Bioengineered skin organoids:from development to applications

Signifcant advancements have been made in recent years in the development of highly sophisticated skin organoids.Serving as three-dimensional(3D)models that mimic human skin,these organoids have evolved into complex structures and are increasingly recognized as efective alternatives to traditional culture models and human skin due to their ability to overcome the limitations of two-dimensional(2D)systems and ethical concerns.The inherent plasticity of skin organoids allows for their construction into physiological and pathological models,enabling the study of skin development and dynamic changes.This review provides an overview of the pivotal work in the progression from 3D layered epidermis to cyst-like skin organoids with appendages.Furthermore,it highlights the latest advancements in organoid construction facilitated by state-of-the-art engineering techniques,such as 3D printing and microfuidic devices.The review also summarizes and discusses the diverse applications of skin organoids in developmental biology,disease modelling,regenerative medicine,and personalized medicine,while considering their prospects and limitations.

Tissue-Engineered Products for Skin Regenerative Medicine

In a general wound healing process, foreign bodies and tissue detritus have to be broken down and then a new tissue is produced. However, the new tissue formation sometimes fails to proceed under the impaired conditions such as burn injury and intractable skin ulcer. A major obstruction to wound healing is infection. Another obstruction to wound healing is deficiency of growth factors. The endogenous levels of growth factors are reduced in some chronic wounds. To improve these wound conditions, researchers have been trying to create several types of artificial skins. The tissue-engineered products include three prime constituents, i.e., cells, growth factors, and materials. In this review, the practical design of tissue-engineered products for skin regenerative medicine is introduced. The first design makes it possible to release silver sulfadiazine (AgSD) from a wound dressing. The second design makes it possible to release Epidermal Growth Factor (EGF) from a wound dressing or a skin care product composed of hyaluronic acid spongy sheet containing bioactive ingredients. The third design makes it possible to release several types of growth factors from allogeneic fibroblasts within cultured dermal substitute. This tissue-engineered product is prepared by seeding allogeneic fibroblasts into a collagen and hyaluronic acid spongy sheet. Although allogeneic cells are rejected gradually in immune system, they are able to release some types of growth factors, thereby regenerating a damaged tissue. The clinical study demonstrates that these tissue-engineered products are promising for the treatment of burn injury and intractable skin ulcer.

Angiogenesis in tissue-engineered nerves evaluated objectively using MICROFIL perfusion and micro-CT scanning

Angiogenesis is a key process in regenerative medicine generally, as well as in the specific field of nerve regeneration. However, no convenient and objective method for evaluating the angiogenesis of tissue-engineered nerves has been reported. In this study, tissue-engineered nerves were constructed in vitro using Schwann cells differentiated from rat skin-derived precursors as supporting cells and chitosan nerve conduits combined with silk fibroin fibers as scaffolds to bridge 10-mm sciatic nerve defects in rats. Four weeks after surgery, three-dimensional blood vessel reconstructions were made through MICROFIL perfusion and micro-CT scanning, and parameter analysis of the tissue-engineered nerves was performed. New blood vessels grew into the tissue-engineered nerves from three main directions： the proximal end, the distal end, and the middle. The parameter analysis of the three-dimensional blood vessel images yielded several parameters, including the number, diameter, connection, and spatial distribution of blood vessels. The new blood vessels were mainly capillaries and microvessels, with diameters ranging from 9 to 301 μm. The blood vessels with diameters from 27 to 155 μm accounted for 82.84% of the new vessels. The microvessels in the tissue-engineered nerves implanted in vivo were relatively well-identified using the MICROFIL perfusion and micro-CT scanning method, which allows the evaluation and comparison of differences and changes of angiogenesis in tissue-engineered nerves implanted in vivo.

Vital roles of stem cells and biomaterials in skin tissue engineering

Tissue engineering essentially refers to technology for growing new human tissue and is distinct from regenerative medicine. Currently, pieces of skin are already being fabricated for clinical use and many other tissue types may be fabricated in the future.Tissue engineering was first defined in 1987 by the United States National Science Foundation which critically discussed the future targets of bioengineering research and its consequences. The principles of tissue engineering are to initiate cell cultures in vitro, grow them on scaffolds in situ and transplant the composite into a recipient in vivo. From the beginning, scaffolds have been necessary in tissue engineering applications. Regardless, the latest technology has redirected established approaches by omitting scaffolds. Currently, scientists from diverse research institutes are engineering skin without scaffolds. Due to their advantageous properties, stem cells have robustly transformed the tissue engineering field as part of an engineered bilayered skin substitute that will later be discussed in detail. Additionally, utilizing biomaterials or skin replacement products in skin tissue engineering as strategy to successfully direct cell proliferation and differentiation as well as to optimize the safety of handling during grafting is beneficial. This approach has also led to the cells' application in developing the novel skin substitute that will be briefly explained in this review.

Realization Feature of Mesenchymal Dermal Cells Tissue Engineering Construction Response in Granulating Wound Transplantation in Relation with Time-Frame

Derma is progenitor cells sours, that are able to differentiate further in several mesodermal lineage and neural and endodermal lineage. Culture conditions, skin taking site and culture medium composition considerably contribute to it. Spheroid cultured mesenchymal dermal cells contribution to skin regeneration in granulating wound in rat model was estimated.

Noncoding RNAs and Their Potential Therapeutic Applications in Tissue Engineering

Tissue engineering is a relatively new but rapidly developing field in the medical sciences. Noncoding RNAs(ncRNAs) are functional RNA molecules without a protein-coding function; they can regulate cellular behavior and change the biological milieu of the tissue. The application of ncRNAs in tissue engineering is starting to attract increasing attention as a means of resolving a large number of unmet healthcare needs, although ncRNA-based approaches have not yet entered clinical practice. In-depth research on the regulation and delivery of ncRNAs may improve their application in tissue engineering.The aim of this review is: to outline essential ncRNAs that are related to tissue engineering for the repair and regeneration of nerve, skin, liver, vascular system, and muscle tissue; to discuss their regulation and delivery; and to anticipate their potential therapeutic applications.

Protein-spatiotemporal partition releasing gradient porous scaffolds and anti-inflammatory and antioxidant regulation remodel tissue engineered anisotropic meniscus

Meniscus is a wedge-shaped fibrocartilaginous tissue,playing important roles in maintaining joint stability and function.Meniscus injuries are difficult to heal and frequently progress into structural breakdown,which then leads to osteoarthritis.Regeneration of heterogeneous tissue engineering meniscus(TEM)continues to be a scientific and translational challenge.The morphology,tissue architecture,mechanical strength,and functional applications of the cultivated TEMs have not been able to meet clinical needs,which may due to the negligent attention on the importance of microenvironment in vitro and in vivo.Herein,we combined the 3D(three-dimensional)-printed gradient porous scaffolds,spatiotemporal partition release of growth factors,and anti-inflammatory and anti-oxidant microenvironment regulation of Ac2-26 peptide to prepare a versatile meniscus composite scaffold with heterogeneous bionic structures,excellent biomechanical properties and anti-inflammatory and anti-oxidant effects.By observing the results of cell activity and differentiation,and biomechanics under anti-inflammatory and anti-oxidant microenvironments in vitro,we explored the effects of anti-inflammatory and anti-oxidant microenvironments on construction of regional and functional heterogeneous TEM via the growth process regulation,with a view to cultivating a high-quality of TEM from bench to bedside.

基于SKP-SCs来源的胞外囊泡构建的组织工程神经移植物的生物安全性评价

目的:评价基于皮肤源性前体细胞(skin-derived precursors,SKPs)分化成的施万细胞(Schwann cells,SCs)来源的细胞外囊泡(extracellular vesicles,EVs)构建的组织工程神经移植物(tissue engineered nerve graft,TENG)的生物安全性。方法:将SKP-SCs来源的EVs(SKP-SC-EVs)注射至带有3根纤维支架的壳聚糖导管中制备成TENGs,修复比格犬坐骨神经40 mm缺损。术后6个月,取心、肝、脾、肺、肾、脑,通过HE染色进行形态学观察,并收集血液进行血液常规和生化指标分析,包括:白细胞、中性粒细胞、红细胞、血小板、总蛋白、白蛋白、谷丙转氨酶和血糖等。结果:形态学分析显示TENGs组比格犬的各脏器组织结构清晰,与自体移植组、壳聚糖导管组相比,各项血液指标差异均无统计学意义(均P>0.05),且未见毒性反应改变。结论:基于SKP-SC-EVs构建的TENGs植入比格犬体内具有良好的生物安全性,为临床应用TENGs治疗周围神经损伤提供安全性数据支持。

Use of autologous tissue engineered skin to treat porcine full-thickness skin defects

Objective: To explore a feasible method to repair full-thickness skin defects utilizing tissue engineered techniques. Methods: The Changfeng hybrid swines were used and the skin specimens were cut from the posterior limb girdle region, from which the keratinocytes and fibroblasts were isolated and harvested by trypsin, EDTA, and type II collagenase. The cells were seeded in Petri dishes for primary culture. When the cells were in logarithmic growth phase, they were treated with trypsin to separate them from the floor of the tissue culture dishes. A biodegradable material, Pluronic F-127, was prefabricated and mixed with these cells, and then the cell-Pluronic compounds were seeded evenly into a polyglycolic acid (PGA). Then the constructs were replanted to the autologous animals to repair the full-thickness skin defects. Histology and immunohistochemistry of the neotissue were observed in 1, 2, 4, and 8 postoperative weeks. Results: The cell-Pluronic F-127-PGA compounds repaired autologous full-thickness skin defects 1 week after implantation. Histologically, the tissue engineered skin was similar to the normal skin with stratified epidermis overlying a moderately thick collageneous dermis. Three of the structural proteins in the epidermal basement membrane zone, type IV collagen, laminin, and type VII collagen were detected using immunohistochemical methods. Conclusions: By studying the histology and immunohistochemistry of the neotissue, the bioengineered skin graft holds great promise for improving healing of the skin defects.

3D-printed fish gelatin scaffolds for cartilage tissue engineering

Knee osteoarthritis is a chronic disease caused by the deterioration of the knee joint due to various factors such as aging,trauma,and obesity,and the nonrenewable nature of the injured cartilage makes the treatment of osteoarthritis challenging.Here,we present a three-dimensional(3D)printed porous multilayer scaffold based on cold-water fish skin gelatin for osteoarticular cartilage regeneration.To make the scaffold,cold-water fish skin gelatin was combined with sodium alginate to increase viscosity,printability,and mechanical strength,and the hybrid hydrogel was printed according to a pre-designed specific structure using 3D printing technology.Then,the printed scaffolds underwent a double-crosslinking process to enhance their mechanical strength even further.These scaffolds mimic the structure of the original cartilage network in a way that allows chondrocytes to adhere,proliferate,and communicate with each other,transport nutrients,and prevent further damage to the joint.More importantly,we found that cold-water fish gelatin scaffolds were nonimmunogenic,nontoxic,and biodegradable.We also implanted the scaffold into defective rat cartilage for 12 weeks and achieved satisfactory repair results in this animal model.Thus,cold-water fish skin gelatin scaffolds may have broad application potential in regenerative medicine.

Recent advancements in applications of chitosan-based biomaterials for skin tissue engineering

The use of polymer based composites in the treatment of skin tissue damages,has got huge attention in clinical demand,which enforced the scientists to improve the methods of biopolymer designing in order to obtain highly efficient system for complete restoration of damaged tissue.In last few decades,chitosan-based biomaterials have major applications in skin tissue engineering due to its biocompatible,hemostatic,antimicrobial and biodegradable capabilities.This article overviewed the promising biological properties of chitosan and further discussed the various preparation methods involved in chitosan-based biomaterials.In addition,this review also gave a comprehensive discussion of different forms of chitosan-based biomaterials including membrane,sponge,nanofiber and hydrogel that were extensively employed in skin tissue engineering.This review will help to form a base for the advanced applications of chitosan-based biomaterials in treatment of skin tissue damages.

Application of collagen-chitosan/fibrin glue asymmetric scaffolds in skin tissue engineering

To create a scaffold that is suitable for the construction of tissue-engineered skin, a novel asymmetric porous scaffold with different pore sizes on either side was prepared by combining a collagen-chitosan porous membrane with fibrin glue. Tissue-engineered skin was fabricated using this asymmetric scaffold, fibroblasts, and a human keratinocyte line (HaCaT). Epidermal cells could be seen growing easily and achieved confluence on the fibrin glue on the upper surface of the scaffold. Scanning electron microscopy showed typical shuttle-like fibroblasts adhering to the wall of the scaffold and fluorescence microscopy showed them growing in the dermal layer of the scaffold. The constructed composite skin substitute had a histological structure similar to that of normal skin tissue after three weeks of culture. The results of our study suggest that the asymmetric scaffold is a promising biologically functional material for skin tissue engineering, with prospects for clinical applications.

Reversibly immortalized keratinocytes(iKera)facilitate re-epithelization and skin wound healing:Potential applications in cell-based skin tissue engineering

Skin injury is repaired through a multi-phase wound healing process of tissue granulation and re-epithelialization.Any failure in the healing process may lead to chronic non-healing wounds or abnormal scar formation.Although significant progress has been made in developing novel scaffolds and/or cell-based therapeutic strategies to promote wound healing,effective management of large chronic skin wounds remains a clinical challenge.Keratinocytes are critical to re-epithelialization and wound healing.Here,we investigated whether exogenous keratinocytes,in combination with a citrate-based scaffold,enhanced skin wound healing.We first established reversibly immortalized mouse keratinocytes(iKera),and confirmed that the iKera cells expressed keratinocyte markers,and were responsive to UVB treatment,and were non-tumorigenic.In a proof-of-principle experiment,we demonstrated that iKera cells embedded in citrate-based scaffold PPCN provided more effective re-epithelialization and cutaneous wound healing than that of either PPCN or iKera cells alone,in a mouse skin wound model.Thus,these results demonstrate that iKera cells may serve as a valuable skin epithelial source when,combining with appropriate biocompatible scaffolds,to investigate cutaneous wound healing and skin regeneration.

壳多糖-胶原-糖胺聚糖凝胶人工皮肤的初步研究

目的 研制一种新型的胶原凝胶类人工皮肤。方法 制备壳多糖 -胶原 -糖胺聚糖 (GAGs) -成纤维细胞真皮替代物 (DE) ,观察成纤维细胞 (FB)在凝胶中的生长情况和不同因素对凝胶收缩的影响 ,并绘制 FB生长曲线和凝胶收缩曲线。了解不同含量壳多糖对 FB和角质形成细胞 (KC)生长的影响 ,不同含量壳多糖 DE的抗感染能力。再于“成熟”的 DE表面接种 KC,先浸没培养 ,后行气液界面培养 ,构建完整的人工皮肤。对 DE和人工皮肤行组织学和电镜分析。结果 DE收缩度与 FB数量呈正比 ,终末收缩度与胶原蛋白浓度成反比 ;FB在凝胶中 2～ 9天呈指数增生。 DE基质配方对 FB的生长无明显抑制作用 ,但可促进 KC的生长 ,对金黄色葡萄球菌的抑制作用随壳多糖含量增大而增强。扫描电镜示 DE有丰富的微孔结构。人工皮肤组织学观察见类似于正常皮肤 ,有分化良好的表皮和致密的真皮。结论壳多糖 -胶原 - GAGs胶原凝胶人工皮肤是一种新型、有一定抗感染能力的活人工皮肤。

3D-SC人工皮肤材料体内降解实验研究

目的测试3D-SC人工皮肤材料在动物体内的降解性。方法将一定大小的材料真空干燥后植入动物背部皮下,分阶段取出植入材料,观察材料及周围组织情况,将取出的材料真空干燥至恒重。计算材料的质量损失百分率。结果未见材料周围组织异常,第3天材料质量增加3.39%,以后逐渐降低,第7、14、28、42、56、70、84、98天材料质量损失百分率分别为2.06%、7.58%、14.31%、26.83%、37.45%、38.08%、85.45%、87.26%。结论3D-SC人工皮肤材料是一种具有优良生物降解性能的材料,降解产物无毒性,在体内降解过程中表现出较好的生物相容性。70d内降解相对较慢,70d后降解速度加快,降解产物被动物吸收。

基于自组装交联的水凝胶在皮肤损伤中的应用

自组装水凝胶具有高吸水性、高保水性、良好的生物相容性、生物降解性和三维立体结构等物理优势,同时具备止血、抗菌、抗炎、抗氧化等功能优势。因此自组装水凝胶作为一种新型伤口敷料,在皮肤损伤的创面愈合和调节再生中具有广阔的应用前景。本文通过分析讨论自组装水凝胶的交联机制,阐述自组装水凝胶的功能,明确其作为伤口敷料在皮肤损伤中的优势,总结自组装水凝胶在皮肤损伤应用中的发展趋势,展望自组装水凝胶的未来方向,有助于更全面地了解自组装水凝胶,为自组装水凝胶的多技术联合应用提供新思路。

壳聚糖-明胶海绵与脐带间充质干细胞修复皮肤伤口的差异

背景:脐带间充质干细胞有多向分化和自我复制能力,在一定条件下可以向骨细胞、软骨细胞、平滑肌细胞、神经细胞以及血管内皮细胞分化,有助于表皮再植和血管生成。目的:比较脐带间充质干细胞与壳聚糖-明胶海绵在伤口愈合方面的作用。方法:将30只雄性SD大鼠等分为模型组、壳聚糖-明胶海绵组和脐带间充质干细胞组。3组大鼠均在背部建立3 cm×3 cm全层皮肤缺损创面。造模后1 d起,模型组连续15 d皮肤伤口边缘注射PBS;壳聚糖-明胶海绵组连续15 d在皮肤伤口边缘注射壳聚糖凝胶;脐带间充质干细胞组在皮肤伤口边缘注射脐带间充质干细胞。结果与结论:与模型组相比,壳聚糖-明胶海绵组和脐带间充质干细胞组大鼠创面愈合率较高,表皮厚度降低,胶原纤维面积升高;且脐带间充质干细胞组效果优于壳聚糖-明胶海绵组。说明壳聚糖-明胶海绵和脐带间充质干细胞均可有效修复皮肤损伤,且脐带间充质干细胞效果更佳。

聚乳酸-羟基乙酸共聚物和胶原膜对体外培养人表皮角质细胞分泌细胞因子的影响

目的探讨聚乳酸-羟基乙酸共聚物(PLGA)和胶原膜对表皮角质细胞分泌细胞因子的影响及其在创面修复中的可能作用机制。方法实验组分为PLGA组和胶原膜组,表皮角质细胞以3×107cm-2密度分别种植于PLGA和胶原膜上;对照组为单层表皮角质细胞培养。于第7天和第14天扫描电镜下观察细胞生长状况;种植后第1,3,5,7,14天收集细胞培养上清液,检测乳酸脱氢酶(LDH)水平观察细胞损伤程度,应用ELISA法检测培养上清液中白细胞介素-1β(IL-1β)、白细胞介素-6(IL-6)和白细胞介素8(IL-8)的水平。结果表皮角质细胞种植后第7天,扫描电镜下可见细胞粘附于PLGA和胶原膜呈原有三维结构稳定均一生长,第14天有纤维丝状细胞外基质生成。实验组和对照组各时相点LDH水平差别无统计学意义。PLGA组和胶原膜组表皮角质细胞分泌IL-1β、IL-6和IL-8水平与对照组比较均有不同程度上升,其差别具有统计学意义(P<0.05或P<0.01)。结论PLGA和胶原膜在构建组织工程皮肤中作为一种生物支架,增强表皮角质细胞分泌IL-1β、IL-6和IL-8能力,对加速创面愈合可能起着积极作用。