Trends in Biotechnology
Available online 28 September 2024
2024 年 9 月 28 日上线
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Review 审查
Engineering next-generation oxygen-generating scaffolds to enhance bone regeneration
设计下一代产氧支架以增强骨再生

工程技术TOPEI检索SCI升级版 工程技术1区SCI基础版 工程技术1区IF 14.3 如果14.3SWJTU A++ 西南交通大学A++
https://doi.org/10.1016/j.tibtech.2024.09.006 Get rights and content 获取权利和内容

Highlights 亮点

  • Oxygen (O2) signaling in the bone microenvironment is tightly regulated with spatiotemporal precision, and this poses challenges when replicating these conditions for healing bone defects.
    骨微环境中的氧 (O 2 ) 信号受到时空精度的严格调控,这在复制这些条件来修复骨缺损时提出了挑战。
  • In bone tissue engineering (BTE), oxygen-generating scaffolds (OGS) provide spatiotemporal control of the O2 supply that is essential for cell viability and tissue regeneration, particularly in poorly vascularized and critical-sized bone defects.
    在骨组织工程 (BTE) 中,产氧支架 (OGS) 提供 O 2供应的时空控制,这对于细胞活力和组织再生至关重要,特别是在血管化不良和临界尺寸的骨缺损中。
  • Current efforts in BTE trend towards the development of stimulus-responsive 'smart' biomaterials for OGS.
    目前 BTE 的努力趋势是开发用于 OGS 的刺激响应“智能”生物材料。
  • Emerging research emphasizes the development of new imaging techniques to monitor the spatiotemporal distribution of O2 and reactive oxygen species (ROS) in vivo.
    新兴研究强调开发新的成像技术来监测体内O 2和活性氧 (ROS) 的时空分布。
  • Combining data-driven machine learning (ML) strategies, in vivo imaging techniques, and materials science with biomanufacturing provides a unique opportunity for the design of novel OGS.
    将数据驱动的机器学习 (ML) 策略、体内成像技术、材料科学与生物制造相结合,为新型 OGS 的设计提供了独特的机会。

Abstract 抽象的

In bone, an adequate oxygen (O2) supply is crucial during development, homeostasis, and healing. Oxygen-generating scaffolds (OGS) have demonstrated significant potential to enhance bone regeneration. However, the complexity of O2 delivery and signaling in vivo makes it challenging to tailor the design of OGS to precisely meet this biological requirement. We review recent advances in OGS and analyze persisting engineering and translational hurdles. We also discuss the potential of computational and machine learning (ML) models to facilitate the integration of novel imaging data with biological readouts and advanced biomanufacturing technologies. By elucidating how to tackle current challenges using cutting-edge technologies, we provide insights for transitioning from traditional to next-generation OGS to improve bone regeneration in patients.
在骨骼中,充足的氧气 (O 2 ) 供应在发育、体内平衡和愈合过程中至关重要。产氧支架(OGS)已被证明具有促进骨再生的巨大潜力。然而,体内O 2传递和信号传导的复杂性使得定制 OGS 的设计以精确满足这种生物学要求具有挑战性。我们回顾了 OGS 的最新进展,并分析了持续存在的工程和转化障碍。我们还讨论了计算和机器学习 (ML) 模型在促进新颖成像数据与生物读数和先进生物制造技术集成方面的潜力。通过阐明如何使用尖端技术应对当前的挑战,我们提供了从传统 OGS 过渡到下一代 OGS 的见解,以改善患者的骨再生。

Keywords 关键词

oxygen generation
biomaterials
hypoxia
imaging
computational modeling
machine learning

氧气产生
生物材料
缺氧
成像
计算建模
机器学习

Oxygen-generating scaffolds in bone tissue engineering: impact and opportunities
骨组织工程中的产氧支架:影响和机遇

Bone tissue engineering (BTE) combines stem cells, bioactive factors, and/or biodegradable carriers and has been developed as a promising therapeutic alternative to autografts (see Glossary) and allografts for treating critical-sized bone defects. A major challenge in developing scaffolds to regenerate bone in large injuries is an inadequate supply of O2 to cells within the regenerating tissue, and this can lead to cell apoptosis, tissue necrosis, and delayed healing due to hypoxic environments [1]. Oxygenated biomaterials can overcome ischemia and stimulate tissue healing and bone regeneration [2]. Within large BTE constructs, oxygenated scaffolds are broadly categorized into O2-carrying scaffolds (OCS) or OGS, both of which enable spatiotemporal control of O2 delivery. In preclinical or animal models, OCS and OGS have resulted in enhanced bone regeneration [3,4]. However, improving the scaffold design requires that the field addresses deficits in three broad areas: (i) biological underpinnings – what are the underlying mechanisms via which O2 enhances bone healing, and what is the optimal delivery profile (dosing and timing) necessary to maximize bone regeneration? (ii) Technical limitations in the ability to manufacture scaffolds with the appropriate features to provide O2 with tailored spatiotemporal profiles based on dynamic physiological demands. (iii) Overcoming the logistic and translational barriers to using OCS and OGS in clinical settings. This review synthesizes recent advances in the design and preclinical applications of OCS and OGS while highlighting ongoing challenges and providing insights into how an integrative framework that incorporates cutting-edge but underexplored technologies can herald the design and clinical translation of next-generation OGS.
骨组织工程 (BTE) 结合了干细胞、生物活性因子和/或可生物降解载体,已被开发为自体移植物(参见术语表)和同种异体移植物的有前景的治疗替代方案,用于治疗临界尺寸的骨缺损。开发用于大损伤骨再生的支架的一个主要挑战是再生组织内细胞的O 2供应不足,这可能导致细胞凋亡、组织坏死以及由于缺氧环境导致的愈合延迟[ 1 ]。含氧生物材料可以克服缺血并刺激组织愈合和骨再生[ 2 ]。在大型 BTE 结构中,含氧支架大致分为 O 2承载支架 (OCS) 或 OGS,这两种支架都能够时空控制 O 2输送。在临床前或动物模型中,OCS 和 OGS 已导致骨再生增强 [ 3 , 4 ]。然而,改进支架设计需要该领域解决三个广泛领域的缺陷:(i) 生物学基础——O 2促进骨愈合的基本机制是什么,以及 O 2 促进骨愈合所需的最佳输送方式(剂量和时间)是什么?最大化骨再生? (ii)制造具有适当特征的支架以根据动态生理需求提供具有定制时空分布的O 2 的能力的技术限制。 (iii) 克服在临床环境中使用 OCS 和 OGS 的后勤和翻译障碍。这篇综述综合了 OCS 和 OGS 的设计和临床前应用的最新进展,同时强调了持续存在的挑战,并提供了关于如何整合尖端但尚未充分探索的技术的综合框架如何预示下一代 OGS 的设计和临床转化的见解。

O2 as a cellular signaling molecule
O 2作为细胞信号分子

O2 is a major signaling molecule that regulates cellular proliferation and differentiation. However, defining normoxia, hypoxia, and hyperoxia for specific biological tissues or organs is complex, as O2 needs vary among different tissues [5]. For instance, the partial O2 pressure (pO2) of arterial blood is only 95 mmHg whereas atmospheric pO2 is 160 mmHg (20%). This is lower in the periosteum, cortical bone, and bone marrow; the latter has a pO2 of <32 mmHg (4%) [6]. Therefore, the level of atmospheric O2 is hyperoxic for the bone microenvironment, increases the production of reactive oxygen species (ROS), and has detrimental effects on osseous cells [7]. Hence, to develop optimized OCS and OGS for bone regeneration, a thorough understanding of variations in the O2 levels in key cell types within the regenerating bone microenvironment is essential.
O 2是调节细胞增殖和分化的主要信号分子。然而,对特定生物组织或器官的常氧、缺氧和高氧的定义是复杂的,因为不同组织对 O 2 的需求有所不同[ 5 ]。例如,动脉血的O 2分压(pO 2 )仅为95 mmHg,而大气pO 2为160 mmHg (20%)。骨膜、皮质骨和骨髓的含量较低;后者的pO 2为<32 id=9> 6 ]。因此,大气中的O 2水平对于骨微环境来说是高氧的,增加了活性氧(ROS)的产生,并对骨细胞产生有害影响[ 7 ]。因此,为了开发用于骨再生的优化 OCS 和 OGS,彻底了解再生骨微环境中关键细胞类型中 O 2水平的变化至关重要。

Effect of O2 on osteogenesis during bone healing
O 2对骨愈合过程中成骨的影响

O2 tensions of 6.6–8.6% are physiologically relevant for overall bone formation and homeostasis [8., 9., 10.]. Even so, excessively low pO2 has detrimental effects on bone cells [11]. For example, exposure to 2% O2 resulted in a tenfold decrease in bone formation, nearly halting it when reduced to 0.2% [12]. This reduction may be due to decreased Runx2 expression [13], inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways [14], or impaired collagen crosslinking which disrupts bone matrix mineralization [12]. Furthermore, osteoclast activity and number increase in response to 2% O2, with a tenfold increase in resorption pit formation and a 21-fold increase in osteoclast activity. During fracture healing, which resembles the healing process of artificial implants, osteoprogenitors were recruited early and proliferated during soft callus formation, and their activity was crucial during hard callus formation and bone remodeling [15]. O2 tension was measured to be 0.8% at the 4 day post-fracture hematoma stage and increased to only 3.8% at the 2 week stage of newly formed fibrous bone [7], suggesting that elevating O2 tension for sustained periods following injury may enhance tissue healing (Figure 1).
6.6-8.6% 的 O 2张力在生理上与整体骨形成和体内平衡相关[ 8. , 9. , 10. ]。即便如此,过低的 pO 2也会对骨细胞产生不利影响[ 11 ]。例如,暴露于 2% O 2会导致骨形成减少十倍,当减少到 0.2% 时,骨形成几乎停止[ 12 ]。这种减少可能是由于 Runx2 表达减少 [ 13 ]、磷脂酰肌醇 3-激酶 (PI3K)/Akt 信号通路抑制 [ 14 ] 或胶原交联受损从而破坏骨基质矿化 [ 12 ]。此外,破骨细胞活性和数量随着2% O 2 的增加而增加,吸收坑形成增加10倍,破骨细胞活性增加21倍。在骨折愈合过程中,类似于人工植入物的愈合过程,骨祖细胞在软愈伤组织形成过程中早期招募并增殖,它们的活性在硬愈伤组织形成和骨重塑过程中至关重要[ 15 ]。在骨折后血肿阶段第 4 天测量 O 2张力为 0.8%,并增加至仅 3。在新形成的纤维骨的第 2 周阶段为 8% [ 7 ],这表明损伤后持续升高 O 2张力可能会增强组织愈合(图 1 )。
Figure 1
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    下载:下载高分辨率图像 (345KB)
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Figure 1. Cellular activity profile based on cell types and O2 demand and desired supply for the design of an oxygen-generating scaffold (OGS).
图1 。基于细胞类型和 O 2需求以及产氧支架 (OGS) 设计所需供应的细胞活性概况。

(A) The cellular activity of osteoprogenitors [122,123], neovascularization processes [33], and M1/M2 macrophages [23,26., 27., 28., 29.] are illustrated for the four stages of bone healing (hematoma formation, soft callus formation, hard callus formation, and bone remodeling). (B) The black curve represents the tissue O2 partial pressure (pO2) at different bone-healing stages without OGS intervention [7,17., 18., 19.]. The healthy bone pO2 range of 6.6–8.6% indicates normal O2 levels in bone homeostasis [8., 9., 10.]. Based on the deficient O2 profile, one can predict a desired O2 supply profile (purple) provided by OGS to meet real-time O2 needs during bone healing. Figure created with BioRender.
(A) 骨祖细胞 [ 122 , 123 ]、新血管形成过程 [ 33 ] 和 M1/M2 巨噬细胞 [ 23 , 26. , 27. , 28. , 29. ] 的细胞活性显示了骨愈合的四个阶段(血肿形成、软愈伤组织形成、硬愈伤组织形成和骨重塑)。 (B) 黑色曲线代表在没有 OGS 干预的情况下不同骨愈合阶段的组织 O 2分压 (pO 2 ) [ 7 , 17. , 18. , 19. ]。健康骨 pO 2范围为 6.6–8.6%,表明骨稳态中 O 2水平正常[ 8.9.10. ]。根据不足的 O 2分布,可以预测 OGS 提供的所需 O 2供应分布(紫色),以满足骨愈合期间的实时 O 2需求。使用 BioRender 创建的图形。

Effect of O2 on angiogenesis during bone healing
O 2对骨愈合过程中血管生成的影响

Hypoxia promotes angiogenesis through multifaceted signaling involving a combination of angiogenic factors and inflammatory cytokines. Although acute hypoxia appears to be essential for stimulating wound healing, prolonged or chronic hypoxia lasting for >7 days has been shown to delay the tissue repair process [16]. Despite vascular infiltration, low local O2 tension persists longer with increasing defect size, extending from 2 weeks [17,18] to 10 weeks post-injury [19]. Since angiogenesis is crucial for bone healing and regeneration, a major concern with O2-releasing scaffolds was that they might hinder vascular infiltration and subsequent tissue regeneration. However, O2-generating calcium peroxide (CaO2)/gelatin microspheres developed for treating osteonecrosis demonstrated enhanced angiogenesis, and CD31+ vessels were prevalent in the defect area 4 weeks post-surgery [20]. Similarly, injectable sodium alginate/carboxymethyl chitosan (CMC)/CaO2 hydrogel led to ectopic osteogenesis in rat subcutaneous defects [21], and significantly greater blood vessel volumes were observed in scaffolds with 25% CaO2 compared with control poly(ε-caprolactone) (PCL) scaffolds [22]. Although not statistically significant, a higher density of 'type H' vessels was observed in CaO2PCL scaffold groups, suggesting that these proregenerative vessel subtypes may be characteristic of the oxygenated microenvironment [22].
缺氧通过涉及血管生成因子和炎症细胞因子组合的多方面信号传导促进血管生成。尽管急性缺氧似乎对于刺激伤口愈合至关重要,但持续 >7 天的长期或慢性缺氧已被证明会延迟组织修复过程 [ 16 ]。尽管有血管浸润,但随着缺损尺寸的增加,局部低O 2张力持续时间更长,从受伤后2周[ 17 , 18 ]延长到10周[ 19 ]。由于血管生成对于骨愈合和再生至关重要,因此释放O 2的支架的一个主要问题是它们可能阻碍血管浸润和随后的组织再生。然而,为治疗骨坏死而开发的产生O 2的过氧化钙(CaO 2 )/明胶微球显示出增强的血管生成,并且术后4周缺损区域普遍存在CD31 +血管[ 20 ]。同样,可注射的海藻酸钠/羧甲基壳聚糖(CMC)/CaO 2水凝胶导致大鼠皮下缺损中的异位成骨[ 21 ],并且与对照聚(ε-己内酯)相比,在含有25% CaO 2的支架中观察到显着更大的血管体积)(PCL)支架[ 22 ]。 虽然没有统计学意义,但在 CaO 2 PCL 支架组中观察到较高密度的“H 型”血管,表明这些再生血管亚型可能是含氧微环境的特征 [ 22 ]。

Effects of O2 on immune responses during bone healing
O 2对骨愈合过程中免疫反应的影响

Hypoxia elevates hypoxia-inducible factor 1α (HIF-1α) expression and induces the recruitment of neutrophils, macrophages, endothelial cells, and subsequently fibroblasts to the wound site [23]. In hypoxic environments, macrophages switch their metabolism from oxidative phosphorylation towards glycolysis, and this biases them toward the M1 phenotype [24,25]. Although the prolonged presence of M1 macrophages causes inflammation and hinders healing, they are crucial for the initiation of bone healing through clearing cell debris and pathogens, and the recruitment of more immune cells [26]. Thus, ideally, acute hypoxia for up to 48 h might benefit bone healing. Subsequent angiogenesis alleviates hypoxia and facilitates the transition of macrophages from M1 to M2, thus promoting tissue repair [27,28]. M2 macrophages continue to be active during the ossification phase and support bone remodeling (Figure 1A) [29]. Oxygenated biomaterials with a transient O2 release profile provide an opportunity to alter immune cell behavior from proinflammatory to proregenerative within a few days post-implantation. Efforts have been directed towards investigating the immunomodulatory potential of ROS-scavenging bone scaffolds which can influence M1 to M2 macrophage polarization [27,30]. O2 release from OGS could facilitate such a transition and stabilize bone repair through M2 polarization.
缺氧会提高缺氧诱导因子 1α (HIF-1α) 的表达,并诱导中性粒细胞、巨噬细胞、内皮细胞以及随后的成纤维细胞募集到伤口部位 [ 23 ]。在缺氧环境中,巨噬细胞将其代谢从氧化磷酸化转变为糖酵解,这使它们偏向于 M1 表型 [ 24 , 25 ]。尽管M1巨噬细胞的长期存在会引起炎症并阻碍愈合,但它们通过清除细胞碎片和病原体以及招募更多免疫细胞,对于启动骨愈合至关重要[ 26 ]。因此,理想情况下,急性缺氧长达 48 小时可能有利于骨愈合。随后的血管生成缓解缺氧并促进巨噬细胞从M1向M2的转变,从而促进组织修复[ 27 , 28 ]。 M2 巨噬细胞在骨化阶段继续活跃并支持骨重塑(图 1 A)[ 29 ]。具有瞬时氧气释放特性的氧化生物材料提供了在植入后几天内将免疫细胞行为从促炎性改变为促再生性的机会。人们一直致力于研究 ROS 清除骨支架的免疫调节潜力,它可以影响 M1 到 M2 巨噬细胞的极化 [ 27 , 30 ]。 OGS 释放的 O 2可以促进这种转变并通过 M2 极化稳定骨修复。
In summary, O2 generation and/or release from an implant should maintain O2 tension between 6.6 and 8.6%, a level that is crucial for bone formation and homeostasis, until blood vessel infiltration is stabilized – a process that typically takes at least 2 weeks (Figure 1B) [17]. An acute moderately hypoxic environment (1–5% O2 for 24–48 h) immediately post-implantation could enhance immune response and angiogenesis [26,31,32], although this is highly dependent on the cell type and might require further consideration regarding the specific experimental conditions. As the BTE construct size increases to a clinically relevant scale, O2 deficiency would progressively become a problem, necessitating adjustments in the O2 delivery profile to ensure immediate O2 availability. Consequently, the release rate of oxygenated scaffolds designed for bone repair should match the physiological O2 demand within the defect site.
总之,植入物产生和/或释放的 O 2应将 O 2张力维持在 6.6% 至 8.6% 之间,这一水平对于骨形成和体内平衡至关重要,直到血管浸润稳定为止——这一过程通常至少需要 2周(图 1 B)[ 17 ]。植入立即处于急性中度缺氧环境(1-5% O 2 ,​​持续 24-48 小时)可以增强免疫反应和血管生成 [26,31,32 ] ,尽管这高度依赖于细胞类型,可能需要进一步考虑关于具体的实验条件。随着 BTE 构造尺寸增加到临床相关规模,O 2缺乏将逐渐成为一个问题,需要调整 O 2输送曲线以确保立即获得 O 2可用性。因此,设计用于骨修复的含氧支架的释放速率应与缺损部位内的生理O 2需求相匹配。

In vivo O2 measurements during bone regeneration
骨再生过程中的体内O 2测量

Measurements of O2 in vivo following fractures could provide further insights into the desired biomaterial designs. However, it is challenging to characterize the complex in vivo dynamics of oxygenation during bone-healing processes. Recent advances in in vivo imaging techniques have provided insights into the role of O2 during bone healing and how tissue-engineering methods can be applied more efficaciously (Table 1). The different imaging methods for characterizing O2 in vivo have their own advantages and disadvantages, as summarized in Table 1. For example, high-resolution optical imaging techniques can suffer from poor tissue penetration [18,33., 34., 35., 36., 37., 38.], whereas methods with deeper tissue penetration tend to have lower spatial resolution [39., 40., 41.] or require complex hardware [42] or specialized contrast agents [43., 44., 45.]. Clinically relevant methods for assessing O2 may provide excellent tissue depth coverage, but may lack sensitivity or have limited probe availability [46., 47., 48.].
骨折后体内O 2的测量可以为所需的生物材料设计提供进一步的见解。然而,表征骨愈合过程中复杂的体内氧合动力学具有挑战性。体内成像技术的最新进展让我们深入了解 O 2在骨愈合过程中的作用以及如何更有效地应用组织工程方法(表 1 )。用于表征体内O 2 的不同成像方法各有优缺点,如表 1所示。例如,高分辨率光学成像技术可能会受到组织穿透力差的影响[ 18、33 .34.35.36.37.38. ],而组织穿透力较深的方法往往具有较低的空间分辨率[ 39.40.41. ]或需要复杂的硬件[ 42 ]或专门的造影剂[ 43.44.45. ]。 用于评估 O 2的临床相关方法可能提供出色的组织深度覆盖,但可能缺乏灵敏度或探头可用性有限[ 46.47.48. ]。

Table 1. Methods suitable for imaging OGSa
表 1 .适用于OGS成像的方法

Imaging modality 成像方式Measured parameter 测量参数Tissue penetration 组织渗透Spatial resolution 空间分辨率Advantages 优点Limitations 局限性Refs 参考文献
Imaging modalities measuring O2-related parameters
测量 O 2相关参数的成像方式
IOS imaging iOS成像SO2<500 μm5–100 μm 5–100微米Easy to implement 易于实施Low penetration, 2D 低穿透力,二维[33,34]
PA imaging PA成像SO2>5 mm >5毫米50–150 μm 50–150 微米Provides both structural and functional information
提供结构和功能信息
Complex system 复杂系统[42]
[ 42 ]
OCTSO21–3 mm 1–3 毫米1–15 μmHigh resolution 高分辨率Limited penetration 渗透有限[35., 36., 37.] [35.、36.、37.]
EPRpO2 氧分压25–10 mm for high frequency, 8 cm or more for low frequency
高频5-10mm,低频8cm以上
0.5–5 mm 0.5–5 毫米High accuracy and precision for O2 measurements
O 2测量的高精度和高精度
Low resolution 低分辨率[39., 40., 41.] [39.、40.、41.]
Imaging modality measuring ROS
测量 ROS 的成像方式
Ultrasound 超声波ROS>10mm20–200 μmCan mediate ROS generation
可以介导 ROS 的生成
Relatively low resolution, a contrast agent (microbubbles) is needed
分辨率相对较低,需要造影剂(微泡)
[43., 44., 45.] [43.、44.、45.]
Imaging modalities measuring O2-related parameters and ROS
测量 O 2相关参数和 ROS 的成像方式
Two/multiphoton 两个/多光子pO2, ROS 氧分压,活性氧500 μm–1 mm 500μm–1毫米Sub-micron 亚微米High resolution, depth-resolved
高分辨率、深度解析
Low penetration, small FOV
穿透力低、视场小
[18,38]
MRIStO2, ROS
氧化钛,活性氧
Full body 全身5–200 μmExcellent imaging penetration depth, clinically relevant
出色的成像穿透深度,临床相关
Low sensitivity, limited molecular probes
灵敏度低,分子探针有限
[46., 47., 48.] [46.、47.、48.]
BLIHypoxia, ROS 缺氧、活性氧10mm 10毫米2–3 mm 2-3毫米High SNR and selectivity 高信噪比和选择性Low resolution 低分辨率[124,125]
PETHypoxia, ROS 缺氧、活性氧Full body 全身1–2 mm 1–2 毫米High sensitivity, various probes available
高灵敏度,多种探头可供选择
Low resolution 低分辨率[126,127]
a
Abbreviations: BLI, bioluminescence imaging; EPR, electron paramagnetic resonance; IOS, intrinsic optical signal; MRI, magnetic resonance imaging; OCT, optical coherence tomography; PA imaging, photoacoustic imaging; PET, positron emission tomography; PO2, oxygen partial pressure; ROS, reactive oxygen species; SNR, signal to noise ratio; SO2, oxygen saturation; StO2, tissue oxygen saturation.
缩写:BLI,生物发光成像; EPR,电子顺磁共振; IOS,本征光信号; MRI、磁共振成像; OCT,光学相干断层扫描; PA成像、光声成像; PET,正电子发射断层扫描; PO 2 ,​​氧分压; ROS,活性氧; SNR,信噪比; SO 2 ,​​氧饱和度; StO 2 ,​​组织氧饱和度。
Given these developments, we foresee that future research on in vivo O2 imaging will be focused on combining the strengths of extant methods while mitigating their inherent weaknesses. This could include the development of multimodality imaging approaches that integrate complementary image contrast mechanisms to provide more comprehensive O2 mapping during the bone-healing cascade [49]. In addition, there is a dearth of imaging techniques tailored for real-time in vivo imaging of OGS designed for bone-healing applications. Although several in vivo imaging methods have been employed to study OGS within wound-healing contexts [50], and other in vivo O2 imaging methods, such as optical coherence tomography (OCT) [51] and electron paramagnetic resonance (EPR) imaging [52], have been utilized for tissue-engineering applications, their use for bone imaging remains limited due to issues related to their widespread availability, tissue penetration, and light scattering. Furthermore, there is a crucial need for novel noninvasive methods with high spatial and temporal resolution to characterize OGS efficacy in vivo. Enhancing the specificity and sensitivity of O2-sensitive imaging probes and sensors, as well as reducing the cost and complexity of imaging hardware, will be essential to advance the field and make such methods accessible and clinically translatable. Looking ahead, we anticipate that technical advances in this area will include the synthesis of novel O2-sensitive imaging probes [53] or sensors, or wearable devices [54] that enable real-time, localized imaging of O2 release within bone.
鉴于这些进展,我们预计体内O 2成像的未来研究将集中于结合现有方法的优点,同时减轻其固有的缺点。这可能包括开发多模态成像方法,整合互补的图像对比机制,以在骨愈合级联过程中提供更全面的 O 2映射[ 49 ]。此外,还缺乏专为骨愈合应用而设计的 OGS 实时体内成像定制的成像技术。尽管已经采用几种体内成像方法来研究伤口愈合背景下的 OGS [ 50 ],以及其他体内O 2成像方法,例如光学相干断层扫描 (OCT) [ 51 ] 和电子顺磁共振 (EPR) 成像 [ [ 52 ],已用于组织工程应用,但由于其广泛可用性、组织穿透和光散射等相关问题,它们在骨成像中的使用仍然受到限制。此外,迫切需要具有高空间和时间分辨率的新型非侵入性方法来表征 OGS体内功效。提高O 2敏感成像探头和传感器的特异性和灵敏度,以及降低成像硬件的成本和复杂性,对于推进该领域并使此类方法易于使用和临床可转化至关重要。 展望未来,我们预计该领域的技术进步将包括合成新型 O 2敏感成像探针 [ 53 ] 或传感器,或可穿戴设备 [ 54 ],从而实现骨内 O 2释放的实时、局部成像。
The methodological advances described earlier are essential for the development of next-generation OGS because they not only can enhance our understanding of the role of O2 in bone healing but can also inform the design of better biomaterials. For example, exciting results from prior imaging studies have guided the design of novel OGS (Figure 2). Multiphoton microscopy has revealed how the early stages of bone repair often involve severe hypoxia, whereas the later stages exhibit O2 fluctuations, indicating the need for targeted oxygenation strategies at the different stages of healing (Figure 2A,B) [18]. Furthermore, continuous monitoring of O2 with multi-wavelength intrinsic optical signal (IOS) imaging revealed intricate changes in intravascular oxygenation in the spatial and temporal domains [33], highlighting the need to factor in spatiotemporal variations in O2 when optimizing OGS design and bone regeneration (Figure 2C,D). In addition, photoacoustic imaging revealed the role of O2 availability for successful healing of union and non-union bone defects, wherein the oxygen saturation (SO2) in non-union defects was much lower compared with union defects at various phases of healing (Figure 2E,F) [19]. Although still in the nascent stage within the context of OGS development, in vivo imaging technologies hold great promise for unraveling the mechanisms underlying bone oxygenation dynamics. The insights derived from these cutting-edge imaging techniques underscore their potential to inform therapeutic tissue-engineering approaches and improve the management of skeletal injuries.
前面描述的方法学进步对于下一代 OGS 的开发至关重要,因为它们不仅可以增强我们对 O 2在骨愈合中作用的理解,而且还可以为更好的生物材料的设计提供信息。例如,先前成像研究的令人兴奋的结果指导了新型 OGS 的设计(图 2 )。多光子显微镜揭示了骨修复的早期阶段经常出现严重缺氧,而后期阶段则表现出O 2波动,这表明在不同的愈合阶段需要有针对性的氧合策略(图2 A,B)[ 18 ]。此外,通过多波长本征光信号(IOS)成像对 O 2进行连续监测,揭示了血管内氧合在空间和时间域中的复杂变化[ 33 ],这凸显了在优化 OGS 设计和优化时需要考虑 O 2 的时空变化。骨再生(图2C 、D)。此外,光声成像揭示了O 2可用性对于愈合和不愈合骨缺损成功愈合的作用,其中在愈合的各个阶段,不愈合缺陷中的氧饱和度(SO 2远低于愈合缺陷。图 2 E、F)[ 19 ]。 尽管 OGS 发展仍处于初级阶段,但体内成像技术对于揭示骨氧合动力学的机制具有巨大的希望。从这些尖端成像技术中得出的见解强调了它们为治疗组织工程方法提供信息并改善骨骼损伤管理的潜力。
Figure 2
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Figure 2. In vivo imaging provides novel insights into O2 changes during bone healing.
图2 .体内成像为骨愈合过程中 O 2 的变化提供了新的见解。

(A,B) Multiphoton microscopy was used to detect changes in O2 tension during calvarial bone healing [18]. (A) PtP-C343, an O2-sensitive probe, was integrated into an electrospun fiber mesh (green) to enable fluorescence-based measurements of O2 tension during calvarial defect (broken-line circle) healing through a cranial window over 32 days. Multiple regions of interest (labeled A–C) were measured within the defect. (B) Quantitative analysis showed a significant decrease in O2 in all the measured regions on the 7th day post-surgery, followed by their recovery over the next few weeks (*P < 0.05). (C,D) In vivo multiwavelength intrinsic optical signal (IOS) imaging reveals intricate changes in intravascular SO2 during calvarial bone defect healing [33]. (C) Intravascular SO2 computed from multiwavelength IOS images indicates that angiogenic vessels near the defect edge (white broken-line circle) exhibited elevated SO2 during the second week of healing (days D10–D16) compared with the rest of the vasculature. (D) Radial plots for the same defect illustrate the spatiotemporal evolution of mean SO2 over 4 weeks. (E,F) Photoacoustic imaging demonstrated differences in O2 saturation during union and non-union bone healing [19]. (E) Hemoglobin O2 saturation was measured in union and non-union mice long bone defects at weeks 2, 5, and 10 after injury. (F) Quantitative analysis revealed significantly lower SO2 in non-union defects compared with union defects at different phases (*P < 0.05 vs. union; a < 0.05 vs. 2 weeks; b < 0.05 vs. 2 and 5 weeks). Image adapted, with permission, from [18,19,33]. Abbreviations: MPSLM, multiphoton laser scanning microscopy; PtP-C343, platinum porphyrin-coumarin-343; SO2, oxygen saturation.
(A,B) 多光子显微镜用于检测颅骨愈合过程中 O 2张力的变化[ 18 ]。 (A) PtP-C343是一种 O 2敏感探针,被集成到电纺纤维网(绿色)中,以便能够在颅骨缺损(虚线圆圈)愈合期间通过超过 32 的颅窗对 O 2张力进行基于荧光的测量天。在缺陷内测量多个感兴趣区域(标记为 A-C)。 (B) 定量分析显示,术后第 7 天所有测量区域的 O 2均显着下降,随后在接下来的几周内恢复 (* P < 0.05)。 (C,D)体内多波长固有光信号 (IOS) 成像揭示了颅骨骨缺损愈合过程中血管内 SO 2的复杂变化[ 33 ]。 (C) 从多波长 IOS 图像计算得出的血管内 SO 2表明,与血管系统的其余部分相比,在愈合第二周(D10–D16 天)期间,缺损边缘(白色虚线圆圈)附近的血管生成血管表现出升高的 SO 2 。 (D) 同一缺陷的径向图说明了 4 周内平均 SO 2的时空演变。 (E,F) 光声成像显示愈合和不愈合骨愈合过程中 O 2饱和度的差异[ 19 ]。 (E)在损伤后第2、5和10周测量愈合和不愈合小鼠长骨缺损的血红蛋白O 2饱和度。 (F) 定量分析显示,与不同阶段的愈合缺陷相比,不愈合缺陷中的 SO 2显着降低(* P < 0.05 与愈合相比;a < 0.05 与 2 周相比;b < 0.05 与 2 周和 5 周相比)。经许可改编的图像来自[18,19,33 ] 缩写:MPSLM,多光子激光扫描显微镜; PtP-C343,铂卟啉-香豆素-343; SO 2 ,​​氧饱和度。

Recent advances in scaffold design
支架设计的最新进展

OCS in bone healing OCS 在骨愈合中的作用

OCS do not generate O2 on their own but serve as vehicles for transporting and delivering O2 at a desired dose to target sites. Examples include hemoglobin-based oxygen carriers (HBOCs), lipid-based O2 microbubbles, O2-laden nanosponges, polymeric microtanks, and perfluorocarbons (PFC). O2 release by these systems is rate-limited by the diffusion of O2 through the polymeric or lipid membrane. For example, O2 was hyperbarically loaded into hollow biodegradable microtanks and incorporated into PCL for subsequent 3D printing into scaffolds. The scaffolds released O2 for up to 8 h – a relatively short period – but enhanced the deposition of extracellular matrix (ECM) in murine calvarial and subcutaneous defects [55], suggesting that even short O2 release at the earliest stages of healing can be beneficial. Owing to their excellent O2 solubility, PFC-based emulsion-loaded hollow microparticles enabled controlled release of O2 for 10 days [56]. They maintained the survival and osteogenic differentiation potential of human periosteal-derived cells under hypoxic conditions and provided a conducive environment for enhanced bone regeneration in miniature pig mandibular defects. However, for PFCs, long-term stability remains a significant concern, as the emulsions often decay during the freeze–thaw storage process or destabilize due to Ostwald ripening [57]. Oxygent, an FDA-approved PFC product, has a half-life of only 12–48 h, which limits its use primarily to temporary blood substitution during surgery [58]. These issues pose significant challenges for the clinical translation of OCS in BTE applications.
OCS 本身并不产生O 2 ,​​而是作为将所需剂量的O 2运输和递送到目标位置的载体。例子包括基于血红蛋白的氧载体(HBOC)、基于脂质的O 2微泡、载有O 2的纳米海绵、聚合物微罐和全氟化碳(PFC)。这些系统释放的O 2受到O 2通过聚合物或脂质膜的扩散的速率限制。例如,O 2被高压加载到中空的可生物降解微型罐中,并掺入 PCL 中,以便随后 3D 打印到支架中。支架释放 O 2 的时间长达 8 小时(相对较短的时间),但增强了小鼠颅骨和皮下缺损中细胞外基质 (ECM) 的沉积 [ 55 ],这表明即使在愈合的最初阶段短暂的 O 2释放也可以是有益的。由于其优异的 O 2溶解度,基于 PFC 的乳液负载中空微粒能够控制 O 2释放 10 天[ 56 ]。它们在缺氧条件下维持了人骨膜来源细胞的存活和成骨分化潜力,并为增强小型猪下颌骨缺损的骨再生提供了有利的环境。然而,对于 PFC 来说,长期稳定性仍然是一个重要问题,因为乳液经常在冻融储存过程中腐烂或由于奥斯特瓦尔德熟化而不稳定[ 57 ]。 Oxygent 是 FDA 批准的 PFC 产品,其半衰期仅为 12-48 小时,这限制了其主要用于手术期间的临时血液替代[ 58 ]。这些问题给 OCS 在 BTE 应用中的临床转化带来了重大挑战。

OGS in bone healing OGS在骨愈合中的应用

Compared with OCS, the maximum O2 load in OGS may be two to four orders of magnitude higher, allowing O2 release lasting from several days to a month. This longer release period potentially provides an advantage in the context of treating critical-sized bone defects. Examples include solid peroxides (sodium percarbonates, manganese oxide, CaO2, etc.), liquid peroxides (hydrogen peroxide, H2O2), and photosynthetic algae [59], of which the solid peroxides are the most promising for BTE applications Sustained O2 release from solid peroxides is achieved by their chemical reaction with the aqueous environment. O2-generating particles are usually encapsulated within micro/nanocarriers such as liposomes, dendrimers, exosomes, nanospheres, nanocapsules, solid–lipid nanoparticles, nanofibers, or polymeric micelles [60], and O2 release from these systems depends on water penetration and polymeric matrix biodegradation.
与OCS相比,OGS中的最大O 2负荷可能高出两到四个数量级,允许O 2释放持续几天到一个月。这种较长的释放期可能在治疗临界尺寸的骨缺损方面提供优势。例子包括固体过氧化物(过碳酸钠、氧化锰、CaO 2等)、液体过氧化物(过氧化氢、H 2 O 2 )和光合藻类[ 59 ],其中固体过氧化物最有希望用于BTE应用。固体过氧化物中O 2 的释放是通过它们与水环境的化学反应来实现的。 O 2生成颗粒通常封装在微/纳米载体中,如脂质体、树枝状聚合物、外泌体、纳米球、纳米胶囊、固体脂质纳米颗粒、纳米纤维或聚合物胶束[ 60 ],这些系统中 O 2 的释放取决于水的渗透和聚合物基质生物降解。
Among solid peroxides, CaO2 is the most prevalently researched in BTE and has been employed in different formulations such as coatings [4,61], composite microspheres and filaments [62., 63., 64.], electrospun nanofibers [60,65,66], and hydrogel systems [3,20,21,67,68]. Used in hydrogel systems [3,67], near-complete bone regeneration in critical-sized calvaria defects was observed after 12 weeks [3], but hydrogels are not suitable for load-bearing applications. Alternatively, CaO2 has been coated onto robocasted biphasic calcium phosphate (BCP) scaffolds [61]. When implanted into a 15 mm segmental radial defect in rabbits, a nearly twofold increase in bone formation was observed 6 months after surgery compared with uncoated scaffolds [4]. In polymer–CaO2 composites, the polymer matrix serves as a hydrophobic barrier that slows O2 release by limiting CaO2–water interactions. However, in electrospinning systems [60,65,66], sustained O2 release does not exceed 2 weeks, probably due to their high surface area. Nevertheless, CaO2-based OGS have shown efficacy in promoting bone growth. PCL–CaO2 microparticles developed by Suvarnapathaki and coworkers demonstrated high viability of preosteoblasts and reduced apoptosis, as confirmed by minimal in vitro caspase 3/7 activity. In vivo results from the same study also revealed that their scaffolds accelerated new bone formation, with less fibrous tissue and better tissue integration over 12 weeks, suggesting long-term safety and efficacy [3]. Gelatin–CaO2 microparticles gave similar in vivo results over 10 weeks, and showed low immunogenicity and a significant reduction in inflammatory cells from the first to the third week post-implantation [69]. These studies collectively highlight the promise of CaO2-based scaffolds in promoting bone regeneration for future clinical applications, while maintaining biocompatibility and reducing adverse immune responses.
在固体过氧化物中,CaO 2在 BTE 中研究最为普遍,并已应用于不同的配方中,例如涂料 [ 4 , 61 ]、复合微球和长丝 [ 62. , 63. , 64. ]、电纺纳米纤维 [ 60 , 65 ] , 66 ] 和水凝胶系统 [ 3 , 20 , 21 , 67 , 68 ]。用于水凝胶系统[ 3 , 67 ],12周后观察到临界大小的颅骨缺损几乎完全再生[ 3 ],但水凝胶不适合承重应用。或者,CaO 2已被涂覆到机器人铸造的双相磷酸钙(BCP)支架上[ 61 ]。当植入兔子的 15 毫米节段性径向缺损时,与未涂层支架相比,术后 6 个月观察到骨形成增加了近两倍 [ 4 ]。 在聚合物-CaO 2复合材料中,聚合物基质充当疏水屏障,通过限制CaO 2 -水相互作用来减缓O 2释放。然而,在静电纺丝系统中[60,65,66 ] ,O 2 的持续释放不会超过2周,这可能是由于它们的高表面积。然而,基于CaO 2的OGS已显示出促进骨生长的功效。 Suvarnapathaki 及其同事开发的 PCL–CaO 2微粒表现出前成骨细胞的高活力并减少了细胞凋亡,这一点通过最小的体外caspase 3/7 活性得到证实。同一项研究的体内结果还显示,他们的支架在 12 周内加速了新骨形成,纤维组织更少,组织整合更好,这表明长期安全性和有效性 [ 3 ]。明胶-CaO 2微粒在 10 周内给出了类似的体内结果,并且显示出较低的免疫原性,并且从植入后第一周到第三周炎症细胞显着减少[ 69 ]。这些研究共同强调了基于CaO 2的支架在促进未来临床应用的骨再生、同时保持生物相容性和减少不良免疫反应方面的前景。
Magnesium peroxide (MgO2), another solid peroxide, exhibits the slowest and most persistent release kinetics of O2 owing to its low decomposition rate [70]. A 3D-printed scaffold composed of PCL, β-tricalcium phosphate (β-TCP), and MgO2 created by Peng and colleagues [70] released O2 over 21 days and facilitated the formation of new bone in a femoral condyle defect model. Mg2+ ions also directly aid bone formation and impede the growth of various tumors through oxidative damage to DNA, making it particularly effective for repairing bone defects after osteosarcoma resection [71]. Similarly, strontium peroxide (SrO2)-based OGS also promoted new bone formation and inhibited bone resorption, leveraging the dual role of strontium in bone metabolism by stimulating osteoblasts and inhibiting osteoclasts [72]. Of note, strontium is recognized not only as a bioactive trace element that supports bone health but also as a component of strontium ranelate, a well-known treatment for postmenopausal osteoporosis.
过氧化镁(MgO 2 )是另一种固体过氧化物,由于其分解速率低,因此表现出最慢且最持久的 O 2释放动力学[ 70 ]。 Peng 及其同事创建的由 PCL、β-磷酸三钙 (β-TCP) 和 MgO 2组成的 3D 打印支架 [ 70 ] 在 21 天内释放 O 2 ,​​并促进股骨髁缺损模型中新骨的形成。 Mg 2+离子还直接帮助骨形成,并通过对 DNA 的氧化损伤阻止各种肿瘤的生长,使其对于修复骨肉瘤切除术后的骨缺损特别有效[ 71 ]。同样,基于过氧化锶(SrO 2 )的OGS也通过刺激成骨细胞和抑制破骨细胞,利用锶在骨代谢中的双重作用,促进新骨形成并抑制骨吸收[ 72 ]。值得注意的是,锶不仅被认为是一种支持骨骼健康的生物活性微量元素,而且还是雷尼酸锶的成分,雷尼酸锶是一种众所周知的绝经后骨质疏松症治疗方法。

Smart stimulus-responsive biomaterials for bone regeneration: harnessing and modulating ROS
用于骨再生的智能刺激响应生物材料:利用和调节 ROS

During the inflammatory and regenerative phases of bone healing, ROS concentrations can increase 100-fold [73., 74., 75.]. This induces oxidative stress in leukocytes and platelets [76], and promotes osteoclast formation and bone resorption [77]. Despite the promise of OGS for bone defect treatment, a significant technical challenge is excessive O2 generation that can exacerbate ROS accumulation [60,72,78]. Addressing this challenge when evaluating OGS performance requires rigorous characterization and quantification of in vivo ROS levels. Various probes are available, such as superoxide, H2O2, peroxynitrite, and reactive halogen species [79], and imaging techniques such as two-photon microscopy, ultrasound imaging, and bioluminescence imaging are widely used for noninvasive monitoring of ROS dynamics in vivo [80]. Despite challenges, in vivo imaging of ROS in bone tissues has been achieved by Xie and colleagues [81] using hydro-indocyanine green injections. Ultimately, the goal of these measurements was to engineer ROS-responsive systems [82,83] to counteract oxidative stress and enhance bone healing. For example, catalase (CAT)-encapsulated particles applied to bone, joints, and tumors with high H2O2 content led to O2 production via the reaction: 2H2O2 → 2H2O + O2 (Figure 3) [84., 85., 86.]. Similarly, MnO2-based nanozymes with CAT-like activity decompose H2O2 [87,88]. Based on the differential spatiotemporal needs of O2 in various preclinical models, smart stimulus-responsive materials have been developed that dynamically respond to chemical changes within the bone-healing environment or to external physical cues such as photo-, acoustic, magnetic field, and electrical stimulation [89]. They combine real-time sensing with the ability to trigger the in situ reconfiguration of the BTE scaffold for therapeutic interventions.
在骨愈合的炎症和再生阶段,ROS 浓度可增加 100 倍 [ 73. , 74. , 75. ]。这会引起白细胞和血小板的氧化应激[ 76 ],并促进破骨细胞的形成和骨吸收[ 77 ]。尽管OGS有望用于骨缺损治疗,一个重大的技术挑战是过量的O 2生成,这会加剧ROS的积累[ 60,72,78 ]。在评估 OGS 性能时应对这一挑战需要对体内ROS 水平进行严格的表征和量化。可以使用各种探针,例如超氧化物、H 2 O 2 、过氧亚硝酸盐和活性卤素[ 79 ],并且双光子显微镜、超声成像和生物发光成像等成像技术广泛用于无创监测ROS动态。体内[ 80 ]。尽管面临挑战,Xie 及其同事 [ 81 ] 使用氢吲哚菁绿注射液实现了骨组织中 ROS 的体内成像。 最终,这些测量的目标是设计 ROS 响应系统 [ 82 , 83 ],以抵消氧化应激并增强骨愈合。例如,将过氧化氢酶 (CAT) 封装的颗粒应用于具有高 H 2 O 2含量的骨骼、关节和肿瘤,通过以下反应产生 O 2 :2H 2 O 2 → 2H 2 O + O 2图 3 )[ 84.85.86. ]。类似地,具有CAT样活性的MnO 2基纳米酶可分解H 2 O 2 [ 87 , 88 ]。基于各种临床前模型中 O 2的不同时空需求,我们开发了智能刺激响应材料,可以动态响应骨愈合环境中的化学变化或外部物理线索,例如光、声、磁场和电刺激[ 89 ]。它们将实时传感与触发 BTE 支架原位重新配置以进行治疗干预的能力相结合。
Figure 3
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Figure 3. Representative oxidative stimulus-responsive biomaterials.
图3 .代表性的氧化刺激响应生物材料。

(A) ROS scavenging and responsive prolonged O2-generating hydrogels (CPP-L/GelMA) which comprise antioxidant enzyme CAT and ROS-responsive O2-releasing nanoparticles (NPs) (PFC@PLGA/PPS), coloaded liposomes (CCP-Ls), and GelMA hydrogels [84]. (B) H2O2-responsive O2-generating PLGA nanoparticles containing CAT for platinum anticancer agent delivery [86]. (C) pH/H2O2-responsive albumin–MnO2 nanoparticles [88]. Image adapted, with permission, from [84,86,88]. Abbreviations: CAT, catalase; CCP-L, co-loaded liposome; GelMA, gelatin methacryloyl; HMCP, human mandible coronoid process; H2O2, hydrogen peroxide; MnO2, manganese dioxide; NPs, nanoparticles; PFC, perfluorocarbon; PLGA, poly(D,L-lactide-co-glycolic acid); PPS, poly(propylene sulfide); [PtLCl]Cl, 4′-bis(pyridine-2-ylmethyl)amino-2-phenylbenzothiazole; ROS, reactive oxygen species.
(A) ROS清除和响应性延长O 2生成水凝胶(CPP-L/GelMA),其包含抗氧化酶CAT和ROS响应性O 2释放纳米粒子(NP)(PFC@PLGA/PPS)、共载脂质体(CCP- Ls) 和 GelMA 水凝胶 [ 84 ]。 (B) 含有 CAT 的 H 2 O 2响应性 O 2生成 PLGA 纳米粒子,用于铂抗癌剂递送 [ 86 ]。 (C) pH/H 2 O 2响应性白蛋白-MnO 2纳米颗粒[ 88 ]。经许可改编的图像来自[84,86,88 ] 缩写:CAT,过氧化氢酶; CCP-L,共载脂质体; GelMA,甲基丙烯酰明胶; HMCP,人类下颌骨冠突; H 2 O 2 、过氧化氢; MnO 2 、二氧化锰; NP、纳米颗粒; PFC、全氟化碳; PLGA,聚(D,L-丙交酯-乙醇酸); PPS,聚(丙烯硫醚); [PtLCl]Cl,4'-双(吡啶-2-基甲基)氨基-2-苯基苯并噻唑; ROS,活性氧。
ROS-responsive scaffolds have been utilized in drug delivery. Lee and colleagues developed poly(D,L-lactide-co-glycolic acid) (PLGA)-based nanoparticles that managed ischemia/reperfusion injuries via the controlled release of heparin and glutathione in response to H2O2, thereby enhancing bone healing [90]. BTE scaffold coatings using ROS-responsive thioketal-based polymers enabled tunable release of BMP-2 and increased bone regeneration by 50% in rat calvarial defect models [91]. Similarly, a titanium implant coated with a hydrogel responsive to ROS in femoral bone defects released Tβ4 to promote macrophage transformation and osteogenic differentiation, and improve bone healing [92]. Aleemardani and colleagues integrated ROS-mitigating quercetin, a plant flavanol, into silk fibroin–CaO2 hydrogel–electrospun fiber–hydrogel constructs [68]. This novel construct released O2 for 12 days while simultaneously performing ROS scavenging, and increased cell viability by 30% under normoxia and by 10% under hypoxia compared with its quercetin-lacking counterpart. Overall, harnessing and modulating ROS within OGS is a promising strategy for overcoming the challenges associated with balancing O2 supply and demand. Continued developments will include fine-tuning their sensitivity to ROS levels. Future research could explore the incorporation of novel O2-sensing elements, chemical bonds, or O2 carriers within the scaffolds. In addition, the long-term stability and biocompatibility of redox-active materials and their byproducts will necessitate further research to fully understand their interactions with the biological environment [93].
ROS 响应支架已用于药物输送。 Lee及其同事开发了基于聚(D,L-丙交酯-乙醇酸) (PLGA) 的纳米颗粒,该纳米颗粒通过响应 H 2 O 2控制释放肝素和谷胱甘肽来控制缺血/再灌注损伤,从而增强骨愈合。 90 ]。使用 ROS 响应性硫缩酮基聚合物的 BTE 支架涂层能够调节 BMP-2 的释放,并将大鼠颅骨缺损模型中的骨再生增加 50% [ 91 ]。同样,股骨缺损中涂有水凝胶的钛植入物会释放 Tβ4,促进巨噬细胞转化和成骨分化,并改善骨愈合[ 92 ]。 Aleemardani 及其同事将减少 ROS 的槲皮素(一种植物黄烷醇)整合到丝素蛋白 - CaO 2水凝胶 - 电纺纤维 - 水凝胶结构中 [ 68 ]。这种新型构建体可释放 O 2 12 天,同时进行 ROS 清除,与不含槲皮素的对应物相比,常氧条件下细胞活力提高了 30%,缺氧条件下细胞活力提高了 10%。总体而言,在 OGS 中利用和调节 ROS 是克服与平衡 O 2供需相关的挑战的一种有前景的策略。持续的开发将包括微调它们对 ROS 水平的敏感性。未来的研究可以探索新型O 2传感元件、化学键或O 2载体在支架内的结合。 此外,氧化还原活性材料及其副产物的长期稳定性和生物相容性需要进一步研究,以充分了解它们与生物环境的相互作用[ 93 ]。

OGS optimization via biophysical modeling and machine learning
通过生物物理建模和机器学习优化 OGS

Biophysical models and machine learning (ML; Box 1) tools have the potential to address some of the challenges associated with the design of OGS by predicting biological responses [94., 95., 96., 97., 98., 99., 100.] to scaffold design and composition [101., 102., 103., 104., 105., 106., 107., 108., 109., 110., 111., 112., 113., 114., 115., 116.]. The ultimate vision of an integrated, iterative workflow involves using ML to analyze biological and imaging data to enhance OGS design and optimize bone regeneration (Figure 4). However, this modeling of complex biological systems remains challenging due to insufficient mechanistic data (e.g., derived from single-cell or spatial transcriptomic approaches [117., 118., 119.]) or phenomenological data (e.g., derived from the imaging strategies described earlier). To date, computational models have been used to predict biological responses and the mechanical properties of scaffolds as a function of their composition, or to enhance the manufacturing process.
生物物理模型和机器学习(ML;框 1 )工具有可能通过预测生物反应来解决与 OGS 设计相关的一些挑战 [ 94.95.96.97.98.99 .、 100. ]支架设计和组成[ 101.102.103.104.105.106.107.108.109.110.111.112.113.114.115.116. ]。集成迭代工作流程的最终愿景涉及使用机器学习来分析生物和成像数据,以增强 OGS 设计并优化骨再生(图 4 )。 然而,由于机械数据不足(例如,源自单细胞或空间转录组学方法[ 117.118.119. ])或现象学数据(例如,源自所描述的成像策略),复杂生物系统的这种建模仍然具有挑战性。较早)。迄今为止,计算模型已用于预测支架的生物反应和机械性能(作为其成分的函数),或用于增强制造过程。
Box 1 盒子1
Fundamental computational and machine learning (ML) models that can be applied to BTE design
可应用于 BTE 设计的基本计算和机器学习 (ML) 模型
ML is a data-driven artificial intelligence (AI) technology that involves creating predictive models by learning from existing data. It operates by fitting models to a small set of 'training data' with known outcomes to develop its predictive capability, and then the models are applied to 'test data' to make generalized predictions about unseen data [128]. ML can be broadly categorized into supervised learning, unsupervised learning, and reinforcement learning. In supervised learning, each training dataset (scaffold geometry, material properties, etc.) is associated with corresponding outputs (permeability, hydrophobicity, etc.) as its labels. Supervised learning learns the input–output relationships from the training data, and therefore is 'supervised' to predict the outputs of the testing data [129].
ML 是一种数据驱动的人工智能 (AI) 技术,涉及通过学习现有数据来创建预测模型。它通过将模型拟合到一小组具有已知结果的“训练数据”来开发其预测能力,然后将模型应用于“测试数据”以对未见过的数据进行广义预测[ 128 ]。机器学习可以大致分为监督学习、无监督学习和强化学习。在监督学习中,每个训练数据集(支架几何形状、材料属性等)都与相应的输出(渗透性、疏水性等)相关联作为其标签。监督学习从训练数据中学习输入输出关系,因此被“监督”以预测测试数据的输出[ 129 ]。
(i) A decision tree is a supervised learning algorithm for classification and regression. In a tree-like model of decisions, each internal node represents a test on an attribute, each leaf node indicates a class label or decision based on the attributes, and each branch represents the outcome of a test [130].
(i) 决策树是一种用于分类和回归的监督学习算法。在决策的树状模型中,每个内部节点代表对属性的测试,每个叶节点指示基于属性的类标签或决策,每个分支代表测试的结果[ 130 ]。
(ii) A support vector machine (SVM) is a supervised learning method for classification, regression, and outlier detection. SVMs work by identifying the hyperplane that optimally divides a dataset into distinct classes with high robustness and a low risk of overfitting [130].
(ii) 支持向量机 (SVM) 是一种用于分类、回归和异常值检测的监督学习方法。 SVM 的工作原理是识别超平面,该超平面可以将数据集最佳地划分为具有高鲁棒性和低过拟合风险的不同类别 [ 130 ]。
Unsupervised learning, by contrast, represents the process of training algorithms with unlabeled data to discover inherent patterns within the input. Finally, reinforcement learning is a method that navigates through uncertain environments by learning from past behaviors to select optimal actions that maximize rewards [129].
相比之下,无监督学习代表了使用未标记数据训练算法以发现输入中固有模式的过程。最后,强化学习是一种通过学习过去的行为来选择最大化奖励的最佳行动来穿越不确定环境的方法[ 129 ]。
Neural networks (NNs) are key architectures in ML, inspired by the biological neural network in the human brain, and are applicable to both supervised and unsupervised learning paradigms. An NN consists of layers of interconnected neurons, which include an input layer, one or more hidden layer(s), and an output layer. The neurons and their connections, associated with different weights, allow each layer to perform transformation on inputs with varying signal strength [130].
神经网络 (NN) 是 ML 的关键架构,其灵感来自于人脑中的生物神经网络,并且适用于监督和无监督学习范例。神经网络由互连的神经元层组成,其中包括输入层、一个或多个隐藏层和输出层。神经元及其连接与不同的权重相关,允许每一层对具有不同信号强度的输入执行转换[ 130 ]。
Ensemble learning in ML trains and combines multiple models to solve specific problems, and improves model performance by aggregating their predictions, which effectively reduces overfitting. Random forest is a notable example of ensemble learning that combines multiple decision trees when each tree is trained on independent input datasets. It is known for its high accuracy, ability to process unbalanced or missing data, and ability to identify important classification variables [130].
机器学习中的集成学习训练并组合多个模型来解决特定问题,并通过聚合它们的预测来提高模型性能,从而有效减少过度拟合。随机森林是集成学习的一个著名示例,当每棵树在独立的输入数据集上进行训练时,它会组合多个决策树。它以其高精度、处理不平衡或缺失数据的能力以及识别重要分类变量的能力而闻名[ 130 ]。
Figure 4
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Figure 4. Framework for next-generation oxygen-generating scaffold (OGS) engineering for bone regeneration.
图4 .用于骨再生的下一代产氧支架(OGS)工程框架。

(1) Scaffold development. Based on our biological understanding of the impact of O2 on bone regeneration, OGS design incorporates empirically derived biomaterial properties and advanced biomanufacturing. Biophysical simulations can predict OGS efficiency and optimize O2 generation for customized biological impact. This step represents the preliminary scaffold optimization before in vitro or in vivo experiments. (2) Biological characterization. In vitro and in vivo behaviors of fabricated OGS are monitored via noninvasive imaging techniques to assess the distribution of O2, reactive oxygen species (ROS), and bone regeneration, while also elucidating the role of O2 in bone regeneration. Transcriptomic analysis could provide comprehensive and versatile RNA profiling to elucidate the molecular mechanisms involved. This step provides essential real-world data for subsequent machine learning (ML)-guided optimization. (3) ML-guided scaffold optimizations. Ideally, ML algorithms will use OGS properties (e.g., biomaterial and biomanufacturing aspects) and preclinical and clinical imaging data as inputs to simulate/predict the biological performance of scaffolds in patients and enable a priori optimization of the scaffold design to maximize bone regeneration. The ML models help to identify the most impactful OGS properties for the desired biological outcome through iterative learning and feature significance analyses. This process enables the focused refinement of scaffold design with high efficiency, leading to accelerated next-generation OGS engineering for optimized bone regeneration. Figure created with BioRender.
(1) 脚手架开发。基于我们对 O 2对骨再生影响的生物学理解,OGS 设计结合了凭经验得出的生物材料特性和先进的生物制造。生物物理模拟可以预测 OGS 效率并优化 O 2生成以实现定制的生物影响。此步骤代表体外体内实验之前的初步支架优化。 (2)生物学特性。通过无创成像技术监测制造的 OGS 的体外体内行为,以评估 O 2 、活性氧 (ROS) 和骨再生的分布,同时还阐明 O 2在骨再生中的作用。转录组分析可以提供全面且多功能的 RNA 分析,以阐明所涉及的分子机制。此步骤为后续机器学习 (ML) 引导的优化提供必要的真实数据。 (3) 机器学习引导的支架优化。理想情况下,机器学习算法将使用 OGS 属性(例如,生物材料和生物制造方面)以及临床前和临床成像数据作为输入,以模拟/预测支架在患者体内的生物性能,并实现支架设计的先验优化,以最大化骨再生。 ML 模型有助于通过迭代学习和特征显着性分析来确定对所需生物学结果最有影响力的 OGS 属性。这一过程能够高效地集中改进支架设计,从而加速下一代 OGS 工程,以优化骨再生。使用 BioRender 创建的图形。

Predictive modeling of biological responses
生物反应的预测模型

Biophysical models applied to cell-seeded PLGA–sodium percarbonate OGS could predict dynamic spatiotemporal O2 interactions during bone healing by accounting for scaffold size, O2 release, and cellular consumption rates in avascular bone defects [94]. Finite element modeling (FEM) has been used to explore how local O2 tension, coupled with the mechanical environment within an implanted osteochondral scaffold, impacted on tissue differentiation and repair outcomes of mesenchymal stem cells (MSCs) [95]. FEM also simulated cellular-level vascular development by mathematically linking O2 sources and Dll4-Notch signaling in endothelial cells [96,97]. At the tissue level, FEM-based approaches have been used to simulate bone regeneration by integrating mechanical stimuli, scaffold degradation, biological responses to VEGF supplementation, vascularization, and O2 delivery [98]. In critical-sized bone defects, spatial variations in these parameters occur during bone regeneration. For accurate FEM simulations, thousands of representative volume elements are needed, resulting in high computational costs. However, the use of neural networks to predict bone regeneration in a sheep tibia model achieved results as accurate as FEM but at one-fifth of the computational cost. The ML model was validated by longitudinal in vivo X-ray images, and showed consistent bone regeneration at 12 month based on remodeling parameters established from the first 9 months of data [99]. Similarly, Ghosh and colleagues used neural networks to substitute tedious FEM analyses in predicting bone growth over macro-textured bone implant surfaces, further demonstrating the efficiency improvements provided by ML compared with traditional FEM methods [100]. Biological parameters for both FEM and ML models are usually sourced from the literature, in vitro/in vivo data, and empirical estimation, which can be updated via iterations and new experimental data [95,99]. ML tools integrate data from in vitro and in vivo experiments, thereby providing a comprehensive framework to elucidate the underlying mechanisms by which spatiotemporal O2 gradients and bone scaffolds enhance osteogenesis, angiogenesis, and overall bone healing. ML approaches can also guide on-demand OGS design to match a desired optimal cellular response. Integrating noninvasive imaging data with ML techniques has the potential to further enhance the simulation of biological processes such as bone regeneration and revascularization. ML models trained on extensive imaging datasets can provide more accurate and robust predictions of the in vivo O2 distribution. Ultimately, these models would be used clinically to facilitate customized interventions tailored to the patient and their defect based on initial imaging data.
应用于细胞接种的 PLGA-过碳酸钠 OGS 的生物物理模型可以通过考虑无血管骨缺损中的支架尺寸、O 2释放和细胞消耗率来预测骨愈合过程中动态时空 O 2相互作用[ 94 ]。有限元模型(FEM)已被用来探索局部O 2张力与植入骨软骨支架内的机械环境如何影响间充质干细胞(MSC)的组织分化和修复结果[ 95 ]。 FEM 还通过数学方式连接内皮细胞中的 O 2源和 Dll4-Notch 信号传导来模拟细胞水平血管发育 [ 96 , 97 ]。在组织水平上,基于 FEM 的方法已被用于通过整合机械刺激、支架降解、对 VEGF 补充的生物反应、血管化和 O 2输送来模拟骨再生 [ 98 ]。在临界尺寸的骨缺损中,这些参数在骨再生过程中会发生空间变化。为了进行精确的有限元模拟,需要数千个有代表性的体积单元,从而导致计算成本很高。然而,使用神经网络来预测绵羊胫骨模型中的骨再生,获得了与有限元法一样准确的结果,但计算成本仅为有限元法的五分之一。 ML 模型通过纵向体内X 射线图像进行验证,并根据前 9 个月数据建立的重塑参数在 12 个月时显示出一致的骨再生 [ 99 ]。同样,Ghosh 及其同事使用神经网络代替繁琐的 FEM 分析来预测宏观纹理骨植入物表面的骨生长,进一步证明了 ML 与传统 FEM 方法相比所提供的效率改进 [ 100 ]。 FEM 和 ML 模型的生物参数通常来源于文献、体外/体内数据和经验估计,可以通过迭代和新的实验数据进行更新 [ 95 , 99 ]。 ML 工具集成了体外体内实验的数据,从而提供了一个全面的框架来阐明时空 O 2梯度和骨支架增强成骨、血管生成和整体骨愈合的潜在机制。机器学习方法还可以指导按需 OGS 设计,以匹配所需的最佳细胞反应。将无创成像数据与机器学习技术相结合有可能进一步增强骨再生和血运重建等生物过程的模拟。在广泛的成像数据集上训练的 ML 模型可以提供更准确、更稳健的体内O 2分布预测。 最终,这些模型将在临床上使用,以促进根据初始成像数据针对患者及其缺陷进行定制干预措施。

Computation-based customization of scaffold material properties
基于计算的支架材料属性定制

Biophysical simulations and ML also offer powerful solutions to address the technical limitations of OGS designs by predicting the effects of different materials on O2 generation, diffusion, and distribution. For example, O2 gradients within CaO2-based scaffolds supporting the high O2 demand of islet cells were simulated using FEM [101., 102., 103.]. These models, based on oxygenated reaction, diffusion, and consumption kinetics, successfully guided the optimization of cell loading [103]. There are limited studies highlighting the potential of ML for advancing biomaterial designs for BTE applications. In the Polymer Genome Project, computational methods were used to predict polymer properties, such as glass transition temperature and solubility parameters, thereby enhancing material selection and design [104]. ML accelerated peptide discovery for self-assembling hydrogels by combining Monte Carlo tree search and random forest algorithms with molecular dynamics simulations, and efficiently identified sequences with high self-assembly potential [105]. In addition, ML could predict the material properties and bone-forming ability of metals using artificial neural networks (ANNs) [106] or in ceramics [106,107]. ML has been used to predict scaffold biodegradability, which affects O2 release kinetics, tissue integration, and scaffold longevity [108]. Bioceramics and natural substances (e.g., collagen, fibrin), commonly used as OGS binding materials, exhibit complex degradation patterns owing to their inherent heterogeneity and bioactivity. Predicting these patterns using traditional mathematical principles is challenging. However, random forest algorithms have been trained on histological images to predict collagen-based scaffold biodegradation [109]. In addition, neural networks trained on the relationships between mechanical properties, crosslinking, and swelling characteristics and degradation rates have predicted gelatin-based bone scaffold degradation [110].
生物物理模拟和机器学习还提供了强大的解决方案,通过预测不同材料对 O 2生成、扩散和分布的影响来解决 OGS 设计的技术限制。例如,使用FEM模拟支持胰岛细胞高O 2需求的基于CaO 2的支架内的O 2梯度[ 101.102.103 .]。这些模型基于氧化反应、扩散和消耗动力学,成功指导了细胞负载的优化[ 103 ]。很少有研究强调机器学习在推进 BTE 应用生物材料设计方面的潜力。在聚合物基因组计划中,计算方法用于预测聚合物特性,例如玻璃化转变温度和溶解度参数,从而增强材料的选择和设计[ 104 ]。机器学习通过将蒙特卡罗树搜索和随机森林算法与分子动力学模拟相结合,加速了自组装水凝胶的肽发现,并有效地识别了具有高自组装潜力的序列[ 105 ]。此外,机器学习还可以使用人工神经网络 (ANN) [ 106 ] 或陶瓷 [ 106 , 107 ] 来预测金属的材料特性和成骨能力。 ML已被用来预测支架的生物降解性,这会影响O 2释放动力学、组织整合和支架寿命[ 108 ]。生物陶瓷和天然物质(例如胶原蛋白、纤维蛋白)通常用作 OGS 结合材料,由于其固有的异质性和生物活性,表现出复杂的降解模式。使用传统数学原理预测这些模式具有挑战性。然而,随机森林算法已经在组织学图像上进行了训练,以预测基于胶原蛋白的支架生物降解[ 109 ]。此外,根据机械性能、交联、膨胀特性和降解率之间的关系训练的神经网络已经预测了基于明胶的骨支架的降解[ 110 ]。

Computation-based customization of advanced biomanufacturing
基于计算的先进生物制造定制

Finally, ML has been used to create bone scaffolds with controlled porosity, Young's modulus, and compression strength, and achieved <5% error from design targets [111,112]. Although integrating FEM and computational fluid dynamics (CFD) helps to simulate mechanical properties and O2 permeability concurrently to iteratively adjust scaffold design [113,114], recent advances have utilized a more efficient ML approach for inverse design, such as supervised learning to generate Voronoi lattices with targeted mechanical properties that were validated through compression tests and simulations [112]. Another study used FEM simulations to create a neural network dataset linking microstructural parameters to the elastic matrix of bone [111]. ML also provides significant benefits to scaffold accuracy and consistency in image-based computer-aided design (CAD) and additive manufacturing (AM)-based biomanufacturing. Creating patient-specific bone scaffolds relies on accurate bone segmentation from computerized tomography (CT) scans. Minnema and colleagues improved this step by using automated convolutional neural networks (CNNs), and achieved a 92% similarity to gold standard segmentation tools in shorter times [115]. During the subsequent bioprinting process, ML models analyzed data signatures from in situ IR sensors in a feedforward process to predict print quality metrics and adjust process parameters in real time, thereby preventing manufacturing flaws and improving print quality [116].
最后,机器学习已用于创建具有受控孔隙率、杨氏模量和压缩强度的骨支架,并实现了设计目标的 <5% 误差 [ 111 , 112 ]。尽管集成 FEM 和计算流体动力学 (CFD)有助于同时模拟机械性能和 O 2渗透性,以迭代调整支架设计 [ 113 , 114 ],但最近的进展利用了更有效的 ML 方法进行逆向设计,例如监督学习来生成Voronoi 晶格具有通过压缩测试和模拟进行验证的目标机械性能 [ 112 ]。另一项研究使用 FEM 模拟创建一个神经网络数据集,将微观结构参数与骨弹性矩阵联系起来 [ 111 ]。机器学习还为基于图像的计算机辅助设计 (CAD)和基于增材制造 (AM)的生物制造中的支架准确性和一致性提供了显着的优势。创建患者特异性骨支架依赖于计算机断层扫描 (CT) 扫描的准确骨分割。 Minnema 和同事通过使用自动卷积神经网络 (CNN) 改进了这一步骤,并在更短的时间内实现了与黄金标准分割工具 92% 的相似度 [ 115 ]。 在随后的生物打印过程中,机器学习模型在前馈过程中分析来自原位红外传感器的数据签名,以预测打印质量指标并实时调整过程参数,从而防止制造缺陷并提高打印质量[ 116 ]。
Challenges to ML for OGS include the need for extensive, high-quality data for model training. The variability in the experimental conditions and requirements for preclinical versus clinical applications require collaborative efforts to build comprehensive datasets for OGS materials. Currently, there are limited publicly available biomaterial databases, and most groups still rely on extracting descriptors from multiple sources, which reduces scalability and increases computing power requirements [120]. High-quality, standardized data collection protocols will be needed in the future to ensure accurate and reproducible experimental data. In addition, the 'black-box' nature of many ML models limits the interpretability of ML-generated designs for in vivo applications. Therefore, ML should be considered as an aid, and not as a replacement for empirical trials, to be accompanied by rigorous experimental validation of OGS performance. Enhancing the transparency of ML algorithms through explainable artificial intelligence (AI) techniques will increase their clinical acceptance among medical professionals [121]. Creating effective ML models for OGS requires interdisciplinary expertise in materials science, tissue engineering, and computer science, which would further advance bone scaffold and next-generation OGS design.
OGS 的 ML 面临的挑战包括需要广泛的高质量数据来进行模型训练。临床前与临床应用的实验条件和要求的可变性需要协作努力来构建 OGS 材料的综合数据集。目前,公开可用的生物材料数据库有限,大多数小组仍然依赖从多个来源提取描述符,这降低了可扩展性并增加了计算能力要求[ 120 ]。未来将需要高质量、标准化的数据收集协议,以确保准确且可重复的实验数据。此外,许多机器学习模型的“黑盒”性质限制了机器学习生成的体内应用设计的可解释性。因此,ML 应被视为一种辅助手段,而不是经验试验的替代品,并伴有对 OGS 性能的严格实验验证。通过可解释的人工智能(AI)技术增强机器学习算法的透明度将提高其在医疗专业人员中的临床接受度[ 121 ]。为 OGS 创建有效的 ML 模型需要材料科学、组织工程和计算机科学方面的跨学科专业知识,这将进一步推进骨支架和下一代 OGS 设计。

Concluding remarks and future perspectives
结束语和未来展望

Overall, computational and ML modeling can predict O2 release, scaffold degradation, and multilevel biological responses to spatiotemporal O2 gradients in bone defects. Integrating these predictions into a collective framework would enhance OGS design and encourage the development of more standardized manufacturing for OGS applications in patients. However, critical-sized craniomaxillofacial bone injuries in patients are more varied and complex than the controlled, predictable injuries in preclinical models. Consequently, the need for varied OGS precludes a one-size-fits-all solution. A major advance would be simulations that identify suitable OGS designs for optimal bone regeneration. Predictions of the design of an OGS for adequate and effective treatment would need to account for multiple parameters including: (i) the number and phenotype of transplanted osteoprogenitors and the impact of pO2 on their survival, proliferation, and differentiation. (ii) The anatomical location of the defect site: the prevailing pO2 and healing outcomes are affected by soft-tissue coverage that facilitates angiogenesis, and the interface with the adjacent host bone that impacts on efficient osteoconduction. (iii) The geometry of the injury: optimizing the shape, size, microstructure, and pore architecture of the scaffold is crucial because it directly influences the mechanical properties as well as the rate and duration of O2 release. Despite advances that enable computer simulations of animal models, a significant barrier to the application of ML or computational models for simulating de novo bone regeneration in patients is the lack of meaningful clinical data (see Outstanding questions). Extrapolating healing dynamics to patients from imaging or transcriptomic data obtained in preclinical models is challenging. Thus, future studies that include longitudinal imaging data on bone healing and revascularization in patients would greatly advance the clinical potential of OGS.
Outstanding questions
What are the physiologically relevant O2 levels for bone healing, given its spatiotemporal variations in vivo?
What innovations are necessary to develop or translate noninvasive imaging techniques for real-time monitoring of in vivo O2 and ROS levels, with the goal of optimizing scaffold performance and successful bone regeneration?
How can ML facilitate the optimization of OGS properties and design for efficacious bone regeneration?
How can we better integrate and leverage ML models in tissue engineering?

总体而言,计算和机器学习建模可以预测骨缺损中 O 2释放、支架降解以及对时空 O 2梯度的多级生物反应。将这些预测整合到一个集体框架中将增强 OGS 设计,并鼓励为患者开发更标准化的 OGS 应用制造。然而,患者的临界大小颅颌面骨损伤比临床前模型中受控、可预测的损伤更加多样化和复杂。因此,对各种 OGS 的需求排除了一种一刀切的解决方案。一项重大进步是通过模拟确定合适的 OGS 设计以实现最佳骨再生。预测 OGS 设计以实现充分且有效的治疗需要考虑多个参数,包括:(i) 移植骨祖细胞的数量和表型以及 pO 2对它们的存活、增殖和分化的影响。 (ii) 缺损部位的解剖位置:主要的 pO 2和愈合结果受到促进血管生成的软组织覆盖以及影响有效骨传导的与相邻宿主骨的界面的影响。 (iii)损伤的几何形状:优化支架的形状、尺寸、微观结构和孔隙结构至关重要,因为它直接影响机械性能以及O 2释放的速率和持续时间。 尽管计算机模拟动物模型取得了进展,但应用机器学习或计算模型来模拟患者从头骨再生的一个重大障碍是缺乏有意义的临床数据(参见未解决的问题)。从临床前模型中获得的成像或转录组数据推断患者的愈合动态具有挑战性。因此,未来的研究,包括患者骨愈合和血运重建的纵向成像数据,将极大地提高 OGS 的临床潜力。
Outstanding questions
What are the physiologically relevant O2 levels for bone healing, given its spatiotemporal variations in vivo?
What innovations are necessary to develop or translate noninvasive imaging techniques for real-time monitoring of in vivo O2 and ROS levels, with the goal of optimizing scaffold performance and successful bone regeneration?
How can ML facilitate the optimization of OGS properties and design for efficacious bone regeneration?
How can we better integrate and leverage ML models in tissue engineering?

Acknowledgments 致谢

This work was supported by funding from the National Institute of Dental and Craniofacial Research (NIDCR; grant 1R01DE027957), the Maryland Stem Cell Research Fund (2022-MSCRFV-5782), and the National Cancer Institute (NCI; 5R01CA237597-05, 5R01CA196701-07, and 5R01CA237597-05).
这项工作得到了国家牙科和颅面研究所( NIDCR ;赠款1R01DE027957 )、马里兰干细胞研究基金2022-MSCRFV-5782 )和国家癌症研究所( NCI5R01CA237597-05、5R01CA196701- 的资助075R01CA237597-05 )。

Declaration of interests 利益申报

W.L.G. hold shares in EpiBone, Inc. The other authors declare no competing interests.
WLG 持有 EpiBone, Inc. 的股份。其他作者声明不存在竞争利益。

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Glossary 词汇表

Additive manufacturing (AM)
增材制造 (AM)
the process of creating objects by adding material layer by layer based on a digital model.
基于数字模型,通过逐层添加材料来创建对象的过程。
Allografts 同种异体移植物
grafts transplanted into a recipient from a genetically non-identical donor of the same species.
从同一物种的基因不相同的供体移植到受体的移植物。
Autografts 自体移植物
grafts harvested from and transferred to another site in the same individual of a species as the 'gold standard' for grafting.
从同一物种个体的另一个部位收获并转移到另一个部位的移植物作为嫁接的“金标准”。
Computational fluid dynamics (CFD)
计算流体动力学 (CFD)
a computational technique that analyzes and predicts fluid flow behaviors in complex systems, often based on Navier–Stokes equations.
一种分析和预测复杂系统中流体流动行为的计算技术,通常基于纳维-斯托克斯方程。
Computer-aided design (CAD)
计算机辅助设计(CAD)
detailed designs and technical drawings of objects generated by computational software to visualize, modify, analyze, and optimize designs before physical production.
由计算软件生成的详细设计和技术图纸,用于在实际生产之前可视化、修改、分析和优化设计。
Cranial window 颅窗
a surgical setup in which the skull is thinned or replaced with a synthetic optical interface such as a glass coverslip, allowing optical access of a microscope.
一种手术装置,其中头骨被减薄或用合成光学接口(例如玻璃盖玻片)替换,从而允许显微镜进行光学访问。
Critical-sized bone defects
临界尺寸的骨缺损
bone defects that do not heal spontaneously without medical intervention to facilitate bone healing.
如果没有医疗干预来促进骨愈合,骨缺损就不会自然愈合。
Finite element modeling (FEM)
有限元建模 (FEM)
a numerical technique that simulates and analyze complex structures or systems by dividing them to smaller elements and solving differential equations to predict their responses to applied loads or stimuli.
一种数值技术,通过将复杂结构或系统划分为更小的元素并求解微分方程来预测其对施加的载荷或刺激的响应,从而模拟和分析复杂的结构或系统。
Hypoxia 缺氧
tissue O2 levels that are insufficient to maintain adequate homeostasis, which can lead to impaired cellular function, reduced tissue regeneration, increased inflammation, and activation of pathways that can trigger adaptive responses.
组织中的 O 2水平不足以维持足够的稳态,这可能导致细胞功能受损、组织再生减少、炎症增加以及可触发适应性反应的途径激活。
Ischemia 缺血
shortage of O2 and nutrients needed for cellular metabolism caused by restriction in the blood supply.
由于血液供应受限而导致细胞代谢所需的O 2和营养物质短缺。
Oxygen saturation (SO2)
氧饱和度(SO 2
the ratio of oxyhemoglobin concentration (HbO2) to the concentration of total functional hemoglobin (HbT), which indicates the utilization of the present O2 transport capacity.
氧合血红蛋白浓度(HbO 2 )与总功能血红蛋白浓度(HbT)的比值,表示现有O 2转运能力的利用率。
Platinum porphyrin-coumarin-343 (PtP-C343)
铂卟啉-香豆素-343 (PtP-C343)
a phosphorescent O2 probe that can be safely delivered into the body for tissue O2 measurements and imaging.
磷光 O 2探针,可以安全地输送到体内进行组织 O 2测量和成像。
Reactive oxygen species (ROS)
活性氧 (ROS)
highly reactive oxygen-containing molecules such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals. ROS are essential for cellular signaling and immune functions, but excessive ROS can cause oxidative damage, contributing to metabolic diseases and cell aging.
高活性含氧分子,如超氧自由基、过氧化氢和羟​​基自由基。 ROS 对于细胞信号传导和免疫功能至关重要,但过多的 ROS 会导致氧化损伤,导致代谢疾病和细胞衰老。
Representative volume elements
代表性体积元素
small representative sections of a structure used in computational modeling for property analysis which capture essential features while minimizing computational complexity.
用于属性分析的计算建模的结构的小代表性部分,其捕获基本特征,同时最小化计算复杂性。
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