Table 5.

MNs for other tissues regeneration.

Tissue	Materials	Structure	Bioactive substances	Mechanisms	Ref.
Spinal cord	Silicon coated with gold and polypyrrole	Arrays: 10 ​× ​10 Height: 500 ​μm Shape: conical Strength:-	Dexamethasone phosphate	Transdural and electronically controlled delivery of drugs to the intrathecal space.	[170]
	GelMA	Arrays: 45 needles Height: 600 ​μm Shape: conical Strength: <1.5 ​N/needle	Mesenchymal stem cell	Maintaining the activity of cells for more than 7 ​d; Achieving sustained delivery of exosome.	[171]
	GelMA	Arrays: 20 ​× ​20 Height: 300 ​μm Shape: conical Strength: Young's modulus of 500 ​kPa	Mesenchymal stem cell-derived exosome	Improving the exosome retention rate, achieved sustained release over 6 ​d.	[172]
Periodontal tissue	GelMA and gelatin	Arrays: 11 ​× ​11 Height: 600 ​μm Shape: conical Strength: about 4 ​N	Tetracycline, IL-4 and TGF-β	Quickly dissolvable gelatin base for burst release of antibiotic; Antibiotic loaded nanoparticles and cytokine loaded silica microparticles in needles for sustained release.	[176]
Oral mucosal	HA	Arrays: 10 ​× ​10 Height: 350 ​μm Shape: conical Strength: penetrate the oral mucosa	dexamethasone acetate, vitamin C and tetracaine hydrochloride	Fully released the encapsulated drug within 10 ​s.	[177]
	HA	Arrays: 15 ​× ​15 Height: 700 ​μm Shape: conical Strength:	Betamethasone	Fully released the encapsulated drug within 3 ​min.	[178]
Brain	GelMA	Arrays: 10 ​× ​10 Height: 600 ​μm Shape: conical Strength: >0.07 ​N/needle	Adeno-associated virus	For sustained and controlled delivery of adeno-associated virus (AAV) expressing human VEGF (AAV-VEGF) that achieves homogenous distribution and high transfection efficiency in ischemic brains.	[182]
Skeletal muscle	PLGA needles coated tungsten	Arrays: 5 ​× ​5 Height: 900 ​μm Shape: pyramidal Strength: modulus of 77 ​MPa	Aspirin and ibuprofen	The base was combined with wireless power transmission system; Transmission of periodic electrical stimulation to regulate cell behavior and tissue regeneration, release anti-inflammatory drug.	45
Cartilage	–	–	cellular microspheroids	Microspheroids on MNs were cultured to permit fusion into a tissue construct.	[187]
Liver	GelMA	Arrays: 11 ​× ​11 Height: 577 ​μm Shape: conical Strength: 0.054 ​N/needle	silicate nanoplatelets	The needle-shaped structure increases the contact area with blood. Adhering to the wound through an interlocking mechanism.	[190]
	HA	Arrays: Height: 750 ​μm Shape: pyramidal Strength: ∼0.2 ​N/needle	Tranexamic acid	Peripheral MN for minimally and site-selectively invasive hemostatic drug delivery. The released drugs were transported from adjacent tissue to the target site through blood flow in capillaries.	[191]
Blood vessel	208CTH-F	Arrays: Height: 200 ​μm Shape: octagonal based cones Strength:	paclitaxel	MNs covered on the surface of drug-eluting balloons. Balloon expansion allowed MNs to penetrate the inner layer of the vessel wall and released the drug on the surface.	[193]
	PLGA	Arrays: 3 ​× ​3 Height: 650 ​μm Shape: conical Strength:	Rhodamine B, paclitaxel	The combination with the cuff-shaped device allowed MNs to be applied to the outer surface of the vessel; Drug released by MNs were uniformly distributed in the vascular tunica media over 2 weeks.	[194]
	PLGA	Arrays: 4 ​× ​4 Height: 480, 640 and 780 ​μm Shape: pyramidal Strength: Young's moduli of 29.7 ​MPa	rhodamine B, sirolimus	The MNs are mounted on a flexible PLGA mesh that released drug to the vessel wall and minimized the mechanical stresses applied to the vessel.	[195]
	Needle: PCL, PLGA, lauric acid Base: Curable resin PCLMA	Arrays: Height: 500 ​μm Shape: conical Strength: >0.2 ​N/neelde	paclitaxel	MNs were mounted on the surface of the balloon; After irradiation by a circular NIR laser inside the catheter, the drug-carrying tip was dislodged and embedded in the vascular system and gradually released the drug for more than six months.	[196]