Bioerodible polymeric semi-interpenetrating network alloys for surgical plates and bone cements, and method for making same

#The invention relates to implantible biomaterials, in particular to bioerodible polymers and more specifically to bioerodible polymers suitable for use in forming internal fixation devices (IFDs) such as bone supports, plates, and pins, and/or bone cements for bone repair.

#A study in the mid-1980's estimated that about four and a half million people suffer fractures each year in the United States alone. In adults, fractures of the radius and/or ulna of the forearm, and fibula or ankle bone are frequently treated by immobilizing the fracture by the surgical attachment of a metal plate adjacent the fracture. Similarly, in some adults and most children, fractures of the neck of the femur or hip are frequently treated by immobilizing the fracture with a metal plate. In addition to its use in treating fractures of the radius, ulna and femur, a metal plate may also used to immobilize other bones in both the treatment of fractures and in corrective surgery. The metal plate, typically made of a titanium-based metal, a stainless-steel, or a cobalt-chromium metal, is attached to the bone by bone screws. It should be noted that although the immobilization device is referred to as a plate, its size and shape is dictated by the application in which it is to be used.

#As the bone heals it is necessary to remove the metal plate by means of a second surgical intervention. The reason for this is that the presence of the metal plate adjacent the bone ultimately results in what is referred to as "plate induced osteopenia" or loss of bone mass. The reasons for this loss of bone mass are not fully understood but appear to be related both to changes in bone stress and changes in bone blood flow. Such bone remodeling in children may lead to growth restriction, especially when plates are used in craniofacial or maxillofacial intervention to repair congenital deformities.

#The invention will be more fully understood by reference to the following Detailed Description Of The Invention in conjunction with the following Drawings, of which:

#FIGS. 1a and 1b are scanning electron micrographs (at 6250.times.) of a bone cement alloy according to the disclosure containing crosslinked PPF scaffolding and PLGA/calcium gluconate after one and two weeks exposure to water.

#FIG. 2 is a graph of distribution of vinyl pyrrolidone between crosslinked poly(propylene fumarate) and poly(vinyl pyrolidone). Linear regression analysis: intercept=-0.082; slope=1.084; correlation coefficient=0.9686. (Example 2.)

#The bioerodible bone cements and internal fixation devices (IFD) made from the bioerodible polymeric semi-IPN alloy material disclosed herein may be advantageously used for surgical repair of orthopaedic and maxillofacial fractures. The bioerodible material is a polymeric semi-IPN alloy which comprises at least a first bioerodible polymer capable of producing acidic products upon hydrolytic degradation; and a second bioerodible polymer, which upon crosslinking provides a biopolymeric scaffolding or internal reinforcement.

#An semi-interpenetrating polymer network (semi-IPN) is defined herein as an internecine combination of two or more polymers, at least one of which is crosslinked (sometimes in the immediate presence of the other) to form a network ("scaffolding" in the present disclosure) in which the other polymer is enclosed, trapped or retained.

#As used herein, the term "bioerodible" is defined as the susceptibility of a biomaterial to degradation over time, usually months. "Buffer" is defined as any material which limits changes in the pH in the implant or cement and its near environment only slightly upon exposure to acid or base. "Acidic product" is defined herein as any product that has a pH less than 7.