研究主旨与现实背景#

在现代医学与生物材料领域，大面积或重度骨缺损的修复一直是一项极具挑战性的临床难题。自然界中的长骨修复主要依赖于一种被称为软骨内成骨（Endochondral Ossification） 的复杂生理过程。这一过程具有极其严密的时间节律性：在创伤初期，身体首先需要招募间充质干细胞并形成软骨模板，随后逐步发生血管入侵，最终在后期转化为坚硬的骨组织。然而，传统的人工骨修复支架或药物递送系统大多采用被动释放机制，药物一旦植入便开始无差别扩散，无法精准匹配人体骨骼修复的动态节律。即便现存的“顺序递送”技术尝试通过材料降解速度来区分给药顺序，也常常因为材料早期的渗漏而导致不同阶段的信号分子重叠错乱。在成骨后期所需的关键生长因子如果过早泄露，会严重破坏早期软骨模板的建立，最终导致骨修复质量大打折扣。针对这一重大临床瓶颈，本研究成功开发出一种兼具结构定向引导与近红外光控按需释放功能的分层电纺纳米纤维支架，实现了对骨修复不同阶段生理信号的精准调控。

核心创新与分层支架设计#

该项研究的核心创新在于打破了传统被动释放药物的局限，构建了一种“早期持续引导 + 后期光控按需触发”的双阶段时空可控递送平台。针对成人骨损伤后早期趋化信号严重不足的问题，研究团队引入了白细胞介素-8（IL-8，一种能够招募干细胞并诱导软骨分化的趋化因子）；而针对后期的骨化阶段，则引入了骨形态发生蛋白-2（BMP-2，一种强效促成骨生长因子）。为了防止这两种生物活性因子发生信号干扰，研究团队巧妙利用共轴静电喷涂与电纺技术，构建了一个多层结构的纳米纤维网格。支架内部采用了具有定向排列特征的聚 sound/聚己内酯（PCL）纳米纤维层，专门用于为干细胞的迁移提供物理“导航跑道”；外部则覆盖了随机取向的纤维层，以保证支架整体的机械强度。IL-8被包裹在软质的胶原微球中，在植入前14天内进行稳定、持续的自然释放；而BMP-2则与近红外光热响应剂印防茅绿（ICG）一同被封存在相变材料（PCM）微球中。这种相变材料在常温下呈固态锁死状态，只有当施加特定的近红外光照射时，光热效应才会促使材料发生固液相变，从而在指定的成骨窗口期实现BMP-2的“按需闸门式”精准释放。

Scheme.1 Schematic illustration of the structure and mechanism of a multi-layered photothermal scaffold for programmatically enhanced bone regeneration. (A) Structural configuration of the scaffold and the distinct roles of IL-8 and BMP-2. (B) Mechanistic overview of the staged bone repair process facilitated by the scaffold. i) IL-8 release induced BMSC recruitment and chondrogenic differentiation; ii) NIR-triggered BMP-2 release and endochondral ossification; iii) Mature bone reconstruction.

实验实施过程与机理验证#

为了验证该系统的实际生物学效应，研究团队从体外细胞实验到体内动物模型进行了全方位的分步验证。在体外阶段，研究人员首先利用大鼠骨髓间充质干细胞（BMSCs）评估了支架对细胞行为的调控能力。实验设计了精确的近红外光（808 nm）照射方案，每次照射短时间增温至42℃以上以触发现场释放，随后迅速冷却。微孔迁移与细胞染色实验直观地展示了微观过程：在前14天的早期阶段，自胶原微球中平稳释放的IL-8高效招募了大量BMSCs向支架中心定向迁移，并成功启动了早期软骨相关基因的表达；在培养中后期，通过施加近红外光刺激，相变微球瞬间响应释放出BMP-2，显著提升了碱性磷酸酶活性及成骨相关蛋白质的沉积。在体内验证环节，研究团队建立了大鼠临界尺寸胫骨缺损模型，将功能化支架植入骨缺损处，并在第4周等关键成骨节点施加近红外光物理刺激，引导组织按顺序经历软骨形成到成熟骨重建的完整级联反应。

Fig.1 Fabrication and characterization of a photothermal scaffold with temporally controlled cytokine release. (A) Schematic illustration of scaffold preparation. (B) SEM images of different sections of the scaffold. (C) Fluorescence images showing the spatial distribution of Rhodamine B–loaded (red) and FITC-loaded (green) microspheres. (D) Water contact angle measurements of various scaffold surfaces. (E) Temperature elevation profiles of the scaffold in PBS under different NIR laser power densities (808 nm). (F) Multi-cycle heating–cooling curves of the scaffold under NIR on/off cycles. (G, H) Infrared thermal images and corresponding quantitative analysis of in vivo temperature changes in scaffolds with or without ICG under NIR irradiation. (I) Cumulative release rate of IL-8 and (J) on-demand BMP-2 release triggered by repeated NIR irradiation cycles. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

实验数据结论与生物学表现#

体内外实验的数据表现有力地证实了这种节律化按需递送策略的优越性。在组织学与分子生物学检测中，该系统展现出了极强的阶段针对性：在植入后第4周的早期软骨形成期，受IL-8持续释放的驱动，软骨标志物S100的表达量达到了对照组的3.63倍，二型胶原蛋白（COL2）的表达量达到了1.57倍，证实了软骨 intermediate 模板的高质量建立；随着后续近红外光触发BMP-2的释放，在第12周的最终检测中，晚期成骨关键标志物骨钙素（OCN）与骨桥蛋白（OPN）的表达量分别达到了对照组的1.68倍和1.47倍。最核心的骨密度与结构分析显示，在植入12周后，采用光响应分层递送支架处理的实验组，其缺损区域的新骨体积分数（Bone Volume Fraction）相比于传统对照组大幅提升了72.1%。数据背后的真实物理与生物学含义表明，成功避免早期生长因子渗漏并严格重现生理时序，是实现高质量大块骨组织再生的关键所在。

Fig.2 In vitro evaluation of BMSC recruitment and osteogenic differentiation induced by scaffolds. (A) Schematic of the Transwell migration assay, showing IL-8 released from the scaffold in the lower chamber and BMSCs seeded in the upper chamber. (B, C) Representative images and quantification of migrated BMSCs stained with crystal violet, respectively. (D, E) ALP staining and corresponding quantification on days 7 and 14, indicating early osteogenic activity. (F, G) ARS staining for matrix mineralization and quantification based on dye extraction at days 7, 14, and 21, respectively. (H, I) Immunofluorescence staining for OPN (H) and OCN (I) on day 14 (red), with F-actin counterstained by phalloidin (green). (J, K) Semi-quantitative analysis of fluorescence intensity for OPN and OCN, respectively. (L, M) Relative mRNA expression levels of OPN and OCN on day 14, measured by qRT-PCR, respectively. Data are presented as mean ± SD (n = 3–4). Statistical significance was assessed using one-way ANOVA followed by Tukey’s post hoc test: p < 0.05, p < 0.01, p < 0.001; n.s., not significant. Scale bars: 100 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) Fig.3 In vivo evaluation of bone regeneration in a rat tibial critical-sized defect model. (A) Schematic of tibial defect creation, scaffold implantation, and subsequent NIR irradiation starting at 5 weeks post-surgery. (B) Representative intraoperative images showing osteotomy site marked by a dotted box (left); scaffold implantation into the defect region (middle two panels), with blue triangles indicating the defect location and scaffold wrapping, and blue asterisks indicating suture positions; excised bone segment shown alongside a ruler for scale (right, 5 mm). (C) Serial X-ray images of the defect region at 1, 4, and 8 weeks post-surgery. (D) Quantitative X-ray analysis of residual length at 1, 4, and 8 weeks. (E) Representative micro-CT 3D reconstructions and sagittal views showing bone regeneration at 8 and 12 weeks. (F–I) Quantitative micro-CT analysis of bone volume fraction (BV/TV, F), trabecular number (Tb.N, G), bone mineral density (BMD, H), and trabecular thickness (Tb.Th, I) at 8, 10, and 12 weeks. Data are presented as mean ± SD (n = 3). Statistical significance was determined by one-way ANOVA with Tukey’s post hoc test: p < 0.05, p < 0.01, p < 0.001; n.s., not significant. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) Fig.4 Histological evaluation of bone regeneration following scaffold implantation. (A) Schematic of the in vivo experimental timeline and the expected transition from chondrogenic to osteogenic differentiation during endochondral bone repair. Scaffolds were implanted into rat tibial segmental defects, and tissue sections were harvested at 4, 8, and 12 weeks for histological analysis. (B) Representative H&E-stained sections at each time point; dashed boxes indicate regions shown at higher magnification. (C) Masson’s trichrome staining of corresponding sections, showing collagen-rich bone matrix in blue. Blue box: bone defect area; red star: newly formed bone; green triangle: newly formed cartilage. Blue line: length of newly formed bone; Yellow line: length of bone defect area. Scale bars: 1 mm (overview); 100 μm (insets). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) Fig.5 Immunohistochemical evaluation of chondrogenic marker expression in the bone defect region at 4, 8, and 12 weeks. (A) S100 immunostaining (brown) indicating chondrocyte-related activity in regenerating tissue. Dashed black boxes denote regions shown at higher magnification. (B) COL2 immunostaining of serial sections, showing cartilage matrix distribution at corresponding time points. (C, D) Semi-quantitative analysis of average optical density (AOD) for S100 (C) and COL2 (D). Data presented as mean ± SD (n = 5). Statistical significance determined by one-way ANOVA followed by Tukey’s post hoc test: p < 0.05, p < 0.01, p < 0.001; n.s., not significant. Scale bars: 1 mm (main panels), 100 μm (insets). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

理论价值、现实应用与未来展望#

本研究在理论与应用两个层面均具有重大意义。在理论层面，它打破了以往组织工程中盲目叠加高剂量生长因子的传统思维，证明了“在正确的时间递送正确的信号”远比简单的药物堆砌更为重要，为仿生复杂组织再生提供了全新的时空调控范式。在现实应用层面，该光响应电纺支架所采用的PCL、胶原等材料均具备良好的生物相容性，结合无创、穿透力强的近红外光控制手段，为临床上难愈合的大块骨缺损、创伤骨科重建提供了一套高度可控、适应性强的全新治疗方案。当然，该研究目前仍存在一定的局限性，例如近红外光在人体更深层组织中的穿透深度受到物理限制，且大动物模型中的时空响应参数仍有待进一步精细化标定。作者团队指出，未来的研究将聚焦于优化光热介质的响应灵敏度、拓展穿透深度更强的光波段，并探索将该“按需节律递送”平台推广应用于关节软骨、肌腱及其他需要多阶段协同修复的复杂软组织再生领域中。