Biomedical subjects

G W Bos

Publications and source records attributed to G W Bos.

7 recordsLinked to original sources

PubMed2004

Biodegradable dextran hydrogels crosslinked by stereocomplex formation for the controlled release of pharmaceutical proteins.

Hydrogels are based on hydrophilic polymers, which are crosslinked to prevent dissolution in water. Because hydrogels can contain large amounts of water, they are interesting devices for the delivery of proteins. In this contribution a biodegradable dextran hydrogel is described which is based on physical interactions and is particularly suitable for the controlled delivery of pharmaceutically active proteins. The unique feature of our system is that the preparation of the hydrogels takes place in an all-aqueous solution, by which the use of organic solvents is avoided. Furthermore, chemical crosslinking agents are not needed to create the hydrogels, since crosslinking is established physically by stereocomplex formation between enantiomeric oligomeric lactic acid chains. The hydrogel is simply obtained after mixing aqueous solutions of dextran(l)-lactate and dextran(d)-lactate. In this contribution, the formation of the hydrogels as well as their protein release properties and degradation behavior are discussed.

Biocompatible Materials↗

PubMed2000

Sterilization of poly(dimethylamino) ethyl methacrylate-based gene transfer complexes.

Parental administration of polyplex formulations for gene therapy or genetic vaccination requires sterile preparations. The possibilities and limitations of autoclaving, filtration and a combination of both methods for sterilization of poly(2-(dimethylamino) ethyl methacrylate) (pDMAEMA) based gene transfer complexes were assessed. Agarose gel electrophoresis and circular dichroism spectroscopy showed that sterile filtration of polyplexes did not change the topology and integrity of the DNA. The transfection potential was fully retained in COS-7 and OVCAR-3 cells, although the concentration of DNA was slightly decreased by the filtration process. Pre-coating of the filter with polyplexes reduced the material loss. In contrast, autoclaving dramatically affected physical characteristics of polyplexes, resulting in complete loss of transfection potential. Sterile filtration or autoclaving of polymer alone did not result in material loss, or in decreased transfection potential after complexation with plasmid DNA. 'Naked' DNA could easily be sterilized by filtration as well. In conclusion, sterilization of complexes between pDMAEMA-based cationic polymeric gene transfer agents and DNA plasmid is feasible by filtration. Depending on the filter type used, the filtered volume should be high enough, to prevent substantial material loss. Separate sterilization of the polymer by autoclaving or filtration and DNA by filtration offers a good alternative to filtration of formed polyplexes.

Animals↗

PubMed1999

Blood compatibility of surfaces with immobilized albumin-heparin conjugate and effect of endothelial cell seeding on platelet adhesion.

Endothelial cell (EC) seeding significantly improves the blood compatibility of artificial surfaces. Although a coating consisting of albumin and heparin (alb-hep) is a suitable substrate for seeded ECs, binding of ECs to the substrate further improves when small amounts of fibronectin are present in the alb-hep coating. Alb-hep conjugate was immobilized on carbon dioxide gas plasma-treated polystyrene (PS-CO(2)), thereby significantly increasing the recalcification time of blood plasma exposed to this surface. Furthermore, surface-immobilized alb-hep conjugate inhibited exogenous thrombin. Heparin activity was reduced by adding fibronectin on top of a monolayer of alb-hep conjugate, but not by simultaneous coating of fibronectin and alb-hep conjugate. Coating of PS-CO(2) with alb-hep conjugate significantly decreased contact activation (FXII activation). The number of platelets deposited from blood plasma on PS-CO(2) coated with alb-hep conjugate was twice as high as on PS-CO(2) coated with albumin. Addition of fibronectin to alb-hep conjugate-coated PS-CO(2) had no significant effect on the number of adhered platelets. Seeding of the substrates with ECs significantly reduced the number of adhered platelets under stationary conditions. Platelets deposited onto endothelialized surfaces were primarily found on endothelial cell edges, and sparingly on areas between ECs. In conclusion, alb-hep conjugate-coated surfaces display anticoagulant activity. ECs adhering to and proliferating on this coating significantly decrease the number of platelets which adhere to the surface. Therefore, alb-hep conjugate-coated surfaces form a suitable substrate for seeding of ECs in low density. Although application of fibronectin on top of the coating decreases the anticoagulant activity to some extent, it might be useful in view of the improved adherence of ECs to the coating.

Animals↗

PubMed1999

Proliferation of endothelial cells on surface-immobilized albumin-heparin conjugate loaded with basic fibroblast growth factor.

Seeding of endothelial cells (ECs) on the luminal surface of small-diameter vascular grafts is a promising method to avoid occlusion of these prostheses. Immobilization of basic fibroblast growth factor (bFGF) to substrates used to coat or fill porous prostheses may enhance the formation of a confluent monolayer of ECs. Human umbilical vein endothelial cells (HUVECs) were grown on bFGF-loaded albumin-heparin conjugate bound to CO2 gas-plasma-treated polystyrene. In the order of 2-3 ng/cm2 bFGF had to be immobilized to form a confluent monolayer of HUVECs. The most prominent effect of surface-immobilized bFGF was stimulation of the proliferation shortly after seeding, resulting within 3 days in confluent cell monolayers with high density. In contrast, in cultures with 0.3 ng/mL bFGF in the medium instead of bFGF bound to the surface, it took almost a week before the cell layers reached confluency. Binding of bFGF to heparin and the biological activity of bFGF towards ECs were not influenced by the (radio-)labeling of bFGF with iodine. However, only a minor part of the bFGF used in this study displayed heparin affinity. Furthermore, degradation and multimerization of labeled bFGF in time occurred when the growth factor was stored at 20 degrees -37 degrees C. This limits the use of labeled bFGF to short-term (hours) experiments. In conclusion, bFGF loading of vascular graft surfaces through complexation of bFGF with a heparin-containing matrix probably will lead to more rapid formation of a confluent monolayer of ECs on graft surfaces upon seeding of the cells.

Blood Vessel Prosthesis↗

PubMed1999

Endothelialization of crosslinked albumin-heparin gels.

Crosslinked gels of albumin as well as heparinized albumin gels, potential sealants of prosthetic vascular grafts, were studied with regard to in vitro stability, binding of basic fibroblast growth factor (bFGF) and cellular interactions. A small percentage of the heparin present in these gels, was released during storage in SDS solution. During storage in cell culture medium at 37 degrees C, heparin release was 21-25 percent. Release of albumin did not occur. Human umbilical vein endothelial cells (HUVECs) rapidly adhered and subsequently spread on (heparinized) albumin gels, but proliferation was only observed if heparin was present in the gel. Binding of 125I-bFGF to heparinized albumin gel was 35 percent higher than to non-heparinized albumin gel. Growth of HUVECs occurred only on heparinized albumin gel loaded with bFGF and not on bFGF-loaded albumin gel. The number of platelets deposited under stationary conditions onto heparinized albumin gel was about twice the number found on nonheparinized albumin gel. Seeding of HUVECs on heparinized albumin gel, significantly reduced the number of platelets adhering to this surface. Moreover, no spreading of platelets was observed on substrates seeded with HUVECs. It can be concluded that crosslinked gels of albumin to which heparin is immobilized, are candidate sealants for prosthetic vascular grafts and suitable substrates for endothelial cell seeding.

Albumins↗

PubMed1998

Small-diameter vascular graft prostheses: current status.

In contrast to large-diameter vascular grafts (i.e. larger than 5 mm) which remain excellent for more than 10 years after implantation, small-diameter vascular grafts of both Dacron and Teflon occlude rapidly upon implantation. In this overview article, the strategies used to improve the patency of these small-diameter grafts, the current status in clinical trials, and further perspectives in the field of artificial vascular graft development are reviewed. It is concluded that, in view of recent developments in tissue engineering approaches, the future of small-diameter vascular prostheses looks promising.

Animals↗

PubMed1998

Adherence and proliferation of endothelial cells on surface-immobilized albumin-heparin conjugate.

Small-diameter vascular grafts rapidly fail after implantation, due to occlusion caused by thrombosis. This problem cannot be overcome using medication. A promising improvement of graft patency is the seeding of endothelial cells (EC) on the luminal surface of the vascular graft. Conjugates of albumin and heparin, which were developed to obtain nonthrombogenic coatings, could form an ideal coating for vascular grafts. Besides presenting anticoagulant function, heparin will bind proteins with cell adhesive properties, thus facilitating adherence of EC to the graft surface. EC were able to grow to confluency on CO(2) gas plasma-treated polystyrene (PS-CO(2)) coated with albumin-heparin conjugate. CO(2) gas plasma treatment resulted in the introduction of functional groups at the surface (e.g., hydroxyl, aldehyde, carboxylic acid, and epoxide groups). Addition of albumin-heparin conjugate to the functionalized surface in an aqueous solution with pH 8.2 yielded a stable monolayer of covalently bound conjugate. The number of cells adhering and proliferating on this surface was comparable to the number of cells on fibronectin-coated PS-CO(2). However, the structure and size of EC proliferating on surface-immobilized albumin-heparin was more irregular. Long-term adherence might be improved by adding fibronectin to the albumin-heparin surface, either as a mixture with albumin-heparin or in a separate incubation step.

Albumins↗