Biogenic polymer-based patches for congenital cardiac surgery: a feasibility study

Abstract

Objective: Currently used patch materials in congenital cardiac surgery do not grow, renew, or remodel. Patch calcification occurs more rapidly in pediatric patients eventually leading to reoperations. Bacterial cellulose (BC) as a biogenic polymer offers high tensile strength, biocompatibility, and hemocompatibility. Thus, we further investigated the biomechanical properties of BC for use as patch material.

Methods: The BC-producing bacteria Acetobacter xylinum were cultured in different environments to investigate optimal culturing conditions. For mechanical characterization, an established method of inflation for biaxial testing was used. The applied static pressure and deflection height of the BC patch were measured. Furthermore, a displacement and strain distribution analysis was performed and compared to a standard xenograft pericardial patch.

Results: The examination of the culturing conditions revealed that the BC became homogenous and stable when cultivated at 29°C, 60% oxygen concentration, and culturing medium exchange every third day for a total culturing period of 12 days. The estimated elastic modulus of the BC patches ranged from 200 to 530 MPa compared to 230 MPa for the pericardial patch. The strain distributions, calculated from preloaded (2 mmHg) to 80 mmHg inflation, show BC patch strains ranging between 0.6% and 4%, which was comparable to the pericardial patch. However, the pressure at rupture and peak deflection height varied greatly, ranging from 67 to around 200 mmHg and 0.96 to 5.28 mm, respectively. The same patch thickness does not automatically result in the same material properties indicating that the manufacturing conditions have a significant impact on durability.

Conclusions: BC patches can achieve comparable results to pericardial patches in terms of strain behavior as well as in the maximum applied pressure that can be withstood without rupture. Bacterial cellulose patches could be a promising material worth further research.

Keywords: biogenic polymers; biomedical engineering; congenital; innovation; patch.

Figure 1

Flow charts of the steps undertaken to produce BC patches. (A) illustrates the extra step of prepreparation. (B) shows the postpreparation each patch underwent after the growing period. BC, bacterial cellulose.

Figure 2

BC patch incubated 6 days at 29°C. (A) shows the patch before the postpreparation. (B) shows the same patch after the post preparation. BC, bacterial cellulose.

Figure 3

Overview of the investigated culturing conditions. (A) examines the use of an incubator: (B) compares different medium exchange and refill schemes. (C) depicts the influence of growth time. (D) depicts the influence of prepreparation. Thickness is in mm.

Figure 4

Pressure vs. deflection height for all four BC patches (BCP1-4) and the pericardium patch. Fit 1–4 and fit 5 are the least squares method fits to estimate the elastic modulus of BC1–4 patches and the pericardium patch, respectively, from Equation 1. BC, bacterial cellulose.

Figure 5

In plane displacements of BCP-4 (A) and the pericardium patch (B). The unit of vectors is mm and the axis are in pixel with respect to the tailored image. BCP, bacterial cellulose patch.

Figure 6

Strain distribution maps for patch BCP1, 2, and 3. For each patch, all (A) show the strain in the horizontal direction and all (B) show the strain in the vertical direction. The strain map is calculated from the preloaded state (approximately p = 2 mmHg) until a pressure of 80 mmHg. BCP, bacterial cellulose patch.

Figure 7

Strain distribution maps for BCP-4 and pericardium patch. For each patch, all (A) show the strain in the horizontal direction and all (B) show the strain in the vertical direction. The strain map is calculated from the preloaded state (approximately p = 2 mmHg) until a pressure of 80 mmHg. BCP, bacterial cellulose patch.