Tissue engineering strategies for the treatment of tendon injuries: a systematic review and meta-analysis of animal models

Current clinical opinion on surgical approaches and rehabilitation of hand flexor tendon injury-a questionnaire study

The management of flexor tendon injury has seen many iterations over the years, but more substantial innovations in practice have been sadly lacking. The aim of this study was to investigate the current practice of flexor tendon injury management, and variation in practice from the previous reports, most troublesome complications, and whether there was a clinical interest in potential innovative tendon repair technologies. An online survey was distributed via the British Society for Surgery of the Hand (BSSH) and a total of 132 responses were collected anonymously. Results showed that although most surgeons followed the current medical recommendation based on the literature, a significant number of surgeons still employed more conventional treatments in clinic, such as general anesthesia, ineffective tendon retrieval techniques, and passive rehabilitation. Complications including adhesion formation and re-rupture remained persistent. The interest in new approaches such as use of minimally invasive instruments, biodegradable materials and additive manufactured devices was not strong, however the surgeons were potentially open to more effective and economic solutions.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

Anisotropic wood-hydrogel composites: Extending mechanical properties of wood towards soft materials' applications

Delignified wood (DW) offers a versatile platform for the manufacturing of composites, with material properties ranging from stiff to soft and flexible by preserving the preferential fiber directionality of natural wood through a structure-retaining production process. This study presents a facile method for fabricating anisotropic and mechanically tunable DW-hydrogel composites. These composites were produced by infiltrating delignified spruce wood with an aqueous gelatin solution followed by chemical crosslinking. The mechanical properties could be modulated across a broad strength and stiffness range (1.2-18.3 MPa and 170-1455 MPa, respectively) by varying the crosslinking time. The diffusion-led crosslinking further allowed to manufacture mechanically graded structures. The resulting uniaxial, tubular structure of the anisotropic DW-hydrogel composite enabled the alignment of murine fibroblasts in vitro, which could be utilized in future studies on potential applications in tissue engineering.

Bioactive Nanostructured Scaffold-Based Approach for Tendon and Ligament Tissue Engineering

An effective therapeutic strategy to treat tendon or ligament injury continues to be a clinical challenge due to the limited natural healing capacity of these tissues. Furthermore, the repaired tendons or ligaments usually possess inferior mechanical properties and impaired functions. Tissue engineering can restore the physiological functions of tissues using biomaterials, cells, and suitable biochemical signals. It has produced encouraging clinical outcomes, forming tendon or ligament-like tissues with similar compositional, structural, and functional attributes to the native tissues. This paper starts by reviewing tendon/ligament structure and healing mechanisms, followed by describing the bioactive nanostructured scaffolds used in tendon and ligament tissue engineering, with emphasis on electrospun fibrous scaffolds. The natural and synthetic polymers for scaffold preparation, as well as the biological and physical cues offered by incorporating growth factors in the scaffolds or by dynamic cyclic stretching of the scaffolds, are also covered. It is expected to present a comprehensive clinical, biological, and biomaterial insight into advanced tissue engineering-based therapeutics for tendon and ligament repair.

Efficacy of electro-acupuncture in postpartum with diastasis recti abdominis: A randomized controlled clinical trial

Background

Electro-acupuncture (EA) has promising effects on diastasis rectus abdominis (DRA), defined as a separation of the two muscle bellies of rectus abdominis. To study, there is scant knowledge or scarce high-quality evidence.

Objective

We aimed to evaluate the long-term efficacy and safety of EA in treating DRA during postpartum. It was assumed that the improvement of DRA was more obvious in the EA group than in the control group.

Design

Randomized, controlled, blinded trial (Clinical Trial Registration: ChiCTR2100041891).

Setting

Hangzhou Hospital of Traditional Chinese Medicine in China.

Participants

Females aged 20-45 years without a past medical history of pathological rectus abdominal dissection were recruited from DRA inclusion criteria from 42 days to 1 year postpartum.

Intervention

110 participants were randomly assigned in a 1:1 ratio to a control group with no EA intervention (n = 55), and EA group (n = 55). The EA group received ten sessions of EA combined with physical exercise or only physical exercise for 2 weeks with a 26-week follow-up.

Measurements

Outcomes were assessed at baseline, week 2, and week 26. The primary outcome was the change of the inter recti distance (IRD) and electromyographic evaluation of the pelvic floor. Secondary outcomes included elasticity of linea alba (LA), paraumbilical subcutaneous adipose tissue (SAT) measurement, body mass index (BMI), percentage body fat (F%), dyspepsia symptoms, menstrual symptoms, quality of life (QoL), pain performance of patients with lower back pain, postnatal depression symptoms (PDS), postpartum self-image, and DRA-related symptom assessment including urine leakage, frequency, and urgency, constipation, sexual dysfunction, and chronic pelvic pain.

Results

A total of 110 maternal (55 in each group) were recruited. The mean difference in IRD from baseline to week 2 and week 26 in all states of the two groups were reduced compared with those before treatment, with statistical significance (P < 0.05). The mean of IRD at the horizontal line of the umbilicus in the end-expiratory state was smaller in the EA group than in the control group, but the difference was not statistically significant (P > 0.05) at week 2. The mean of IRD at the horizontal line of the umbilicus in head-up and flexed knee state was smaller in the EA group than in the control group, and the difference was statistically significant (P < 0.05) at week 26. Five (9.1%) and thirteen (23.64%) adverse events were reported in EA and control groups, respectively. No serious adverse events were reported.

Limitation

The frequency intensity of EA parameters was selected between 4 and 6 because of individual tolerance differences.

Conclusion

EA is an effective approach to improve IRD, electromyographic evaluation of the pelvic floor, BMI, the elasticity of LA, paraumbilical SAT, and symptoms of DRA, with durable effects at 26 weeks.

Primary funding source

The Construction Fund of Medical Key Disciplines of Hangzhou (Project Number: OO20200097), Hangzhou Medical and Health Science and Technology Project No. A20200483, and Zhejiang Traditional Chinese Medicine Science and Technology Plan Project (Project Number: 2021ZQ065).

Clinical trial registration

http://www.chictr.org.cn/index.aspx, identifier: ChiCTR2100041891.

Tendon 3D Scaffolds Establish a Tailored Microenvironment Instructing Paracrine Mediated Regenerative Amniotic Epithelial Stem Cells Potential

Tendon tissue engineering aims to develop effective implantable scaffolds, with ideally the native tissue’s characteristics, able to drive tissue regeneration. This research focused on fabricating tendon-like PLGA 3D biomimetic scaffolds with highly aligned fibers and verifying their influence on the biological potential of amniotic epithelial stem cells (AECs), in terms of tenodifferentiation and immunomodulation, with respect to fleeces. The produced 3D scaffolds better resemble native tendon tissue, both macroscopically, microscopically, and biomechanically. From a biological point of view, these constructs were able to instruct AECs genotypically and phenotypically. In fact, cells engineered on 3D scaffolds acquired an elongated tenocyte-like morphology; this was different from control AECs, which retained their polygonal morphology. The boosted AECs tenodifferentiation by 3D scaffolds was confirmed by the upregulation of tendon-related genes (SCX, COL1 and TNMD) and TNMD protein expression. The produced constructs also prompted AECs’ immunomodulatory potential, both at the gene and paracrine level. This enhanced immunomodulatory profile was confirmed by a greater stimulatory effect on THP-1-activated macrophages. These biological effects have been related to the mechanotransducer YAP activation evidenced by its nuclear translocation. Overall, these results support the biomimicry of PLGA 3D scaffolds, revealing that not only fiber alignment but also scaffold topology provide an in vitro favorable tenodifferentiative and immunomodulatory microenvironment for AECs that could potentially stimulate tendon regeneration.

Basic Quality Controls Used in Skin Tissue Engineering

Reconstruction of skin defects is often a challenging effort due to the currently limited reconstructive options. In this sense, tissue engineering has emerged as a possible alternative to replace or repair diseased or damaged tissues from the patient's own cells. A substantial number of tissue-engineered skin substitutes (TESSs) have been conceived and evaluated in vitro and in vivo showing promising results in the preclinical stage. However, only a few constructs have been used in the clinic. The lack of standardization in evaluation methods employed may in part be responsible for this discrepancy. This review covers the most well-known and up-to-date methods for evaluating the optimization of new TESSs and orientative guidelines for the evaluation of TESSs are proposed.

Autologous bone marrow-derived mesenchymal stem cells provide complete regeneration in a rabbit model of the Achilles tendon bundle rupture

PURPOSE

To ascertain the role of autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) in the tendon regeneration.

METHODS

The study was conducted on 58 Achilles tendons from 29 laboratory Chinchilla adult rabbits. The central bundles of 48 tendons were partially removed and substituted with a tissue-engineered construct consisting of a collagen sponge either loaded with BM-MSCs (n = 24) or cell free (n = 24), placed inside a Vicryl mesh tube. The ends of the resected tendon were inserted in the construct to reach a direct contact with the sponge and sutured to the tube. The animals were sacrificed three and six months post-surgery. Ten intact tendons from five rabbits were used as an untreated control. The tissue samples (n = 30) were stained with haematoxylin and eosin, Picrosirius red, primary antibodies to collagen types I and III and studied by bright-field, phase-contrast, polarized light, and scanning electron microscopies followed by semi-quantitative morphometry.

RESULTS

Six months results of cell-loaded scaffolds demonstrated parallel collagen fibres, spindle-shaped tenocytes, and neoangiogenesis. In the control cell-free group, the injured areas were filled with a nonspecific fibrotic tissue with minor foci of incomplete regeneration. The biomechanical tests of 28 tendons taken from 14 rabbits showed that the stiffness of the cell-based reconstructed tendons increased to 98% of the value for the intact samples.

CONCLUSION

The obtained results support the hypothesis that the application of BM-MSCs in a tissue-engineered tendon construct leads to the restitution of the tendon tissue.

Tendon-bioinspired wavy nanofibrous scaffolds provide tunable anisotropy and promote tenogenesis for tendon tissue engineering

The development of tendon-biomimetic nanofibrous scaffolds with mesenchymal stem cells may represent a promising strategy to improve the unsatisfactory outcomes of traditional treatments in tendon repair. In the present study, the nanofibrous scaffolds comprised of poly(p-dioxanone) (PPDO) and silk fibroin (SF) composites were fabricated by using electrospinning technique and subsequent thermal ethanol treatment. The PPDO/SF composite scaffolds presented parallel fiber arrangement with crimped features and nonlinear mechanical properties, which mimic the structure-function relationship of native tendon tissue mechanics. We demonstrated that the fiber crimp degree and mechanical properties of as-prepared PPDO/SF wavy nanofibrous scaffolds (WNSs) could be tunable by adjusting the mass ratio of PPDO/SF. The biological tests revealed that the addition of SF obviously promoted the cell adhesion, proliferation, and phenotypic maintenance of human tenocytes on the WNSs. A preliminary study on the subcutaneous implantation showed that the PPDO/SF WNSs notably decreased the inflammatory response compared with pure PPDO WNSs. More importantly, a combination of growth factor induction and mechanical stimulation was found to notably enhance the tenogenic differentiation of human adipose derived mesenchymal stem cells on the PPDO/SF WNSs by upregulating the expressions of tendon-associated protein and gene markers. Overall, this study demonstrated that our PPDO/SF WNSs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate for tendon tissue engineering research.

Tendon tissue engineering: Cells, growth factors, scaffolds and production techniques

Tendon injuries are a global health problem that affects millions of people annually. The properties of tendons make their natural rehabilitation a very complex and long-lasting process. Thanks to the development of the fields of biomaterials, bioengineering and cell biology, a new discipline has emerged, tissue engineering. Within this discipline, diverse approaches have been proposed. The obtained results turn out to be promising, as increasingly more complex and natural tendon-like structures are obtained. In this review, the nature of the tendon and the conventional treatments that have been applied so far are underlined. Then, a comparison between the different tendon tissue engineering approaches that have been proposed to date is made, focusing on each of the elements necessary to obtain the structures that allow adequate regeneration of the tendon: growth factors, cells, scaffolds and techniques for scaffold development. The analysis of all these aspects allows understanding, in a global way, the effect that each element used in the regeneration of the tendon has and, thus, clarify the possible future approaches by making new combinations of materials, designs, cells and bioactive molecules to achieve a personalized regeneration of a functional tendon.

Tendinopathy

Tendinopathy describes a complex multifaceted pathology of the tendon, characterized by pain, decline in function and reduced exercise tolerance. The most common overuse tendinopathies involve the rotator cuff tendon, medial and lateral elbow epicondyles, patellar tendon, gluteal tendons and the Achilles tendon. The prominent histological and molecular features of tendinopathy include disorganization of collagen fibres, an increase in the microvasculature and sensory nerve innervation, dysregulated extracellular matrix homeostasis, increased immune cells and inflammatory mediators, and enhanced cellular apoptosis. Although diagnosis is mostly achieved based on clinical symptoms, in some cases, additional pain-provoking tests and imaging might be necessary. Management consists of different exercise and loading programmes, therapeutic modalities and surgical interventions; however, their effectiveness remains ambiguous. Future research should focus on elucidating the key functional pathways implicated in clinical disease and on improved rehabilitation protocols.

Development of collagen-poly(caprolactone)-based core-shell scaffolds supplemented with proteoglycans and glycosaminoglycans for ligament repair

Core-shell scaffolds offer a promising regenerative solution to debilitating injuries to anterior cruciate ligament (ACL) thanks to a unique biphasic structure. Nevertheless, current core-shell designs are impaired by an imbalance between permeability, biochemical and mechanical cues. This study aimed to address this issue by creating a porous core-shell construct which favors cell infiltration and matrix production, while providing mechanical stability at the site of injury. The developed core-shell scaffold combines an outer shell of electrospun poly(caprolactone) fibers with a freeze-dried core of type I collagen doped with proteoglycans (biglycan, decorin) or glycosaminoglycans (chondroitin sulphate, dermatan sulphate). The aligned fibrous shell achieved an elastic modulus akin of the human ACL, while the porous collagen core is permeable to human mesenchymal stem cell (hMSC). Doping of the core with the aforementioned biomolecules led to structural and mechanical changes in the pore network. Assessment of cellular metabolic activity and scaffold contraction shows that hMSCs actively remodel the matrix at different degrees, depending on the core's doping formulation. Additionally, immunohistochemical staining and mRNA transcript levels show that the collagen-chondroitin sulphate formulation has the highest matrix production activity, while the collagen-decorin formulation featured a matrix production profile more characteristic of the undamaged tissue. Together, this demonstrates that scaffold doping with target biomolecules leads to distinct levels of cell-mediated matrix remodeling. Overall, this work resulted in the development of a versatile and robust platform with a combination of mechanical and biochemical features that have a significant potential in promoting the repair process of ACL tissue.

Improving the regenerative microenvironment during tendon healing by using nanostructured fibrin/agarose-based hydrogels in a rat Achilles tendon injury model

AIMS

Achilles tendon injuries are a frequent problem in orthopaedic surgery due to their limited healing capacity and the controversy surrounding surgical treatment. In recent years, tissue engineering research has focused on the development of biomaterials to improve this healing process. The aim of this study was to analyze the effect of tendon augmentation with a nanostructured fibrin-agarose hydrogel (NFAH) or genipin cross-linked nanostructured fibrin-agarose hydrogel (GP-NFAH), on the healing process of the Achilles tendon in rats.

METHODS

NFAH, GP-NFAH, and MatriDerm (control) scaffolds were generated (five in each group). A biomechanical and cell-biomaterial-interaction characterization of these biomaterials was then performed: Live/Dead Cell Viability Assay, water-soluble tetrazolium salt-1 (WST-1) assay, and DNA-released after 48 hours. Additionally, a complete section of the left Achilles tendon was made in 24 Wistar rats. Animals were separated into four treatment groups (six in each group): direct repair (Control), tendon repair with MatriDerm, or NFAH, or GP-NFAH. Animals were euthanized for further histological analyses after four or eight weeks post-surgery. The Achilles tendons were harvested and a histopathological analysis was performed.

RESULTS

Tensile test revealed that NFAH and GP-NFAH had significantly higher overall biomechanical properties compared with MatriDerm. Moreover, biological studies confirmed a high cell viability in all biomaterials, especially in NFAH. In addition, in vivo evaluation of repaired tendons using biomaterials (NFAH, GP-NFAH, and MatriDerm) resulted in better organization of the collagen fibres and cell alignment without clinical complications than direct repair, with a better histological score in GP-NFAH.

CONCLUSION

In this animal model we demonstrated that NFAH and GP-NFAH had the potential to improve tendon healing following a surgical repair. However, future studies are needed to determine the clinical usefulness of these engineered strategies. Cite this article: Bone Joint J 2020;102-B(8):1095-1106.

Tenocyte-imprinted substrate: a topography-based inducer for tenogenic differentiation in adipose tissue-derived mesenchymal stem cells

Tendon tissue engineering based on stem cell differentiation has attracted a great deal of attention in recent years. Previous studies have examined the effect of cell-imprinted polydimethylsiloxane (PDMS) substrate on induction differentiation in stem cells. In this study, we used tenocyte morphology as a positive mold to create a tenocyte-imprinted substrate on PDMS. The morphology and topography of this tenocyte replica on PDMS was evaluated with scanning electron microscopy (SEM) and atomic force microscopy. The tenogenic differentiation induction capacity of the tenocyte replica in adipose tissue-derived mesenchymal stem cells (ADSCs) was then investigated and compared with other groups, including tissue replica (which was produced similarly to the tenocyte replica and was evaluated by SEM), decellularized tendon, and bone morphogenic protein (BMP)-12, as other potential inducers. This comparison gives us an estimate of the ability of tenocyte-imprinted PDMS (called cell replica in the present study) to induce differentiation compared to other inducers. For this reason, ADSCs were divided into five groups, including control, cell replica, tissue replica, decellularized tendon and BMP-12. ADSCs were seeded on each group separately and investigated by the real-time reverse transcription polymerase chain reaction (RT-PCR) technique after seven and 14 days. Our results showed that in spite of the higher effect of the growth factor on tenogenic differentiation, the cell replica can also induce tenocyte marker expression (scleraxis and tenomodulin) in ADSCs. Moreover, the tenogenic differentiation induction capacity of the cell replica was greater than tissue replica. Immunocytochemistry analysis revealed that ADSCs seeding on the cell replica for 14 days led to scleraxis and tenomodulin expression at the protein level. In addition, immunohistochemistry indicated that contrary to the promising results in vitro, there was little difference between ADSCs cultured on tenocyte-imprinted PDMS and untreated ADSCs. The results of such studies could lead to the production of inexpensive cell culture plates or biomaterials that can induce differentiation in stem cells without growth factors or other supplements.

Nanocomposite Films of Chitosan-Grafted Carbon Nano-Onions for Biomedical Applications

The design of scaffolding from biocompatible and resistant materials such as carbon nanomaterials and biopolymers has become very important, given the high rate of injured patients. Graphene and carbon nanotubes, for example, have been used to improve the physical, mechanical, and biological properties of different materials and devices. In this work, we report the grafting of carbon nano-onions with chitosan (CS-g-CNO) through an amide-type bond. These compounds were blended with chitosan and polyvinyl alcohol composites to produce films for subdermal implantation in Wistar rats. Films with physical mixture between chitosan, polyvinyl alcohol, and carbon nano-onions were also prepared for comparison purposes. Film characterization was performed with Fourier Transformation Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Tensile strength, X-ray Diffraction Spectroscopy (XRD), and Scanning Electron Microscopy (SEM). The degradation of films into simulated body fluid (SBF) showed losses between 14% and 16% of the initial weight after 25 days of treatment. Still, a faster degradation (weight loss and pH changes) was obtained with composites of CS-g-CNO due to a higher SBF interaction by hydrogen bonding. On the other hand, in vivo evaluation of nanocomposites during 30 days in Wistar rats, subdermal tissue demonstrated normal resorption of the materials with lower inflammation processes as compared with the physical blends of ox-CNO formulations. SBF hydrolytic results agreed with the in vivo degradation for all samples, demonstrating that with a higher ox-CNO content increased the stability of the material and decreased its degradation capacity; however, we observed greater reabsorption with the formulations including CS-g-CNO. With this research, we demonstrated the future impact of CS/PVA/CS-g-CNO nanocomposite films for biomedical applications.

Effects of rabbit pinna-derived blastema cells on tendon healing

OBJECTIVES

Tendon healing is substantially slow and often associated with suboptimal repair. Cell therapy is one of the promising methods to improve tendon repair. Blastema, a population of undifferentiated cells, represents characteristics of pluripotent mesenchymal stem cells and has the potentials to be used in regenerative medicine. The aim of this study was to investigate the use of blastema allotransplantation in rabbit tendon healing.

MATERIALS AND METHODS

In this study, one rabbit was used as a blastema donor, and twenty-four rabbits were divided into control and treatment groups. Blastema cells were obtained from ear pinna upon punch hole injury in the donor rabbit. Under general anesthesia, a complete transverse tenotomy was performed on the midsubstance of deep digital flexor tendon followed by suture-repair. In the treatment group, 1 × 106 blastema cells suspended in buffer saline were injected intratendinously at the repair site, while the control group received only the buffer saline. Cast coaptation was maintained for two weeks. Eight weeks after the operation, tendons were harvested, and histopathological, biomechanical, and biochemical assays were performed on samples.

RESULTS

Mechanical testing showed a significant increase in ultimate load, energy absorption, stiffness, yield load, stress, and strain in blastema-treated tendons compared to controls. Also, higher hydroxyproline content and improved collagen alignment along with lower inflammatory cell infiltration and decreased angiogenesis were observed in blastema-treated tendons.

CONCLUSION

Increased levels of hydroxyproline and improved histopathological and biomechanical parameters in the treatment group suggest that blastema cells could be considered an adjunct to tendon repair in rabbits.

Preparation of Chitosan/Poly(Vinyl Alcohol) Nanocomposite Films Incorporated with Oxidized Carbon Nano-Onions (Multi-Layer Fullerenes) for Tissue-Engineering Applications

Recently, tissue engineering became a very important medical alternative in patients who need to regenerate damaged or lost tissues through the use of scaffolds that support cell adhesion and proliferation. Carbon nanomaterials (carbon nanotubes, fullerenes, multi-wall fullerenes, and graphene) became a very important alternative to reinforce the mechanical, thermal, and antimicrobial properties of several biopolymers. In this work, five different formulations of chitosan/poly(vinyl alcohol)/oxidized carbon nano-onions (CS/PVA/ox-CNO) were used to prepare biodegradable scaffolds with potential biomedical applications. Film characterization consisted of Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tension strength, Young's modulus, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The degradation in a simulated body fluid (FBS) demonstrated that all the formulations lost between 75% and 80% of their weight after 15 days of treatment, but the degradation decreased with the ox-CNO content. In vivo tests after 90 days of subdermal implantation of the nanocomposite films in Wistar rats' tissue demonstrated good biocompatibility without allergenic reactions or pus formation. There was a good correlation between FBS hydrolytic degradation and degradation in vivo for all the samples, since the ox-CNO content increased the stability of the material. All these results indicate the potential of the CS/PVA/ox-CNO nanocomposite films in tissue engineering, especially for long-term applications.

The ins and outs of engineering functional tissues and organs: evaluating the in-vitro and in-situ processes

PURPOSE OF REVIEW

For many disorders that result in loss of organ function, the only curative treatment is organ transplantation. However, this approach is severely limited by the shortage of donor organs. Tissue engineering has emerged as an alternative solution to this issue. This review discusses the concept of tissue engineering from a technical viewpoint and summarizes the state of the art as well as the current shortcomings, with the aim of identifying the key lessons that we can learn to further advance the engineering of functional tissues and organs.

RECENT FINDINGS

A plethora of tissue-engineering strategies have been recently developed. Notably, these strategies put different emphases on the in-vitro and in-situ processes (i.e. preimplantation and postimplantation) that take place during tissue formation. Biophysical and biomechanical interactions between the cells and the scaffold/biomaterial play a crucial role in all steps and have started to be exploited to steer tissue regeneration.

SUMMARY

Recent works have demonstrated the need to better understand the in-vitro and in-situ processes during tissue formation, in order to regenerate complex, functional organs with desired cellular organization and tissue architecture. A concerted effort from both fundamental and tissue-specific research has the potential to accelerate progress in the field.