* Tissue Engineering Strategies to Improve Osteogenesis in the Juvenile Swine Alveolar Cleft Model

Stem Cell-Based Tissue Engineering for Cleft Defects: Systematic Review and Meta-Analysis

This study aimed to analyze the efficacy of stem cell-based tissue engineering for the treatment of alveolar cleft (AC) and cleft palate (CP) defects in animal models.

Systematic review and meta-analysis.

Preclinical studies on alveolar cleft repair in maxillofacial practice.

Electronic search was performed using PubMed, Embase, and Cochrane databases. Pre-clinical studies, where stem cell-based tissue engineering was used in the reconstruction of AC and CP in animal models were included. Quality of the selected articles was evaluated using SYRCLE (SYstematic Review Centre for Laboratory animal Experimentation).

Review of alveolar cleft bone augmentation interventions in preclinical models.

Outcome parameters registered were new bone formation (NBF) and/or bone mineral density (BMD).

Thirteen large and twelve small animal studies on AC (21) and CP (4) reconstructions were included. Studies had an unclear-to-high risk of bias. Bone marrow mesenchymal stem cells were the most widely used cell source. Meta-analyses for AC indicated non-significant benefits in favor of: (1) scaffold + cells over scaffold-only (NBF P = .13); and (2) scaffold + cells over empty control (NBF P = .66; BMD P = .31). Interestingly, dog studies using regenerative grafts showed similar to superior bone formation compared to autografts. Meta analysis for the CP group was not possible.

AC and CP reconstructions are enhanced by addition of osteogenic cells to biomaterials. Directions and estimates of treatment effect are useful to predict therapeutic efficacy and guide future clinical trials of bone tissue engineering.

Stem Cell-Based Regenerative Approaches for the Treatment of Cleft Lip and Palate: A Comprehensive Review

Cleft lip and/or palate (CLP) is a prevalent congenital craniofacial abnormality that can lead to difficulties in eating, speaking, hearing, and psychological distress. The traditional approach for treating CLP involves bone graft surgery, which has limitations, post-surgical complications, and donor site morbidity. However, regenerative medicine has emerged as a promising alternative, employing a combination of stem cells, growth factors, and scaffolds to promote tissue regeneration. This review aims to provide a comprehensive overview of stem cell-based regenerative approaches in the management of CLP. A thorough search was conducted in the Medline/PubMed and Scopus databases, including cohort studies, randomized controlled trials, case series, case controls, case reports, and animal studies. The identified studies were categorized into two main groups: clinical studies involving human subjects and in vivo studies using animal models. While there are only a limited number of studies investigating the combined use of stem cells and scaffolds for CLP treatment, they have shown promising results. Various types of stem cells have been utilized in conjunction with scaffolds. Importantly, regenerative methods have been successfully applied to patients across a broad range of age groups. The collective findings derived from the reviewed studies consistently support the notion that regenerative medicine holds potential advantages over conventional bone grafting and represents a promising therapeutic option for CLP. However, future well-designed clinical trials, encompassing diverse combinations of stem cells and scaffolds, are warranted to establish the clinical efficacy of these interventions with a larger number of patients.

New insight into biodegradable macropore filler on tuning mechanical properties and bone tissue ingrowth in sparingly dissolvable bioceramic scaffolds

Structural parameters of the implants such as shape, size, and porosity of the pores have been extensively investigated to promote bone tissue repair, however, it is unknown how the pore interconnectivity affects the bone growth behaviors in the scaffolds. Herein we systematically evaluated the effect of biodegradable bioceramics as a secondary phase filler in the macroporous networks on the mechanical and osteogenic behaviors in sparingly dissolvable bioceramic scaffolds. The pure hardystonite (HT) scaffolds with ∼550 & 800 μm in pore sizes were prepared by digital light processing, and then the Sr-doped calcium silicate (SrCSi) bioceramic slurry without and with 30 % organic porogens were intruded into the HT scaffolds with 800 μm pore size and sintered at 1150 °C. It indicated that the organic porogens could endow spherical micropores in the SrCSi filler, and the invasion of the SrCSi component could not only significantly enhance the compressive strength and modulus of the HT-based scaffolds, but also induce osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). The pure HT scaffolds showed extremely slow bio-dissolution in Tris buffer after immersion for 8 weeks (∼1 % mass decay); in contrast, the SrCSi filler would readily dissolve into the aqueous medium and produced a steady mass decay (>6 % mass loss). In vivo experiments in rabbit femoral bone defect models showed that the pure HT scaffolds showed bone tissue ingrowth but the bone growth was impeded in the SrCSi-intruded scaffolds within 4 weeks; however, the group with higher porosity of SrCSi filler showed appreciable osteogenesis after 8 weeks of implantation and the whole scaffold was uniformly covered by new bone tissues after 16 weeks. These findings provide some new insights that the pore interconnectivity is not inevitable to impede bone ingrowth with the prolongation of implantation time, and such a highly biodegradable and bioactive filler intrusion strategy may be beneficial for optimizing the performances of scaffolds in bone regenerative medicine applications.

TyroFill-Titanium Implant Constructs for the Coordinated Repair of Rabbit Mandible and Tooth Defects

Currently used methods to repair craniomaxillofacial (CMF) bone and tooth defects require a multi-staged surgical approach for bone repair followed by dental implant placement. Our previously published results demonstrated significant bioengineered bone formation using human dental pulp stem cell (hDPSC)-seeded tyrosine-derived polycarbonate scaffolds (E1001(1K)-bTCP). Here, we improved upon this approach using a modified TyroFill (E1001(1K)/dicalcium phosphate dihydrate (DCPD)) scaffold-supported titanium dental implant model for simultaneous bone-dental implant repair. TyroFill scaffolds containing an embedded titanium implant, with (n = 3 each time point) or without (n = 2 each time point) seeded hDPCs and Human Umbilical Vein Endothelial Cells (HUVECs), were cultured in vitro. Each implant was then implanted into a 10 mm full-thickness critical-sized defect prepared on a rabbit mandibulee. After 1 and 3 months, replicate constructs were harvested and analyzed using Micro-CT histological and IHC analyses. Our results showed significant new bone formation surrounding the titanium implants in cell-seeded TyroFill constructs. This study indicates the potential utility of hDPSC/HUVEC-seeded TyroFill scaffolds for coordinated CMF bone-dental implant repair.

Bone Tissue Engineering Strategies for Alveolar Cleft: Review of Preclinical Results and Guidelines for Future Studies

The current standard of care for an alveolar cleft defect is an autogenous bone graft, typically from the iliac crest. Given the limitations of alveolar bone graft surgery, such as limited supply, donor site morbidity, graft failure, and need for secondary surgery, there has been growing interest in regenerative medicine strategies to supplement and replace traditional alveolar bone grafts. Though there have been preliminary clinical studies investigating bone tissue engineering methods in human subjects, lack of consistent results as well as limitations in study design make it difficult to determine the efficacy of these interventions. As the field of bone tissue engineering is rapidly advancing, reconstructive surgeons should be aware of the preclinical studies informing these regenerative strategies. We review preclinical studies investigating bone tissue engineering strategies in large animal maxillary or mandibular defects and provide an overview of scaffolds, stem cells, and osteogenic agents applicable to tissue engineering of the alveolar cleft. An electronic search conducted in the PubMed database up to December 2021 resulted in 35 studies for inclusion in our review. Most studies showed increased bone growth with a tissue engineering construct compared to negative control. However, heterogeneity in the length of follow up, method of bone growth analysis, and inconsistent use of positive control groups make comparisons across studies difficult. Future studies should incorporate a pediatric study model specific to alveolar cleft with long-term follow up to fully characterize volumetric defect filling, cellular ingrowth, bone strength, tooth movement, and implant support.

Three-Dimensional Printing Bioceramic Scaffolds Using Direct-Ink-Writing for Craniomaxillofacial Bone Regeneration

Defects characterized as large osseous voids in bone, in certain circumstances, are difficult to treat, requiring extensive treatments which lead to an increased financial burden, pain, and prolonged hospital stays. Grafts exist to aid in bone tissue regeneration (BTR), among which ceramic-based grafts have become increasingly popular due to their biocompatibility and resorbability. BTR using bioceramic materials such as β-tricalcium phosphate has seen tremendous progress and has been extensively used in the fabrication of biomimetic scaffolds through the three-dimensional printing (3DP) workflow. 3DP has hence revolutionized BTR by offering unparalleled potential for the creation of complex, patient, and anatomic location-specific structures. More importantly, it has enabled the production of biomimetic scaffolds with porous structures that mimic the natural extracellular matrix while allowing for cell growth-a critical factor in determining the overall success of the BTR modality. While the concept of 3DP bioceramic bone tissue scaffolds for human applications is nascent, numerous studies have highlighted its potential in restoring both form and function of critically sized defects in a wide variety of translational models. In this review, we summarize these recent advancements and present a review of the engineering principles and methodologies that are vital for using 3DP technology for craniomaxillofacial reconstructive applications. Moreover, we highlight future advances in the field of dynamic 3D printed constructs via shape-memory effect, and comment on pharmacological manipulation and bioactive molecules required to treat a wider range of boney defects.

Use of stem cells in bone regeneration in cleft palate patients: review and recommendations

This study was conducted to review the efficacy of different sources of stem cells in bone regeneration of cleft palate patients. The majority of previous studies focused on the transplantation of bone marrow mesenchymal stem cells. However, other sources of stem cells have also gained considerable attention, and dental stem cells have shown especially favorable outcomes. Additionally, approaches that apply the co-culture and co-transplantation of stem cells have shown promising results. The use of different types of stem cells, based on their accessibility and efficacy in bone regeneration, is a promising method in cleft palate bone regeneration. In this regard, dental stem cells may be an ideal choice due to their efficacy and accessibility. In conclusion, stem cells, despite the lengthy procedures required for culture and preparation, are a suitable alternative to conventional bone grafting techniques.

Construction of a Pig Alveolar Cleft Model in Imitation of Cleft Lip and Palate Congenital Deformity

Alveolar cleft repair is a key step in multiple disciplinary treatment for patients with cleft lip/and palate. Although autologous bone grafting has been used worldwide over the past half century, alternative advanced techniques, such as the use of bone substitutes and guided tissue regeneration, have shown their great potentials and have been recommended by a growing number of physicians and surgeons. The employment of new therapeutic approaches and devices in clinical routine requires tremendous experimental efforts and appropriate animal models with similar sizes and sites of deformity to that of human both anatomically and physiologically. The aim of this study is to develop a juvenile porcine model with surgically created alveolar clefts imitating congenital alveolar cleft in the cleft lip and palate. Alveolar defects between second incisor and canine were surgically created in two miniature pigs (unilateral cleft in P1 and P2); bilateral alveolar defects were surgically created between first and third incisor in one miniature pig (P3) using piezo surgery. Pigs were sacrificed (P1 at 1 month after the surgery and P2 at 3 months postoperatively) and the evaluation of defects were performed by assessing result from the computed tomography (CT) scan and histopathological examination. Postoperative CT scan results showed that the size of the defect remained the same, whereas the edge of the defect became irregular 3 months after the surgery. In all pig subjects, histopathological examination found no sign of osteogenesis in the area of defect, indicating that our surgical procedure was successful in establishing porcine models for alveolar cleft in congenital cleft lip and palate. In conclusion, we developed alveolar cleft in porcine models to mimic the size, site, and environment of congenital alveolar cleft in cleft lip and palate. The novel animal model can be employed in pilot studies for the purpose of optimizing the current surgical treatment techniques as well as developing new treatment procedures and test the bone substitute materials. The bilateral model can be applied in further control studies. Impact statement Cancellous iliac bone graft was the most popular surgical technique as well as the gold standard to reconstruct alveolar cleft. Nevertheless, several disadvantages exist regarding the additional surgical field of donor side and delayed age of alveolar bone grafting. Bone tissue-engineered strategy offers a promising alternative to address the gap in the current limitation of autologous bone to treat the growing craniofacial skeleton. Among different species of laboratory animals, porcine is suitable for oral and maxillofacial bone and implant-related research, where alveolar defect can be surgically developed simulating the size and site of alveolar cleft occurring together with cleft lip and palate. In this proposal, a reproducible porcine model of alveolar bone defect imitating congenital alveolar cleft during craniofacial growing stage is successfully constructed that will show great potential application in the field of tissue engineering and regenerative medicine. The model for bilateral alveolar cleft can be potentially applied in a controlled study in future.

Sources, Characteristics, and Therapeutic Applications of Mesenchymal Cells in Tissue Engineering

Tissue engineering (TE) is a therapeutic option within regenerative medicine that allows to mimic the original cell environment and functional organization of the cell types necessary for the recovery or regeneration of damaged tissue using cell sources, scaffolds, and bioreactors. Among the cell sources, the utilization of mesenchymal cells (MSCs) has gained great interest because these multipotent cells are capable of differentiating into diverse tissues, in addition to their self-renewal capacity to maintain their cell population, thus representing a therapeutic alternative for those diseases that can only be controlled with palliative treatments. This review aimed to summarize the state of the art of the main sources of MSCs as well as particular characteristics of each subtype and applications of MSCs in TE in seven different areas (neural, osseous, epithelial, cartilage, osteochondral, muscle, and cardiac) with a systemic revision of advances made in the last 10 years. It was observed that bone marrow-derived MSCs are the principal type of MSCs used in TE, and the most commonly employed techniques for MSCs characterization are immunodetection techniques. Moreover, the utilization of natural biomaterials is higher (41.96%) than that of synthetic biomaterials (18.75%) for the construction of the scaffolds in which cells are seeded. Further, this review shows alternatives of MSCs derived from other tissues and diverse strategies that can improve this area of regenerative medicine.

Characteristics of Large Animal Models for Current Cell-Based Oral Tissue Regeneration

The recent advances in the field of cell-based therapeutics open promising perspectives for oral tissue regeneration. The development of large animal models, which overcome the limits of the rodent models and allow to emulate clinical situations, is crucial for the validation of regenerative strategies to move toward clinical application. Currently, porcine, canine, and ovine models are mainly developed for oral regeneration and their specific characteristics have an impact on the outcomes of the studies. Thus, this systematic review investigates the application of porcine, canine, and ovine models in present cell-based oral regeneration, according to the species characteristics and the targeted tissue to regenerate. A customized search of PubMed, EMBASE, Scopus, and Web of Science databases from January 2015 to March 2020 was conducted. Relevant articles about cell-based oral tissues engineering in porcine, canine, and ovine models were evaluated. Among the evaluated articles, 58 relevant studies about cell-based oral regeneration in porcine, canine, and ovine models matched the eligibility criteria and were selected for full analysis. Porcine models, the most similar species with humans, were mostly used for bone and periodontium regeneration; tooth regeneration was reported only in pig, except for one study in dog. Canine models were the most transversal models, successfully involved for all oral tissue regeneration and notably in implantology. However, differences with humans and ethical concerns affect the use of these models. Ovine models, alternative to porcine and canine ones, were mainly used for bone and, scarcely, periodontium regeneration. The anatomy and physiology of these animals restrain their involvement. If consistency was found in defect specificities and cell trends among different species animal models of bone, dentin-pulp complex, or tooth regeneration, variability appeared in periodontium. Regeneration assessment methods were more elaborate in porcines and canines than in ovines. Risk of bias was low for selection, attrition and reporting, but unclear for performance and detection. Overall, if none of the large animal models can be considered an ideal one, they are of deemed importance for oral cell-based tissue engineering and researchers should consider their relevance to establish favorable conditions for a given preclinical cell-based therapeutics.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

Predifferentiated Gingival Stem Cell-Induced Bone Regeneration in Rat Alveolar Bone Defect Model

Cleft alveolus, a common birth defect of the maxillary bone, affects one in 700 live births every year. This defect is traditionally restored by autogenous bone grafts or allografts, which may possibly cause complications. Cell-based therapies using the mesenchymal stem cells (MSCs) derived from human gingiva (gingiva-derived mesenchymal stem cells [GMSCs]) is attracting the research interest due to their highly proliferative and multilineage differentiation capacity. Undifferentiated GMSCs expressed high level of MSC-distinctive surface antigens, including CD73, CD105, CD90, and CD166. Importantly, GMSCs induced with osteogenic medium for a week increased the surface markers of osteogenic phenotypes, such as CD10, CD92, and CD140b, indicating their osteogenic potential. The objective of this study was to assess the bone regenerative efficacy of predifferentiated GMSCs (dGMSCs) toward an osteogenic lineage in combination with a self-assembling hydrogel scaffold PuraMatrix™ (PM) and/or bone morphogenetic protein 2 (BMP2), on a rodent model of maxillary alveolar bone defect. A critical size maxillary alveolar defect of 7 mm × 1 mm × 1 mm was surgically created in athymic nude rats. The defect was filled with either PM/BMP2 or PM/dGMSCs or the combination of three (PM/dGMSCs/BMP2) and the bone regeneration was evaluated at 4 and 8 weeks postsurgery. New bone formation was evaluated by microcomputed tomography and histology using Hematoxylin and Eosin staining. The results demonstrated the absence of spontaneous bone healing, either at 4 or 8 weeks postsurgery in the defect group. However, the PM/dGMSCs/BMP2 group showed significant enhancement in bone regeneration at 4 and 8 weeks postsurgery, compared with the transplantation of individual material/cells alone. Apart from developing the smallest critical size defect, results showed that PM/dGMSCs/BMP2 could serve as a promising option for the regeneration of bone in the cranio/maxillofacial region in humans.

Use of Human Dental Pulp and Endothelial Cell Seeded Tyrosine-Derived Polycarbonate Scaffolds for Robust in vivo Alveolar Jaw Bone Regeneration

The ability to effectively repair craniomaxillofacial (CMF) bone defects in a fully functional and aesthetically pleasing manner is essential to maintain physical and psychological health. Current challenges for CMF repair therapies include the facts that craniofacial bones exhibit highly distinct properties as compared to axial and appendicular bones, including their unique sizes, shapes and contours, and mechanical properties that enable the ability to support teeth and withstand the strong forces of mastication. The study described here examined the ability for tyrosine-derived polycarbonate, E1001(1K)/β-TCP scaffolds seeded with human dental pulp stem cells (hDPSCs) and human umbilical vein endothelial cells (HUVECs) to repair critical sized alveolar bone defects in an in vivo rabbit mandible defect model. Human dental pulp stem cells are uniquely suited for use in CMF repair in that they are derived from the neural crest, which naturally contributes to CMF development. E1001(1k)/β-TCP scaffolds provide tunable mechanical and biodegradation properties, and are highly porous, consisting of interconnected macro- and micropores, to promote cell infiltration and attachment throughout the construct. Human dental pulp stem cells/HUVECs seeded and acellular E1001(1k)/β-TCP constructs were implanted for one and three months, harvested and analyzed by micro-computed tomography, then demineralized, processed and sectioned for histological and immunohistochemical analyses. Our results showed that hDPSC seeded E1001(1k)/β-TCP constructs to support the formation of osteodentin-like mineralized jawbone tissue closely resembling that of natural rabbit jaw bone. Although unseeded scaffolds supported limited alveolar bone regeneration, more robust and homogeneous bone formation was observed in hDPSC/HUVEC-seeded constructs, suggesting that hDPSCs/HUVECs contributed to enhanced bone formation. Importantly, bioengineered jaw bone recapitulated the characteristic morphology of natural rabbit jaw bone, was highly vascularized, and exhibited active remodeling by the presence of osteoblasts and osteoclasts on newly formed bone surfaces. In conclusion, these results demonstrate, for the first time, that E1001(1K)/ β-TCP scaffolds pre-seeded with human hDPSCs and HUVECs contributed to enhanced bone formation in an in vivo rabbit mandible defect repair model as compared to acellular E1001(1K)/β-TCP constructs. These studies demonstrate the utility of hDPSC/HUVEC-seeded E1001(1K)/β-TCP scaffolds as a potentially superior clinically relevant therapy to repair craniomaxillofacial bone defects.

Dipyridamole-loaded 3D-printed bioceramic scaffolds stimulate pediatric bone regeneration in vivo without disruption of craniofacial growth through facial maturity

This study investigates a comprehensive model of bone regeneration capacity of dypiridamole-loaded 3D-printed bioceramic (DIPY-3DPBC) scaffolds composed of 100% beta-tricalcium phosphate (β -TCP) in an immature rabbit model through the time of facial maturity. The efficacy of this construct was compared to autologous bone graft, the clinical standard of care in pediatric craniofacial reconstruction, with attention paid to volume of regenerated bone by 3D reconstruction, histologic and mechanical properties of regenerated bone, and long-term safety regarding potential craniofacial growth restriction. Additionally, long-term degradation of scaffold constructs was evaluated. At 24 weeks in vivo, DIPY-3DPBC scaffolds demonstrated volumetrically significant osteogenic regeneration of calvarial and alveolar defects comparable to autogenous bone graft with favorable biodegradation of the bioactive ceramic component in vivo. Characterization of regenerated bone reveals osteogenesis of organized, vascularized bone with histologic and mechanical characteristics comparable to native bone. Radiographic and histologic analyses were consistent with patent craniofacial sutures. Lastly, through application of 3D morphometric facial surface analysis, our results support that DIPY-3DPBC scaffolds do not cause premature closure of sutures and preserve normal craniofacial growth. Based on this novel evaluation model, this DIPY-3DPBC scaffold strategy is a promising candidate as a safe, efficacious pediatric bone tissue engineering strategy.

Functional organic cation transporters mediate osteogenic response to metformin in human umbilical cord mesenchymal stromal cells

BACKGROUND

Compelling evidence indicates that metformin, a low-cost and safe orally administered biguanide prescribed to millions of type 2 diabetics worldwide, induces the osteoblastic differentiation of mesenchymal stromal cells (MSCs) through the 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway. As a highly hydrophilic cationic compound, metformin uptake is facilitated by cell membrane organic cation transporters (OCTs) of the solute carrier 22A gene family. We hypothesized that to effectively enhance osteogenic differentiation, and ultimately bone regeneration, metformin must gain access into functional OCT-expressing MSCs.

METHODS

Data was obtained through immunoblotting, cellular uptake, mineralization and gene expression assays.

RESULTS

We demonstrate for the first time that functional OCTs are expressed in human-derived MSCs from umbilical cord Wharton's jelly, an inexhaustible source of nonembryonic MSCs with proven osteogenic potential. A clinically relevant concentration of metformin led to AMPK activation, enhanced mineralized nodule formation and increased expression of the osteogenic transcription factor Runt-related transcription factor 2 (RUNX2). Indeed, targeting OCT function through pharmacological and genetic approaches markedly blunted these responses.

CONCLUSIONS

Our findings indicate that functional OCT expression in UC-MSCs is a biological prerequisite that facilitates the intracellular uptake of metformin to induce an osteogenic effect. Future pre-clinical studies are warranted to investigate whether the expression of functional OCTs may serve as a potential biomarker to predict osteogenic responses to metformin.