Jorma Rautavuori

Histological study of tissue reactions to ε-caprolactone–lactide copolymer in paste form

In previous studies, e-caprolactone–lactide copolymer in solid form has been used in experimental animals as suture material, and as a biodegradable nerve guide. The aim of the study reported here was to assess tissue reactions to e-caprolactone–lactide copolymer in paste form, histologically, and to compare bone healing at the sites of implantation versus that at control sites. The other purpose of the study was to evaluate the properties of the implanted material as a filling material for bone defects. Resorption time and intensity of inflammatory reaction were also evaluated. Material was implanted into the abdominal walls and femurs of 34 rats. Follow-up times were from 2 weeks to 1 year. The results showed that e-caprolactone–lactide copolymer in paste form induces a severe inflammatory reaction when placed in muscle, and moderate inflammation when implanted into bone. The resorption time was more than 1 year. Bone healing at sites of implantation was slower than at control sites.

The effect of transforming growth factor-β1, released from a bioabsorbable self-reinforced polylactide pin, on a bone defect

Transforming growth factor-beta 1 (TGF-beta1)is a polypeptide growth factor which has been shown to increase bone formation in experimental studies. In this study it was combined to a bioabsorbable self-reinforced poly-LD-lactic acid fracture fixation pin. To assess the effect of TGF-beta1 on the healing of a bone defect, the pins were implanted in the rat distal femur next to a bone defect filled with a viscose cellulose sponge. The pins used in the study group (13 rats) contained 50 microg of TGF-beta1, whereas in the control group of nine rats an identical pin without the growth factor was used. In the histologic examination at 1, 3 and 6 weeks no difference was detected in the amount of bone inside the viscose cellulose sponge between the rats treated with TGF-beta1 and those with no added growth factor. At 3 weeks there was more fibroblast-rich mesenchymal tissue inside the viscose cellulose sponge in the rats treated with TGF-beta1. In the radiographic examination at 3 weeks there was an increase in the amount of new periosteal bone on the bone defect in the TGF-beta1-treated rats.

MIXTURE OF EPSILON -CAPROLACTONE-LACTIDE COPOLYMER AND TRICALCIUM PHOSPHATE : A HISTOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY OF TISSUE REACTIONS

In cranio-maxillofacial surgery, bone transplantation is needed for treatment of bony defects. An autograft, allograft or biomaterial can be used. Autogenous bone grafts are considered to be the best materials available, but there are some disadvantages in their use including donorsite morbidity, need for a second operative site and limited graft supply. A search for new bone-graft materials therefore remains necessary. We prepared a mixture of tricalcium phosphate (TCP), which is a resorbable, non-toxic, osteoconductive ceramic material and ε-caprolactone-lactide copolymer P(ε-CL/DL-LA), a resorbable polymer, and placed it in the dermis and in mandibular bone defects in 13 rabbits. Follow-up times were two, three, seven, eight, 12, 15 and 18 weeks, tissue reactions were assessed, histologically and immunohistochemically. Times of resorption of the material from tissues were reported. We found that the mixture caused a mild inflammatory reaction when placed in bone and severe inflammation when placed in dermis. No highly fluorescent layer of tenascin or fibronectin was found surrounding the implant area. The mixture was excellent to handle and very easy to place into bone defects. The results are promising and have led us to continue development of the mixture.

Shear strength of loaded porous-glassy-carbon/bone interface—an experimental study on rabbits

The aim of the study was to measure the shear strength of bone/porous-glassycarbon interface in rabbit. Glassy carbon pellets were implanted into drill holes made through the medial articular surface of the proximal tibia of 15 rabbits. Shear strengths grew statistically significantly from 1 to 6 weeks ana reached a maximum of 4.6 MN/m2. Microscopical examination of the sheared surfaces revealed that at 1 and 2 weeks the shearing occurred through the tissue surrounding the implant, and at 3, 6 and 12 weeks through the porous coating of the implant. To diminish the fragility of the porous coating, its porosity should be adjusted to 40%. Results of shear strength studies on current implant materials are reviewed.

Bone remodelling in the pores and around load bearing transchondral isoelastic porous-coated glassy carbon implants: Experimental study in rabbits

Cylinders of porous-coated glassy carbon were implanted into drill holes made through the articular surface of the medial condyle of both tibiae of ten rabbits for six and 12 weeks. Bone ingrowth and remodelling was examined by radiographic, histologic, oxytetracycline-fluorescence and microradiographic methods. Bone ingrowth into pores and load bearing implants was seen by all examination methods. Bone ingrowth occurred earlier when the pores were facing cancellous bone than cortical bone. Appositional bone formation occurred on the trabeculae a few millimetres from the interface during the early phase of remodelling at six weeks. At 12 weeks resorptive remodelling had occurred both in the surroundings and in those pores that face cancellous bone, whereas the amount of bone still increased in the pores facing cortical bone. In its porous-coated form glassy carbon functions well as a frame for ingrowing bone and it shows good osteoconductivity. Its mechanical properties are suitable for functioning as a structural bone substitute in places where the loads are mainly compressive. The difference between findings at six and 12 weeks indicated physiologic stress distribution and the adverse effects of stiff materials on bone remodelling were avoided by using this isoelastic material.

Interaction of microporous glassy carbon and living tissue

Preliminary animal implantation tests with rats showed that microporous glassy carbon has good biocompatibility. Microporous glassy carbon is also stable and suitable for a hard biocompatible implant.