Development of personalize bone replacement materials


Healthy, fit and sprightly into old age - especially in view of increasing life expectancy, these wishes are on top on the list of many people. However, bone and joint degradation as well as tissue, muscle and tendon loss are not absent from the 60+ life span. But younger people can also be affected by bone and joint damage after illness or accidents. To repair such defects and enhance quality of life, the Fraunhofer IKTS group "Biologized Materials and Structures" develops and researches implants and implant materials that mimic the human bone structure.

The aim of biomimetic material allocation is to stimulate and promote the body's own cell organization build-up through selectively degradable and/or bioinert bone substitute materials as well as naturally structured assembly. The ceramic bone substitute serves as a scaffold and lead structure into which the body's own cells grow into. Such mechanically stable bone substitute materials are also combined with growth factors. In recent works we found that the theoretically biodegradable artifical bone structures of the group are degradable also in reality as was proven in animal models on new bone formation in that very area of the implant.

How is a biocompatible bone implant created and what are its characteristics?


The artificial bone is replicated in a personalized way. The customized bone implants ("Scaffolds”) are realized by combining additively manufactured support structures (corticalis-like surrounding and/or as biomechanically optimized scaffolds) and a porous bioceramic filling (spongiosa-like).

For the fabrication of the biomechanical support structures, the Ceramic Additive Manufacturing Vat Photopolymerization (CerAM VPP) is used at Fraunhofer IKTS.

© Fraunhofer IKTS
Artificial femoral bone segment made by CerAM VPP and Freeze Foaming.
© Fraunhofer IKTS
Hybrid shaping of complex bone structures.
© Fraunhofer IKTS
Printed on the outside, foamed on the inside - ceramic bone substitute.

The scaffolds are filled with porous bioceramics, produced via Freeze Foaming. In this process, the ambient pressure is lowered around an aqueous ceramic suspension in a freeze dryer. This causes the suspension to expand until the resulting foam is stabilized by freezing. Via freeze-drying, the structure is freed from ice and dried. After heat treatment, which is common for ceramic materials, a solid foam is formed that can be used as a bone substitute material.

Common freeze-foamed biomaterial structures have a predominantly open porosity between 70 and 90 percent and pore sizes in the micro/meso range of 0.1 to 20 μm and in the macro range of 100 to 1000 μm. In addition, they are interconnected and feature pore-connecting struts that are filled and microporous at the same time. They thus contribute to the stabilization of the otherwise highly porous structure.

© Fraunhofer IKTS
SEM images of a Tricalciumphosphat (TCP) foam.
© Fraunhofer IKTS
Collagen I proof on a TCP foam.
© Fraunhofer IKTS
Freeze foamed thumb bone replicas.

Advantages of Freeze Foaming for new products and applications

Freeze Foaming offers the possibility to foam not only different materials (metals, MOFs, polymers, etc.) but also several materials simultaneously, time-delayed, interpenetrating or layered on top of each other. Resulting structures can be produced close to final (near-net) shape and thus application specific.

Material selection is crucial to avoid inflammation and rejection reactions. The IKTS group is testing various biocompatible material classes and examines their biocompatibility together with partners. Bioceramics, biopolymers and cellular material are combined. For example, the scientists are producing a bone implant from bioactive hydroxyapatite (HAp), biodegradable tricalcium phosphate (TCP) and bioinert zirconium oxide to combine the material-related advantages. HAp and TCP are proving to be versatile bone substitute materials. For example, in the project “Hybrid-Bone – Development customizable ceramic bone graft substitutes and structures for improved regeneration in the facial skull region", a complex hybrid scaffold made of tricalcium phosphate is being tested and verified as a mandibular bone partial implant (grant no. 03VP07633).

© Fraunhofer IKTS
Hybrid-bone test implant: inner CerAM VPP support (TCP/ZrO2; left) and foamed-in freeze foam(TCP).
© Fraunhofer IKTS
Live-dead staining of the porous, degradable TCP foam in the hybrid bone (green = living cells, red = dead cells).
© Fraunhofer IKTS
Excellent biocompatibility and biodegradability of the hybrid bone implant in an animal model.

HAp offers advantages not only as a bone substitute, but also in dental medicine. Approximately 95 percent of it occurs naturally in tooth enamel, and its hardness and resistance to acids, bases, compression resistance or abrasion are impressive.

New applications of HAp and other bioactive material combinations in the dental and medical industries are to be intensively researched further in the coming years. This includes studies on biologization (e.g., by additional laser surface structuring) and biomineralization, in order to realize the incorporation of an implant or bio-substitute material into the human skeletal structure in a biomimetic, patient-friendly and comprehensive way.

The working group "Biologized Materials and Structures" offers its expertise to its research partners and customers in joint projects. We are glad to develop new ideas with you and jointly open up new subject areas and industrial applications in both feasibility studies and specific product developments.