Clinical Applications of Bone Tissue Engineering in Orthopedic Trauma

Bilayer scaffolds/membranes for bone tissue engineering applications: A systematic review

OBJECTIVE

This systematic review evaluates the purpose, materials, physio-mechanical, and biological effects of bilayer scaffolds/membranes used for bone tissue engineering applications.

METHODS

A comprehensive electronic search of English-language literature from 2012 to October 2022 was conducted in PubMed, Scopus, ScienceDirect, and Google Scholar online databases according to the PRISMA 2020 guidelines. The quality of animal studies was evaluated through the SYRCLE's risk of bias tool.

RESULTS

A total of 77 studies were sought for retrieval, and 39 studies met the inclusion criteria. According to the synthesis results, most bilayers had a dense barrier layer that prevented connective tissue penetration and a loose osteogenic layer that supported cell migration and osteogenesis. PLGA, PCL, and chitosan were the most common polymers in the barrier layers, while the most utilized polymers in osteogenic layers were PLGA and gelatin. Electrospinning and solvent casting were the most common fabrication methods to design the bilayer structures. Many studies reported higher biological results for bilayers compared to their single layers. Also, fabricated bilayers' in vitro osteogenesis and in vivo new bone formation were significantly superior or at least comparable to the frequently used commercial membranes.

CONCLUSION

1) Bilayers with two distinct layers and different materials, porosities, mechanical properties, and biological behavior can significantly improve heterogeneous bone regeneration; 2) the addition of ceramics and/or drugs to the osteogenic layer enhances the osteogenic properties of the bilayers; 3) fabrication method and pore size of the layers play an important role in determining the mechanical and biological behavior of them.

An automated 3D-printed perfusion bioreactor combinable with pulsed electromagnetic field stimulators for bone tissue investigations

In bone tissue engineering research, bioreactors designed for replicating the main features of the complex native environment represent powerful investigation tools. Moreover, when equipped with automation, their use allows reducing user intervention and dependence, increasing reproducibility and the overall quality of the culture process. In this study, an automated uni-/bi-directional perfusion bioreactor combinable with pulsed electromagnetic field (PEMF) stimulation for culturing 3D bone tissue models is proposed. A user-friendly control unit automates the perfusion, minimizing the user dependency. Computational fluid dynamics simulations supported the culture chamber design and allowed the estimation of the shear stress values within the construct. Electromagnetic field simulations demonstrated that, in case of combination with a PEMF stimulator, the construct can be exposed to uniform magnetic fields. Preliminary biological tests on 3D bone tissue models showed that perfusion promotes the release of the early differentiation marker alkaline phosphatase. The histological analysis confirmed that perfusion favors cells to deposit more extracellular matrix (ECM) with respect to the static culture and revealed that bi-directional perfusion better promotes ECM deposition across the construct with respect to uni-directional perfusion. Lastly, the Real-time PCR results of 3D bone tissue models cultured under bi-directional perfusion without and with PEMF stimulation revealed that the only perfusion induced a ~ 40-fold up-regulation of the expression of the osteogenic gene collagen type I with respect to the static control, while a ~ 80-fold up-regulation was measured when perfusion was combined with PEMF stimulation, indicating a positive synergic pro-osteogenic effect of combined physical stimulations.

Preparation and characterization of electrospun polycaprolactone/brushite scaffolds to promote osteogenic differentiation of mesenchymal stem cells

Bone tissue engineering aims to develop effective strategies for repairing or replacing damaged bone tissue. In this study, composite scaffolds consisting of dicalcium phosphate dihydrate (DCDP, brushite) as a bone phase mineral precursor with different weight percentages (0%, 1%, 3%, 5%, and 10%) in combination with polycaprolactone (PCL) were fabricated by electrospinning technique. The morphology and mechanical behavior of scaffolds were characterized using scanning electron microscopy and tensile strength test, respectively. The bioactivity of scaffolds was assessed in simulated body fluid. Adhesion, viability, proliferation, and differentiation of mesenchymal stem cells derived from the human bone marrow on scaffolds were investigated using electron microscopy, MTT assay, live-dead assay, alizarin red staining, alkaline phosphatase activity and, gene expression analysis by real-time PCR. The results showed that the scaffold containing 3 wt. % of DCDP had the highest tensile strength (15.35 MPa). Furthermore, cells seeded on scaffolds showed over 80% viability after 1, 3, 7 days of incubation. Also, the results showed that the addition of DCDP to the PCL significantly increased the alkaline phosphatase activity. The osteocalcin gene expression in the composite scaffold showed a 6.1-fold increase compared to the pure PCL scaffold. It is concluded that electrospun PCL scaffolds containing DCDP with optimum concentration can be a proper candidate for bone tissue engineering applications.

Experimental Validation and Evaluation of the Bending Properties of Additively Manufactured Metallic Cellular Scaffold Structures for Bone Tissue Engineering

The availability of additive manufacturing enables the fabrication of cellular bone tissue engineering scaffolds with a wide range of structural and architectural possibilities. The purpose of bone tissue engineering scaffolds is to repair critical size bone defects due to extreme traumas, tumors, or infections. This research study presented the experimental validation and evaluation of the bending properties of optimized bone scaffolds with an elastic modulus that is equivalent to the young’s modulus of the cortical bone. The specimens were manufactured using laser powder bed fusion technology. The morphological properties of the manufactured specimens were evaluated using both dry weighing and Archimedes techniques, and minor variations in the relative densities were observed in comparison with the computer-aided design files. The bending modulus of the cubic and diagonal scaffolds were experimentally investigated using a three-point bending test, and the results were found to agree with the numerical findings. A higher bending modulus was observed in the diagonal scaffold design. The diagonal scaffold was substantially tougher, with considerably higher energy absorption before fracture. The shear modulus of the diagonal scaffold was observed to be significantly higher than the cubic scaffold. Due to bending, the pores at the top side of the diagonal scaffold were heavily compressed compared to the cubic scaffold due to the extensive plastic deformation occurring in diagonal scaffolds and the rapid fracture of struts in the tension side of the cubic scaffold. The failure in struts in tension showed signs of ductility as necking was observed in fractured struts. Moreover, the fractured surface was observed to be rough and dull as opposed to being smooth and bright like in brittle fractures. Dimple fracture was observed using scanning electron microscopy as a result of microvoids emerging in places of high localized plastic deformation. Finally, a comparison of the mechanical properties of the studied BTE scaffolds with the cortical bone properties under longitudinal and transverse loading was investigated. In conclusion, we showed the capabilities of finite element analysis and additive manufacturing in designing and manufacturing promising scaffold designs that can replace bone segments in the human body.

Cultivation of hierarchical 3D scaffolds inside a perfusion bioreactor: scaffold design and finite-element analysis of fluid flow

The use of porous 3D scaffolds for the repair of bone nonunion and osteoporotic bone is currently an area of great interest. Using a combination of thermally-induced phase separation (TIPS) and 3D-plotting (3DP), we have generated hierarchical 3DP/TIPS scaffolds made of poly(lactic-co-glycolic acid) (PLGA) and nanohydroxyapatite (nHA). A full factorial design of experiments was conducted, in which the PLGA and nHA compositions were varied between 6‒12% w/v and 10‒40% w/w, respectively, totaling 16 scaffold formulations with an overall porosity ranging between 87%‒93%. These formulations included an optimal scaffold design identified in our previous study. The internal structures of the scaffolds were examined using scanning electron microscopy and microcomputed tomography. Our optimal scaffold was seeded with MC3T3-E1 murine preosteoblastic cells and subjected to cell culture inside a tissue culture dish and a perfusion bioreactor. The results were compared to those of a commercial CellCeram™ scaffold with a composition of 40% β-tricalcium phosphate and 60% hydroxyapatite (β-TCP/HA). Media flow within the macrochannels of 3DP/TIPS scaffolds was modeled in COMSOL software in order to fine tune the wall shear stress. CyQUANT DNA assay was performed to assess cell proliferation. The normalized number of cells for the optimal scaffold was more than twofold that of CellCeram™ scaffold after two weeks of culture inside the bioreactor. Despite the substantial variability in the results, the observed improvement in cell proliferation upon culture inside the perfusion bioreactor (vs. static culture) demonstrated the role of macrochannels in making the 3DP/TIPS scaffolds a promising candidate for scaffold-based tissue engineering.

Biofabrication of natural hydrogels for cardiac, neural, and bone Tissue engineering Applications

Natural hydrogels are one of the most promising biomaterials for tissue engineering applications, due to their biocompatibility, biodegradability, and extracellular matrix mimicking ability. To surpass the limitations of conventional fabrication techniques and to recapitulate the complex architecture of native tissue structure, natural hydrogels are being constructed using novel biofabrication strategies, such as textile techniques and three-dimensional bioprinting. These innovative techniques play an enormous role in the development of advanced scaffolds for various tissue engineering applications. The progress, advantages, and shortcomings of the emerging biofabrication techniques are highlighted in this review. Additionally, the novel applications of biofabricated natural hydrogels in cardiac, neural, and bone tissue engineering are discussed as well.

Biofabrication of Prevascularised Hypertrophic Cartilage Microtissues for Bone Tissue Engineering

Bone tissue engineering (TE) has the potential to transform the treatment of challenging musculoskeletal pathologies. To date, clinical translation of many traditional TE strategies has been impaired by poor vascularisation of the implant. Addressing such challenges has motivated research into developmentally inspired TE strategies, whereby implants mimicking earlier stages of a tissue's development are engineered in vitro and then implanted in vivo to fully mature into the adult tissue. The goal of this study was to engineer in vitro tissues mimicking the immediate developmental precursor to long bones, specifically a vascularised hypertrophic cartilage template, and to then assess the capacity of such a construct to support endochondral bone formation in vivo. To this end, we first developed a method for the generation of large numbers of hypertrophic cartilage microtissues using a microwell system, and encapsulated these microtissues into a fibrin-based hydrogel capable of supporting vasculogenesis by human umbilical vein endothelial cells (HUVECs). The microwells supported the formation of bone marrow derived stem/stromal cell (BMSC) aggregates and their differentiation toward a hypertrophic cartilage phenotype over 5 weeks of cultivation, as evident by the development of a matrix rich in sulphated glycosaminoglycan (sGAG), collagen types I, II, and X, and calcium. Prevascularisation of these microtissues, undertaken in vitro 1 week prior to implantation, enhanced their capacity to mineralise, with significantly higher levels of mineralised tissue observed within such implants after 4 weeks in vivo within an ectopic murine model for bone formation. It is also possible to integrate such microtissues into 3D bioprinting systems, thereby enabling the bioprinting of scaled-up, patient-specific prevascularised implants. Taken together, these results demonstrate the development of an effective strategy for prevascularising a tissue engineered construct comprised of multiple individual microtissue "building blocks," which could potentially be used in the treatment of challenging bone defects.

Enhancing osteoregenerative potential of biphasic calcium phosphates by using bioinspired ZIF8 coating

Biphasic calcium phosphate ceramics (BCPs) have been extensively used as a bone graft in dental clinics to reconstruct lost bone in the jaw and peri-implant hard tissue due to their good bone conduction and similar chemical structure to the teeth and bone. However, BCPs are not inherently osteoinductive and need additional modification and treatment to enhance their osteoinductivity. The present study aims to develop an innovative strategy to improve the osteoinductivity of BCPs using unique features of zeolitic imidazolate framework-8 (ZIF8). In this method, commercial BCPs (Osteon II) were pre-coated with a zeolitic imidazolate framework-8/polydopamine/polyethyleneimine (ZIF8/PDA/PEI) layer to form a uniform and compact thin film of ZIF8 on the surface of BCPs. The surface morphology and chemical structure of ZIF8 modified Osteon II (ZIF8-Osteon) were confirmed using various analytical techniques such as XRD, FTIR, SEM, and EDX. We evaluated the effect of ZIF8 coating on cell attachment, growth, and osteogenic differentiation of human adipose-derived mesenchymal stem cells (hADSCs). The results revealed that altering the surface chemistry and topography of Osteon II using ZIF8 can effectively promote cell attachment, proliferation, and bone regeneration in both in vitro and in vivo conditions. In conclusion, the method applied in this study is simple, low-cost, and time-efficient and can be used as a versatile approach for improving osteoinductivity and osteoconductivity of other types of alloplastic bone grafts.

Tissue engineering using a combined cell sheet technology and scaffolding approach

Cell sheet technology has remained quite popular among tissue engineering techniques over the last several years. Meanwhile, there is an apparent trend in modern scientific research towards combining different approaches and strategies. Accordingly, a large body of work has arisen where cell sheets are used not as separate structures, but in combination with scaffolds as supporting constructions. The aim of this review is to analyze the intersection of these two vast areas of tissue engineering described in the literature mainly within the last five years. Some practical and technical details are emphasized to provide information that can be useful in research design and planning. The first part of the paper describes the general issues concerning the use of combined technology, its advantages and limitations in comparison with those of other tissue engineering approaches. Next, the detailed literature analysis of in vivo studies aimed at the regeneration of different tissues is performed. A significant part of this section concerns bone regeneration. In addition to that, other connective tissue structures, including articular cartilage and fibrocartilage, ligaments and tendons, and some soft tissues are discussed. STATEMENT OF SIGNIFICANCE: This paper describes the intersection of two technologies used in designing of tissue-engineered constructions for regenerative medicine: cell sheets as extracellular matrix-rich structures and supporting scaffolds as essentials in tissue engineering. A large number of reviews are devoted to each of these scientific problems. However, the solution of complex problems of tissue engineering requires an integrated approach that includes both three-dimensional scaffolds and cell sheets. This manuscript serves as a description of advantages and limitations of this method, its use in regeneration of bones, connective tissues and soft tissues and some other details.