Biomedical subjects

Dirk W Grijpma

Publications and source records attributed to Dirk W Grijpma.

9 recordsLinked to original sources

PubMed2003

Adhesion and growth of human Schwann cells on trimethylene carbonate (co)polymers.

Seeding of artificial nerve grafts with Schwann cells is a promising strategy for bridging large nerve defects. The aim of the present study was to evaluate the adhesion and growth of human Schwann cells (HSCs) on 1,3-trimethylene carbonate (TMC) and epsilon-caprolactone copolymers, with the final goal of using these materials in the development of an artificial nerve graft. The adhesion, proliferation, and morphology of HSCs on copolymers containing 10 and 82 mol % of TMC and on the parent homopolymers were investigated. HSCs adhered faster and in greater numbers on the copolymer with 82 mol % of TMC and on the TMC homopolymer compared with the other (co)polymers. On all polymer films, cell adhesion was lower than on gelatin (positive control). Despite differences in cell adhesion, cells displayed exponential growth on all tested surfaces, with similar growth rates. Cell numbers doubled approximately every 3 days on all substrates. When the polymer films were coated with fibronectin, no significant differences in cell adhesion and proliferation were observed between coated polymer surfaces and gelatin. The results indicate that all tested materials support the adhesion and proliferation of HSCs and can in principle be used for the preparation of flexible and slowly degrading nerve guides.

Cell Adhesion↗

PubMed2003

Preparation of interconnected highly porous polymeric structures by a replication and freeze-drying process.

Three-dimensional degradable porous polymeric structures with high porosities (93-98%) and well-interconnected pore networks have been prepared by freeze-drying polymer solutions in the presence of a leachable template followed by leaching of the template. Templates of the pore network were prepared by fusing sugar or salt particles to form a well-connected structure. The interstices of the template were then filled with a polymer solution (5-15% w/v) in 1,4-dioxane, followed by freeze-drying of the solvent. Subsequent leaching of the sugar template ensures the connectivity of the pore network. The scaffold architecture consists of relatively large interconnected pores modeled after the template and smaller pores resulting from the freeze-drying process. The total porosity of the resultant porous structures is determined by the interstitial space of the leachable template and by the polymer concentration in the freeze-drying solution. The freezing temperature also has an effect on the final morphology of the porous structures. Compared with freeze-drying and combination of freeze-drying /particulate leaching techniques, this method facilitates higher interconnectivity of the scaffolds. Porous structures have been prepared from several relevant polymers in the biomedical and tissue-engineering field: poly(D,L-lactide) (PDLLA), 1000PEOT70PBT30, a segmented poly(ether ester) based on polyethylene oxide and polybutylene terephthalate, and poly(epsilon-caprolactone) (PCL). The mechanical properties of the porous structures prepared by this technique depend on the nature of the polymer, porosity, and the freezing temperature. With porosities in the range of 95-97%, the compression moduli of scaffolds prepared from the different polymers could be varied between 13.0 and 301.5 kPa.

Biocompatible Materials↗

PubMed2003

The preparation of monodisperse biodegradable polyester nanoparticles with a controlled size.

In local drug delivery, nanoparticles based on biodegradable polymers can function as vehicles with controlled drug-release properties. To achieve a well-controlled drug-release profile, control over the particle size is of great importance. Therefore, biodegradable polyester nanoparticles were prepared by the salting-out method. Process variables were varied to study the effect on the particle size. The monodisperse particles obtained were between 100 and 400 nm in size and spherical in shape. It was found that the particle size could be adjusted by varying the preparation conditions upon which the polymer concentration had the most pronounced effect.

Chemistry, Pharmaceutical↗

PubMed2003

Biodegradable elastomeric scaffolds for soft tissue engineering.

Elastomeric copolymers of 1,3-trimethylene carbonate (TMC) and epsilon-caprolactone (CL) and copolymers of TMC and D,L-lactide (DLLA) have been evaluated as candidate materials for the preparation of biodegradable scaffolds for soft tissue engineering. TMC-DLLA copolymers are amorphous and degrade more rapidly in phosphate-buffered saline (PBS) of pH 7.4 at 37 degrees C than (semi-crystalline) TMC-CL copolymers. TMC-DLLA with 20 or 50 mol% TMC loose their tensile strength in less than 5 months and are totally resorbed in 11 months. In PBS, TMC-CL copolymers retain suitable mechanical properties for more than a year. Cell seeding studies show that rat cardiomyocytes and human Schwann cells attach and proliferate well on the TMC-based copolymers. TMC-DLLA copolymers with either 20 or 50 mol% of TMC are totally amorphous and very flexible, making them excellent polymers for the preparation of porous scaffolds for heart tissue engineering. Porous structures of TMC-DLLA copolymers were prepared by compression molding and particulate leaching techniques. TMC-CL (co)polymers were processed into porous two-ply tubes by means of salt leaching (inner layer) and fiber winding (outer layer) techniques. These grafts, seeded with Schwann cells, will be used as nerve guides for the bridging of large peripheral nerve defects.

Animals↗

PubMed2003

Porous PEOT/PBT scaffolds for bone tissue engineering: preparation, characterization, and in vitro bone marrow cell culturing.

The preparation, characterization, and in vitro bone marrow cell culturing on porous PEOT/PBT copolymer scaffolds are described. These scaffolds are meant for use in bone tissue engineering. Previous research has shown that PEOT/PBT copolymers showed in vivo degradation, calcification, and bone bonding. Despite this, several of these copolymers do not support bone marrow cell growth in vitro. Surface modification, such as gas-plasma treatment, is needed to improve the in vitro cell attachment. Porous structures were prepared using a freeze-drying and a salt-leaching technique, the latter one resulting in highly porous interconnected structures of large pore size. Gas-plasma treatment with CO(2) generated a surface throughout the entire structure that enabled bone marrow cells to attach. The amount of DNA was determined as a measure for the amount of cells present on the scaffolds. No significant effect of pore size on the amount of DNA present was seen for scaffolds with pore sizes between 250-1000 microm. Light microscopy data showed cells in the center of the scaffolds, more cells were observed in the scaffolds of 425-500 microm and 500-710 microm pore size compared to the ones with 250-425 microm and 710-1000 microm pores.

Alkaline Phosphatase↗

PubMed2003

Porous polymeric structures for tissue engineering prepared by a coagulation, compression moulding and salt leaching technique.

A technique for the preparation of porous polymeric structures involving coagulation, compression moulding and particulate leaching has been developed. The technique combines the advantages of thermal processing methods and particulate leaching. A high molecular weight polymer solution in an organic solvent containing dispersed water-soluble salt particles is precipitated into an excess of non-solvent. The polymer-salt composite is then processed by thermal processing methods into devices of varying shapes and sizes, which can subsequently be extracted to give the desired porous structures. The porosities of the scaffolds could be varied between 70% and 95% by adjusting the polymer to salt ratio and the pore size could be controlled independently by varying the leachable particle size. This versatility provides for the optimisation of scaffolds used in medicine and in tissue engineering. Compared with commonly used porosifying methods such as sintering, compression moulding combined with salt leaching, and freeze-drying, this process allows excellent control over pore size and porosity and yields scaffolds with a much more homogeneous pore morphology. We have prepared porous structures from several relevant polymers in the biomedical field: poly(D,L-lactide), poly(epsilon-caprolactone) and 1000PEOT70PBT30, a segmented poly(ether ester) based on polyethylene oxide and polybutylene terephthalate.

Absorbable Implants↗

PubMed2003

Positively charged biomaterials exert antimicrobial effects on gram-negative bacilli in rats.

Biomaterial-centered infection is a much-dreaded complication associated with the use of biomedical implants. Although positively charged biomaterial surfaces stimulate bacterial adhesion, it has been suggested that surface growth of adhering Gram-negative bacilli is inhibited on positively charged surfaces. In the present paper, we determined the infection rate of differently charged poly(methacrylates) in rats. To this end, 2 x 10(6)/cm(2) Escherichia coli O2K2 or 2 x 10(4)/cm(2) Pseudomonas aeruginosa AK1 were seeded on glass discs coated with three differently charged poly(methacrylates) coatings in a parallel plate flow chamber. Three rats received six subcutaneous discs (two discs of each charge variant) seeded with E. coli, while three other rats received discs seeded with P. aeruginosa. The numbers of viable bacteria on the surfaces were determined 48h after implantation. On 50% of all positively charged discs viable E. coli were absent, while the negatively charged discs were all colonized by E. coli. P. aeruginosa, however, were isolated from both positively and negatively charged discs. Probably, P. aeruginosa can circumvent the antimicrobial effect of the positive charge through the formation of extracellular polysaccharides.

Animals↗

PubMed2002

Design of segmented poly(ether ester) materials and structures for the tissue engineering of bone.

In this study, PEOT/PBT segmented copolymers of different compositions have been evaluated as possible scaffold materials for the tissue engineering of bone. By changing the composition of PEOT/PBT copolymers, very different mechanical and swelling behaviors are observed. Tensile strengths vary from 8 to 23 MPa and elongations at break from 500 to 1300%. Water-uptake ranges from 4 up to as high as 210%. The in vitro degradation of PEOT/PBT copolymers occurs both by hydrolysis and oxidation. In both cases degradation is more rapid for copolymers with high PEO content. PEOT/PBT scaffolds with varying porosities and pore sizes have been prepared by molding and freeze-drying techniques in combination with particulate-leaching. The most hydrophilic PEOT/PBT copolymers did not sustain goat bone marrow cell adhesion and growth. However, surface modification by gas plasma treatment showed a very much improved polymer-cell interaction for all PEOT/PBT copolymer compositions. Their mechanical properties, degradability and ability to sustain bone marrow cell growth make PEOT/PBT copolymers excellent materials for bone tissue engineering.

Animals↗

PubMedDate not supplied

Enhanced bone marrow stromal cell adhesion and growth on segmented poly(ether ester)s based on poly(ethylene oxide) and poly(butylene terephthalate).

In previous studies in rats and goats, hydrophilic compositions of the PEOT/PBT block copolymer family have shown in vivo calcification and bone bonding. These copolymers are therefore interesting candidates as scaffolding materials in bone tissue engineering applications. Model studies using goat bone marrow stromal cells, however, showed that it was not possible to culture bone marrow stromal cells in vitro on these hydrophilic copolymers. In this paper two ways of surface modifying these materials to improve in vitro bone marrow stromal cell attachment and growth are discussed. Two different approaches are described: (1) blending of hydroxyapatite (HA) followed by CO(2) gas plasma etching; (2) surface modification using CO(2) gas plasma treatments. It was observed that not only HA but also the CO(2) plasma treatment by itself has a positive effect on bone marrow stromal cell attachment and growth. Gas plasma treatment appeared to be the most successful approach, resulting in a large increase in the amount of bone marrow stromal cells present on the surface (determined by a DNA assay). The amount of DNA present on the plasma-treated copolymer 1000/70/30 PEOT/PBT, based on poly(ethylene oxide, M(w) = 1000, 70 m% soft segment), was comparable to the amount present on PDLLA and significantly higher than the amount present on PCL after 7 days of cell culturing. The fact that after gas plasma treatment bone marrow stromal cells do attach to PEOT/PBT copolymers, enables in vitro bone marrow stromal cell culturing, making bone tissue engineering applications of these materials possible.

Animals↗