Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment

Abstract

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials.

Keywords: bioactive organic/inorganic hybrid biomaterials; biodegradable bioceramics; bone tissue engineering; sol-gel process; stem cells.

Figure 1

Schematic illustration of the formation of composite fibers. Method I: Plasma-treated electrospun polycaprolactone (PCL) fibers were coated with polydopamine prior to mineralization in 10xSBF. Method II: Plasma-treated electrospun PCL fibers were mineralized in the 10xSBF solution containing dopamine. Reproduced with permission from reference [107].

Figure 2

(A) Interaction between phases in composites and organic-inorganic (O/I) hybrid materials (B) compressive modulus of class II PCL–BPSG (borophosphosilicate glass) hybrid compared to composite of PCL and BPSG and PCL alone [146] (C) SEM image of electrospun class I PCL-tertiary bioactive glass (unpublished data from Mequanint Lab) (D) class II PCL–BPSG hybrid scaffold fabricated by solvent-free casting and particulate leaching [78]. Reproduced with permission from the cited references.

Figure 3

(A) Chemical structure of the linkage of organic and inorganic components by (3-glycidoxypropyl) trimethoxysilane (GPTMS) in class II gelatin/silica hybrids [162] (B) chemical structure of hybrids of silica and copolymer of caprolactone and glycidoxypropyl trimethoxysilane [163] (C) schematic illustration of the expected chemical structure of the calcium-containing silica/γ-PGA hybrid [164] (D) digital photo and chemical structure of class II PCL-borophosphosilicate hybrids [78]. Reproduced with permission from the cited references.

Figure 4

Various types of functionalization of polymer with trialkoxysilane (A) monofunctionalization (B) difunctionalization; pendant functionalization with side chains (C) random copolymerization (D) block copolymerization.

Figure 5

Schematic illustration of calcium incorporated in the glass network at room temperature using calcium methoxyethoxide (CME) as a calcium source in the sol-gel synthesis [209]. Reproduced with permission from the cited reference.

Figure 6

Schematic illustration of mesoporous bioactive glass (MBG) scaffold coated with reduced graphene oxide (rGO) and conjugated with osteoblast-specific aptamer [228]. Reproduced with permission from the cited reference.