Bone tissue engineering using polyetherketoneketone scaffolds combined with autologous mesenchymal stem cells in a sheep calvarial defect model

Branched Channels in Porous β-Tricalcium Phosphate Scaffold Promote Vascularization

Rapid and efficient vascularization is still considerably challenging for a porous β-tricalcium phosphate (β-TCP) scaffold to achieve. To overcome this challenge, branched channels were created in the porous β-TCP scaffold by using 3D printing and a template-casting method to facilitate the instant flow of blood supply. Human bone mesenchymal stem cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs) were seeded in the channeled porous scaffolds and characterized through a double-stranded DNA (dsDNA) assay, alkaline phosphatase (ALP) assay, and cell migration. Channeled porous β-TCP scaffolds were then implanted in the subcutaneous pockets of mice. Histological staining and immunohistochemical staining on vascularization and bone-related markers were carried out on the embedded paraffin sections. Results from in vitro experiments showed that branched channels significantly promoted HUVECs' infiltration, migration, proliferation, and angiogenesis, and also promoted the proliferation and osteogenesis differentiation of hBMSCs. In vivo implantation results showed that, in the early stage after implantation, cells significantly migrated into branched channeled scaffolds. More matured blood vessels formed in the branched channeled scaffolds compared to that in nonchanneled and straight channeled scaffolds. Beside promoting vascularization, the branched channels also stimulated the infiltration of bone-related cells into the scaffolds. These results suggested that the geometric design of branched channels in the porous β-TCP scaffold promoted rapid vascularization and potentially stimulated bone cells recruitment.

Synthesis of bioactive heat cured PMMA/PEKK blend reinforced by nano titanium dioxide for bone scaffold applications

In bone tissue engineering (BTE), defects in large bones remain the greatest issue which can be addressed using bone scaffolds. In this work, blends of heat cured polymethylmethacrylate (HC PMMA) and various weight percentages of poly-ether-ketone-ketone (PEKK) (0, 2, 4, 8, and 10%) were made using a porogen leaching process. The blends were then subjected to tensile, compression and bending tests to select the optimum blend. Based on the results obtained, HC PMMA blended with 2 wt% PEKK was selected to produce the bio-porous blends. Here, the porosity was imparted using tartaric acid (C4H6O6) and sodium hydrogen carbonate (NaHCO3) as porogen leaching components. Porous blends resulted were then reinforced with a nano titanium dioxide powder (nTiO2) at different weight percentages of (0, 1, 3, and 5). The results showed that porous composites made of (HC PMMA: 2 wt% PEKK) blend reinforced with 5 wt % nTiO2 exhibit the highest strength values under various loadings. The FTIR identified the functional groups of the bone scaffold components. The mean pore size and pore depth were measured using atomic force microscopy (AFM) analysis and the values are 92.6 nm and 42.78 nm, respectively. The good distribution of the PEKK and nTiO2 within the HC PMMA and the uniform porous structure with multi-scale pores between 535 nm and 1.187 mm were confirmed by the AFM data and SEM images, respectively. This research expected that the porous composite (HC PMMA: 2% PEKK: 5% nTiO2) is a good candidate for bone scaffold applications.

A review on the recent applications of synthetic biopolymers in 3D printing for biomedical applications

3D printing technology is an emerging method that gained extensive attention from researchers worldwide, especially in the health and medical fields. Biopolymers are an emerging class of materials offering excellent properties and flexibility for additive manufacturing. Biopolymers are widely used in biomedical applications in biosensing, immunotherapy, drug delivery, tissue engineering and regeneration, implants, and medical devices. Various biodegradable and non-biodegradable polymeric materials are considered as bio-ink for 3d printing. Here, we offer an extensive literature review on the current applications of synthetic biopolymers in the field of 3D printing. A trend in the publication of biopolymers in the last 10 years are focused on the review by analyzing more than 100 publications. Their application and classification based on biodegradability are discussed. The various studies, along with their practical applications, are elaborated in the subsequent sections for polyethylene, polypropylene, polycaprolactone, polylactide, etc. for biomedical applications. The disadvantages of various biopolymers are discussed, and future perspectives like combating biocompatibility problems using 3D printed biomaterials to build compatible prosthetics are also discussed and the potential application of using resin with the combination of biopolymers to build customized implants, personalized drug delivery systems and organ on a chip technologies are expected to open a new set of chances for the development of healthcare and regenerative medicine in the future.

Biomaterials-based additive manufacturing for customized bioengineering in management of otolaryngology: a comprehensive review

Three-dimensional (3D)/four-dimensional (4D) printing, also known as additive manufacturing or fast prototyping, is a manufacturing technique that uses a digital model to generate a 3D/4D solid product. The usage of biomaterials with 3D/4D printers in the pharma and healthcare industries is gaining significant popularity. 3D printing has mostly been employed in the domain of otolaryngology to build portable anatomical models, personalized patient-centric implants, biologic tissue scaffolds, surgical planning in individuals with challenging conditions, and surgical training. Although identical to 3D printing technology in this application, 4D printing technology comprises a fourth dimension of time. With the use of 4D printing, a printed structure may alter over time under various stimuli. Smart polymeric materials are also generally denoted as bioinks are frequently employed in tissue engineering applications of 3D/4D printing. In general, 4D printing could significantly improve the safety and efficacy of otolaryngology therapies. The use of bioprinting in otolaryngology has an opportunity to transform the treatment of diseases influencing the ear, nose, and throat as well as the field of tissue regeneration. The present review briefs on polymeric material including biomaterials and cells used in the manufacturing of patient centric 3D/4D bio-printed products utilized in management of otolaryngology.

Evaluation of in vitro biocompatibility of human pulp stem cells with allogeneic, alloplastic, and xenogeneic grafts under the influence of extracellular vesicles

Therapies using dental pulp stem cells (DPSCs) or stem cell-derived extracellular vesicles (EVs) have shown promising applications for bone tissue engineering. This in vitro experiment evaluated the joint osteogenic capability of DPSCs and EVs on alloplastic (maxresorp), allogeneic (maxgraft), and xenogeneic (cerabone) bone grafts. We hypothesize that osteogenic differentiation and the proliferation of human DPSCs vary between bone grafts and are favorable under the influence of EVs. DPSCs were obtained from human wisdom teeth, and EVs derived from DPSCs were isolated from cell culture medium. DPSCs were seeded on alloplastic, allogeneic, and xenogeneic bone graft substitutes for control, and the same scaffolds were administered with EVs in further groups. The cellular uptake of EVs into DPSC cells was assessed by confocal laser scanning microscopy. Cell vitality staining and calcein acetoxymethyl ester staining were used to evaluate cell attachment and proliferation. Cell morphology was determined using scanning electron microscopy, and osteogenic differentiation was explored by alkaline phosphatase and Alizarin red staining. Within the limitations of an in vitro study without pathologies, the results suggest that especially the use of xenogeneic bone graft substitutes with DPSCS and EVs may represent a promising treatment approach for alveolar bone defects.

3D printed PEKK bone analogs with internal porosity and surface modification for mandibular reconstruction: An in vivo rabbit model study

Polyetheretherketone (PEEK) and its derivative polyetherketoneketone (PEKK) have been used as implant materials for spinal fusing and enjoyed their success for many years because of their mechanical properties similar to bone and their chemical inertness. The osseointegration of PEEKs is datable. Our strategy was to use custom-designed and 3D printed bone analogs with an optimized structure design and a modified PEKK surface to augment bone regeneration for mandibular reconstruction. Those bone analogs had internal porosities and a bioactive titanium oxide surface coating to promote osseointegration between native bone and PEKK analogs. Our workflow was 3D modeling, bone analog designing, structural optimization, mechanical analysis via finite element modeling, 3D printing of bone analogs and subsequently, an in vivo rabbit model study on mandibular reconstruction and histology evaluation. Our results showed the finite element analysis validated that the porous PEKK analogs provided a mechanical-sound structure for functional loadings. The bone analogs offered a perfect replacement for segmented bones in the terms of shape, form and volume for surgical reconstruction. The in vivo results showed that bioactive titanium oxide coating enhanced new bone in-growth into the porous PEKK analogs. We have validated our new approach in surgical mandibular reconstruction and we believe our strategy has a significant potential to improve mechanical and biological outcomes for patients who require mandibular reconstruction procedures.

Hydrogels-A Promising Materials for 3D Printing Technology

Hydrogels are a promising material for a variety of applications after appropriate functional and structural design, which alters the physicochemical properties and cell signaling pathways of the hydrogels. Over the past few decades, considerable scientific research has made breakthroughs in a variety of applications such as pharmaceuticals, biotechnology, agriculture, biosensors, bioseparation, defense, and cosmetics. In the present review, different classifications of hydrogels and their limitations have been discussed. In addition, techniques involved in improving the physical, mechanical, and biological properties of hydrogels by admixing various organic and inorganic materials are explored. Future 3D printing technology will substantially advance the ability to pattern molecules, cells, and organs. With significant potential for producing living tissue structures or organs, hydrogels can successfully print mammalian cells and retain their functionalities. Furthermore, recent advances in functional hydrogels such as photo- and pH-responsive hydrogels and drug-delivery hydrogels are discussed in detail for biomedical applications.

Comparison of a Thiolated Demineralized Bone Matrix Hydrogel to a Clinical Product Control for Regeneration of Large Sheep Cranial Defects

Regeneration of calvarial bone remains a major challenge in the clinic as available options do not sufficiently regenerate bone in larger defect sizes. Calvarial bone regeneration cases involving secondary medical conditions, such as brain herniation during traumatic brain injury (TBI) treatment, further exacerbate treatment options. Hydrogels are well-positioned for severe TBI treatment, given their innate flexibility and potential for bone regeneration to treat TBI in a single-stage surgery. The current study evaluated a photocrosslinking pentenoate-modified hyaluronic acid polymer with thiolated demineralized bone matrix (i.e., TDBM hydrogel) capable of forming a completely interconnected hydrogel matrix for calvarial bone regeneration. The TDBM hydrogel demonstrated a setting time of 120 s, working time of 3 to 7 days, negligible change in setting temperature, physiological setting pH, and negligible cytotoxicity, illustrating suitable performance for in vivo application. Side-by-side ovine calvarial bone defects (19 mm diameter) were employed to compare the TDBM hydrogel to the standard-of-care control material DBX®. After 16 weeks, the TDBM hydrogel had comparable healing to DBX® as demonstrated by mechanical push-out testing (~800 N) and histology. Although DBX® had 59% greater new bone volume compared to the TDBM hydrogel via micro-computed tomography, both demonstrated minimal bone regeneration overall (15 to 25% of defect volume). The current work presents a method for comparing the regenerative potential of new materials to clinical products using a side-by-side cranial bone defect model. Comparison of novel biomaterials to a clinical product control (i.e., standard-of-care) provides an important baseline for successful regeneration and potential for clinical translation.

Biomedical applications of three-dimensional bioprinted craniofacial tissue engineering

Anatomical complications of the craniofacial regions often present considerable challenges to the surgical repair or replacement of the damaged tissues. Surgical repair has its own set of limitations, including scarcity of the donor tissues, immune rejection, use of immune suppressors followed by the surgery, and restriction in restoring the natural aesthetic appeal. Rapid advancement in the field of biomaterials, cell biology, and engineering has helped scientists to create cellularized skeletal muscle-like structures. However, the existing method still has limitations in building large, highly vascular tissue with clinical application. With the advance in the three-dimensional (3D) bioprinting technique, scientists and clinicians now can produce the functional implants of skeletal muscles and bones that are more patient-specific with the perfect match to the architecture of their craniofacial defects. Craniofacial tissue regeneration using 3D bioprinting can manage and eliminate the restrictions of the surgical transplant from the donor site. The concept of creating the new functional tissue, exactly mimicking the anatomical and physiological function of the damaged tissue, looks highly attractive. This is crucial to reduce the donor site morbidity and retain the esthetics. 3D bioprinting can integrate all three essential components of tissue engineering, that is, rehabilitation, reconstruction, and regeneration of the lost craniofacial tissues. Such integration essentially helps to develop the patient-specific treatment plans and damage site-driven creation of the functional implants for the craniofacial defects. This article is the bird's eye view on the latest development and application of 3D bioprinting in the regeneration of the skeletal muscle tissues and their application in restoring the functional abilities of the damaged craniofacial tissue. We also discussed current challenges in craniofacial bone vascularization and gave our view on the future direction, including establishing the interactions between tissue-engineered skeletal muscle and the peripheral nervous system.

Development of a new critical size defect model in the paranasal sinus and first approach for defect reconstruction-An in vivo maxillary bone defect study in sheep

Fractures of the paranasal sinuses often require surgical intervention. Persisting bone defects lead to permanent visible deformities of the facial contours. Bone substitutes for reconstruction of defects with simultaneous induction of new bone formation are not commercially available for the paranasal sinus. New materials are urgently needed and have to be tested in their future area of application. For this purpose critical size defect models for the paranasal sinus have to be developed. A ≥2.4 cm large bilateral circular defect was created in the anterior wall of the maxillary sinus in six sheep via an extraoral approach. The defect was filled with two types of an osteoconductive titanium scaffold (empty scaffold vs. scaffold filled with a calcium phosphate bone cement paste) or covered with a titanium mesh either. Sheep were euthanized after four months. All animals performed well, no postoperative complications occured. Meshes and scaffolds were safely covered with soft tissue at the end of the study. The initial defect size of ≥2.4 cm only shrunk minimally during the investigation period confirming a critical size defect. No ingrowth of bone into any of the scaffolds was observed. The anterior wall of the maxillary sinus is a region with low complication rate for performing critical size defect experiments in sheep. We recommend this region for experiments with future scaffold materials whose intended use is not only limited to the paranasal sinus, as the defect is challenging even for bone graft substitutes with proven osteoconductivity. Graphical abstract.

A systematic review of bone marrow stromal cells and periosteum-derived cells for bone regeneration

Bone marrow stromal cells (BMSCs) and periosteum-derived cells (PDCs) represent promising skeletal stem cell sources to treat critical-size bone defects. However, the large number of preclinical tests with a variety of in vivo data complicates the selection of cells for further clinical translation. This systematic review aims to analyze the in vivo bone-forming efficacy of BMSCs- and PDCs-based approaches in all published preclinical experiments until November 2020. For this purpose, four databases (PubMed, Embase, Cochrane Central Register of Controlled Trial, and Web of Science) were searched for eligible literature, which yielded a total of 94 full-text articles for systematic review. This review generated an evidence-based list of BMSC- or PDC-based approaches, which have been evaluated for bone formation in different animal models. Among them, 74 studies were included for pairwise and network meta-analysis. The results revealed that both PDC and BMSC had beneficial bone-forming efficacy compared to bare scaffold. In addition, BMSC- and PDC-based approaches had no significant difference regarding in vivo bone-forming efficacy. However, BMSC-based approach had a higher probability to be ranked better than PDC-based approach. Furthermore, the review discusses (i) the possible risk of bias of the in vivo evaluation of cell-based approaches, (ii) the difficulty in replication of such experiments due to frequent poor reporting of the methods and results, and (iii) the clinical relevance of the currently utilized BMSC- and PDC-based approaches. Systematic review registration: The study was prospectively registered in PROSPERO, Registration No. CRD42021270922.

Machine Learning-Driven Biomaterials Evolution

Biomaterials is an exciting and dynamic field, which uses a collection of diverse materials to achieve desired biological responses. While there is constant evolution and innovation in materials with time, biomaterials research has been hampered by the relatively long development period required. In recent years, driven by the need to accelerate materials development, the applications of machine learning in materials science has progressed in leaps and bounds. The combination of machine learning with high-throughput theoretical predictions and high-throughput experiments (HTE) has shifted the traditional Edisonian (trial and error) paradigm to a data-driven paradigm. In this review, each type of biomaterial and their key properties and use cases are systematically discussed, followed by how machine learning can be applied in the development and design process. The discussions are classified according to various types of materials used including polymers, metals, ceramics, and nanomaterials, and implants using additive manufacturing. Last, the current gaps and potential of machine learning to further aid biomaterials discovery and application are also discussed.

Multiple channels with interconnected pores in a bioceramic scaffold promote bone tissue formation

Insufficient nutrition exchange and limited transportation of blood supply in a porous only scaffold often hinder bone formation, even though the porous scaffold is loaded with cells or growth factors. To overcome these issues, we developed a cell- and growth factor-free approach to induce bone formation in a critical-size bone defect by using an interconnected porous beta-tricalcium phosphate (β-TCP) scaffold with multiple channels. In vitro cell experimental results showed that multiple channels significantly promoted cell attachment and proliferation of human bone marrow mesenchymal stem cells, stimulated their alkaline phosphatase activity, and up-regulated the osteogenic gene expression. Multiple channels also considerably stimulated the expression of various mechanosensing markers of the cells, such as focal adhesion kinase, filamentous actin, and Yes-associated protein-1 at both static and dynamic culturing conditions. The in vivo bone defect implantation results demonstrated more bone formation inside multiple-channeled scaffolds compared to non-channeled scaffolds. Multiple channels prominently accelerated collagen type I, bone sialoprotein and osteocalcin protein expression. Fluorochrome images and angiogenic marker CD31 staining exhibited more mineral deposition and longer vasculature structures in multiple-channeled scaffolds, compared to non-channeled scaffolds. All the findings suggested that the creation of interconnected multiple channels in the porous β-TCP scaffold is a very promising approach to promote bone tissue regeneration.

Neural crest-derived mesenchymal progenitor cells enhance cranial allograft integration

Replacement of lost cranial bone (partly mesodermal and partly neural crest‐derived) is challenging and includes the use of nonviable allografts. To revitalize allografts, bone marrow‐derived mesenchymal stromal cells (mesoderm‐derived BM‐MSCs) have been used with limited success. We hypothesize that coating of allografts with induced neural crest cell‐mesenchymal progenitor cells (iNCC‐MPCs) improves implant‐to‐bone integration in mouse cranial defects. Human induced pluripotent stem cells were reprogramed from dermal fibroblasts, differentiated to iNCCs and then to iNCC‐MPCs. BM‐MSCs were used as reference. Cells were labeled with luciferase (Luc2) and characterized for MSC consensus markers expression, differentiation, and risk of cellular transformation. A calvarial defect was created in non‐obese diabetic/severe combined immunodeficiency (NOD/SCID) mice and allografts were implanted, with or without cell coating. Bioluminescence imaging (BLI), microcomputed tomography (μCT), histology, immunofluorescence, and biomechanical tests were performed. Characterization of iNCC‐MPC‐Luc2 vs BM‐MSC‐Luc2 showed no difference in MSC markers expression and differentiation in vitro. In vivo, BLI indicated survival of both cell types for at least 8 weeks. At week 8, μCT analysis showed enhanced structural parameters in the iNCC‐MPC‐Luc2 group and increased bone volume in the BM‐MSC‐Luc2 group compared to controls. Histology demonstrated improved integration of iNCC‐MPC‐Luc2 allografts compared to BM‐MSC‐Luc2 group and controls. Human osteocalcin and collagen type 1 were detected at the allograft‐host interphase in cell‐seeded groups. The iNCC‐MPC‐Luc2 group also demonstrated improved biomechanical properties compared to BM‐MSC‐Luc2 implants and cell‐free controls. Our results show an improved integration of iNCC‐MPC‐Luc2‐coated allografts compared to BM‐MSC‐Luc2 and controls, suggesting the use of iNCC‐MPCs as potential cell source for cranial bone repair.

Additive Manufacturing of Material Scaffolds for Bone Regeneration: Toward Application in the Clinics

Additive manufacturing (AM) allows the fabrication of customized bone scaffolds in terms of shape, pore size, material type and mechanical properties. Combined with the possibility to obtain a precise 3D image of the bone defects using computed tomography or magnetic resonance imaging, it is now possible to manufacture implants for patient-specific bone regeneration. This paper reviews the state-of-the-art of the different materials and AM techniques used for the fabrication of 3D-printed scaffolds in the field of bone tissue engineering. Their advantages and drawbacks are highlighted. For materials, specific criteria, were extracted from a literature study: biomimetism to native bone, mechanical properties, biodegradability, ability to be imaged (implantation and follow-up period), histological performances and sterilization process. AM techniques can be classified in three major categories: extrusion-based, powder-based and liquid-base. Their price, ease of use and space requirement are analyzed. Different combinations of materials/AM techniques appear to be the most relevant depending on the targeted clinical applications (implantation site, presence of mechanical constraints, temporary or permanent implant). Finally, some barriers impeding the translation to human clinics are identified, notably the sterilization process.

MiR-17-3p inhibits osteoblast differentiation by downregulating Sox6 expression

Osteoporosis and osteoarthritis are orthopedic disorders that affect millions of elderly people worldwide; stimulation of bone formation is a potential therapeutic strategy for the treatment of these conditions. As the only bone‐forming cells, osteoblasts play a key role in bone reconstruction. The microRNA miR‐17‐3p is downregulated during osteogenic differentiation of human bone marrow mesenchymal stem cells, but its precise role in this process is unknown. Here, we investigated the role of miR‐17‐3p in osteoblast differentiation. An in vitro model of osteogenesis was established by treating MC3T3‐E1 murine preosteoblast cells with bone morphogenetic protein 2 (BMP2). The expression of miR‐17‐3p in BMP2‐induced MC3T3‐E1 cells was detected by reverse transcription‐quantitative PCR, and its effects on cells transfected with miR‐17‐3p mimic or inhibitor were evaluated by Alizarin Red staining, alkaline phosphatase (ALP) activity assay, and by detection of osteoblast markers including the ALP, collagen type I α1 chain, and osteopontin genes. Bioinformatics analysis was carried out to identify putative target genes of miR‐17‐3p, and the luciferase reporter assay was used for functional validation. Rescue experiments were performed to determine whether SRY‐box transcription factor 6 (Sox6) plays a role in the regulation of osteoblast differentiation by miR‐17‐3p. We report that miR‐17‐3p was downregulated upon BMP2‐induced osteoblast differentiation in MC3T3‐E1 cells, and this was accompanied by decreased differentiation and mineralization, ALP activity, and expression of osteogenesis‐related genes. Sox6 was confirmed to be a target gene of miR‐17‐3p in osteoblasts, and the inhibitory effect of miR‐17‐3p on osteoblast differentiation was observed to occur via Sox6. These results suggest the existence of a novel mechanism underlying miRNA‐mediated regulation of osteogenesis, which has potential implications for the treatment of orthopedic disorders.

3D bioprinting and craniofacial regeneration

BACKGROUND

Considering the structural and functional complexity of the craniofacial tissues, 3D bioprinting can be a valuable tool to design and create functional 3D tissues or organs in situ for in vivo applications. This review aims to explore the various aspects of this emerging 3D bioprinting technology and its application in the craniofacial bone or cartilage regeneration.

METHOD

Electronic database searches were undertaken on pubmed, google scholar, medline, embase, and science direct for english language literature, published for 3D bioprinting in craniofacial regeneration. The search items used were 'craniofacial regeneration' OR 'jaw regeneration' OR 'maxillofacial regeneration' AND '3D bioprinting' OR 'three dimensional bioprinting' OR 'Additive manufacturing' OR 'rapid prototyping' OR 'patient specific bioprinting'. Reviews and duplicates were excluded.

RESULTS

Search with above described criteria yielded 476 articles, which reduced to 108 after excluding reviews. Further screening of individual articles led to 77 articles to which 9 additional articles were included from references, and 18 duplicate articles were excluded. Finally we were left with 68 articles to be included in the review.

CONCLUSION

Craniofacial tissue and organ regeneration has been reported a success using bioink with different biomaterial and incorporated stem cells in 3D bioprinters. Though several attempts have been made to fabricate craniofacial bone and cartilage, the strive to achieve desired outcome still continues.

Polyetherketoneketone (PEKK): An emerging biomaterial for oral implants and dental prostheses

Polyetherketoneketone (PEKK) is a new evolving polymeric material. The present article comprehensively reviewed an overview of various applications of PEKK in prosthodontics and oral implantology, highlighting its prospects for clinical applications. PEKK biomaterials is an elastic material with good shock absorbance and fracture resistance and present ultra-high performance among all thermoplastic composites for excellent mechanical strength, chemical resistance, and high thermal stability. Available articles on PEKK for dental applications were reviewed from January 1957 to August 2020) using MEDLINE/PubMed, Web of Science, and ScienceDirect resources. PEKK presents suitable physical, mechanical, and chemical properties for applications in prosthodontics and oral implantology. PEKK has good potential for a wide range of dental applications, including tooth restorations, crowns, bridge, endoposts, denture framework, implant-supported fixed prosthesis, and dental implants. PEKK dental implants have shown lesser stress shielding compared to titanium for dental implant applications. Further modifications and improving material properties can result in broader applications in the field of dentistry. Long term evaluations are needed as PEKK is recently applied in dentistry, and there are limited studies published on PEKK.

Tissue engineering applications in otolaryngology-The state of translation

While tissue engineering holds significant potential to address current limitations in reconstructive surgery of the head and neck, few constructs have made their way into routine clinical use. In this review, we aim to appraise the state of head and neck tissue engineering over the past five years, with a specific focus on otologic, nasal, craniofacial bone, and laryngotracheal applications. A comprehensive scoping search of the PubMed database was performed and over 2000 article hits were returned with 290 articles included in the final review. These publications have addressed the hallmark characteristics of tissue engineering (cellular source, scaffold, and growth signaling) for head and neck anatomical sites. While there have been promising reports of effective tissue engineered interventions in small groups of human patients, the majority of research remains constrained to in vitro and in vivo studies aimed at furthering the understanding of the biological processes involved in tissue engineering. Further, differences in functional and cosmetic properties of the ear, nose, airway, and craniofacial bone affect the emphasis of investigation at each site. While otolaryngologists currently play a role in tissue engineering translational research, continued multidisciplinary efforts will likely be required to push the state of translation towards tissue-engineered constructs available for routine clinical use.

LEVEL OF EVIDENCE

NA.

Biomimetic Cell-Laden MeHA Hydrogels for the Regeneration of Cartilage Tissue

Methacrylated hyaluronic acid (MeHA) and chondroitin sulfate (CS)-biofunctionalized MeHA (CS-MeHA), were crosslinked in the presence of a matrix metalloproteinase 7 (MMP7)-sensitive peptide. The synthesized hydrogels were embedded with either human mesenchymal stem cells (hMSCs) or chondrocytes, at low concentrations, and subsequently cultured in a stem cell medium (SCM) or chondrogenic induction medium (CiM). The pivotal role of the synthesized hydrogels in promoting the expression of cartilage-related genes and the formation of neocartilage tissue despite the low concentration of encapsulated cells was assessed. It was found that hMSC-laden MeHA hydrogels cultured in an expansion medium exhibited a significant increase in the expression of chondrogenic markers compared to hMSCs cultured on a tissue culture polystyrene plate (TCPS). This favorable outcome was further enhanced for hMSC-laden CS-MeHA hydrogels, indicating the positive effect of the glycosaminoglycan binding peptide on the differentiation of hMSCs towards a chondrogenic phenotype. However, it was shown that an induction medium is necessary to achieve full span chondrogenesis. Finally, the histological analysis of chondrocyte-laden MeHA hydrogels cultured on an ex vivo osteochondral platform revealed the deposition of glycosaminoglycans (GAGs) and the arrangement of chondrocyte clusters in isogenous groups, which is characteristic of hyaline cartilage morphology.

The Applications of 3D Printing for Craniofacial Tissue Engineering

Three-dimensional (3D) printing is an emerging technology in the field of dentistry. It uses a layer-by-layer manufacturing technique to create scaffolds that can be used for dental tissue engineering applications. While several 3D printing methodologies exist, such as selective laser sintering or fused deposition modeling, this paper will review the applications of 3D printing for craniofacial tissue engineering; in particular for the periodontal complex, dental pulp, alveolar bone, and cartilage. For the periodontal complex, a 3D printed scaffold was attempted to treat a periodontal defect; for dental pulp, hydrogels were created that can support an odontoblastic cell line; for bone and cartilage, a polycaprolactone scaffold with microspheres induced the formation of multiphase fibrocartilaginous tissues. While the current research highlights the development and potential of 3D printing, more research is required to fully understand this technology and for its incorporation into the dental field.

Design of Additively Manufactured Structures for Biomedical Applications: A Review of the Additive Manufacturing Processes Applied to the Biomedical Sector

Additive manufacturing (AM) is a disruptive technology as it pushes the frontier of manufacturing towards a new design perspective, such as the ability to shape geometries that cannot be formed with any other traditional technique. AM has today shown successful applications in several fields such as the biomedical sector in which it provides a relatively fast and effective way to solve even complex medical cases. From this point of view, the purpose of this paper is to illustrate AM technologies currently used in the medical field and their benefits along with contemporary. The review highlights differences in processes, materials, and design of additive manufacturing techniques used in biomedical applications. Successful case studies are presented to emphasise the potentiality of AM processes. The presented review supports improvements in materials and design for future researches in biomedical surgeries using instruments and implants made by AM.

Microporous Coatings of PEKK/SN Composites Integration with PEKK Exhibiting Antibacterial and Osteogenic Activity, and Promotion of Osseointegration for Bone Substitutes

To improve the antibacterial and osteogenic activities of poly(etherketoneketone) (PEKK), concentrated sulfuric acid (H₂SO₄) suspension with silicon nitride (SN) microparticle was utilized to modify PEKK surface. Through sulfonation reaction, microporous coatings of PEKK/SN composites were created on PEKK surface, which were integrated with PEKK substrate. The results showed that the content of SN in the microporous coatings increased with the increase of SN content in H₂SO₄ suspension (PKS without SN, PKSC5 and PKSC10 with 5 and 10 wt % SN content in H₂SO₄) and that the surface roughness and hydrophilicity of microporous coatings on PEKK were significantly improved with the SN content increasing. In addition, the microporous coating of PKSC10 with high SN content exhibited excellent antibacterial activity due to the synergistic action of the presence of amino (-NH₂) and sulfonic acid (-SO₃H) groups as well as the improvement of protein absorption. Moreover, the microporous coating of PKSC10 obviously stimulated adhesion, proliferation, and osteogenic differentiation of rat bone mesenchymal stem cells. Furthermore, histological and push-out load evaluation indicated that the microporous coating of PKSC10 significantly promoted osteogenesis and osseointegration in vivo. The results suggested that the microporous coating of PKSC10 with high SN content display good biocompatibility, antibacterial and osteogenic activities, and osseointegration ability, which would have great potential for bone substitutes.

Combination of polyetherketoneketone scaffold and human mesenchymal stem cells from temporomandibular joint synovial fluid enhances bone regeneration

Therapies using human mesenchymal stem cells (MSCs) combined with three-dimensional (3D) printed scaffolds are a promising strategy for bone grafting. But the harvest of MSCs still remains invasive for patients. Human synovial fluid MSCs (hSF-MSCs), which can be obtained by a minimally invasive needle-aspiration procedure, have been used for cartilage repair. However, little is known of hSF-MSCs in bone regeneration. Polyetherketoneketone (PEKK) is an attractive bone scaffold due to its mechanical properties comparable to bone. In this study, 3D-printed PEKK scaffolds were fabricated using laser sintering technique. hSF-MSCs were characterized and cultured on PEKK to evaluate their cell attachment, proliferation, and osteogenic potential. Rabbit calvarial critical-sized bone defects were created to test the bone regenerative effect of PEKK with hSF-MSCs. In vitro results showed that hSF-MSCs attached, proliferated, and were osteogenic on PEKK. In vivo results indicated that PEKK seeded with hSF-MSCs regenerated twice the amount of newly formed bone when compared to PEKK seeded with osteogenically-induced hSF-MSCs or PEKK scaffolds alone. These results suggested that there was no need to induce hSF-MSCs into osteoblasts prior to their transplantations in vivo. In conclusion, the combined use of PEKK and hSF-MSCs was effective in regenerating critical-sized bone defects.

Micro-CT - a digital 3D microstructural voyage into scaffolds: a systematic review of the reported methods and results

BACKGROUND

Cell behavior is the key to tissue regeneration. Given the fact that most of the cells used in tissue engineering are anchorage-dependent, their behavior including adhesion, growth, migration, matrix synthesis, and differentiation is related to the design of the scaffolds. Thus, characterization of the scaffolds is highly required. Micro-computed tomography (micro-CT) provides a powerful platform to analyze, visualize, and explore any portion of interest in the scaffold in a 3D fashion without cutting or destroying it with the benefit of almost no sample preparation need.

MAIN BODY

This review highlights the relationship between the scaffold microstructure and cell behavior, and provides the basics of the micro-CT method. In this work, we also analyzed the original papers that were published in 2016 through a systematic search to address the need for specific improvements in the methods section of the papers including the amount of provided information from the obtained results.

CONCLUSION

Micro-CT offers a unique microstructural analysis of biomaterials, notwithstanding the associated challenges and limitations. Future studies that will include micro-CT characterization of scaffolds should report the important details of the method, and the derived quantitative and qualitative information can be maximized.

Characteristics and multi‑lineage differentiation of bone marrow mesenchymal stem cells derived from the Tibetan mastiff

Bone marrow mesenchymal stem cells (BM-MSCs) are pluripotent stem cells that are regarded as ideal resources for the reconstruction of tissues and organs. The Tibetan mastiff is a breed of domesticated Chinese native dog that is well-adjusted to the high-altitude environments of Tibet. To the best of our knowledge, the biological characterization and multi-lineage differentiation of Tibetan mastiff BM-MSCs have not been reported previously. Therefore, the present study aimed to investigate the biological characteristics and therapeutic potential of Tibetan mastiff BM-MSCs. A cell culture system was constructed and cells were cultured to 23 passages in vitro. Growth curves and colony formation studies suggested that BM-MSCs had a high self-renewal capacity and that their proliferation rate declined with age. Karyotype analysis demonstrated that BM-MSCs were diploid and genetically stable. Semi-quantitative polymerase chain reaction analysis revealed that BM-MSCs positively expressed cluster of differentiation (CD)73, CD90, CD105, CD166 and vimentin, although they were negative for the endothelial cell marker CD31. Additionally, immunofluorescence staining revealed that the cells expressed CD29, CD44, CD90, CD105 and vimentin. Flow cytometric analysis revealed that the rates of positive expression of vimentin, CD44, CD90 and CD105 were all >97%. BM-MSCs were able to differentiate into adipocytes, osteoblasts, cartilage cells, hepatocytes and functional insulin-secreting cells. In conclusion, Tibetan mastiff BM-MSCs may be purified successfully using a whole bone marrow culture method. The findings of the current study suggested important potential applications of BM-MSCs as a source for regenerative therapies.

Applying chlorogenic acid in an alginate scaffold of chondrocytes can improve the repair of damaged articular cartilage

Damaged cartilage has very low regenerative potential which has led to the search for novel tissue-engineering approaches to help treat cartilage defects. While various approaches have been reported, there is no perfect treatment currently. In this study we evaluated the effects of a plant extract, chlorogenic acid (CGA), as part of chondrocyte transplantation on a model of knee joint injury in chicks. First, primary cultured chondrocytes used to evaluate the effects of CGA on chondrogenesis. Then using an articular cartilage injury model of chick knee we assessed the functional recovery after transplantation of the complexes containing chondrocytes and CGA in an alginate scaffold. Histological analysis, PCR, and western blot were further used to understand the underlying mechanisms. We showed that 60 μM CGA in alginate exhibited notable effects on stimulating chondrogenesis in vitro. Secondly, it was shown that the application of these complexes accelerated the recovery of injury-induced dysfunction by gait analysis when followed for 21 days. Histochemical analysis demonstrated that there was less abnormal vasculature formation, more chondrocyte proliferation and cartilage matrix synthesis in the presence of the complexes containing CGA. We discovered CGA treated transplantation up-regulated the expressions of Sox9 and Col2a1 which were responsible for the stimulation of chondrogenesis. Furthermore, the application of these complexes could suppress the abnormal angiogenesis and fibrosis at the injury site. Lastly, the elevated levels of inflammatory cytokines IL-1β, TNF-α, p-p65, and MMPs expression were decreased in the presence of CGA. This may be caused through adjusting cellular redox homeostasis associated with Nrf2. This study suggests that combining chondrocytes and CGA on an alginate scaffold can improve the recovery of damaged articular cartilage.

Autocrine signals increase ovine mesenchymal stem cells migration through Aquaporin-1 and CXCR4 overexpression

Sheep is a relevant large animal model that is frequently used to test innovative tissue engineering (TE) approaches especially for bone reconstruction. Mesenchymal stem cells (MSCs) are used in TE applications because they represent key component of adult tissue repair. Importantly, MSCs from different species show similar characteristics, which facilitated their application in translational studies using animal models. Nowadays, many researches are focusing on the use of ovine mesenchymal stem cells (oMSCs) in orthopedic preclinical settings for regenerative medicine purposes. Therefore, there is a need to amplify our knowledge on the mechanisms underlying the behaviour of these cells. Recently, several studies have shown that MSC function is largely dependent on factors that MSCs release in the environment, as well as, in conditioned medium (CM). It has been demonstrated that MSCs through autocrine and paracrine signals are able to stimulate proliferation, migration, and differentiation of different type of cells including themselves. In this study, we investigated the effects of the CM produced by oMSCs on oMSCs themselves and we explored the signal pathways involved. We observed that CM caused an enhancement of oMSC migration. Furthermore, we found that CM increased levels of two membrane proteins involved in cell migration, Aquaporin 1 (AQP1), and C-X-C chemokine receptor type 4 (CXCR4), and activated Akt and Erk intracellular signal pathways. In conclusion, taken together our results suggest the high potential of autologous CM as a promising tool to modulate behaviour of MSCs thus improving their use in therapeutically approaches.

Engineering biomimetic periosteum with β-TCP scaffolds to promote bone formation in calvarial defects of rats

Background

There is a critical need for the management of large bone defects. The purpose of this study was to engineer a biomimetic periosteum and to combine this with a macroporous β-tricalcium phosphate (β-TCP) scaffold for bone tissue regeneration.

Methods

Rat bone marrow-derived mesenchymal stem cells (rBMSCs) were harvested and cultured in different culture media to form undifferentiated rBMSC sheets (undifferentiated medium (UM)) and osteogenic cell sheets (osteogenic medium (OM)). Simultaneously, rBMSCs were differentiated to induced endothelial-like cells (iECs), and the iECs were further cultured on a UM to form a vascularized cell sheet. At the same time, flow cytometry was used to detect the conversion rates of rBMSCs to iECs. The pre-vascularized cell sheet (iECs/UM) and the osteogenic cell sheet (OM) were stacked together to form a biomimetic periosteum with two distinct layers, which mimicked the fibrous layer and cambium layer of native periosteum. The biomimetic periostea were wrapped onto porous β-TCP scaffolds (BP/β-TCP) and implanted in the calvarial bone defects of rats. As controls, autologous periostea with β-TCP (AP/β-TCP) and β-TCP alone were implanted in the calvarial defects of rats, with a no implantation group as another control. At 2, 4, and 8 weeks post-surgery, implants were retrieved and X-ray, microcomputed tomography (micro-CT), histology, and immunohistochemistry staining analyses were performed.

Results

Flow cytometry results showed that rBMSCs were partially differentiated into iECs with a 35.1% conversion rate in terms of CD31. There were still 20.97% rBMSCs expressing CD90. Scanning electron microscopy (SEM) results indicated that cells from the wrapped cell sheet on the β-TCP scaffold apparently migrated into the pores of the β-TCP scaffold. The histology and immunohistochemistry staining results from in vivo implantation indicated that the BP/β-TCP and AP/β-TCP groups promoted the formation of blood vessels and new bone tissues in the bone defects more than the other two control groups. In addition, micro-CT showed that more new bone tissue formed in the BP/β-TCP and AP/β-TCP groups than the other groups.

Conclusions

Inducing rBMSCs to iECs could be a good strategy to obtain an endothelial cell source for prevascularization. Our findings indicate that the biomimetic periosteum with porous β-TCP scaffold has a similar ability to promote osteogenesis and angiogenesis in vivo compared to the autologous periosteum. This function could result from the double layers of biomimetic periosteum. The prevascularized cell sheet served a mimetic fibrous layer and the osteogenic cell sheet served a cambium layer of native periosteum. The biomimetic periosteum with a porous ceramic scaffold provides a new promising method for bone healing.