Poly-Alanine-ε-Caprolacton-Methacrylate as Scaffold Material with Tuneable Biomechanical Properties for Osteochondral Implants

Abstract

An aging population and injury-related damage of the bone substance lead to an increasing need of innovative materials for the regeneration of osteochondral defects. Biodegradable polymers form the basis for suitable artificial implants intended for bone replacement or bone augmentation. The great advantage of these structures is the site-specific implant design, which leads to a considerable improvement in patient outcomes and significantly reduced post-operative regeneration times. Thus, biomechanical and biochemical parameters as well as the rate of degradation can be set by the selection of the polymer system and the processing technology. Within this study, we developed a polymer platform based on the amino acid Alanine and ε-Caprolacton for use as raw material for osteochondral implants. The biomechanical and degradation properties of these Poly-(Alanine-co-ε-Caprolacton)-Methacrylate (ACM) copolymers can be adjusted by changing the ratio of the monomers. Fabrication of artificial structures for musculo-skeletal tissue engineering was done by Two-Photon-Polymerization (2PP), which represents an innovative technique for generating defined scaffolds with tailor-made mechanical and structural properties. Here we show the synthesis, physicochemical characterization, as well as first results for structuring ACM using 2PP technology. The data demonstrate the high potential of ACM copolymers as precursors for the fabrication of biomimetic implants for bone-cartilage reconstruction.

Keywords: Poly-Alanine-ε-Caprolacton-Methacrylate; Two-Photon-Polymerization; amino acid; biodegradable polymer; biomechanics; osteochondral implant; scaffold.

Figure 1

Synthesis of (A) Cyclic monomer: N-Morpholino-2,5-dion and (B) Poly-(Alanine-ε-Caprolacton)dime thacrylate (a…2, 4, 6, 8 and b…8, 6, 4, 2).

Figure 2

¹H-NMR Spectra of Poly-(Alanine-ε-Caprolactone)dimethacrylate 2:8.

Figure 3

1H-NMR Spectra of Poly-(Alanine-ε-Caprolactone)dimethacrylate with different ratios of alanine and caprolacton.

Figure 4

Physicochemical properties of ACM. (A) Temperature-dependent viscosity and (B) UV-Vis Spectra.

Figure 5

(A) Water contact angles of the different ACM copolymers in dry and hydrated states (data are presented as mean ± standard deviation for n = 90) and (B) Swelling behavior of the ACM copolymers.

Figure 6

Master curves of the complex viscoelastic modulus for ACM 2:8 and ACM 4:6; solid lines: median value, dotted lines: 50% quantile.

Figure 7

Characteristic values for both copolymers; (A) relaxed modulus at f = 0; (B) unrelaxed modulus at f = ∞; (C) height of global dispersion relative to unrelaxed modulus; (D) width of relaxation region-1; (E) width of relaxation region-2.

Figure 8

SEM (scanning electron microscopy) images of cuboids fabricated by 2PP with variation of fabrication parameters for ACM 2:8. For each row the laser power was modified (blue labeling). The focusing offset with respect to the detected interface is varied within each row (yellow labeling). In the inset, a close-up of one of the cuboids is shown. Scale bars are 500 µm for overview image and 50 µm for close-up.

Figure 9

Effective shrinkage of cuboids in ACM 2:8 dependent on the applied laser power reveals the occurrence of a non-constant shrinkage behavior. The dotted line is a guide-to-the-eye.

Figure 10

Confocal fluorescence images of bone marrow mesenchymal stem cells (BMSCs) cultured on ACM (A,B). (B) was coated with Poly-L-Lysin/Heparin to avoid any hemostatic reaction after blood contact. Green: Phalloidin488. Scale bars are 100 µm each.