A new multilayered membrane for tissue engineering of oral hard- and soft tissue by means of melt electrospinning writing and film casting – An in vitro study

Bone Scaffold Materials in Periodontal and Tooth-supporting Tissue Regeneration: A Review

BACKGROUND AND OBJECTIVES

Periodontium is an important tooth-supporting tissue composed of both hard (alveolar bone and cementum) and soft (gingival and periodontal ligament) sections. Due to the multi-tissue architecture of periodontium, reconstruction of each part can be influenced by others. This review focuses on the bone section of the periodontium and presents the materials used in tissue engineering scaffolds for its reconstruction.

MATERIALS AND METHODS

The following databases (2015 to 2021) were electronically searched: ProQuest, EMBASE, SciFinder, MRS Online Proceedings Library, Medline, and Compendex. The search was limited to English-language publications and in vivo studies.

RESULTS

Eighty-three articles were found in primary searching. After applying the inclusion criteria, seventeen articles were incorporated into this study.

CONCLUSION

In complex periodontal defects, various types of scaffolds, including multilayered ones, have been used for the functional reconstruction of different parts of periodontium. While there are some multilayered scaffolds designed to regenerate alveolar bone/periodontal ligament/cementum tissues of periodontium in a hierarchically organized construct, no scaffold could so far consider all four tissues involved in a complete periodontal defect. The progress and material considerations in the regeneration of the bony part of periodontium are presented in this work to help investigators develop tissue engineering scaffolds suitable for complete periodontal regeneration.

Composite grafts made of polycaprolactone fiber mats and oil-based calcium phosphate cement pastes for the reconstruction of cranial and maxillofacial defects

OBJECTIVES

Synthetic bone substitutes which can be adapted preoperatively and patient specific may be helpful in various bony defects in the field of oral- and maxillofacial surgery. For this purpose, composite grafts made of self-setting and oil-based calcium phosphate cement (CPC) pastes, which were reinforced with 3D-printed polycaprolactone (PCL) fiber mats were manufactured.

MATERIALS AND METHODS

Bone defect models were acquired using patient data from real defect situations of patients from our clinic. Using a mirror imaging technique, templates of the defect situation were fabricated via a commercially available 3D-printing system. The composite grafts were assembled layer by layer, aligned on top of these templates and fitted into the defect situation. Besides, PCL-reinforced CPC samples were evaluated regarding their structural and mechanical properties via X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), and 3-point-bending testing.

RESULTS

The process sequence including data acquisition, template fabrication, and manufacturing of patient specific implants proved to be accurate and uncomplicated. The individual implants consisting mainly of hydroxyapatite and tetracalcium phosphate displayed good processability and a high precision of fit. The mechanical properties of the CPC cements in terms of maximum force and stress load to material fatigue were not negatively affected by the PCL fiber reinforcement, whereas clinical handling properties increased remarkably.

CONCLUSION

PCL fiber reinforcement of CPC cements enables the production of very freely modelable three-dimensional implants with adequate chemical and mechanical properties for bone replacement applications.

CLINICAL RELEVANCE

The complex bone morphology in the region of the facial skull often poses a great challenge for a sufficient reconstruction of bony defects. A full-fledged bone replacement here often requires the replication of filigree three-dimensional structures partly without support from the surrounding tissue. With regard to this problem, the combination of smooth 3D-printed fiber mats and oil-based CPC pastes represents a promising method for fabricating patient specific degradable implants for the treatment of various craniofacial bone defects.

Design and bioprinting for tissue interfaces

Tissue interfaces include complex gradient structures formed by transitioning of biochemical and mechanical properties in micro-scale. This characteristic allows the communication and synchronistic functioning of two adjacent but distinct tissues. It is particularly challenging to restore the function of these complex structures by transplantation of scaffolds exclusively produced by conventional tissue engineering methods. Three-dimensional (3D) bioprinting technology has opened an unprecedented approach for precise and graded patterning of chemical, biological and mechanical cues in a single construct mimicking natural tissue interfaces. This paper reviews and highlights biochemical and biomechanical design for 3D bioprinting of various tissue interfaces, including cartilage-bone, muscle-tendon, tendon/ligament-bone, skin, and neuro-vascular/muscular interfaces. Future directions and translational challenges are also provided at the end of the paper.

Electrospinning of Potential Medical Devices (Wound Dressings, Tissue Engineering Scaffolds, Face Masks) and Their Regulatory Approach

Electrospinning is the simplest and most widely used technology for producing ultra-thin fibers. During electrospinning, the high voltage causes a thin jet to be launched from the liquid polymer and then deposited onto the grounded collector. Depending on the type of the fluid, solution and melt electrospinning are distinguished. The morphology and physicochemical properties of the produced fibers depend on many factors, which can be categorized into three groups: process parameters, material properties, and ambient parameters. In the biomedical field, electrospun nanofibers have a wide variety of applications ranging from medication delivery systems to tissue engineering scaffolds and soft electronics. Many of these showed promising results for potential use as medical devices in the future. Medical devices are used to cure, prevent, or diagnose diseases without the presence of any active pharmaceutical ingredients. The regulation of conventional medical devices is strict and carefully controlled; however, it is not yet properly defined in the case of nanotechnology-made devices. This review is divided into two parts. The first part provides an overview on electrospinning through several examples, while the second part focuses on developments in the field of electrospun medical devices. Additionally, the relevant regulatory framework is summarized at the end of this paper.

Unveiling the potential of melt electrowriting in regenerative dental medicine

For nearly three decades, tissue engineering strategies have been leveraged to devise effective therapeutics for dental, oral, and craniofacial (DOC) regenerative medicine and treat permanent deformities caused by many debilitating health conditions. In this regard, additive manufacturing (AM) allows the fabrication of personalized scaffolds that have the potential to recapitulate native tissue morphology and biomechanics through the utilization of several 3D printing techniques. Among these, melt electrowriting (MEW) is a versatile direct electrowriting process that permits the development of well-organized fibrous constructs with fiber resolutions ranging from micron to nanoscale. Indeed, MEW offers great prospects for the fabrication of scaffolds mimicking tissue specificity, healthy and pathophysiological microenvironments, personalized multi-scale transitions, and functional interfaces for tissue regeneration in medicine and dentistry. Excitingly, recent work has demonstrated the potential of converging MEW with other AM technologies and/or cell-laden scaffold fabrication (bioprinting) as a favorable route to overcome some of the limitations of MEW for DOC tissue regeneration. In particular, such convergency fabrication strategy has opened great promise in terms of supporting multi-tissue compartmentalization and predetermined cell commitment. In this review, we offer a critical appraisal on the latest advances in MEW and its convergence with other biofabrication technologies for DOC tissue regeneration. We first present the engineering principles of MEW and the most relevant design aspects for transition from flat to more anatomically relevant 3D structures while printing highly-ordered constructs. Secondly, we provide a thorough assessment of contemporary achievements using MEW scaffolds to study and guide soft and hard tissue regeneration, and draw a parallel on how to extrapolate proven concepts for applications in DOC tissue regeneration. Finally, we offer a combined engineering/clinical perspective on the fabrication of hierarchically organized MEW scaffold architectures and the future translational potential of site-specific, single-step scaffold fabrication to address tissue and tissue interfaces in dental, oral, and craniofacial regenerative medicine. STATEMENT OF SIGNIFICANCE: Melt electrowriting (MEW) techniques can further replicate the complexity of native tissues and could be the foundation for novel personalized (defect-specific) and tissue-specific clinical approaches in regenerative dental medicine. This work presents a unique perspective on how MEW has been translated towards the application of highly-ordered personalized multi-scale and functional interfaces for tissue regeneration, targeting the transition from flat to anatomically-relevant three-dimensional structures. Furthermore, we address the value of convergence of biofabrication technologies to overcome the traditional manufacturing limitations provided by multi-tissue complexity. Taken together, this work offers abundant engineering and clinical perspectives on the fabrication of hierarchically MEW architectures aiming towards site-specific implants to address complex tissue damage in regenerative dental medicine.

Highlighting the Compositional Changes of the Sm2O3/MgO-Containing Cellulose Acetate Films for Wound Dressings

The development of wound dressing materials with appropriate specifications is still a challenge to overcome the current limitations of conventional medical bandages. In this regard, simple and fast methods are highly recommended, such as film casting. In addition, deliverable nanoparticles that can act to accelerate wound integration, such as samarium oxide (Sm₂O₃) and magnesium oxide (MgO), might represent a potential design with a novel compositional combination. In the present research, the casted film of cellulose acetate (CA) was mixed with different ratios of metal oxides, such as samarium oxide (Sm₂O₃) and magnesium oxide (MgO). The tests used for the film examination were X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The SEM graphs of CA films represent the surface morphology of Sm₂O₃@CA, MgO@CA, and Sm₂O₃/MgO/GO@CA. It was found that the scaffolds' surface contained a high porosity ratio with diameters of 1.5-5 µm. On the other hand, the measurement of contact angle exhibits a variable trend starting from 27° to 29° for pristine CA and Sm₂O₃/MgO/GO@CA. The cell viability test exhibits a noticeable increase in cell growth with a decrease in the concentration. In addition, the IC₅₀ was determined at 6 mg/mL, while the concentration of scaffolds of 20 mg/mL caused cellular growth to be around 106%.

A Highly Ordered, Nanostructured Fluorinated CaP-Coated Melt Electrowritten Scaffold for Periodontal Tissue Regeneration

Periodontitis is a chronic inflammatory, bacteria-triggered disorder affecting nearly half of American adults. Although some level of tissue regeneration is realized, its low success in complex cases demands superior strategies to amplify regenerative capacity. Herein, highly ordered scaffolds are engineered via Melt ElectroWriting (MEW), and the effects of strand spacing, as well as the presence of a nanostructured fluorinated calcium phosphate (F/CaP) coating on the adhesion/proliferation, and osteogenic differentiation of human-derived periodontal ligament stem cells, are investigated. Upon initial cell-scaffold interaction screening aimed at defining the most suitable design, MEW poly(ε-caprolactone) scaffolds with 500 µm strand spacing are chosen. Following an alkali treatment, scaffolds are immersed in a pre-established solution to allow for coating formation. The presence of a nanostructured F/CaP coating leads to a marked upregulation of osteogenic genes and attenuated bacterial growth. In vivo findings confirm that the F/CaP-coated scaffolds are biocompatible and lead to periodontal regeneration when implanted in a rat mandibular periodontal fenestration defect model. In aggregate, it is considered that this work can contribute to the development of personalized scaffolds capable of enabling tissue-specific differentiation of progenitor cells, and thus guide simultaneous and coordinated regeneration of soft and hard periodontal tissues, while providing antimicrobial protection.

Recent advances in polymer scaffolds for biomedical applications

The review provides insights into current advancements in electrospinning-assisted manufacturing for optimally designing biomedical devices for their prospective applications in tissue engineering, wound healing, drug delivery, sensing, and enzyme immobilization, and others. Further, the evolution of electrospinning-based hybrid biomedical devices using a combined approach of 3 D printing and/or film casting/molding, to design dimensionally stable membranes/micro-nanofibrous assemblies/patches/porous surfaces, etc. is reported. The influence of various electrospinning parameters, polymeric material, testing environment, and other allied factors on the morphological and physico-mechanical properties of electrospun (nano-/micro-fibrous) mats (EMs) and fibrous assemblies have been compiled and critically discussed. The spectrum of operational research and statistical approaches that are now being adopted for efficient optimization of electrospinning process parameters so as to obtain the desired response (physical and structural attributes) has prospectively been looked into. Further, the present review summarizes some current limitations and future perspectives for modeling architecturally novel hybrid 3 D/selectively textured structural assemblies, such as biocompatible, non-toxic, and bioresorbable mats/scaffolds/membranes/patches with apt mechanical stability, as biological substrates for various regenerative and non-regenerative therapeutic devices.

Fabrication and in vitro evaluation of PCL/gelatin hierarchical scaffolds based on melt electrospinning writing and solution electrospinning for bone regeneration

As an emerging 3D printing technique, melt electrospinning writing (MEW) has been used to fabricate scaffolds with controllable structure and good mechanical strength for bone regeneration. However, how to further improve MEW scaffolds with nanoscale extracellular matrix (ECM) mimic structure and bioactivity is still challenging. In this study, we proposed a simple composite process by combining MEW and solution electrospinning (SE) to fabricate a micro/nano hierarchical scaffold for bone tissue engineering. The morphological results confirmed the hierarchical structure with both well-defined MEW microfibrous grid structure and SE random nanofiber morphology. The addition of gelatin nanofibers turned the scaffolds to be hydrophilic, and led to a slight enhancement of mechanical strength. Compared with PCL MEW scaffolds, higher cell adhesion efficiency, improved cell proliferation and higher osteoinductive ability were achieved for the MEW/SE composite scaffolds. Finally, multilayer composite scaffolds were fabricated by alternately stacking of MEW layer and SE layer and used to assess the effect on cell ingrowth in the scaffolds. The results showed that gelatin nanofibers did not inhibit cell penetration, but promoted the three-dimensional growth of bone cells. Thus, the strategy of the combined use of MEW and SE is a potential method to fabricate micro/nano hierarchical scaffolds to improve bone regeneration.

Biodegradable and Biocompatible 3D Constructs for Dental Applications: Manufacturing Options and Perspectives

Designing 3D constructs with appropriate materials and structural frameworks for complex dental restorative/regenerative procedures has always remained a multi-criteria optimization challenge. In this regard, 3D printing has long been known to be a potent tool for various tissue regenerative applications, however, the preparation of biocompatible, biodegradable, and stable inks is yet to be explored and revolutionized for overall performance improvisation. The review reports the currently employed manufacturing processes for the development of engineered self-supporting, easily processable, and cost-effective 3D constructs with target-specific tuneable mechanics, bioactivity, and degradability aspects in the oral cavity for their potential use in numerous dental applications ranging from soft pulp tissues to hard alveolar bone tissues. A hybrid synergistic approach, comprising of development of multi-layered, structurally stable, composite building blocks with desired physicomechanical performance and bioactivity presents an optimal solution to circumvent the major limitations and develop new-age advanced dental restorations and implants. Further, the review summarizes some manufacturing perspectives which may inspire the readers to design appropriate structures for clinical trials so as to pave the way for their routine applications in dentistry in the near future.

Hard Dental Tissues Regeneration-Approaches and Challenges

With the development of the modern concept of tissue engineering approach and the discovery of the potential of stem cells in dentistry, the regeneration of hard dental tissues has become a reality and a priority of modern dentistry. The present review reports the recent advances on stem-cell based regeneration strategies for hard dental tissues and analyze the feasibility of stem cells and of growth factors in scaffolds-based or scaffold-free approaches in inducing the regeneration of either the whole tooth or only of its component structures.

Precise locating and cutting of the bone lid with a digital template during the treatment of large mandibular cysts: A case series study

The aim of the study was to investigate the efficacy and safety of a digital template in the bone lid technique during enucleation of large mandibular cysts. Six patients were enrolled in this study. Patients' preoperative CT data were collected to design and produce the digital templates. The bone lids were located and cut under the guidance of the digital templates, and then replanted and fixed following cyst enucleation. Postoperative clinical symptoms were observed and recorded from postoperative days 1-7. The follow-up visits were set at 3, 6, and 12 months. The cystic lesions were exactly and fully exposed without the need for secondary bone removal. The contours of the mandibles recovered well, with excellent sealing of the defects. Apart from one case with postoperative infection and one case with 2-month numbness of the lower lip, no other complications occurred. Six months after the surgery, patients' appearance and function were well-restored. A digital template in the bone lid technique during enucleation of large mandibular cysts was effective and safe.

Melt Electrospinning of Polymers: Blends, Nanocomposites, Additives and Applications

Melt electrospinning has been developed in the last decade as an eco-friendly and solvent-free process to fill the gap between the advantages of solution electrospinning and the need of a cost-effective technique for industrial applications. Although the benefits of using melt electrospinning compared to solution electrospinning are impressive, there are still challenges that should be solved. These mainly concern to the improvement of polymer melt processability with reduction of polymer degradation and enhancement of fiber stability; and the achievement of a good control over the fiber size and especially for the production of large scale ultrafine fibers. This review is focused in the last research works discussing the different melt processing techniques, the most significant melt processing parameters, the incorporation of different additives (e.g., viscosity and conductivity modifiers), the development of polymer blends and nanocomposites, the new potential applications and the use of drug-loaded melt electrospun scaffolds for biomedical applications.

High-resolution electrohydrodynamic bioprinting: a new biofabrication strategy for biomimetic micro/nanoscale architectures and living tissue constructs

Electrohydrodynamic (EHD) printing is a newly emerging additive manufacturing strategy for the controlled fabrication of three-dimensional (3D) micro/nanoscale architectures. This unique superiority makes it particularly suitable for the biofabrication of artificial tissue analogs with biomimetic structural organizations similar to the scales of native extracellular matrix (ECM) or living cells, which shows great potentials to precisely regulate cellular behaviors and tissue regeneration. Here the state-of-the-art advancements of high-resolution EHD bioprinting were reviewed mainly including melt-based and solution-based processes for the fabrication of micro/nanoscale fibrous scaffolds and living tissues constructs. The related printing materials, innovations on structure design and printing processes, functionalization of the resultant architectures as well as their effects on the mechanical and biological properties of the EHD-printed structures were introduced and analyzed. The recent explorations on the EHD cell printing for high-resolution cell-laden microgel patterning and 3D construct fabrication were highlighted. The major challenges as well as possible solutions to translate EHD bioprinting into a mature and prevalent biofabrication strategy were finally discussed.

The effect of melt electrospun writing fiber orientation onto cellular organization and mechanical properties for application in Anterior Cruciate Ligament tissue engineering

The effect of melt electrospun writing fiber arrangement on cellular behavior has not yet been thoroughly investigated. Cellular orientation is particularly important in the context of ligament tissue engineering for orthopedic applications whereby a high degree of cell alignment is present in the native tissue. The aim of this study was to investigate the response of human mesenchymal stem cells (hMSC) to three different patterned porous polycaprolactone scaffolds (aligned, crimped and random) fabricated by melt electrospinning writing, resulting in 20 μm diameter electrospun fibers. Cell orientation was investigated over 4 weeks in vitro and it was demonstrated that the aligned pattern was capable of orientating the hMSCs towards the main direction of the fibers and this feature was maintained over the entire culture period whereas the orientation was rapidly lost in the crimped pattern. In order to fabricate a functional scaffold for ligament tissue engineering, the scaffolds were rolled in three bundles, subsequently braided and combined with a bone compartment (consisting of a melt electrospun scaffold seeded with osteogenically induced hMSCs) for the development of a Bone-Ligament-Bone (BLB) construct. The mechanical properties of non-cellularized and cellularized BLB constructs were assessed under both quasi-static and cyclic conditions. This revealed that the in vitro maturation significantly softened the BLB constructs and that the mechanical properties were several fold lower than those of native tissue. The cyclic testing demonstrated that the presence of cell sheets resulted in increased resilience and elasticity, even though the global mechanical properties were decreased for the in vitro matured constructs (regardless of the pattern). In conclusion, we demonstrated that melt electrospinning writing fiber organization can induce spontaneous cell alignment and that large cellularized BLB constructs with complex geometry can achieve mechanical resilience under cyclic stretching.

Polycaprolactone as biomaterial for bone scaffolds: Review of literature

Bone tissue engineering using polymer based scaffolds have been studied a lot in last decades. Considering the qualities of all the polymers desired to be used as scaffolds, Polycaprolactone (PCL) polyester apart from being biocompatible and biodegradable qualifies to an appreciable level due its easy availability, cost efficacy and suitability for modification. Its adjustable physio-chemical state, biological properties and mechanical strength renders it to withstand physical, chemical and mechanical, insults without significant loss of its properties. This review aims to critically analyse the efficacy of PCL as a biomaterial for bone scaffolds.

Biomimicry in Bio-Manufacturing: Developments in Melt Electrospinning Writing Technology Towards Hybrid Biomanufacturing

Melt electrospinning writing has been emerged as a promising technique in the field of tissue engineering, with the capability of fabricating controllable and highly ordered complex three-dimensional geometries from a wide range of polymers. This three-dimensional (3D) printing method can be used to fabricate scaffolds biomimicking extracellular matrix of replaced tissue with the required mechanical properties. However, controlled and homogeneous cell attachment on melt electrospun fibers is a challenge. The combination of melt electrospinning writing with other tissue engineering approaches, called hybrid biomanufacturing, has introduced new perspectives and increased its potential applications in tissue engineering. In this review, principles and key parameters, challenges, and opportunities of melt electrospinning writing, and particularly, recent approaches and materials in this field are introduced. Subsequently, hybrid biomanufacturing strategies are presented for improved biological and mechanical properties of the manufactured porous structures. An overview of the possible hybrid setups and applications, future perspective of hybrid processes, guidelines, and opportunities in different areas of tissue/organ engineering are also highlighted.