Remineralization of demineralized bone matrix (DBM) via alternating solution immersion (ASI)

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Bioartificial injectable cartilage implants from demineralized bone matrix/PVA and related studies in rabbit animal model

Functional cartilage tissue engineering needs a substantial, easy to handle scaffold with proper mechanical strength to repair defected area in articular cartilage. In this study, we report the development and characterization of demineralized bone matrix (DBM) in with a poly vinyl alcohol (PVA) to have a proper homogenous injectable scaffold. Injectabiliy of the biodegradable scaffolds, degradation rate, swelling ratio compression and tensile mechanical properties, and viability and proliferation of bone marrow mesenchymal stem cells (BM-MSCs) followed by differentiation of them In-vitro and In-vivo seeded within the scaffold were studied. It demonstrated that the PVA 20% could increase significantly (p < 0.05) the biodegradability of DBM after 720 hours.DBM with 20% of PVA scaffold has significantly higher (p < 0.05) compression and tensile mechanical strength and viscosity. SEM images showed a multilayer of cells on DBM scaffold incorporated with PVA 20%.BM-MSCs on scaffolds, DBM+PVA 20% had a significant growth rate (p < 0.0001) compare to 2D and low concentration of PVA after 21 days of culture. Viability of cells was significantly higher (p < 0.05) on DBM+PVA scaffold compare to DBM. DBM+PVA 20% enhanced cell viability (P < 0.05) compare to DBM scaffold. The PVA presence enhanced chondrogenesis differentiation at the cellular and molecular levels, as evidenced by increased COL II (P < 0.05) and SOX2 upregulation of Chondrogensis-specific genes (p < 0.001). Hyline-like cartilage covered the defect which was confirmed by microscopy and histology assessments. Having considered percentages of PVA with a constant amount of DBM, injectability, compressive mechanical properties, homogeneity of the scaffold, and providing sufficient surface area (12.25 cm²/ml) for cell attachment; 0.35 g/ml of DBM in 20% PVA (w/v) has applicable properties within the ranges of studies which can be proposed for the injectable engineered articular cartilage.

Tunability of collagen matrix mechanical properties via multiple modes of mineralization

Functionally graded, mineralized collagen tissues exist at soft-to-hard material attachments throughout the body. However, the details of how collagen and hydroxyapatite mineral (HA) interact are not fully understood, hampering efforts to develop tissue-engineered constructs that can assist with repair of injuries at the attachments of soft tissues to bone. In this study, spatial control of mineralization was achieved in collagen matrices using simulated body fluids (SBFs). Based upon previous observations of poor bonding between reconstituted collagen and HA deposited using SBF, we hypothesized that mineralizing collagen in the presence of fetuin (which inhibits surface mineralization) would lead to more mineral deposition within the scaffold and therefore a greater increase in stiffness and toughness compared with collagen mineralized without fetuin. We tested this hypothesis through integrated synthesis, mechanical testing and modelling of graded, mineralized reconstituted collagen constructs. Results supported the hypothesis, and further suggested that mineralization on the interior of reconstituted collagen constructs, as promoted by fetuin, led to superior bonding between HA and collagen. The results provide us guidance for the development of mineralized collagen scaffolds, with implications for bone and tendon-to-bone tissue engineering.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Biomimetically enhanced demineralized bone matrix for bone regenerative applications

Demineralized bone matrix (DBM) is one of the most widely used bone graft materials in dentistry. However, the ability of DBM to reliably and predictably induce bone regeneration has always been a cause for concern. The quality of DBM varies greatly depending on several donor dependent factors and also manufacturing techniques. In order to standardize the quality and to enable reliable and predictable bone regeneration, we have generated a biomimetically-enhanced version of DBM (BE-DBM) using clinical grade commercial DBM as a control. We have generated the BE-DBM by incorporating a cell-derived pro-osteogenic extracellular matrix (ECM) within clinical grade DBM. In the present study, we have characterized the BE-DBM and evaluated its ability to induce osteogenic differentiation of human marrow derived stromal cells (HMSCs) with respect to clinical grade commercial DBM. Our results indicate that the BE-DBM contains significantly more pro-osteogenic factors than DBM and enhances HMSC differentiation and mineralized matrix formation in vitro and in vivo. Based on our results, we envision that the BE-DBM has the potential to replace DBM as the bone graft material of choice.

Remineralization of demineralized bone matrix in critical size cranial defects in rats: A 6-month follow-up study

The key drawback of using demineralized bone matrix (DBM) is its low initial mechanical stability due to the severe depletion of mineral content. In the present study, we investigated the long-term regeneration of DBM in a critical size bone defect model and investigated the remineralization after 6 months. Bone defects were created in the cranium of male Wistar rats which were filled with DBM or left empty as negative control. In vivo bone formation was monitored with computed tomography after 11, 19, and 26 weeks postoperatively. After 6 months, parietal bones were subjected to micro-CT. Mineral content was determined with spectrophotometric analysis. After 11 weeks the DBM-filled bone defects were completely closed, while empty defects were still open. Density of the DBM-treated group increased significantly while the controls remained unchanged. Quantitative analysis by micro-CT confirmed the in vivo results, bone volume/tissue volume was significantly lower in the controls than in the DBM group. The demineralization procedure depleted the key minerals of the bone to a very low level. Six months after implantation Ca, P, Na, Mg, Zn, and Cr contents were completely restored to the normal level, while K, Sr, and Mn were only partially restored. The remineralization process of DBM is largely complete by the 6th month after implantation in terms of bone density, structure, and key mineral levels. Although DBM does not provide sufficient sources for any of these minerals, it induces a faster and more complete regeneration process. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1336-1342, 2016.

Remineralized bone matrix as a scaffold for bone tissue engineering

There is a need for improved biomaterials for use in treating non-healing bone defects. A number of natural and synthetic biomaterials have been used for the regeneration of bone tissue with mixed results. One approach is to modify native tissue via decellularization or other treatment for use as natural scaffolding for tissue repair. In this study, our goal was to improve on our previously published alternating solution immersion (ASI) method to fabricate a robust, biocompatible, and mechanically competent biomaterial from natural demineralized bone matrix (DBM). The improved method includes an antigen removal (AR) treatment step which improves mineralization and stiffness while removing unwanted proteins. The chemistry of the mineral in the remineralized bone matrix (RBM) was consistent with dicalcium phosphate dihydrate (brushite), a material used clinically in bone healing applications. Mass spectrometry identified proteins removed from the matrix with AR treatment to include α-2 HS-glycoprotein and osteopontin, noncollagenous proteins (NCPs) and known inhibitors of biomineralization. Additionally, the RBM supported the survival, proliferation, and differentiation of human mesenchymal stromal cells (MSCs) in vitro as well or better than other widely used biomaterials including DBM and PLG scaffolds. DNA content increased more than 10-fold on RBM compared to DBM and PLG; likewise, osteogenic gene expression was significantly increased after 1 and 2 weeks. We demonstrated that ASI remineralization has the capacity to fabricate mechanically stiff and biocompatible RBM, a suitable biomaterial for cell culture applications.