A Novel Resorbable Composite Material Containing Poly(ester-co-urethane) and Precipitated Calcium Carbonate Spherulites for Bone Augmentation-Development and Preclinical Pilot Trials

Abstract

Polyurethanes have the potential to impart cell-relevant properties like excellent biocompatibility, high and interconnecting porosity and controlled degradability into biomaterials in a relatively simple way. In this context, a biodegradable composite material made of an isocyanate-terminated co-oligoester prepolymer and precipitated calcium carbonated spherulites (up to 60% w/w) was synthesized and investigated with regard to an application as bone substitute in dental and orthodontic application. After foaming the composite material, a predominantly interconnecting porous structure is obtained, which can be easily machined. The compressive strength of the foamed composites increases with raising calcium carbonate content and decreasing calcium carbonate particle size. When stored in an aqueous medium, there is a decrease in pressure stability of the composite, but this decrease is smaller the higher the proportion of the calcium carbonate component is. In vitro cytocompatibility studies of the foamed composites on MC3T3-E1 pre-osteoblasts revealed an excellent cytocompatibility. The in vitro degradation behaviour of foamed composite is characterised by a continuous loss of mass, which is slower with higher calcium carbonate contents. In a first pre-clinical pilot trial the foamed composite bone substitute material (fcm) was successfully evaluated in a model of vertical augmentation in an established animal model on the calvaria and on the lateral mandible of pigs.

Keywords: bioresorbable composite; bone regeneration; calcium carbonate; degradable polyurethane; foam.

Scheme 1

Reaction scheme of the synthesis of the oligoester component 1a and the isocyanate-terminated prepolymer ITP 1b.

Figure 1

Macroscopic view of fCM samples prepared from polymer 1b and different amounts of calcium carbonate (type SP01).

Figure 2

Density and open/closed cell volume of fCM samples with different amounts of calcium carbonate (type SP01).

Figure 3

Compressive strength of cylindrical fCM samples (a) softened with 80 µL/g DMSO and 60% calcium carbonate (type 02, 47 and SP01 (b) with and 30–60% calcium carbonate (SP01, 80 µL/g DMSO) and (c) with and different amounts of DMSO (60% calcium carbonate of SP01).

Figure 4

Compressive strength of cylindrical fCM samples containing 0–60% calcium carbonate type SP01, without DMSO addition) after storage in PBS solution.

Figure 5

Weight change of fCM samples with 0–60% calcium carbonate (type SP01), stored in water or PBS.

Figure 6

Live/dead staining of MC3T3-E1 cells cultured on fCM with each 60% of type SP01 (top), type 47 (middle) and type 02 (bottom) for 1 day (left) and 3 days (right).

Figure 7

Results of WST-1^® assay from eluates of fCM samples; (a) prepared with 50% calcium carbonate (type SP01), unleached, test time: 14 days; (b) samples prepared with different calcium carbonate contents, leached in water for 72 h at 37 °C, test time: 1 day. Statistical differences with regard to the negative control are marked with an asterisk.

Figure 8

Results of remaining bone substitute material after vertical augmentation of (a) the calvaria and (c) the mandible. Boxplots show remaining bone substitute material in the area (bone substitute material volume/tissue volume; BSM/TV). Results of newly formed bone after vertical augmentation of (b) the calvaria and (d) the mandible. Boxplots show the newly formed bone in the total area (bone volume/tissue volume; BV/TV).

Figure 9

Histological sections 30 (a,b), 60 (c–e), and 180 days (f–i) postoperatively showing the skull (a,c,f,g), and the mandible (b,d,e,h,i) region, resp.

Figure 10

SEM-images of particular calcium carbonate modifications (mean particle diameter in brackets): (a) type 47 (12 µm), (b) type 02 (22 µm) and (c) type SP01 (5 µm), scale bar: 50 µm.

Figure 11

Images of the interoperative situation of the mandible (bottom right) and the calvaria (left) as well as schematic drawing (upper right) of the distributions of the fCM samples (assigned by numbers) on the skull, and on the left and right mandible as seen from the surgeon’s perspective.