Search

We investigated the effects of the time course of addition of osteogenic supplements dexamethasone, beta-glycerolphosphate, and L-ascorbic acid to rat marrow stromal cells, and the exposure time on the proliferation and differentiation of the cells. It was the goal of these experiments to determine the time point for supplement addition to optimize marrow stromal cell proliferation and osteoblastic differentiation. To determine this, two studies were performed; one study was based on the age of the cells from harvest, and the other study was based on the duration of exposure to supplemented medium. Cells were seen to proliferate rapidly at early time points in the presence and absence of osteogenic supplements as determined by 3H-thymidine incorporation into the DNA of replicating cells. These results were supported by cell counts ascertained through total DNA analysis. Alkaline phosphatase (ALP) activity and osteocalcin production at 21 days were highest for both experimental designs when the cells were exposed to supplemented medium immediately upon harvest. The ALP levels at 21 days were six times greater for cells maintained in supplements throughout than for control cells cultured in the absence of supplements for both studies, reaching an absolute value of 75 x 10(-7) micromole/min/cell. Osteocalcin production reached 20 x 10(-6) ng/cell at 21 days in both studies for cells maintained in supplemented medium throughout the study, whereas the control cells produced an insignificant amount of osteocalcin. These results suggest that the addition of osteogenic supplements to marrow-derived cells early in the culture period did not inhibit proliferation and greatly enhanced the osteoblastic phenotype of cells in a rat model.

This study involves investigating the in vitro degradation of a poly(propylene fumarate) (PPF) based composite material for orthopaedic applications. The effects of PPF molecular weight, PPF to vin...

The present study provides in vivo trials of poly(L-lactic acid) (PLLA) as a porous biodegradable nerve conduit using a 10 mm sciatic nerve defect model in rats. The PLLA conduits, fabricated by an extrusion technique, had an inner diameter of 1.6 mm, an outer diameter of 3.2 mm, and a length of 12 mm. They were highly porous with an interconnected pore structure (of 83.5% porosity and 12.1 microm mean pore size). The conduits were interposed into the right sciatic nerve defect of Sprague Dawley rats using microsurgical techniques; nerve isografts served as controls. Walking track analysis was performed after conduit placement monthly through 16 weeks. At the conclusion of 6 and 16 weeks, sections from the isograft/conduit and distal nerve were harvested for histomorphometric analysis. The right gastrocnemius muscle was also harvested and its weight was determined. All conduits remained intact without breakage. Moreover, no conduit elongated during the 16 weeks of placement. Walking track analysis and gastrocnemius muscle weight demonstrated increasing regeneration over the 16 weeks in both the conduit and isograft control groups, with control values significantly greater. The nerve fiber density in the distal sciatic nerve for the PLLA conduits (0.16+/-0.07) was similar to that for the control isografts (0.19+/-0.05) at 16 weeks. The number of axons/mm2 in the distal sciatic nerve for the PLLA conduits was lower than that for the isografts (13 800+/-2500 vs. 10700+/-4700) at 16 weeks. The results for PLLA were significantly improved over those for 75:25 poly(DL-lactic-co-glycolic acid) of a previous study and suggest that PLLA porous conduits may serve as a scaffold for peripheral nerve regeneration.

We have fabricated porous, biodegradable tubular conduits for guided tissue regeneration using a combined solvent casting and extrusion technique. The biodegradable polymers used in this study were poly(DL-lactic-co-glycolic acid) (PLGA) and poly(L-lactic acid) (PLLA). A polymer/salt composite was first prepared by a solvent casting process. After drying, the composite was extruded to form a tubular construct. The salt particles in the construct were then leached out leaving a conduit with an open-pore structure. PLGA was studied as a model polymer to analyze the effects of salt weight fraction, salt particle size, and processing temperature on porosity and pore size of the extruded conduits. The porosity and pore size were found to increase with increasing salt weight fraction. Increasing the salt particle size increased the pore diameter but did not affect the porosity. High extrusion temperatures decreased the pore diameter without altering the porosity. Greater decrease in molecular weight was observed for conduits manufactured at higher temperatures. The mechanical properties of both PLGA and PLLA conduits were tested after degradation in vitro for up to 8 weeks. The modulus and failure strength of PLLA conduits were approximately 10 times higher than those of PLGA conduits. Failure strain was similar for both conduits. After degradation for 8 weeks, the molecular weights of the PLGA and PLLA conduits decreased to 38% and 43% of the initial values, respectively. However, both conduits maintained their shape and did not collapse. The PLGA also remained amorphous throughout the time course, while the crystallinity of PLLA increased from 5.2% to 11.5%. The potential of seeding the conduits with cells for transplantation or with biodegradable polymer microparticles for drug delivery was also tested with dyed microspheres. These porous tubular structures hold great promise for the regeneration of tissues which require tubular scaffolds such as peripheral nerve, long bone, intestine, or blood vessel.

We describe the preparation and bulk characterization of a cross-linked poly(propylene fumarate-co-ethylene glycol), p(PF-co-EG), hydrogel. Eight block copolymer formulations were made varying four different design parameters including: poly(ethylene glycol) (PEG) molecular weight, poly(propylene fumarate) (PPF) molecular weight, copolymer molecular weight, and ratio of PEG to PPF. Two different cross-linking formulations were also tested, one with a cross-linking monomer and one without. The extent of the cross-linking reaction and the degree of swelling in aqueous solution were determined on copolymer formulations made without a cross-linking monomer. The values of molecular weight between cross-links, Mc ranged from 300 +/- 120 to 1190 +/- 320 as determined from swelling data (n = 3). The equilibrium volume swelling ratios, Q, varied from 1.5 +/- 0.1 to 3.0 +/- 0.1. This ratio was found to increase with increasing PEG content in the copolymer and decrease with increasing PPF molecular weight. The values for complex dynamic elastic moduli magnitudes of E*, ranged from 0.9 +/- 0.2 to 13.1 +/- 1.1 MPa for the formulations with the cross-linking monomer, N-vinyl pyrrolidinone (VP) (n = 3). The ultimate tensile stresses on the formulations made with VP ranged from 0.15 +/- 0.03 to 1.44 +/- 1.06 MPa, and tensile moduli ranged from 1.11 +/- 0.20 to 20.66 +/- 2.42 MPa (n = 5). All of the mechanical properties increased with increasing PPF molecular weight and decreased with increasing PEG content in the copolymer. These data show that the physical properties of p(PF-co-EG) hydrogels can be tailored for specific applications by altering the material composition.

Introducion. Tissue engineering holds great promise for nerve replacement and restoration. The present study evaluated the efficacy of utilizing poly-DL-lactic-co-glycolic acid (PLGA) formed tubes through an extrusion process for peripheral nerve regeneration.

Publisher Summary A large variety of processes have been applied to manufacture scaffolds. However, there is no universal technique to produce scaffolds for the regeneration of all tissues. Often the requirements for a desired scaffold dictate the method of processing and the type of material used. This is dependent on the shape of a scaffold, the pore structure, a required degradation rate, drug delivery purposes, or the mechanical properties. In addition, different kinds of tissues require different scaffolds. For the repair of hard and brittle tissue, such as bone, scaffolds need to have a high elastic modulus to maintain the space designated to them and provide the tissue with enough space for growth. If scaffolds are used as a temporary load-bearing device, they should be strong enough to maintain that load for the required time without showing any symptoms of fatigue failure. Used in combination with soft tissues, the flexibility and the stiffness of the scaffold have to be within the same order of magnitude as the surrounding tissues in order to prevent the scaffold from either breaking or collapsing. The choice of a scaffold-processing technique is therefore a question of assessing critical requirements for each application of such scaffolds. However, many challenges remain in the fabrication of high load-bearing scaffolds, scaffolds with high flexibility, and the incorporation and delivery of drugs, bioactive molecules, and cells to stimulate and enhance the growth of a specific tissue.