Development of a Two-Phase Scaffold-Nanoparticle System for the Sustained Delivery of Growth Factors in Bone Tissue Engineering Applications

In recent years, bone tissue engineering has emerged as a promising strategy to overcome the limitations of current ‘gold standard’ treatment options for bone disorders such as bone autografts and allografts. Bone tissue engineering strategies rely on the development of a scaffold that mimics the extracellular matrix, thereby providing an architecture that guides the natural bone regeneration process. Recently, scaffold systems have been developed to incorporate important extracellular signaling molecules which promote fracture healing and bone formation pathways. Among these signaling molecules, naturally occurring growth factors are of particular interest. This interest is due to their ability to enhance cell recruitment and ingress into the scaffold and promote osteogenic differentiation and angiogenesis, each of which is crucial to successful bone regeneration. However, a key challenge in growth factor delivery is that the molecule must reach the site of injury without losing bioactivity and remain in the location for an extended time in order to effectively aid in the formation of new bone. Among various strategies explored in the literature, incorporation of growth factors into particles can offer both protection of bioactivity and a sustained release profile. However, the particles can easily diffuse through the scaffold macropores and traverse to other areas of the body. In this work, a novel two-phase system for the sustained delivery of BMP-2 growth factors has been developed. The system consists of growth factors encapsulated in degradable nanoparticles (nanocarriers) which are immobilized in a porous scaffold. The nanoparticles incorporate a hydrolytically degradable crosslinker that can be easily tuned to achieve desired sustained release profiles. By chemically conjugating the nanocarriers to the scaffold backbone, this two-phase system is able to protect the growth factor from rapid degradation, improve the release kinetics, and achieve longer-term retention within the scaffold. Ultimately, the tunability of this novel growth factor delivery platform can be adapted to a wide variety of applications. Ultimately, this work shows that two-phase systems consisting of growth factor-loaded nanoparticles covalently bound to scaffolds have great promise, both by providing sustained release over a therapeutically relevant timeframe and the potential to sequentially deliver multiple growth factors

Bone tissue engineering via growth factor delivery: from scaffolds to complex matrices

In recent years, bone tissue engineering has emerged as a promising solution to the limitations of current gold standard treatment options for bone related-disorders such as bone grafts. Bone tissue engineering provides a scaffold design that mimics the extracellular matrix, providing an architecture that guides the natural bone regeneration process. During this period, a new generation of bone tissue engineering scaffolds has been designed and characterized that explores the incorporation of signaling molecules in order to enhance cell recruitment and ingress into the scaffold, as well as osteogenic differentiation and angiogenesis, each of which is crucial to successful bone regeneration. Here, we outline and critically analyze key characteristics of successful bone tissue engineering scaffolds. We also explore candidate materials used to fabricate these scaffolds. Different growth factors involved in the highly coordinated process of bone repair are discussed, and the key requirements of a growth factor delivery system are described. Finally, we concentrate on an analysis of scaffold-based growth factor delivery strategies found in the recent literature. In particular, the incorporation of two-phase systems consisting of growth factor-loaded nanoparticles embedded into scaffolds shows great promise, both by providing sustained release over a therapeutically relevant timeframe and the potential to sequentially deliver multiple growth factors.Biomaterials & Tissue Biomechanic

Immobilization of nanocarriers within a porous chitosan scaffold for the sustained delivery of growth factors in bone tissue engineering applications

To guide the natural bone regeneration process, bone tissue engineering strategies rely on the development of a scaffold architecture that mimics the extracellular matrix and incorporates important extracellular signaling molecules, which promote fracture healing and bone formation pathways. Incorporation of growth factors into particles embedded within the scaffold can offer both protection of protein bioactivity and a sustained release profile. In this work, a novel method to immobilize carrier nanoparticles within scaffold pores is proposed. A biodegradable, osteoconductive, porous chitosan scaffold was fabricated via the “freeze-drying method,” leading to scaffolds with a storage modulus of 8.5 kPa and 300 μm pores, in line with existing bone scaffold properties. Next, poly(methyl methacrylate-co-methacrylic acid) nanoparticles were synthesized and immobilized to the scaffold via carbodiimide-crosslinker chemistry. A fluorescent imaging study confirmed that the conventional methods of protein and nanocarrier incorporation into scaffolds can lead to over 60% diffusion out of the scaffold within the first 5 min of implantation, and total disappearance within 4 weeks. The novel method of nanocarrier immobilization to the scaffold backbone via carbodiimide-crosslinker chemistry allows full retention of particles for up to 4 weeks within the scaffold bulk, with no negative effects on the viability and proliferation of human umbilical vein endothelial cells.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomaterials & Tissue Biomechanic

Degradable poly(methyl methacrylate)-co-methacrylic acid nanoparticles for controlled delivery of growth factors for bone regeneration

Bone tissue engineering strategies have been developed to address the limitations of the current gold standard treatment options for bone-related disorders. These systems consist of an engineered scaffold that mimics the extracellular matrix and provides an architecture to guide the natural bone regeneration process, and incorporated growth factors that enhance cell recruitment and ingress into the scaffold and promote the osteogenic differentiation of stem cells and angiogenesis. In particular, the osteogenic growth factor bone morphogenetic protein 2 (BMP-2) has been widely studied as a potent agent to improve bone regeneration. A key challenge in growth factor delivery is that the growth factors must reach their target sites without losing bioactivity and remain in the location for an extended period to effectively aid in the formation of new bone. Protein incorporation into nanoparticles can both protect protein bioactivity and enable its sustained release. In this study, a poly(methyl methacrylate-co-methacrylic acid) nanoparticle-based system was synthesized incorporating a custom poly(ethylene glycol) dimethacrylate crosslinker. It was demonstrated that the nanoparticle degradation rate can be controlled by tuning the number of hydrolytically degradable ester units along the crosslinker. We also showed that the nanoparticles had high affinity for a model protein for BMP-2, and optimal conditions for maximum protein loading efficiency were elucidated. Ultimately, the proposed system and its high degree of tunability can be applied to a wide range of growth factors and tissue engineering applications.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomaterials & Tissue Biomechanic