micronized drug in dichloromethane as dispersed phase (S/O/W method) significantly improved the process. Whereas low concentrations of FLU dissolved in the dispersed phase led to smooth-surface homogeneous microparticles and poor incorporation efficiency (5.8-7.3%); suspensions of FLU led to microparticles with numerous crystals on their surfaces (S/O/W microparticles) and high incorporation efficiency (about 79%). However, the best release profiles were obtained with microparticles prepared with 7.5 mg/ml of dichloromethane, near saturation. Moreover, the use of mixtures of poly(epsilon-caprolactone), Eudragit RS and RL did not improve the release profiles.

Treatment of osteomyelitis with local antibiotics delivered via bioabsorbable polymer

The purpose of the current study was to show the efficacy and safety of an absorbable polymer (polycaprolactone) as an antibiotic delivery vehicle for treatment of osteomyelitis. An intramedullary osteomyelitis was induced in the femur of adult rabbits by Staphylococcus aureus inoculation after use of a sclerosing agent, and then treatment was done with intramedullary irrigation and implantation of a rod made of polycaprolactone, polycaprolactone plus 6% tobramycin, or polymethylmethacrylate plus 6% tobramycin. A control group received irrigation only. At defined intervals, the animals were euthanized and culture of the inoculated site was done. In addition, histologic sections of body tissues were made to look for signs of systemic toxicity of the implant. After 4 weeks of treatment, a statistically significant difference was found between the animals that were treated with irrigation alone and the animals that were treated with antibiotic-laden rods of polycaprolactone or polymethylmethacrylate. There was no difference between the antibiotic rod types. No histologic evidence of toxicity was found. Bioabsorbable rods of polycaprolactone are a safe and effective means of antibiotic delivery for treatment of osteomyelitis.

Elution characteristics of tobramycin from polycaprolactone in a rabbit model

This study investigated the elution characteristics of tobramycin from polycaprolactone, a bioabsorbable polymer, in a rabbit model. Sixty rabbits were divided into two groups. Group 1 had polycaprolactone rods impregnated with 6% tobramycin surgically implanted into the proximal femoral intramedullary canal. Group 2 received polymethylmethacrylate rods of like size, shape, and antibiotic concentration. Serum and urine samples were obtained, and tobramycin levels were determined via fluorescent immunosorbent assay. Rabbits were sacrificed as long as 56 days after surgery. Local bone tobramycin concentration was determined using the agar diffusion method. Polycaprolactone delivered a significantly higher peak bone concentration of tobramycin (22.4 microg/mL) than did polymethylmethacrylate (13.59 microg/mL). Polycaprolactone also had a more gradual decrease in local tobramycin concentration than did polymethylmethacrylate. Neither polycaprolactone nor polymethylmethacrylate yielded consistently detectable (> 0.1 microg/mL) serum tobramycin levels. Urine concentrations mirrored those seen in bone, with polycaprolactone achieving significantly higher tobramycin concentrations than did polymethylmethacrylate. Polycaprolactone had superior elution characteristics compared with polymethylmethacrylate in this lapine model, suggesting that polycaprolactone might be a promising local antibiotic delivery vehicle for the treatment of osteomyelitis.

In vitro elution of tobramycin from bioabsorbable polycaprolactone beads

OBJECTIVES

To compare the in vitro elution characteristics of tobramycin impregnated beads made of polycaprolactone (PCL) and polymethylmethacrylate (PMMA).

DESIGN

Six-millimeter PCL and PMMA beads with 6% tobramycin were formed and placed in phosphate-buffered saline or newborn calf serum and incubated at room temperature or 37 degrees C. Aliquots were taken at intervals for eight weeks. Tobramycin levels were determined by fluorescent assay and antibacterial efficacy was assessed by measuring the zones of inhibition against Staphylococcus aureus and Pseudomonas aeruginosa on agar diffusion plates.

RESULTS

Tobramycin elution rates at room temperature were similar up to three weeks. At three weeks, elution rates from PCL beads were twice those from PMMA beads, and at eight weeks, elution from PCL was quadruple that from PMMA. At 37 degrees C, tobramycin elution rates from PCL were eight times greater than those from PMMA by eight weeks. Total tobramycin eluted from PCL beads was 38.9% and 20% in PMMA beads. All samples showed bacteriostatic activity against S. aureus and P. aeruginosa at eight weeks.

CONCLUSIONS

These in vitro results show that PCL has superior antibiotic elution characteristics compared with PMMA, and this may translate into a more effective antibiotic delivery vehicle. In addition, PCL is a bioabsorbable polymer, which may decrease the need for a second surgical procedure to remove retained beads.

Pre-clinical in vivo evaluation of orthopaedic bioabsorbable devices

The presence of bioabsorbable materials in orthopaedics has grown significantly over the past two decades with applications in fracture fixation, bone replacement, cartilage repair, meniscal repair, fixation of ligaments, and drug delivery. Numerous biocompatible, biodegradable polymers are now available for both experimental and clinical use. Not surprisingly, there have been a wealth of studies investigating the biomechanical properties, biocompatibility, degradation characteristics, osteoconductivity, potential toxicity, and histologic effects of various materials. Promising results have been reported in the areas of fracture fixation, ligament repair, and drug delivery. In this article we review the pre-clinical in vivo testing of bioabsorbable devices with particular emphasis on implants used for these applications.