Repair of bone defects using a new biomimetic construction fabricated by adipose-derived stem cells, collagen I, and porous beta-tricalcium phosphate scaffolds

Direct inkjet writing type 1 bovine collagen/β-tricalcium phosphate scaffolds for bone regeneration

Bone tissue has the capacity to regenerate under healthy conditions, but complex cases like critically sized defects hinder natural bone regeneration, necessitating surgery, and use of a grafting material for rehabilitation. The field of bone tissue engineering (BTE) has pioneered ways to address such issues utilizing different biomaterials to create a platform for cell migration and tissue formation, leading to improved bone reconstruction. One such approach involves 3D-printed patient-specific scaffolds designed to aid in regeneration of boney defects. This study aimed to develop and characterize 3D printed scaffolds composed of type I collagen augmented with β-tricalcium phosphate (COL/β-TCP). A custom-built direct inkjet write (DIW) printer was used to fabricate β-TCP, COL, and COL/β-TCP scaffolds using synthesized colloidal gels. After chemical crosslinking, the scaffolds were lyophilized and subjected to several characterization techniques, including light microscopy, scanning electron microscopy, and x-ray diffraction to evaluate morphological and chemical properties. In vitro evaluation was performed using human osteoprogenitor cells to assess cytotoxicity and proliferative capacity of the different scaffold types. Characterization results confirmed the presence of β-TCP in the 3D printed COL/β-TCP scaffolds, which exhibited crystals that were attributed to β-TCP due to the presence of calcium and phosphorus, detected through energy dispersive x-ray spectroscopy. In vitro studies showed that the COL/β-TCP scaffolds yielded more favorable results in terms of cell viability and proliferation compared to β-TCP and COL scaffolds. The novel COL/β-TCP scaffold constructs hold promise for improving BTE applications and may offer a superior environment for bone regeneration compared with conventional COL and β-TCP scaffolds.

Remotely Temporal Scheduled Macrophage Phenotypic Transition Enables Optimized Immunomodulatory Bone Regeneration

Precise timing of macrophage polarization plays a pivotal role in immunomodulation of tissue regeneration, yet most studies mainly focus on M2 macrophages for their anti-inflammatory and regenerative effects while the essential proinflammatory role of the M1 phenotype on the early inflammation stage is largely underestimated. Herein, a superparamagnetic hydrogel capable of timely controlling macrophage polarization is constructed by grafting superparamagnetic nanoparticles on collagen nanofibers. The magnetic responsive hydrogel network enables efficient polarization of encapsulated macrophage to the M2 phenotype through the podosome/Rho/ROCK mechanical pathway in response to static magnetic field (MF) as needed. Taking advantage of remote accessibility of magnetic field together with the superparamagnetic hydrogels, a temporal engineered M1 to M2 transition course preserving the essential role of M1 at the early stage of tissue healing, as well as enhancing the prohealing effect of M2 at the middle/late stages is established via delayed MF switch. Such precise timing of macrophage polarization matching the regenerative process of injured tissue eventually leads to optimized immunomodulatory bone healing in vivo. Overall, this study offers a remotely time-scheduled approach for macrophage polarization, which enables precise manipulation of inflammation progression during tissue healing.

Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment

Bi-phasic calcium phosphates (BCPs) are considered prominent candidate materials for the fabrication of bone graft substitutes. Currently, supplemental cation-doping is suggested as a powerful path to boost biofunctionality, however, there is still a lack of knowledge on the structural role of such substituents in BCPs, which in turn, could influence the intensity and extent of the biological effects. In this work, pure and Mg- and Sr-doped BCP scaffolds were fabricated by robocasting from hydrothermally synthesized powders, and then preliminarily tested in vitro and thoroughly investigated physically and chemically. Collectively, the osteoblast cell culture assays indicated that all types of BCP scaffolds (pure, Sr- or Sr–Mg-doped) delivered in vitro performances similar to the biological control, with emphasis on the Sr–Mg-doped ones. An important result was that double Mg–Sr doping obtained the ceramic with the highest β-tricalcium phosphate (β-TCP)/hydroxyapatite mass concentration ratio of ~1.8. Remarkably, Mg and Sr were found to be predominantly incorporated in the β-TCP lattice. These findings could be important for the future development of BCP-based bone graft substitutes since the higher dissolution rate of β-TCP enables an easier release of the therapeutic ions. This may pave the road toward medical devices with more predictable in vivo performance.

Is induced membrane technique effective in reconstruction of mandibular segmental bone defects? An experimental study

This study aimed to compare the effectiveness of different graft materials using induced membrane technique for reconstruction of mandibular segmental bone defects. New Zealand rabbits were used as the experimental animal. As first-stage surgical procedure, segmental bone defects were created at the lower border of the mandibula in all groups. Polymethylmethacrylate (PMMA) cement was inserted into the defects. After 6 weeks, PMMA cement was removed in all groups. In the Control group, defect areas were left empty. Defects were filled with autogenous graft in the Autograft group, xenograft in the Xenograft group, and a mixture of autogenous graft and xenograft in the Autograft + Xenograft group. Histopathological, stereological, and immunohistochemical analyses were performed. A total of 40 New Zealand rabbits were used. Rabbits were randomly divided into four subgroups as Control, Autograft, Xenograft and Autograft + Xenograft groups (n = 10). When the groups were compared in terms of newly formed bone tissue volumes, significant difference was found between the Control group and Autograft group, Xenograft group and Autograft + Xenograft group (p < 0.001, p < 0.001, p = 0.003). The results of immunohistochemical examination were consistent with this finding. Stereological and immunohistochemical results can be used as a justification to adopt the induced membrane technique on an experimental basis in humans when it comes to the reconstruction of small segmental mandibular defects.

Assessment of stem cell viability in the initial healing period in rabbits with a cranial bone defect according to the type and form of scaffold

Purpose

Increased bone regeneration has been achieved through the use of stem cells in combination with graft material. However, the survival of transplanted stem cells remains a major concern. The purpose of this study was to evaluate the viability of transplanted mesenchymal stem cells (MSCs) at an early time point (24 hours) based on the type and form of the scaffold used, including type I collagen membrane and synthetic bone.

Methods

The stem cells were obtained from the periosteum of the otherwise healthy dental patients. Four symmetrical circular defects measuring 6 mm in diameter were made in New Zealand white rabbits using a trephine drill. The defects were grafted with 1) synthetic bone (β-tricalcium phosphate/hydroxyapatite [β-TCP/HA]) and 1×10⁵ MSCs, 2) collagen membrane and 1×10⁵ MSCs, 3) β-TCP/HA+collagen membrane and 1×10⁵ MSCs, or 4) β-TCP/HA, a chipped collagen membrane and 1×10⁵ MSCs. Cellular viability and the cell migration rate were analyzed.

Results

Cells were easily separated from the collagen membrane, but not from synthetic bone. The number of stem cells attached to synthetic bone in groups 1, 3, and 4 seemed to be similar. Cellular viability in group 2 was significantly higher than in the other groups (P<0.05). The cell migration rate was highest in group 2, but this difference was not statistically significant (P>0.05).

Conclusions

This study showed that stem cells can be applied when a membrane is used as a scaffold under no or minimal pressure. When space maintenance is needed, stem cells can be loaded onto synthetic bone with a chipped membrane to enhance the survival rate.

Adult Stem Cells Spheroids to Optimize Cell Colonization in Scaffolds for Cartilage and Bone Tissue Engineering

Top-down tissue engineering aims to produce functional tissues using biomaterials as scaffolds, thus providing cues for cell proliferation and differentiation. Conversely, the bottom-up approach aims to precondition cells to form modular tissues units (building-blocks) represented by spheroids. In spheroid culture, adult stem cells are responsible for their extracellular matrix synthesis, re-creating structures at the tissue level. Spheroids from adult stem cells can be considered as organoids, since stem cells recapitulate differentiation pathways and also represent a promising approach for identifying new molecular targets (biomarkers) for diagnosis and therapy. Currently, spheroids can be used for scaffold-free (developmental engineering) or scaffold-based approaches. The scaffold promotes better spatial organization of individual spheroids and provides a defined geometry for their 3D assembly in larger and complex tissues. Furthermore, spheroids exhibit potent angiogenic and vasculogenic capacity and serve as efficient vascularization units in porous scaffolds for bone tissue engineering. An automated combinatorial approach that integrates spheroids into scaffolds is starting to be investigated for macro-scale tissue biofabrication.

The Role of Fibroblast Growth Factors in Tooth Development and Incisor Renewal

The mineralized tissue of the tooth is composed of enamel, dentin, cementum, and alveolar bone; enamel is a calcified tissue with no living cells that originates from oral ectoderm, while the three other tissues derive from the cranial neural crest. The fibroblast growth factors (FGFs) are critical during the tooth development. Accumulating evidence has shown that the formation of dental tissues, that is, enamel, dentin, and supporting alveolar bone, as well as the development and homeostasis of the stem cells in the continuously growing mouse incisor is mediated by multiple FGF family members. This review discusses the role of FGF signaling in these mineralized tissues, trying to separate its different functions and highlighting the crosstalk between FGFs and other signaling pathways.

Prevascularization of 3D printed bone scaffolds by bioactive hydrogels and cell co-culture

Vascularization is a fundamental prerequisite for large bone construct development and remains one of the main challenges of bone tissue engineering. Our current study presents the combination of 3D printing technique with a hydrogel-based prevascularization strategy to generate prevascularized bone constructs. Human adipose derived mesenchymal stem cells (ADMSC) and human umbilical vein endothelial cells (HUVEC) were encapsulated within our bioactive hydrogels, and the effects of culture conditions on in vitro vascularization were determined. We further generated composite constructs by forming 3D printed polycaprolactone/hydroxyapatite scaffolds coated with cell-laden hydrogels and determined how the co-culture affected vascularization and osteogenesis. It was demonstrated that 3D co-cultured ADMSC-HUVEC generated capillary-like networks within the porous 3D printed scaffold. The co-culture systems promoted in vitro vascularization, but had no significant effects on osteogenesis. The prevascularized constructs were subcutaneously implanted into nude mice to evaluate the in vivo vascularization capacity and the functionality of engineered vessels. The hydrogel systems facilitated microvessel and lumen formation and promoted anastomosis of vascular networks of human origin with host murine vasculature. These findings demonstrate the potential of prevascularized 3D printed scaffolds with anatomical shape for the healing of larger bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1788-1798, 2018.

The performance of bone tissue engineering scaffolds in in vivo animal models: A systematic review

Bone tissue engineering is an excellent alternative for the regeneration of large bone defects caused by trauma or bone pathologies. Scaffolds, stem cells, and bioactive molecules are the three key components of bone regeneration. Although a wide range of biomaterials of various compositions and structures has been proposed in the literature, these materials are rarely used in clinical applications. Therefore, more standardized studies are required to design scaffolds that enable better bone regeneration and are suitable for clinical use. The aim of this systematic review was to compare the performance of scaffolds used in preclinical animal studies to determine which class of materials has achieved a higher rate of bone neoformation (osteoinduction and osteoconduction). The selected studies were divided into three groups according to the following experimental models: studies that used subcutaneous models, bone defects in calvaria, and bone defects in long bones. Despite the large number of parameters in the included studies, we generally concluded that biomaterials containing calcium phosphates had important osteoinductive effects and were essential for better performance of the materials. Furthermore, natural polymers generally had better performance than synthetic polymers did, especially when the materials were associated with stem cells. The combination of materials from different classes was the most promising strategy for bone tissue regeneration.

Strategies to engineer tendon/ligament-to-bone interface: Biomaterials, cells and growth factors

Integration between tendon/ligament and bone occurs through a specialized tissue interface called enthesis. The complex and heterogeneous structure of the enthesis is essential to ensure smooth mechanical stress transfer between bone and soft tissues. Following injury, the interface is not regenerated, resulting in high rupture recurrence rates. Tissue engineering is a promising strategy for the regeneration of a functional enthesis. However, the complex structural and cellular composition of the native interface makes enthesis tissue engineering particularly challenging. Thus, it is likely that a combination of biomaterials and cells stimulated with appropriate biochemical and mechanical cues will be needed. The objective of this review is to describe the current state-of-the-art, challenges and future directions in the field of enthesis tissue engineering focusing on four key parameters: (1) scaffold and biomaterials, (2) cells, (3) growth factors and (4) mechanical stimuli.

Repair of urethral defects with polylactid acid fibrous membrane seeded with adipose-derived stem cells in a rabbit model

AIM

The aim of this study is to evaluate the capacity of polylactid acid (PLA) fibrous membrane seeded with allogeneic rabbit adipose tissue-derived stem cells (ADSCs) to repair urethral defects in a rabbit model.

MATERIALS AND METHODS

Rabbit ADSCs were harvested and phenotypically characterized. Twenty-four New Zealand male rabbits with 5-mm urethral mucosal defects were randomly divided into two groups. They underwent urethroplasty either with PLA fibrous membrane seeded with ADSCs (group A) or blank PLA fibrous membrane (group B). At 4 and 6 weeks after urethroplasty, the urethral grafts were collected and analyzed grossly and histologically. The incidence rate of urethrostenosis was measured.

RESULTS

The adipose tissue-derived cells in monolayer culture showed a typical morphology of mesenchymal stem cells (MSCs). They were positive for the MSC marker CD44 but negative for lineage markers CD45 and CD105. Six weeks after surgery, the incidence rate of urethrostenosis in group A was significantly lower than that in group B (p < 0.05). In group A, the ADSC-seeded grafts showed a normal urethral architecture with a thickened muscle layer. In contrast, the newly developed urethra in group B demonstrated a fewer number of urothelial layers and scarce or no smooth muscle cells.

CONCLUSION

The PLA scaffold seeded with ADSCs is effective in urethral regeneration in a rabbit model. ADSCs may represent a promising source of seed cells for urethral tissue engineering.

The effect of mechanical stimulation on mineralization in differentiating osteoblasts in collagen-I scaffolds

Developing a viable and functional bone scaffold in vitro that is capable of surviving and bearing mechanical load in vivo requires an understanding of the cell biology of osteoprogenitor cells, particularly how they are influenced by mechanical stimulation during cell differentiation and maturation. In this study, mechanical load was applied using a modified FlexCell plate to impart confined compression to collagen-I scaffolds seeded with undifferentiated murine embryonic stem cells. The activity, presence, and expression of osteoblast-cadherin (OB-Cad) and connexin-43, as well as various pluripotent and osteogenic markers were examined at 5-30 days of differentiation as cells were stimulated to differentiate to osteoblasts with and without applied mechanical load. Fluorescence recovery after photobleaching, immunofluorescence, viability, von Kossa, and real-time polymerase chain reaction assessments revealed that mechanical prestimulation of this cell-seeded scaffold altered the expression of OB-Cad and connexin-43 and resulted in significant differences in the structure and organization of mineralization present in the collagen matrix. Specifically, cells in gels that were loaded for 40 h after 5 days of differentiation and then left to fully differentiate for 30 days produced a highly structured honeycomb-shaped mineralization in the matrix; an outcome that was previously shown to be indicative of late osteoblast/early osteocyte activity. This study highlights the potential of mechanical load to accelerate differentiation and enhance osteoblast communication and function during the differentiation process, and highlights a time point of cell differentiation within this scaffold to apply load in order to most effectively transduce a mechanical signal.

Evaluation of the ability of natural and synthetic scaffolds in providing an appropriate environment for growth and chondrogenic differentiation of adipose-derived mesenchymal stem cells

BACKGROUND

Although progenitor cells have been observed in articular cartilage, this part has a limited ability to repair due to a lack of blood supply. Formerly, tissue engineering was mainly based on collecting chondrocytes from the joint surface, culturing them on resorbable scaffolds such as poly D, L-lactic glycolic acid (PLGA) and then autologous transplantation. In recent times, due to difficulties in collecting chondrocytes, most of the researchers are focused on stem cells for producing these cells. Among the important factors in this approach, is using appropriate scaffolds with good mechanical and biological properties to provide optimal environment for growth and development of stem cells. In this study, we evaluated the potential of fibrin glue, PLGA and alginate scaffolds in providing a suitable environment for growth and chondrogenic differentiation of mesenchymal stem cells (MSCs) in the presence of transforming growth factor-β3.

MATERIALS AND METHODS

Fibrin glue, PLGA and alginate scaffolds were prepared and MSCs were isolated from human adipose tissue. Cells were cultured separately on the scaffolds and 2 weeks after differentiation, chondrogenic genes, cell proliferation ability and morphology in each scaffold were evaluated using real time-polymerase chain reaction, MTT chondrogenic assay and histological examination, respectively.

RESULTS

Proliferation of differentiated adipose tissue derived mesenchymal stem cells (AD-MSCs) to chondrogenic cells in Fibrin glue were significantly higher than in other scaffolds. Also, Fibrin glue caused the highest expression of chondrogenic genes compared to the other scaffolds. Histological examination revealed that the pores of the Fibrin glue scaffolds were filled with cells uniformly distributed.

CONCLUSION

According to the results of the study, it can be concluded that natural scaffolds such as fibrin can be used as an appropriate environment for cartilage differentiation.

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

INTRODUCTION

Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

AREAS COVERED

In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

EXPERT OPINION

Enhanced results have been found when combining bone marrow-derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue-derived stem cells and umbilical cord tissue-derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.

Stem cell regenerative therapy in alveolar cleft reconstruction

Achieving a successful and well-functioning reconstruction of craniofacial deformities still remains a challenge. As for now, autologous bone grafting remains the gold standard for alveolar cleft reconstruction. However, its aesthetic and functional results often remain unsatisfactory, which carries a long-term psychosocial and medical sequelae. Therefore, searching for novel therapeutic approaches is strongly indicated. With the recent advances in stem cell research, cell-based tissue engineering strategies move from the bench to the patients' bedside. Successful stem cell engineering employs a carefully selected stem cell source, a biodegradable scaffold with osteoconductive and osteoinductive properties, as well as an addition of growth factors or cytokines to enhance osteogenesis. This review highlights recent advances in mesenchymal stem cell tissue engineering, discusses animal models and case reports of stem cell enhanced bone regeneration, as well as ongoing clinical trials.

Human Adipose Stem Cells: From Bench to Bedside

Stem cell-based therapies for repair and regeneration of different tissues are becoming more important in the treatment of several diseases. Adult stem cells currently symbolize the most available source of cell progenitors for tissue engineering and repair and can be harvested using minimally invasive procedures. Moreover, mesenchymal stem cells (MSCs), the most widely used stem cells in stem cell-based therapies, are multipotent progenitors, with capability to differentiate into cartilage, bone, connective, muscle, and adipose tissue. So far, bone marrow has been regarded as the main source of MSCs. To date, human adult adipose tissue may be the best suitable alternative source of MSCs. Adipose stem cells (ASCs) can be largely extracted from subcutaneous human adult adipose tissue. A large number of studies show that adipose tissue contains a biologically and clinically interesting heterogeneous cell population called stromal vascular fraction (SVF). The SVF may be employed directly or cultured for selection and expansion of an adherent population, so called adipose-derived stem cells (ASCs). In recent years, literature based on data related to SVF cells and ASCs has augmented considerably: These studies have demonstrated the efficacy and safety of SVF cells and ASCs in vivo in animal models. On the basis of these observations, in several countries, various clinical trials involving SVF cells and ASCs have been permitted. This review aims at summarizing data regarding either ASCs cellular biology or ASCs-based clinical trials and at discussing the possible future clinical translation of ASCs and their potentiality in cell-based tissue engineering.

Advances in biology and mechanics of rotator cuff repair

High initial fixation strength, mechanical stability and biological healing of the tendon-to-bone interface are the main goals after rotator cuff repair surgery. Advances in the understanding of rotator cuff biology and biomechanics as well as improvements in surgical techniques have led to the development of new strategies that may allow a tendon-to-bone interface healing process, rather than the formation of a fibrovascular scar tissue. Although single-row repair remains the most cost-effective technique to address a rotator cuff tear, some biological intervention has been recently introduced to improve tissue healing and clinical outcome of rotator cuff repair. Animal models are critical to ensure safety and efficacy of new treatment strategies; however, although rat shoulders as well as sheep and goats are considered the most appropriate models for studying rotator cuff pathology, no one of them can fully reproduce the human condition. Emerging therapies involve growth factors, stem cells and tissue engineering. Experimental application of growth factors and platelet-rich plasma demonstrated promising results, but has not yet been transferred into standardized clinical practice. Although preclinical animal studies showed promising results on the efficacy of enhanced biological approaches, application of these techniques in human rotator cuff repairs is still very limited. Randomized controlled clinical trials and post-marketing surveillance are needed to clearly prove the clinical efficacy and define proper indications for the use of combined biological approaches. The following review article outlines the state of the art of rotator cuff repair and the use of growth factors, scaffolds and stem cells therapy, providing future directions to improve tendon healing after rotator cuff repair.

LEVEL OF EVIDENCE

Expert opinion, Level V.

Current concepts of bone tissue engineering for craniofacial bone defect repair

Craniofacial fractures and bony defects are common causes of morbidity and contribute to increasing health care costs. Successful regeneration of bone requires the concomitant processes of osteogenesis and neovascularization. Current methods of repair and reconstruction include rigid fixation, grafting, and free tissue transfer. However, these methods carry innate complications, including plate extrusion, nonunion, graft/flap failure, and donor site morbidity. Recent research efforts have focused on using stem cells and synthetic scaffolds to heal critical-sized bone defects similar to those sustained from traumatic injury or ablative oncologic surgery. Growth factors can be used to augment both osteogenesis and neovascularization across these defects. Many different growth factor delivery techniques and scaffold compositions have been explored yet none have emerged as the universally accepted standard. In this review, we will discuss the recent literature regarding the use of stem cells, growth factors, and synthetic scaffolds as alternative methods of craniofacial fracture repair.

Repair of Achilles tendon defect with autologous ASCs engineered tendon in a rabbit model

Adipose derived stem cells (ASCs) are an important cell source for tissue regeneration and have been demonstrated the potential of tenogenic differentiation in vitro. This study explored the feasibility of using ASCs for engineered tendon repair in vivo in a rabbit Achilles tendon model. Total 30 rabbits were involved in this study. A composite tendon scaffold composed of an inner part of polyglycolic acid (PGA) unwoven fibers and an outer part of a net knitted with PGA/PLA (polylactic acid) fibers was used to provide mechanical strength. Autologous ASCs were harvested from nuchal subcutaneous adipose tissues and in vitro expanded. The expanded ASCs were harvested and resuspended in culture medium and evenly seeded onto the scaffold in the experimental group, whereas cell-free scaffolds served as the control group. The constructs of both groups were cultured inside a bioreactor under dynamic stretch for 5 weeks. In each of 30 rabbits, a 2 cm defect was created on right side of Achilles tendon followed by the transplantation of a 3 cm cell-seeded scaffold in the experimental group of 15 rabbits, or by the transplantation of a 3 cm cell-free scaffold in the control group of 15 rabbits. Animals were sacrificed at 12, 21 and 45 weeks post-surgery for gross view, histology, and mechanical analysis. The results showed that short term in vitro culture enabled ASCs to produce matrix on the PGA fibers and the constructs showed tensile strength around 50 MPa in both groups (p > 0.05). With the increase of implantation time, cell-seeded constructs gradually form neo-tendon and became more mature at 45 weeks with histological structure similar to that of native tendon and with the presence of bipolar pattern and D-periodic structure of formed collagen fibrils. Additionally, both collagen fibril diameters and tensile strength increased continuously with significant difference among different time points (p < 0.05). In contrast, cell-free constructs failed to form good quality tendon tissue with fibril structure observable only at 45 weeks. There were significant differences in both collagen fibril diameter and tensile strength between two groups at all examined time points (p < 0.05). The results of this study support that ASCs are likely to be a potential cell source for in vivo tendon engineering and regeneration.

Bone regenerative medicine: classic options, novel strategies, and future directions

This review analyzes the literature of bone grafts and introduces tissue engineering as a strategy in this field of orthopedic surgery. We evaluated articles concerning bone grafts; analyzed characteristics, advantages, and limitations of the grafts; and provided explanations about bone-tissue engineering technologies. Many bone grafting materials are available to enhance bone healing and regeneration, from bone autografts to graft substitutes; they can be used alone or in combination. Autografts are the gold standard for this purpose, since they provide osteogenic cells, osteoinductive growth factors, and an osteoconductive scaffold, all essential for new bone growth. Autografts carry the limitations of morbidity at the harvesting site and limited availability. Allografts and xenografts carry the risk of disease transmission and rejection. Tissue engineering is a new and developing option that had been introduced to reduce limitations of bone grafts and improve the healing processes of the bone fractures and defects. The combined use of scaffolds, healing promoting factors, together with gene therapy, and, more recently, three-dimensional printing of tissue-engineered constructs may open new insights in the near future.

Bone regenerative medicine: classic options, novel strategies, and future directions

This review analyzes the literature of bone grafts and introduces tissue engineering as a strategy in this field of orthopedic surgery. We evaluated articles concerning bone grafts; analyzed characteristics, advantages, and limitations of the grafts; and provided explanations about bone-tissue engineering technologies. Many bone grafting materials are available to enhance bone healing and regeneration, from bone autografts to graft substitutes; they can be used alone or in combination. Autografts are the gold standard for this purpose, since they provide osteogenic cells, osteoinductive growth factors, and an osteoconductive scaffold, all essential for new bone growth. Autografts carry the limitations of morbidity at the harvesting site and limited availability. Allografts and xenografts carry the risk of disease transmission and rejection. Tissue engineering is a new and developing option that had been introduced to reduce limitations of bone grafts and improve the healing processes of the bone fractures and defects. The combined use of scaffolds, healing promoting factors, together with gene therapy, and, more recently, three-dimensional printing of tissue-engineered constructs may open new insights in the near future.