Within the field of tissue engineering, the ability to repair small blood vessels or reconstruct the delicate lymphatic network has represented a fascinating yet highly complex technological objective for decades. Unlike large-diameter vessels, which can be replaced using inert synthetic grafts, microvessels and lymphatic capillaries require a three-dimensional environment capable of replicating the softness and architecture of the native extracellular matrix. In this context, silk fibroin has emerged as an exceptionally promising candidate. Fibroin not only possesses superior mechanical strength compared to other natural materials such as collagen, but also offers chemical versatility that enables its fabrication into highly porous and biocompatible structures.
The strategic role of porosity
The primary function of a scaffold in microvascular regeneration is not simply to provide a static structure, but rather to act as a dynamic architect that guides cellular migration and the formation of new vessels. The most advanced research in this field has demonstrated that the integration of microchannels within fibroin scaffolds is crucial to preventing necrosis at the center of the construct and to promoting rapid and efficient vascularization. Recent studies have shown that combining interconnected pores of varying dimensions—ranging from 120 to 450 micrometers—with specific directional channels promotes organized collagen alignment and endothelial cell migration within the material. In practice, porosity is not merely an empty space to be filled, but a physical signal that cells interpret as an instruction to build functional new blood vessels.
An additional aspect of particular interest concerns the interaction between the scaffold and the immune system. Contrary to what might be expected, scaffold degradation is not simply a passive disintegration process, but an active phase of regeneration. Highly porous fibroin architectures have been shown to accelerate the recruitment of reparative phenotype macrophages (M2), which not only remove biodegradable material but also secrete growth factors that stimulate neoangiogenesis. This discovery shifts the paradigm from simple passive biocompatibility toward a genuinely immunomodulatory bioactive scaffold.
Toward lymphatic engineering
While vascular regeneration has achieved remarkable progress, lymphatic regeneration presents unique challenges. The lymphatic system is characterized by thin vessels and delicate valves that are difficult to replicate artificially. Fibroin offers an elegant solution thanks to its capacity for biological functionalization. Cutting-edge research projects are exploring the use of fibroin scaffolds as vehicles for the controlled release of lymphatic-specific growth factors (such as VEGF-C) and as physical supports for the implantation of primary lymphatic endothelial cells. The objective is to create an artificial “niche” that deceives lymphatic cells into perceiving a native microenvironment, thereby stimulating the formation of new lymphatic capillaries and restoring interstitial fluid drainage—an essential condition for reducing postoperative or post-traumatic edema.
To further enhance fibroin’s regenerative potential, biofunctionalization strategies are proving particularly effective. A porous scaffold alone is not sufficient; its surface must directly communicate with cells. Applied research has demonstrated that the addition of substances such as injectable platelet-rich fibrin (iPRF) or enamel matrix proteins (EMP) onto fibroin scaffolds dramatically increases their ability to attract blood vessels, as observed in chorioallantoic membrane (CAM) models. Similarly, loading the scaffold with compounds such as lithium chloride (LiCl) has demonstrated antibacterial effects together with enhanced angiogenesis, which is particularly important in challenging contexts such as wound healing in diabetic patients, where vascularization is often compromised.
The versatility of fibroin also allows it to overcome many of the limitations associated with traditional materials. While synthetic polymers may release acidic degradation products that inflame tissues, and purely natural materials such as alginate or collagen often fail under mechanical stress, fibroin maintains an excellent balance between strength and biocompatibility. Its tensile resistance, comparable to that of silk sutures already approved by the FDA, ensures that the scaffold preserves its structural integrity long enough to support the growth of new vessels, before degrading without inducing chronic inflammation.
