Biomedical subjects

Jan Feijen

Publications and source records attributed to Jan Feijen.

At least 19 recordsLinked to original sources

PubMed2007

Morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) block copolymer.

The morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) (PCL-b-PEO) block copolymer has been studied with in situ simultaneously small and wide-angle x-ray scattering as well as atomic force microscopy. The molecular masses Mn of the PCL and PEO blocks are 24,000 and 5800, respectively. X-ray scattering and rheological measurements indicate that no microphase separation occurs in the melt. Decreasing the temperature simultaneously triggers off a crystallization of PCL and microphase separation between the PCL and PEO blocks. Coupling and competition between microphase separation and crystallization results in a morphology of PEO spheres surrounded by PCL partially crystallized in lamella. Further decreasing temperature induces the crystallization of PEO spheres, which have a preferred orientation due to the confinements from hard PCL crystalline lamella and from soft amorphous PCL segments in different sides. The final morphology of this highly asymmetric block copolymer is similar to the granular morphology reported for syndiotactic polypropylene and other (co-) polymers. This implies a similar underlying mechanism of coupling and competition of various phase transitions, which is worth further exploration.

Biocompatible Materials↗

PubMed2007

Reducible poly(amido ethylenimine) directed to enhance RNA interference.

Designing synthetic macromolecular vehicles with high transfection efficiency and low cytotoxicity has been a major interest in the development of non-viral gene carriers. A reducible poly(amido ethylenimine) (SS-PAEI) synthesized by addition copolymerization of triethylenetetramine and cystamine bis-acrylamide (poly(TETA/CBA)) was used as a carrier for small interference RNA (siRNA). Poly(TETA/CBA) could efficiently condense siRNA to form stable complexes under physiological conditions and perform complete release of siRNA in a reductive environment. When formulated with VEGF-directed siRNA, poly(TETA/CBA) demonstrated significantly higher suppression of VEGF than linear-polyethylenimine (PEI) (L-PEI, 25kDa) in human prostate cancer cells (PC-3). After 5h of transfection, substantial dissociation and intracellular distribution of siRNA was observed in the poly(TETA/CBA) formulation, but not in the L-PEI formulation. The triggered release of siRNA by reductive degradation of poly(TETA/CBA) in the cytoplasm may affect the RNAi activity by increasing cytoplasmic availability of siRNA. These results suggest that the rational design of non-viral carriers should involve considerations for intracellular dissociation and trafficking of a nucleic acid drug to maximize its effect, in conjunction with formation of stable complexes under physiological conditions.

Aziridines↗

PubMed2006

Linear poly(amido amine)s with secondary and tertiary amino groups and variable amounts of disulfide linkages: synthesis and in vitro gene transfer properties.

A group of novel poly(amido amine) homo- and copolymers (PAAs) containing secondary and tertiary amine groups in their main chain and different structures in the bisacrylamide segments were synthesized and evaluated as non-viral gene delivery vectors. Among these, also the disulfide-containing cystaminebisacrylamide was employed as a (co)monomer, yielding PAAs with variable amounts of bioreducible disulfide linkages in the main chain. Michael addition the trifunctional 1-(2-aminoethyl) piperazine to equimolar amounts of the appropriate bis(acrylamide) yielded linear polymers as was elucidated by their (13)C NMR spectra. The polymers possess buffering capacities between pH 5.1 and pH 7.4 higher than branched polyethylenimine (pEI) and are able to efficiently condense DNA into nanosized (<150 nm) and positively charged complexes. Transfection experiments with COS-7 cells showed that polyplexes from PAAs with disulfide linkages give significant higher transfections than those from PAAs lacking the disulfide linkage, and XTT assays showed that these polymers are essentially non-toxic. Variation of the disulfide content revealed that polyplexes of PAA copolymers with appropriate disulfide content have largely improved biophysical properties, yielding enhanced levels of gene expression along with low toxicity. The results demonstrate that bioreducible poly(amido amine)s are a very promising class of polymers for safe and efficient gene delivery.

Acrylamides↗

PubMed2006

Micromechanical testing of individual collagen fibrils.

A novel method based on AFM was used to attach individual collagen fibrils between a glass surface and the AFM tip, to allow force spectroscopy studies of these. The fibrils were deposited on glass substrates that are partly coated with Teflon AF. A modified AFM tip was used to accurately deposit epoxy glue droplets on either end of the collagen fibril that cross the glass-Teflon AF interface, as to such attach it with one end to the glass and the other end to the AFM tip. Single collagen fibrils have been mechanically tested in ambient conditions and were found to behave reversibly up to stresses of 90 MPa. Within this regime a Young's modulus of 2-7 GPa was obtained. In aqueous media, the collagen fibrils could be tested reversibly up to about 15 MPa, revealing Young's moduli ranging from 0.2 to at most 0.8 GPa.

Achilles Tendon↗

PubMed2006

Release of anti-restenosis drugs from poly(ethylene oxide)-poly(DL-lactic-co-glycolic acid) nanoparticles.

Dexamethasone- or rapamycin-loaded nanoparticles based on poly(ethylene oxide) and poly(dl-lactic-co-glycolic acid) block copolymers (PEO-PLGA) were prepared without additional stabilizer using the salting-out method. A fast release of drug in PBS (pH 7.4) at 37 degrees C resulting in 100% release within 5 h was observed for both drugs. The rate of drug release was substantially reduced by treating the particles with gelatin or albumin after drug loading, resulting in a linear drug release in time. It was shown that the rate of drug release is related to the amount of protein associated with the nanoparticles. After gelatin treatment of drug-loaded nanoparticles, sustained release of dexamethasone for 17 days and of rapamycin for 50 days could be achieved.

Coronary Restenosis↗

PubMed2006

Biocompatibility and degradation of aliphatic segmented poly(ester amide)s: in vitro and in vivo evaluation.

Aliphatic segmented poly(ester amide)s, comprising a crystallizable amide phase and a flexible amorphous ester phase, were investigated for potential use in biomedical applications. By varying the amide content and the type of crystallizable amide segments, the polymer's thermal and mechanical properties can readily be tuned. Polymers with 25 and 50 mol % of amide content are noncytotoxic and sustain growth of fibroblasts onto polymer films. The in vitro degradation of these polymers was followed in PBS (pH 7.4) at 37 degrees C up to 7 months. The poly(ester amide)s showed the characteristics of bulk degradation with a gradual decrease in molecular weight and almost no mass loss. The in vivo degradation of these polymers, followed by subcutaneous implantation in rats up to 6 weeks, was slow and similar to the in vitro degradation. The tissue response upon implantation was followed over 6 weeks. A mild foreign-body reaction, characterized by the presence of macrophages, and sporadically a lymphocyte, were observed in the first week of implantation. After 6 weeks the implant site is characterized by fibrous encapsulation with no signs of inflammation. The poly(ester amide)s tested are biocompatible, but their in vitro as well as in vivo degradation is very slow.

Amides↗

PubMed2006

Thermo-sensitive transition of monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) films to micellar-like nanoparticles.

Monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) (mPEG(3)-PTMC(11), M(n) of mPEG=3.1 x 10(3) and M(n) of PTMC=10.8 x 10(3)g/mol) was synthesized by ring-opening polymerization of TMC using mPEG(3) as an initiator and stannous octoate as a catalyst. The block copolymer has a broad melting range with a peak at 49.5 degrees C and a heat of fusion of 47.6J/g. The heat of fusion normalized to the mPEG content is higher than that of the mPEG(3) polymer, suggesting that PTMC segments are also semi-crystalline. The mPEG(3)-PTMC(11) films were stable in water at room temperature, whereas at 37 degrees C the film specimens disintegrated and the amphiphilic block copolymer self-assembled into micellar-like nanoparticles with average sizes up to 210nm. The critical association concentration (CAC) of the formed micellar-like particles is 1.35 x 10(-3)mg/ml. The average size and polydispersity index of the formed mPEG(3)-PTMC(11) nanoparticles depend on temperature and storage time: the values decrease with increases in temperature and in storage time. By co-dissolving dexamethasone with mPEG(3)-PTMC(11) during the film preparation, micellar-like nanoparticles loaded with dexamethasone can be obtained after the film to micellar-like nanoparticles transition. A high loading efficiency of 93.3 wt.% was achieved. The sustained release of the drug was complete in 20d.

Delayed-Action Preparations↗

PubMed2006

Poly(trimethylene carbonate) and monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) nanoparticles for the controlled release of dexamethasone.

In this study, single emulsion and salting out methods were employed to prepare poly(trimethylene carbonate) (PTMC) and monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) (mPEG-PTMC) nanoparticles. Well-defined nanoparticles of a PTMC homopolymer were prepared using poly(vinyl alcohol) (PVA) as a stabilizer. The average size of the nanoparticles can be adjusted by varying the stirring speed and polymer concentration. These particles can be readily freeze-dried and redispersed, with little influence on the average particle size and size distribution. Nanoparticles based on amphiphilic mPEG-PTMC can be prepared without an additional stabilizer. In this case, the size of the obtained nanoparticles did not vary much and ranged between 95 and 120 nm. These nanoparticles could be freeze-dried and redispersed as well. Using the salting out method, dexamethasone was loaded into PTMC and mPEG-PTMC nanoparticles at a highest efficiency of respectively 54% and 88%. With the single emulsion method, the loading efficiencies were, respectively, 91% and 72%. These drug-loaded particles were stable in time for at least 20 weeks. It was found that the release of dexamethasone from these nanoparticles was diffusion-controlled and could be sustained for 14 to 60 days. Depending on the nature of the polymer employed and the preparation method, dexamethasone diffusion coefficients varied between 4.8 x 10(-18) and 22.6 x 10(-18) cm(2)/s.

Anti-Inflammatory Agents↗

PubMed2006

Porous hybrid structures based on P(DLLA-co-TMC) and collagen for tissue engineering of small-diameter blood vessels.

Poly (D,L-lactide)-7co-(1,3-trimethylene carbonate) [P(DLLA-co-TMC)] (83 mol % DLLA) was used to produce matrices suitable for tissue engineering of small-diameter blood vessels. The copolymer was processed into tubular structures with a porosity of approximately 98% by melt spinning and fiber winding, thus obviating the need of organic solvents that may compromise subsequent cell culture. Unexpectedly, incubation in culture medium at 37 degrees C resulted in disconnection of the contact points between the polymer fibers. To improve the structural stability of these P(DLLA-co-TMC) scaffolds, a collagen microsponge was formed inside the pores of the synthetic matrix by dip coating and freeze drying. Hybrid structures with a porosity of 97% and an average pore size of 102 mum were obtained. Structural stability was preserved during incubation in culture medium at 37 degrees C. Smooth-muscle cells (SMCs) were seeded in these hybrid scaffolds and cultured under pulsatile flow conditions in a bioreactor (120 beats/min, 80-120 mmHg). After 7 days of culture in a dynamic environment viable SMCs were homogeneously distributed throughout the constructs, which were five times stronger and stiffer than noncultured scaffolds. Values for yield stress (2.8 +/- 0.6 MPa), stiffness (1.6 +/- 0.4 MPa), and yield strain (120% +/- 20%) were comparable to those of the human artery mesenterica.

Blood Vessel Prosthesis↗

PubMed2006

In-situ formation of biodegradable hydrogels by stereocomplexation of PEG-(PLLA)8 and PEG-(PDLA)8 star block copolymers.

Eight-arm poly(ethylene glycol)-poly(L-lactide), PEG-(PLLA)(8), and poly(ethylene glycol)-poly(D-lactide), PEG-(PDLA)(8), star block copolymers were synthesized by ring-opening polymerization of either L-lactide or D-lactide at room temperature in the presence of a single-site ethylzinc complex and 8-arm PEG (M(n) = 21.8 x 10(3) or 43.5 x 10(3)) as a catalyst and initiator, respectively. High lactide conversions (>95%) and well-defined copolymers with PLLA or PDLA blocks of the desired molecular weights were obtained. Star block copolymers were water-soluble when the number of lactyl units per poly(lactide) (PLA) block did not exceed 14 and 17 for PEG21800-(PLA)(8) and PEG43500-(PLA)(8), respectively. PEG-(PLA)(8) stereocomplexed hydrogels were prepared by mixing aqueous solutions with equimolar amounts of PEG-(PLLA)(8) and PEG-(PDLA)(8) in a polymer concentration range of 5-25 w/v % for PEG21800-(PLA)(8) star block copolymers and of 6-8 w/v % for PEG43500-(PLA)(8) star block copolymers. The gelation is driven by stereocomplexation of the PLLA and PDLA blocks, as confirmed by wide-angle X-ray scattering experiments. The stereocomplexed hydrogels were stable in a range from 10 to 70 degrees C, depending on their aqueous concentration and the PLA block length. Stereocomplexed hydrogels at 10 w/v % polymer concentration showed larger hydrophilic and hydrophobic domains as compared to 10 w/v % single enantiomer solutions, as determined by cryo-TEM. Correspondingly, dynamic light scattering showed that 1 w/v % solutions containing both PEG-(PLLA)(8) and PEG-(PDLA)(8) have larger "micelles" as compared to 1 w/v % single enantiomer solutions. With increasing polymer concentration and PLLA and PDLA block length, the storage modulus of the stereocomplexed hydrogels increases and the gelation time decreases. Stereocomplexed hydrogels with high storage moduli (up to 14 kPa) could be obtained at 37 degrees C in PBS. These stereocomplexed hydrogels are promising for use in biomedical applications, including drug delivery and tissue engineering, because they are biodegradable and the in-situ formation allows for easy immobilization of drugs and cells.

Biocompatible Materials↗

PubMed2006

Reduction of calcification of carbodiimide-processed heart valve tissue by prior blocking of amine groups with monoaldehydes.

BACKGROUND AND AIM OF THE STUDY: Failure of implanted bioprostheses due to calcification is a commonly occurring phenomenon. In order to prevent calcification, many alternative cross-linking methods to glutaraldehyde (GA) have been developed and evaluated. METHODS: In a novel approach an improved carbodiimide (EDC) cross-linking method that comprises a two-step process was developed. First, the available amine groups in (tissue) collagen were blocked with a monoaldehyde, followed by an EDC-activated cross-linking reaction of the carboxyl groups in the tissue with a poly (propylene glycol) bis 2-(amino-propyl) ether (Jeffamine). RESULTS: Samples processed via this method have shown a significantly reduced calcification in a subdermal juvenile rat model compared to samples with standard GA treatment. In the present study, heart valve tissue was blocked with various monoaldehydes, followed by reaction with Jeffamine using carbodiimide cross-linking chemistry. Leaflet calcification was almost eliminated using different aldehydes, whereas wall calcification was maximally 95% reduced when propionaldehyde was used as blocking agent, as compared to a carbodiimide cross-linked control without Jeffamine and blocked amine groups. CONCLUSION: Amine blocking and cross-linking technology appears promising in the design of the next generation of tissue valves. Calcification was significantly reduced compared to GA cross-linking. The mechanistic insight of decreased wall calcification is still unknown, and research investigations are ongoing.

Animals↗

PubMed2005

Biological characterisation of vascular grafts cultured in a bioreactor.

In this study, the development is described of a tissue-engineered construct mimicking the structure of a natural blood vessel. Smooth muscle cells (SMC) were cultured under pulsatile flow conditions in porous tubular scaffolds composed of crosslinked type I insoluble collagen and insoluble elastin. Under these dynamic culture conditions, average wall shear rate, systolic and diastolic pressures and pressure wave-forms comparable to conditions in the human carotid artery were obtained. Culturing of SMC in tubular scaffolds under dynamic conditions resulted in enhanced tissue formation compared to static conditions. Higher SMC numbers, a more homogeneous distribution of SMC throughout the scaffolds and higher collagen mRNA expression levels were found when cells were cultured under dynamic compared to static conditions. mRNA expression levels of markers of proliferation and apoptosis showed that the higher cell numbers in the scaffolds cultured under dynamic conditions can be explained by increased cell proliferation but not by decreased apoptosis. Glucose consumption and lactate formation by the cells showed that cell metabolism was more aerobic under dynamic compared to static conditions. Lining of the dynamically cultured constructs with a luminal monolayer of endothelial cells might result in vessels suitable for in vivo applications.

Biocompatible Materials↗

PubMed2005

Physical characterization of vascular grafts cultured in a bioreactor.

Tubular scaffolds of collagen and elastin (weight ratio 1:1) with interconnected pores were prepared by freeze drying and crosslinked with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) in the presence or absence of a Jeffamine spacer (poly(propylene glycol)-bis-(2-aminopropyl ether), J230). The crosslinked and uncrosslinked matrices had porosities of 90% and average pore sizes of 131-151 microm. Smooth muscle cells (SMC) were cultured in the crosslinked and uncrosslinked tubular scaffolds under pulsatile flow conditions (mean flow rate 9.6 ml/min, 120 beats/min, pressure 80-120 mmHg). All the constructs could withstand cyclic mechanical strain in the absence of any mechanical support without cracking or suffering permanent deformation. After 7d, SMC were homogeneously distributed throughout the uncrosslinked and EDC/NHS crosslinked constructs, whereas hardly any cell was observed on the luminal side of J230/EDC/NHS crosslinked matrices. Considering the better mechanical performance of EDC/NHS crosslinked matrices compared to non-crosslinked constructs after 7d of culture, SMC were dynamically cultured in the former scaffolds for 14d. During this period, the high strain stiffness of the constructs increased more than two-fold to 38+/-2 kPa, whereas the low strain stiffness doubled to 8+/-2 kPa. The yield stress and yield strain were 30+/-10 kPa and 120+/-20%, respectively. SMC were homogeneously distributed throughout the EDC/NHS crosslinked collagen/elastin constructs and collagen fibres tended to orient in the circumferential direction.

Biocompatible Materials↗

PubMed2005

The in vivo and in vitro degradation behavior of poly(trimethylene carbonate).

The in vivo and in vitro degradation behavior of poly(trimethylene carbonate) (PTMC) polymers with number average molecular weights of 69 x 10(3), 89 x 10(3), 291 x 10(3) and 457 x 10(3)g/mol (respectively abbreviated as PTMC(69), PTMC(89), PTMC(291) and PTMC(457)) was investigated in detail. PTMC rods (3mm in diameter and 4mm in length) implanted in the femur and tibia of rabbits degraded by surface erosion. The mass loss of high molecular weight PTMC(457) specimens was 60wt% in 8 wks, whereas the mass loss of the lower molecular weight PTMC(89) specimens in the same period was 3 times lower. PTMC discs of different molecular weights immersed in lipase solutions (lipase from Thermomyces lanuginosus) degraded by surface erosion as well. The mass and thickness of high molecular weight PTMC(291) discs decreased linearly in time with an erosion rate of 6.7 microm/d. The erosion rate of the lower molecular weight PTMC(69) specimens was only 1.4mum/d. It is suggested that the more hydrophilic surface of the PTMC(69) specimens prevents the enzyme from acquiring a (hyper)active conformation. When PTMC discs were immersed in media varying in pH from 1 to 13, the non-enzymatic hydrolysis was extremely slow for both the high and low molecular weight samples. It can be concluded that enzymatic degradation plays an important role in the surface erosion of PTMC in vivo.

Absorbable Implants↗

PubMed2005

A versatile family of degradable non-viral gene carriers based on hyperbranched poly(ester amine)s.

A variety of degradable hyperbranched poly(ester amine)s containing primary, secondary and tertiary amino groups, were synthesized and evaluated as non-viral gene carriers. The polymers were obtained in high yields through a Michael-type conjugate addition of diacrylate monomers with trifunctional amine monomers. Analysis of degradation products using liquid chromatography-mass spectroscopy (LC-MS) demonstrated that all poly(ester amine)s had a hyperbranched structure with a degree of branching of approximately 0.30. These poly(ester amine)s were readily water-soluble and degradable under physiological conditions (pH 7.4, 37 degrees C), in which more than 10% ester bonds were hydrolyzed within 4 h. Moreover, these hyperbranched poly(ester amine)s showed high buffering capacities between pH 5.1 and 7.4. Three out of nine synthesized polymers, i.e. p(HDDA-AEP), p(HDDA-AMP), and p(BDDA-AMP), were shown to effectively condense plasmid DNA into small-sized (approximately 94-135 nm) and positively charged complexes. Polymer/DNA complexes ('polyplexes') based on these three polymers, and larger complexes of p(BDDA-AEP) (approximately 497 nm) were able to transfect COS-7 cells in vitro. Importantly, the transfection activity of polyplexes was preserved in the presence of serum proteins. The highest transfection level was observed for p(HDDA-AEP) polyplex which had a transfection efficiency higher than or comparable to that polyplexes of polyethylenimine (PEI) and poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA). Furthermore, these poly(ester amine)s revealed no or low cytotoxicity. These results demonstrated that hyperbranched poly(ester amine)s can be applied as safe and efficient gene delivery polymers.

Algorithms↗

PubMed2005

Biodegradable polymersomes as a basis for artificial cells: encapsulation, release and targeting.

The encapsulation of biofunctional compounds, release properties and targetability of polymersomes of amphiphilic block-copolymers based on poly(ethylene glycol) (PEG) and biodegradable polyesters or polycarbonate are described. Carboxyfluorescein (CF), as a model for hydrophilic biofunctional compounds, could be readily incorporated in the polymersomes by adding the compound to the aqueous phase during polymersome preparation. The release of encapsulated material from the polymersomes can be adjusted by changing the copolymer composition, especially the molecular weight and type of hydrophobic block of the copolymer. The presence of plasma proteins other than albumin suppressed the release of CF. CF release in PBS both at room temperature and at 60 degrees C followed first order kinetics, confirming that the CF containing polymersome system is a membrane controlled reservoir system. These biodegradable polymersomes have the potential to be targeted to specific sites in the body as shown by the specific interaction of anti-human serum albumin immobilized polymersomes with a human serum albumin coated sensor surface.

Biodegradation, Environmental↗

PubMed2005

Preparation of biodegradable networks by photo-crosslinking lactide, epsilon-caprolactone and trimethylene carbonate-based oligomers functionalized with fumaric acid monoethyl ester.

Biodegradable polymer networks were prepared from fumaric acid derivatives of oligomeric esters. Photo-crosslinkable macromers were prepared by reacting star-shaped hydroxyl-group terminated lactide, epsilon-caprolactone and trimethylene carbonate based oligomers and fumaric acid monoethyl ester in the presence of N,N-dicyclohexylcarbodiimide and 4-dimethylamino pyridine at room temperature. The functionalization method is facile and suited for many hydroxyl-terminated oligomers. The reactivity of the fumarate end groups is such that, upon crosslinking by UV radical polymerization, networks with high gel contents (up to 96%) can be obtained without the addition of reactive diluents. The physical properties of the networks can be tuned by adjusting the composition, architecture and molecular weight of the oligomeric precursors. Such networks, built up of non-toxic compounds and designed to release benign degradation products, may find wide application in tissue engineering and other areas of biomedical research.

4-Aminopyridine↗

PubMed2004

In vitro degradation of nanoparticles prepared from polymers based on DL-lactide, glycolide and poly(ethylene oxide).

Nanoparticles of poly(DL-lactic acid) (PDLLA), poly(DL-lactic-co-glycolic acid) (PLGA) and poly(ethylene oxide)-PLGA diblock copolymer (PEO-PLGA) were prepared by the salting-out method. The in vitro degradation of PDLLA, PLGA and PEO-PLGA nanoparticles in PBS (pH 7.4) at 37 degrees C was studied. The particle size, molecular weight of the polymers and the amount of lactic and glycolic acids formed were followed in time. PDLLA nanoparticles gradually degraded over a period of 2 years and retain their size during that period. A faster degradation was observed for PLGA nanoparticles, which was nearly complete after 10 weeks. PLGA nanoparticles retained their size during that period. In PEO-PLGA nanoparticles, the ester bond connecting the PEO and the PLGA segments was preferentially cleaved, which led to a relatively fast decrease in molecular weight and to (partial) aggregation, as multimodal size distributions were observed. PEO-PLGA nanoparticles were almost completely degraded within 8 weeks.

Algorithms↗