Hierarchical Nanofibrous Microspheres with Controlled Growth Factor Delivery for Bone Regeneration

Abstract

The integration of controlled growth factor delivery and biomimetic architecture into a microsphere is a challenging but attractive strategy for developing new injectable biomaterials for tissue engineering. In this work, we developed a unique hierarchical nanosphere-encapsulated-in-microsphere scaffolding system for bone tissue regeneration. First, we synthesized heparin-conjugated gelatin (HG) that provides binding domains for bone morphogenetic protein 2 (BMP2) to stabilize this growth factor, protect it from denaturation and proteolytic degradation, and subsequently prolong its sustained release. Next, we developed a unique approach that includes a water-in-oil-in-oil (W/O/O) double emulsion process and a thermally induced phase separation to encapsulate BMP2-binding HG nanospheres into nanofibrous microspheres. The nanofibrous microsphere was self-assembled from synthetic nanofibers, and had superior surface area, high porosity, low density, and was an excellent carrier to support cell adhesion and tissue in-growth. BMP2 in the hierarchical microsphere was released in a multiple-controlled manner (by the binding with heparin and encapsulation of the nanosphere and microsphere) and retained its high bioactivity. An in vivo calvarial defect model confirmed that this unique hierarchical microsphere was an excellent osteoinductive scaffold for enhanced bone regeneration. By choosing different growth factors, this hierarchical microsphere system can be easily applied to other types of tissue regeneration. Our work expands the ability to develop new injectable biomaterials for advanced regenerative therapies.

Bioresorbable Microspheres with Surface‐Loaded Nanosilver and Apatite as Dual‐Functional Injectable Cell Carriers for Bone Regeneration

“…Ma and co‐workers developed nanofibrous microspheres using thermally induced phase separation for cartilage regeneration and knee repairing . Intending to promote regeneration efficiency, growth factors like BMP‐2 and IGF‐1 were incorporated into microspheres, if for bone regeneration, osteoactive inorganic components as calcium phosphates and bioactive glasses were usually introduced . These attempts have shown the feasibility and the effectiveness of using bioresorbable microspheres as injectable cell microcarriers in treating bone defects.…”

Injectable scaffolds: Preparation and application in dental and craniofacial regeneration

“…To further incorporate bioactive molecules into the nanofibrous microsphere and temporally and spatially control its release, we developed a unique hierarchical nanosphere-encapsulated-in-microsphere scaffolding system [166]. In that system, the growth factor BMP2 binds with heparin and is encapsulated into heparin-conjugated gelatin nanospheres, which are further immobilized in the injectable nanofibrous microspheres, as shown in Fig.…”

“…To visualize the nanospheres and microspheres, TRITC-conjugated gelatin blended with heparin-modified gelatin was used and FITC-conjugated bovine serum albumin (BSA) was adsorbed on the nanofibers of the microspheres. Adapted with permission from [166]. Copyright 2015 WILEY-VCH Verlag GmbH & Co.…”

Recent Progress in Developing Injectable Matrices for Enhancing Cell Delivery and Tissue Regeneration

“…To allow injectability of these polymers as cell carriers, recent approaches explored methods to fabricate these polymers into injectable microspheres, with diameter ranging from 30 to 100 μm, instead of tissue-scale scaffolds. [6a, 20a, 53] For example, Kuang et al developed injectable, nanofibrous, hollow microspheres from biodegradable poly(L-lactic acid)-block-poly(L-lysine) (Fig 5A). [6a, 53b] These hollow structures allowed dental pulp stem cells to attach to the surface and the inner pores of the spheres (Fig.…”

“…5D-G). [53b] One limitation of the injectable microspheres is the lack of control on the distribution of microspheres post-injection. As such, injectable microspheres may move away from the injection sites under mechanical stress.…”