Stimulation o f Bone Formation by a Swelling Endosseous Implant
As previously reported,'q2 a polymer-ceramic composite designed for endosseous implant applications has been developed. The composites were prepared by the free-radical polymerization of an acrylic acid solution and a difunctional acrylate in the presence of 0.3 pm akunina powder. Mechanical testing indicated that the material had a compressive yield strength of 89-102 MPa (13-15 ksi) and an elastic modulus of 2055-2740 MPa (300-400 ksi). The average porosity of the composite was determined to be in the range of 50-55 ~0 1 % .
A unique property of this material is its ability to gradually swell in aqueous media to a degree which can be precisely controlled via the extent of matrix cross-linking. The present material was designed to obtain an equilibrium swelling level of 15-25 vol % in Ringers solution a t 40OC. The advantages of such controlled swelling in an endosseous implant material are twofold. First, it allows for rapid adaptation of the prosthesis to the contour of the socket. Second, it induces a state of compressive stress around the implant site. It has been suggested that the presence of such a force field will result in the stimulation of bone f o r m a t i ~n . ~~ This paper reports the initial results obtained from a series of animal implantation experiments utilizing this swelling composite material.
EXPERIMENTAL PROCEDURE
Six adult mongrel dogs were used in these experiments. Following standard aseptic procedures, four holes were made in each canine femoral shaft with a 3/16-in. (4.76 mm) Michelle 1aminect.omy trephine. Cylindrical implant specimens which had been machined to a diameter of 4.65-4.67 mm were placed in the right femur of each animal.
Approximately 4 weeks later, additional specimens were inserted into the animal's left