Improving bone marrow stromal cell attachment on chitosan/hydroxyapatite scaffolds by an immobilized RGD peptide

Self-assembled chitosan/gelatin nanofibrous aggregates incorporated thermosensitive nanocomposite bioink for bone tissue engineering

Chitosan-based thermosensitive bioink can be a potential option as bioinks for bone tissue engineering because of their excellent biocompatibility and crosslinker-free gelation at physiological temperature. However, their low mechanical strength, poor printability, and low post-printing cell viability are some of their limitations. In this work, self-assembled nanofibrous aggregates of chitosan and gelatin were prepared and incorporated in chitosan-based bioinks to enhance printability, mechanical properties, post-printing cell viability, and proliferation. Subsequently, the optimal concentration of nanohydroxyapatite was determined, and the potential of the nanocomposite bioink was evaluated. Physiochemical, mechanical, and in vitro characterizations were carried out for the developed nanocomposite bioink. The bioink had optimum printability at 10 % nanohydroxyapatite and cell viability >88 %. The composite bioink had a low water uptake capacity (2.5 %) and degraded within 3 weeks in the presence of lysozyme. Mechanical characterization revealed an elastic modulus of about 15.5 kPa. Rheological analysis indicated a higher storage modulus of the bioink samples at 37 °C. ALP activity of 36.8 units/ml after 14 days of scaffold culture in osteogenic media indicated high cellular activity. These results suggested that the incorporation of osteogenic nanohydroxyapatite and nanofibrous aggregates improved the overall osteogenic and physiochemical potential of the thermosensitive bioink.

Biophysical and Biochemical Cues of Biomaterials Guide Mesenchymal Stem Cell Behaviors

Mesenchymal stem cells (MSCs) have been widely used in the fields of tissue engineering and regenerative medicine due to their self-renewal capabilities and multipotential differentiation assurance. However, capitalizing on specific factors to precisely guide MSC behaviors is the cornerstone of biomedical applications. Fortunately, several key biophysical and biochemical cues of biomaterials that can synergistically regulate cell behavior have paved the way for the development of cell-instructive biomaterials that serve as delivery vehicles for promoting MSC application prospects. Therefore, the identification of these cues in guiding MSC behavior, including cell migration, proliferation, and differentiation, may be of particular importance for better clinical performance. This review focuses on providing a comprehensive and systematic understanding of biophysical and biochemical cues, as well as the strategic engineering of these signals in current scaffold designs, and we believe that integrating biophysical and biochemical cues in next-generation biomaterials would potentially help functionally regulate MSCs for diverse applications in regenerative medicine and cell therapy in the future.

Natural Polymeric Scaffolds in Bone Regeneration

Despite considerable advances in microsurgical techniques over the past decades, bone tissue remains a challenging arena to obtain a satisfying functional and structural restoration after damage. Through the production of substituting materials mimicking the physical and biological properties of the healthy tissue, tissue engineering strategies address an urgent clinical need for therapeutic alternatives to bone autografts. By virtue of their structural versatility, polymers have a predominant role in generating the biodegradable matrices that hold the cells in situ to sustain the growth of new tissue until integration into the transplantation area (i.e., scaffolds). As compared to synthetic ones, polymers of natural origin generally present superior biocompatibility and bioactivity. Their assembly and further engineering give rise to a wide plethora of advanced supporting materials, accounting for systems based on hydrogels or scaffolds with either fibrous or porous architecture. The present review offers an overview of the various types of natural polymers currently adopted in bone tissue engineering, describing their manufacturing techniques and procedures of functionalization with active biomolecules, and listing the advantages and disadvantages in their respective use in order to critically compare their actual applicability potential. Their combination to other classes of materials (such as micro and nanomaterials) and other innovative strategies to reproduce physiological bone microenvironments in a more faithful way are also illustrated. The regeneration outcomes achieved in vitro and in vivo when the scaffolds are enriched with different cell types, as well as the preliminary clinical applications are presented, before the prospects in this research field are finally discussed. The collection of studies herein considered confirms that advances in natural polymer research will be determinant in designing translatable materials for efficient tissue regeneration with forthcoming impact expected in the treatment of bone defects.

Orthopedic tissue regeneration: cells, scaffolds, and small molecules

Orthopedic tissue regeneration would benefit the aging population or patients with degenerative bone and cartilage diseases, especially osteoporosis and osteoarthritis. Despite progress in surgical and pharmacological interventions, new regenerative approaches are needed to meet the challenge of creating bone and articular cartilage tissues that are not only structurally sound but also functional, primarily to maintain mechanical integrity in their high load-bearing environments. In this review, we discuss new advances made in exploiting the three classes of materials in bone and cartilage regenerative medicine--cells, biomaterial-based scaffolds, and small molecules--and their successes and challenges reported in the clinic. In particular, the focus will be on the development of tissue-engineered bone and cartilage ex vivo by combining stem cells with biomaterials, providing appropriate structural, compositional, and mechanical cues to restore damaged tissue function. In addition, using small molecules to locally promote regeneration will be discussed, with potential approaches that combine bone and cartilage targeted therapeutics for the orthopedic-related disease, especially osteoporosis and osteoarthritis.

PNIPAAM modified mesoporous hydroxyapatite for sustained osteogenic drug release and promoting cell attachment

This work presented a sustained release system of simvastatin (SIM) based on the mesoporous hydroxyapatite (MHA) capped with poly(N-isopropylacrylamide) (PNIPAAM). The MHA was prepared by using cetyltrimethylammonium bromide (CTAB) as a template and the modified PNIPAAM layer on the surface of MHA was fabricated through surface-initiated atom transfer radical polymerization (SI-ATRP). The SIM loaded MHA-PNIPAAM showed a sustained release of SIM at 37 °C over 16 days. The bone marrow mesenchymal stem cell (BMSC) proliferation was assessed by cell counting kit-8 (CCK-8) assay, and the osteogenic differentiation was evaluated by alkaline phosphatase (ALP) activity and Alizarin Red staining. The release profile showed that the release of SIM from MHA-SIM-PNIPAAM lasted 16 days and the cumulative amount of released SIM was almost seven-fold than MHA-SIM. Besides, SIM loaded MHA-PNIPAAM exhibited better performance on cell proliferation, ALP activity, and calcium deposition than pure MHA due to the sustained release of SIM. The quantity of ALP in MHA-SIM-PNIPAAM group was more than two fold than pure MHA group at 7 days. Compared to pure MHA, better BMSC attachment on PNIPAAM modified MHA was observed using fluorescent microscopy, indicating the better biocompatibility of MHA-PNIPAAM.

Collagen-containing scaffolds enhance attachment and proliferation of non-cultured bone marrow multipotential stromal cells

Large bone defects are ideally treated with autografts, which have many limitations. Therefore, osteoconductive scaffolds loaded with autologous bone marrow (BM) aspirate are increasingly used as alternatives. The purpose of this study was to compare the growth of multipotential stromal cells (MSCs) from unprocessed BM on a collagen-containing bovine bone scaffold (Orthoss(®) Collagen) with a non-collagen-containing bovine bone scaffold, Orthoss(®) . Another collagen-containing synthetic scaffold, Vitoss(®) was included in the comparison. Colonization of scaffolds by BM MSCs (n = 23 donors) was evaluated using microscopy, colony forming unit-fibroblast assay and flow-cytometry. The number of BM MSCs initially attached to Orthoss(®) Collagen and Vitoss(®) was similar but greater than Orthoss(®) (p = 0.001 and p = 0.041, respectively). Furthermore, the number of MSCs released from Orthoss(®) Collagen and Vitoss(®) after 2-week culture was also higher compared to Orthoss(®) (p = 0.010 and p = 0.023, respectively). Interestingly, collagen-containing scaffolds accommodated larger numbers of lymphocytic and myelomonocytic cells. Additionally, the proliferation of culture-expanded MSCs on Orthoss(®) collagen and Vitoss(®) was greater compared to Orthoss(®) (p = 0.047 and p = 0.004, respectively). Collectively, collagen-containing scaffolds were superior in supporting the attachment and proliferation of MSCs when they were loaded with unprocessed BM aspirates. This highlights the benefit of collagen incorporation into bone scaffolds for use with autologous bone marrow aspirates as autograft substitutes.

Preparation and evaluation of an Arg-Gly-Asp-modified chitosan/hydroxyapatite scaffold for application in bone tissue engineering

Bone tissue engineering has become a promising method for the repair of bone defects, and the production of a scaffold with high cell affinity and osseointegrative properties is crucial for successful bone substitute. Chitosan (CS)/hydroxyapatite (HA) composite was prepared by in situ compositing combined with lyophilization, and further modified by arginine‑glycine‑aspartic acid (RGD) via physical adsorption. In order to evaluate the cell adhesion rate, viability, morphology, and alkaline phosphatase (ALP) activity, the RGD‑CS/HA scaffold was seeded with bone marrow stromal cells (BMSCs). The osseointegrative properties of the RGD‑CS/HA scaffold were evaluated by in vivo heterotopic ossification and in vivo bone defect repair. After 4 h culture with the RGD‑CS/HA scaffold, the adhesion rate of the BMSCs was 80.7%. After 3 days, BMSCs were fusiform in shape and evenly distributed on the RGD‑CS/HA scaffold. Formation of extracellular matrix and numerous cell‑cell interactions were observed after 48 h of culture, with an ALP content of 0.006 ± 0.0008 U/l/ng. Furthermore, the osseointegrative ability and biomechanical properties of the RGD‑CS/HA scaffold were comparable to that of normal bone tissue. The biocompatibility, cytocompatibility, histocompatibility and osseointegrative properties of the RGD‑CS/HA scaffold support its use in bone tissue engineering applications.

Smart scaffolds in bone tissue engineering: A systematic review of literature

AIM: To improve osteogenic differentiation and attachment of cells.

METHODS: An electronic search was conducted in PubMed from January 2004 to December 2013. Studies which performed smart modifications on conventional bone scaffold materials were included. Scaffolds with controlled release or encapsulation of bioactive molecules were not included. Experiments which did not investigate response of cells toward the scaffold (cell attachment, proliferation or osteoblastic differentiation) were excluded.

RESULTS: Among 1458 studies, 38 met the inclusion and exclusion criteria. The main scaffold varied extensively among the included studies. Smart modifications included addition of growth factors (group I-11 studies), extracellular matrix-like molecules (group II-13 studies) and nanoparticles (nano-HA) (group III-17 studies). In all groups, surface coating was the most commonly applied approach for smart modification of scaffolds. In group I, bone morphogenetic proteins were mainly used as growth factor stabilized on polycaprolactone (PCL). In group II, collagen 1 in combination with PCL, hydroxyapatite (HA) and tricalcium phosphate were the most frequent scaffolds used. In the third group, nano-HA with PCL and chitosan were used the most. As variable methods were used, a thorough and comprehensible compare between the results and approaches was unattainable.

CONCLUSION: Regarding the variability in methodology of these in vitro studies it was demonstrated that smart modification of scaffolds can improve tissue properties.

The 'Ziran' wrap: reconstruction of critical-sized long bone defects using a fascial autograft and reamer-irrigator-aspirator autograft

Reconstruction of critical-size bony defects remains a challenge to surgeons despite recent technological advances. Current treatments include distraction osteogenesis, cancellous autograft, induced membranes (Masquelet procedure), polymeric membranes, and titanium-mesh cages filled with bone graft. In this article, the authors presents two cases in which critical-sized defects were reconstructed using a meshed fascial autograft encasing reamer-irrigator-aspirator (RIA) autograft and cancellous allograft. This article will discuss the clinical outcomes of the technique, comparison to other current techniques, and technical insight into the potential biological mechanism.

RGD-conjugated rod-like viral nanoparticles on 2D scaffold improve bone differentiation of mesenchymal stem cells

Viral nanoparticles have uniform and well-defined nano-structures and can be produced in large quantities. Several plant viral nanoparticles have been tested in biomedical applications due to the lack of mammalian cell infectivity. We are particularly interested in using Tobacco mosaic virus (TMV), which has been demonstrated to enhance bone tissue regeneration, as a tunable nanoscale building block for biomaterials development. Unmodified TMV particles have been shown to accelerate osteogenic differentiation of adult stem cells by synergistically upregulating bone morphogenetic protein 2 (BMP2) and integrin-binding bone sialoprotein (IBSP) expression with dexamethasone. However, their lack of affinity to mammalian cell surface resulted in low initial cell adhesion. In this study, to increase cell binding capacity of TMV based material the chemical functionalization of TMV with arginine-glycine-aspartic acid (RGD) peptide was explored. An azide-derivatized RGD peptide was "clicked" to tyrosine residues on TMV outer surface via an efficient copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The ligand spacing is calculated to be 2-4 nm, which could offer a polyvalent ligand clustering effect for enhanced cell receptor signaling, further promoting the proliferation and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs).

The key regulatory roles of the PI3K/Akt signaling pathway in the functionalities of mesenchymal stem cells and applications in tissue regeneration

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into various cell types and have been widely used in tissue engineering application. In tissue engineering, a scaffold, MSCs and growth factors are used as essential components and their interactions have been regarded to be important for regeneration of tissues. A critical problem for MSCs in tissue engineering is their low survival ability and functionality. Most MSCs are going to be apoptotic after transplantation. Therefore, increasing MSC survival ability and functionalities is the key for potential applications of MSCs. Several approaches have been studied to increase MSC tissue forming capacity including application of growth factors, overexpression of stem cell regulatory genes, and improvement of biomaterials for scaffolds. The effects of these approaches on MSCs have been associated with activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. The pathway plays central regulatory roles in MSC survival, proliferation, migration, angiogenesis, cytokine production, and differentiation. In this review, we summarize and discuss the literatures related to the roles of the PI3K/Akt pathway in the functionalities of MSCs and the involvement of the pathway in biomaterials-increased MSC functionalities. Biomaterials have been modified in their properties and surface structure and loaded with growth factors to increase MSC functionalities. Several studies demonstrated that the biomaterials-increased MSC functionalities are mediated by the activation of the PI3K/Akt pathway.

Reinforcement of a new calcium phosphate cement with RGD-chitosan-fiber

Calcium phosphate cement (CPC) has been widely used in orthopedic and dental applications. A critical limitation of CPC is low strength and high susceptibility to severe fracture. Surgeons can use it only to reconstruct non-stress bearing bone, raising the need for a tougher new generation of CPC. Fibers have been used as a reinforcement of CPC to improve the strength of a pure CPC scaffold. The RGD peptides (Arg-Gly-Asp) have been used to improve the biocompatibility of the scaffold, via physical adsorption. The purpose of this study was to develop a novel CPC scaffold reinforced by RGD peptide-bearing chitosan fibers (RGD-fiber-CPC). Our data showed that the RGD-fiber-CPC scaffold had an increased flexural strength, and stimulated new bone formation in an animal model. The RGD-fiber-CPC is a novel bone graft substitute in orthopedic surgery.

Biofunctionalized calcium phosphate cement to enhance the attachment and osteodifferentiation of stem cells released from fast-degradable alginate-fibrin microbeads

Stem cell-encapsulating microbeads could be mixed into a paste such as calcium phosphate cement (CPC), where the microbeads could protect the cells from the mixing and injection forces. After being placed, the microbeads could quickly degrade to release the cells throughout the scaffold, while creating macropores. The objectives of this study were to (1) construct alginate-fibrin microbeads encapsulating human umbilical cord mesenchymal stem cells (hUCMSCs) embedded in the surface of novel biofunctionalized CPC and (2) investigate microbead degradation, cell release, and osteodifferentiation on CPC. Hydrogel microbeads were fabricated that encapsulated hUCMSCs at 1×10(6) cells/mL. CPC was biofunctionalized with fibronectin (Fn) and Arg-Gly-Asp (RGD). Four scaffolds were tested: CPC control, CPC mixed with Fn, CPC mixed with RGD, and CPC grafted with RGD. The degradable microbeads released hUCMSCs at 7 days, which attached to CPC. Adding Fn or RGD to CPC greatly improved cell attachment. CPC grafted with RGD showed the fastest cell proliferation, with cell density being ninefold that on CPC control. The released hUCMSCs underwent osteodifferentiation. Alkaline phosphatase, osteocalcin, collagen 1, and runt-related transcription factor 2 (Runx2) gene expression increased by 10 to 30 fold at 7-21 days, compared with day 1. The released cells on CPC synthesized bone minerals, with the mineralization amount at 21 days being two orders of magnitude higher than that at 7 days. In conclusion, alginate-fibrin microbeads embedded in CPC surface were able to quickly release the hUCMSCs that attached to biofunctionalized CPC. Incorporating Fn and RGD into CPC greatly improved cell function, and CPC grafted with RGD had the fastest cell proliferation. The released cells on CPC differentiated into the osteogenic lineage and synthesized bone minerals. The new biofunctionalized CPC with hUCMSC-encapsulating microbeads is promising for bone regeneration applications.

Polyvalent display of RGD motifs on turnip yellow mosaic virus for enhanced stem cell adhesion and spreading

Turnip yellow mosaic virus (TYMV) is a stable 28 nm icosahedral plant virus that can be isolated in gram quantities. In order to study the polyvalent effect of Arg-Gly-Asp (RGD) clustering on the response of bone marrow stem cells (BMSCs), an RGD motif was genetically displayed on the coat protein of the TYMV capsid. Composite films composed of either wild-type TYMV or TYMV-RGD44, in combination with poly(allylamine hydrochloride) (PAH), were fabricated by a layer-by-layer adsorption of virus and PAH. The deposition process was studied by quartz crystal microbalance, UV-visible spectroscopy and atomic force microscopy. BMSC adhesion assays showed enhanced cell adhesion and spreading on TYMV-RGD44 coated substrates compared to native TYMV. These results demonstrate the potential of TYMV as a viable scaffold for bioactive peptide display and cell culturing studies.

Surface phosphorylation for polyelectrolyte complex of chitosan and its sulfonated derivative: surface analysis, blood compatibility and adipose derived stem cell contact properties

Many studies have tried to look for the application of chitosan in tissue engineering since its structure is similar to glycoaminoglycans, the main components of the extracellular matrix. Previous studies had indicated that the incorporation of sulfonic or phosphonic functionalities would be beneficial to the growth of certain cells. However, no study has explored the effect of incorporation of both above-mentioned anionic functionalities onto the chitosan structure. In this study, we have surface-phosphorylated the polyelectrolyte film formed by chitosan and water-soluble sulfonated chitosan with the aim to incorporate phosphonic and sulfonic functionalities onto the film surface. Surface analyses by ESCA and ATR-FT-IR have shown that these two functional groups have been successfully grafted onto the surface, and that the ratio of P/S was dependent upon the weight ratio of phosphorylation agents added. Blood compatibility evaluation indicated that phosphorylated polyelectrolyte complexes extended the plasma recalcification time as compared to non-treated chitosan and direct-phosphorylated chitosan film. In addition, these phosphorylated polyelectrolyte complexes showed similar or slightly less platelet reactivity than the non-phosphorylated counterpart. In contrast, significant platelet activation and adhesion were noted on the direct-phosphorylated chitosan. This implicated the incorporation of sulfonic acid onto the phosphorylated surface can increase the platelet compatibility. An adipose-derived stem cell incubation study has demonstrated that the incorporation of both phosphonic and sulfonic acid functionalities onto the chitosan surface can enhance the stem cell growth. Therefore, the phosphorylated polyelectrolyte complexes were not only blood compatible but also stem cell compatible, and could be a novel biomaterial in tissue-engineering applications.