Microneedle-based interstitial fluid extraction for drug analysis:Advances,challenges,and prospects

Similar to blood,interstitial fluid(ISF)contains exogenous drugs and biomarkers and may therefore substitute blood in drug analysis.However,current ISF extraction techniques require bulky instruments and are both time-consuming and complicated,which has inspired the development of viable alternatives such as those relying on skin or tissue puncturing with microneedles.Currently,microneedles are widely employed for transdermal drug delivery and have been successfully used for ISF extraction by different mechanisms to facilitate subsequent analysis.The integration of microneedles with sensors enables in situ ISF analysis and specific compound monitoring,while the integration of monitoring and delivery functions in wearable devices allows real-time dose modification.Herein,we review the progress in drug analysis based on microneedle-assisted ISF extraction and discuss the related future opportunities and challenges.

Effect of Third Interstitial Fluid on Adverse Outcomes in Patients with Severe Pre-eclampsia and Twin Pregnancy:A 5-year Single-center Retrospective Study

Objective This study aims to identify the effect of third interstitial fluid on adverse outcomes in twin pregnancies with severe pre-eclampsia,and explore the differences in bad ending between twins and singletons.Methods The present retrospective cohort study was conducted on patients with severe pre-eclampsia,who delivered in Tongji Hospital,Wuhan,China,between 2017 and 2022.The adverse outcomes in singleton and twin pregnancies with severe pre-eclampsia were initially investigated.Then,the diverse maternal and fetal consequences between singleton and twin pregnancies in patients with severe pre-eclampsia were compared after merging with the third interstitial fluid.Results A total of 709 patients were included for the present study.Among these patients,68 patients had twin pregnancies,and 641 patients had singleton pregnancies.The rate of postpartum hemorrhage(2.81%vs.13.24%,P<0.001),and admission rate to the Neonatal Intensive Care Unit(NICU)after birth(30.73%vs.63.24%,P=0.011)were significantly higher in twin pregnancies.The neonatal weight of twins was statistically lower than singletons(1964.73±510.61 g vs.2142.92±731.25 g,P=0.008).For the groups with the third interstitial fluid,the delivery week(P=0.001)and rate of admission to the NICU after birth were significantly advanced in twin pregnancy group,when compared to singleton pregnancy group(P=0.032),and the length of hospital stay was shorter(P=0.044).Furthermore,there was no statistically significant difference between the twin pregnancy group and the singletony pregnancy group without the third interstitial fluid.Conclusion The maternal and fetal adverse outcomes of patients with severe pre-eclampsia increased in twin pregnancies,when compared to singleton pregnancies.Thus,when patients develop the third interstitial fluid,twin pregnancies would more likely lead to adverse fetal outcomes,when compared to singleton pregnancies,and there would be no significant difference in maternal adverse outcomes.More attention should be given to patients who merge with the third interstitial fluid.

Non-invasive assessment for intratumoural distribution of interstitial fluid flow

Interstitial fluid plays a vital role in drug delivery and tumour treatment.However,few non-invasive measurement methods are available for measuring low-velocity biological fluid flow.Therefore,this study aimed to develop a novel technology called interstitial flow velocity-MRI.The interstitial flow velocity-MRI sequence consists of a dual inversion recovery preparation and an improved stimulated echo sequence(ISTE)combined with phase-contrast MRI.A homemade flow phantom was used to assess the feasibility and sensitivity of interstitial flow velocity-MRI.In addition,xenografts of female BALB/c mouse models of 4T1 breast cancer administered losartan(40 mg/kg)or saline(n?6)were subjected to imaging on a 7.0 T scanner to assess the in vivo interstitial fluid flow velocity.The results showed a significant correlation(P<0.001)between the theoretical velocities and velocities measured using the flow phantom.Interstitial flow velocity-MRI could detect a velocity as low as 10.21±2.65 mm/s with a spatial resolution of 0.313 mm.The losartan group had a lower mean interstitial fluid velocity than the control group(85±16 vs 113±24 mm/s).In addition,compared to the saline treatment,losartan treatment reduced the proportion of collagen fibres by 10%and 12%in the Masson and Sirius red staining groups,respectively.Interstitial flow velocity-MRI has the potential to determine interstitial fluid flow velocity non-invasively and exhibits an intuitive velocity map.

Computer Simulation of Gd(III) Speciation in Human Interstitial Fluid

The speciation and distribution of Gd(III) in human interstitial fluid was studied by computer simulation. Meantime artificial neural network was applied to the estimation of log ?values of complexes. The results show that the precipitate species, GdPO4 and Gd2(CO3)3, are the predominant species. Among soluble species, the free Gd(III), [Gd(HSA)] , [Gd(Ox)] and then the ternary complexes of Gd(III) with citrate are main species and [Gd3(OH)4] becomes the predominant species at the Gd(III) total concentration of 2.2?0-2mol/L.

Interstitial fluid flow:simulation of mechanical environment of cells in the interosseous membrane

In vitro experiments have shown that subtle fluid flow environment plays a significant role in living biological tissues, while there is no in vivo practical dynamical measurement of the interstitial fluid flow velocity. On the basis of a new finding that capillaries and collagen fibrils in the interosseous membrane form a parallel array, we set up a porous media model simulating the flow field with FLUENT software, studied the shear stress on interstitial cells＇ surface due to the interstitial fluid flow, and analyzed the effect of flow on protein space distribution around the ceils. The numerical simulation results show that the parallel nature of capillaries could lead to directional interstitial fluid flow in the direction of capillaries. Interstitial fluid flow would induce shear stress on the membrane of interstitial cells, up to 30 Pa or so, which reaches or exceeds the threshold values of cells＇ biological response observed in vitro. Interstitial fluid flow would induce nonuniform spacial distribution of secretion protein of mast cells. Shear tress on cells could be affected by capillary parameters such as the distance between the adjacent capillaries, blood pressure and the permeability coefficient of capillary＇s wall. The interstitial pressure and the interstitial porosity could also affect the shear stress on cells. In conclusion, numerical simulation provides an effective way for in vivo dynamic interstitial velocity research, helps to set up the vivid subtle interstitial flow environment of cells, and is beneficial to understanding the physiological functions of interstitial fluid flow.

Computer Simulation of Insoluble Pr(III) Speciation in Human Interstitial Fluid

A multi-phase model of Pr(III) speciation in human interstitial fluid was constructed and insoluble Pr(III) speciation was studied. When the total concentration of Pr(III) is below 8.401E-10 mol/L, soluble Pr(III) species are main species. With rising the total concentration of Pr(III), Pr(III) is firstly bound to phosphate to form precipitate of PrPO4, then bound to carbonate and another precipitate of Pr2(CO3)3 was obtained. When the total concentration is between 1.583E-9 mol/L and 4.000E-3 mol/L, the insoluble species are predominant Pr(III) species.

Fundamental kinematics laws of interstitial fluid flows on vascular walls

In the previous studies,the phenomenon that the interstitial fluid(ISF)can flow along tunica adventitia of the arteries and veins in both human and animal bodies was reported.On the basis of these studies,this paper aims to:(i)summarize the basic properties of the ISF flows in the walls of arteries and veins,(ii)combine the basic properties with axiomaticism and abstract the axiom for ISF flows,and(iii)propose three fundamental laws of the ISF flow,(i.e.,the existence law,the homotropic law and the reverse law).The three laws provide solid theoretical basement for exploring the kinematic patterns of interstitial fluid flow in the cardiovascular system.

A novel neuroprotective method against ischemic stroke by accelerating the drainage of brain interstitial fluid

Ischemic stroke is a leading cause of death and disability worldwide.Inflammatory response after stroke determines the outcome of ischemic injury.A recent study has reported an efficient method,epidural arterial implantation(EAI),for accelerating interstitial fluid(ISF)drainage,which provides a promising strategy to clear pro-inflammatory cytokines in the brain extracellular space(ECS).In this study,the method of EAI was modified(m-EAI)to control its function of accelerating the ISF drainage at different time points following ischemic attack.The neuroprotective effect of m-EAI on ischemic stroke was evaluated with the transient middle cerebral artery occlusion(tMCAO)rat model.The results demonstrated the accumulation of IL-1β,IL-6,and TNF-αwas significantly decreased by activating m-EAI at 7 d before and immediately after ischemic attack in tMCAO rats,accompanied with decreased infarct volume and improved neurological function.This study consolidates the hypothesis of exacerbated ischemic damage by inflammatory response and provides a new perspective to treat encephalopathy via brain ECS.Further research is essential to investigate whether m-EAI combined with neuroprotective drugs could enhance the therapeutic effect on ischemic stroke.

An in vivo study with an MRI tracer method reveals the biophysical properties of interstitial fluid in the rat brain

The nature of brain interstitial fluid （ISF） has long been a subject of controversy. Most of the previous studies on brain ISF were carded out in vitro. In the present study, a novel method was developed to characterize ISF in the living rat brain by magnetic resonance （MR） imaging using gadolinium-diethylenetriaminepentaacetic acid （Gd-DTPA） as a tracer. Sprague Dawley rats （n=8） were subjected to MR scanning before and after the introduction of Gd-DTPA into the caudate nucleus. A one-way drainage of brain ISF was demonstrated on the dynamic MR images. According to the traditional diffusion model, the diffusion and clearance rate constants of the tracer within brain extracellular space （ECS） were derived as （3.38±1.07）×10^-4 mm2 s^-1 and （7.60±4.18）×10^-5 s^-1. Both diffusion and bulk flow contributed to the drainage of ISF from the caudate nucleus, which demonstrated an ISF-cerebrospinal fluid confluence in the subarachnoid space at the lateral and ventral surface of the brain cortex at 3 h after the injection. By using this newly developed method, the brain ECS and ISF can be quantitatively measured simultaneously in the living brain, which will enhance the understanding of ISF and improve the efficiency of drug therapy via the brain interstitium.

Understanding Qi Running in the Meridians as Interstitial Fluid Flowing via Interstitial Space of Low Hydraulic Resistance

Qi, blood and the meridians are fundamental concepts in Chinese medicine（CM）, which are components of the human body and maintain physiological function. Pathological changes of qi, blood and meridians may lead to discomfort and disease. Treatment with acupuncture or herbal medicine aims to regulate qi and blood so as to recover normal function of the meridians. This paper explores the nature of qi as well as compares and correlates them with the structures of the human body. We propose a conceptualization of qi as being similar to the interstitial fluid, and the meridians as being similar to interstitial space of low hydraulic resistance in the body. Hence, qi running in the meridians can be understood as interstitial fluid flowing via interstitial space of low hydraulic resistance.

Tumor Interstitial Fluid and Postoperative Recurrence of Tumors: an Experimental Study for Verifying Hypothesis of "Tumor-phlegm Microenvironment"

Objective： To explore a method of extracting tumor interstitial fluid （TIF） which is similar to muddy phlegm in Chinese medicine （CM）, interleukin-8 （IL-8） in concentration was taken as the representative of the content of TIF, analyzed in the extracted TIF and the original tumor tissue, and examined to see whether TIF has an interfering effect on tumor recurrence. Methods： Tumor tissue was ground, centrifuged, and filtered for intercellular substances. Tumor-bearing Kunming S180 mice were raised for 21 days and then the tumors were removed to observe the influence of intervention with TIF, normal saline （NS） and a blank control on tumor recurrence. Results： The content of IL-8 in the filtered and unfiltered tumor tissue was not significantly different （P0.05）. Postoperative tumor recurrence in TIF intervention group was significantly higher than that in the NS intervention and control groups （60%, 12/20 vs. 20%, 4/20 vs. 15%, 3/20, χ2=11.058, P0.01）. Tumor cells grew vigorously and infiltrated to muscular tissue in TIF intervention group. Large numbers of tumor cells were seen necrotic in the NS intervention group, and small numbers of tumor cells were seen necrotic in the blank control group. Conclusions： TIF can be effectively extracted by the means described. It does not contain tumor cells, but its contents such as IL-8 may stimulate tumor cell growth and promote postoperative tumor recurrence, which provided preliminary experimental basis for hypothesis of ＂tumor-phlegm microenvironment＂.

Tumor Interstitial Fluid and Gastric Cancer Metastasis:An Experimental Study to Verify the Hypothesis of "Tumor-Phlegm Microenvironment"

Objective： To extract tumor interstitial fluid （TIF） from MKN-45 gastric cancer which is similar to ＂muddy phlegm＂ in Chinese medicine and observe influences of MKN-45 tumor interstitial fluid （MKN-45 TIF） intervention on metastasis of gastric cancer and on the expressions of vascular endothelial growth factor （VEGF）, kinase insert domain containing receptor （KDR）, epithelial-cadherin （E-cad）, cyclooxygenase-2 （COX-2）, intercellular adhesion molecule-1 （ICAM-1） and telomerase genes and proteins in primary tumor tissue. Methods： An MKN-45 tumor-bearing model was established in 50 nude mice. The modeled animals were equally randomized to 5 groups： the simple tumor-bearing group （model group）, the normal saline （NS） via tail vein injection （i.v.） group （NS i.v. group）, MKN-45 TIF i.v. group （TIF i.v. group）, NS intraperitoneal injection （i.p.） group （NS i.p. group）, and MKN-45 TIF i.p. group （TIF i.p. group）. The TIF and NS intervention groups received injection （i.p. or i.v.） of MKN-45 TIF or NS twice a week, 0.2 mL at a time. After 8 weeks, the primary tumors were removed, weighed and HE stained to observe tumor metastasis. The primary tumor tissues were analyzed by immunohistochemistry and real-time quantitative PCR to detect expressions of VEGF, KDR, E-cad, COX-2, ICAM-1, and telomerase genes and proteins in different groups. Results： There were significant differences in tumor weight between TIF intervention groups and the model and NS intervention groups. Tumor metastasis was observed in all 5 groups, but the tumor metastasis rate in TIF intervention groups was significantly higher than those in the model and NS intervention groups. The gene and protein expressions of gastric cancer-related factors VEGF, KDR, COX-2, ICAM-1 and telomerase were unregulated while the gene and protein expressions of E-cad were downregulated in TIF intervention groups. Conclusions： TIF promotes tumor growth, invasion and metastasis of gastric cancer. These findings provide preliminary experimental clues for verifying the hypothesis of ＂tumor-phlegm microenvironment＂.

Brain interstitial fluid drainage and extracellular space affected by inhalational isoflurane: in comparison with intravenous sedative dexmedetomidine and pentobarbital sodium

Brain interstitial fluid drainage and extracellular space are closely related to waste clearance from the brain. Different anesthetics may cause different changes of brain interstitial fluid drainage and extracellular space but these still remain unknown. Herein,effects of the inhalational isoflurane, intravenous sedative dexmedetomidine and pentobarbital sodium on deep brain matters’ interstitial fluid drainage and extracellular space and underlying mechanisms were investigated. When compared to intravenous anesthetic dexmedetomidine or pentobarbital sodium, inhalational isoflurane induced a restricted diffusion of extracellular space, a decreased extracellular space volume fraction, and an increased norepinephrine level in the caudate nucleus or thalamus with the slowdown of brain interstitial fluid drainage. A local administration of norepinephrine receptor antagonists, propranolol,atipamezole and prazosin into extracellular space increased diffusion of extracellular space and interstitial fluid drainage whilst norepinephrine decreased diffusion of extracellular space and interstitial fluid drainage. These findings suggested that restricted diffusion in brain extracellular space can cause slowdown of interstitial fluid drainage, which may contribute to the neurotoxicity following the waste accumulation in extracellular space under inhaled anesthesia per se.

Layers of interstitial fluid flow along a“slit-shaped”vascular adventitia

Interstitial fluid(ISF)flow through vascular adventitia has been discovered recently.However,its kinetic pattern was unclear.We used histological and topographical identification to observe ISF flow along venous vessels in rabbits.By magnetic resonance imaging(MRI)in live subjects,the inherent pathways of ISF flow from the ankle dermis through the legs,abdomen,and thorax were enhanced by paramagnetic contrast.By fluorescence stereomicroscopy and layer-by-layer dissection after the rabbits were sacrificed,the perivascular and adventitial connective tissues(PACTs)along the saphenous veins and inferior vena cava were found to be stained by sodium fluorescein from the ankle dermis,which coincided with the findings by MRI.The direction of ISF transport in a venous PACT pathway was the same as that of venous blood flow.By confocal microscopy and histological analysis,the stained PACT pathways were verified to be the fibrous connective tissues,consisting of longitudinally assembled fibers.Real-time observations by fluorescence stereomicroscopy revealed at least two types of spaces for ISF flow:one along adventitial fibers and another one between the vascular adventitia and its covering fascia.Using nanoparticles and surfactants,a PACT pathway was found to be accessible by a nanoparticle of<100 nm and contained two parts:a transport channel and an absorptive part.The calculated velocity of continuous ISF flow along fibers of the PACT pathway was 3.6-15.6 mm/s.These data revealed that a PACT pathway was a"slit-shaped"porous biomaterial,comprising a longitudinal transport channel and an absorptive part for imbibition.The use of surfactants suggested that interfacial tension might play an essential role in layers of continuous ISF flow along vascular vessels.A hypothetical"gel pump"is proposed based on interfacial tension and interactions to regulate ISF flow.These experimental findings may inspire future studies to explore the physiological and pathophysiological functions of vascular ISF or interfacial fluid flow among interstitial connective tissues throughout the body.

Research on the Interstitial Fluid Load Support Characteristics and Start-Up Friction Mechanisms of PVA-HA-Silk Composite Hydrogel

Hydrogel has been extensively studied as an articular cartilage repair and replacement material. PVA-HA-Silk composite hydrogel was prepared by freezing-thawing method in this paper. Mechanical properties were determined by experiments and the friction coefficient of PVA-HA-Silk composite hydrogel against steel ball was verified using micro-tribometer. Finite Element Method （FEM） was used to study the lubrication mechanism of PVA-HA-Silk composite hydrogel and the relation between the interstitial fluid load support and the start-up friction resistance. The results show that the elastic modulus and the permeability are 2.07 MPa and 10^-15m^4N^-1s^-1, respectively, and the start-up friction coefficients of PVA-HA-Silk composite hydrogel are in the range of 0.154）.2 at different contact loads, contact time and sliding speeds. The start-up friction resistance of PVA-HA-Silk composite hydrogel increases with the contact load and contact time. With the increase in sliding speed, the start-up friction resistance of PVA-HA-Silk composite hydrogel decreases. There is an inverse relation between the start-up friction resistance and the interstitial fluid load support. The change of fluid flow with the increase in sliding displacement has an important effect on the interstitial fluid load support and friction resistance. The interstitial fluid load support decreases with the increase in contact load and contact time, while the interstitial fluid load support reinforces with the increase in sliding speed. Moreover, PVA-HA-Silk composite hydrogel has mechanical properties of recovery and self-lubricating.

Bloodletting at Jing-well points decreases interstitial fluid flow in the thalamus of rats

OBJECTIVE：To investigate the changes in the neuronal microenvironment of the middle cerebral artery （MCA） territory induced by Jing-well points bloodletting acupuncture （WPBA） and to explore the neuroprotective mechanism of WPBA in stroke. METHODS： Adult male Sprague Dawley （n = 32） rats were randomly divided into four groups of eight animals each： WPBA-thalamus group （WT）, WPBA-caudate nucleus group （WC）, sham-control thalamus group （ST） and sham-control caudate nucleus group （SC）. Animals in the WT and WC groups received 2 I-μL of the extracellular tracer gadolinium-diethylene triamine pentaacetic acid （Gd-DTPA） injected into the thalamus or caudate nucleus, respectively, and 12 Jing-well points in the distal ends of the rats＇ digits were used for WPBA. Although 2 μL of Gd-DTPA was injected into the thalamus or caudate nucleus, respectively, for animals in the two sham groups （ST and SC）, no acupuncture or bloodletting was performed. Brain extracellular space and interstitial fluid flow parameters were measured using Gd-DTPA-enhanced magnetic reso- nance imaging. RESULTS： The brain interstitial fluid flow speed was decreased in the thalamus after WPBA, with a significantly lower Gd-DTPA clearance rate and longer half-life of Gd-DTPA in the thalamus of treated rats than those in sham-control rats [WPBA-treated rats＇clearance rate, （7.47 ± 3.15） x 10^-5/s （P = 0.009）; half-life, （1.52 ± 0.13） h, P = 0.000]. By contrast, no significant changes in brain extracellular space and interstitial fluid flow parameters were detected in the caudate nucleus after WPBA （P = 0.649）. In addi- tion, no differences in the morphology of the brain extracellular space or the final distribution of the traced brain interstitial fluid were demonstrated be- tween theWT and WC groups （P = 0.631, P = 0.970, respectively）. CONCLUSION： The WPBA decreased the speed of the local thalamic ISF flow in rats, which is assumed to be a beneficial protection by down-modulated the metabolic rate of the attacked neurons under stroke.

Analytic solutions of the interstitial fluid flow models

In this paper, we present the analytic solutions of several continuum porous media models that describe the interstitial fluid flow in the interosseous membrane. We first compare the results of the Brinkman, Stokes and Darcy systems in describing the isotropic interstitial fluid flows. Our calculations show that the Stokes equations can well approximate the Brinkman equations when the Darcy number Da 〉 0.2, while the Darcy model is an appropriate approximation to the Brinkman model in the interosseous membrane when Da 〈 2 × 10-4. Yet, in most cases, the anisotropy dominates the interstitial fluid. Therefore, we build an anisotropic Darcy model and show that an isotropic model can be used as a suitable approximation when the ratio between the transverse and longitudinal permeabilities is no larger than 20. Lastly, we take the blood flow in capillaries into consideration as well and introduce the coupled Stokes-Darcy system to describe the cases comprising both the capillary and the interstitial domain. Our results reveal that the profile of the interface exchange flow is not exactly in the linear form as was widely adopted in the numerical simulation, instead, the flux near the artery and the vein is more significant, which in turn results in the increase of the maximum horizontal velocity in the interstitial space while the outflow rate remains the same.

Dynamics of Calcium Signal and Leukotriene C_(4) Release in Mast Cells Network Induced by Mechanical Stimuli and Modulated by Interstitial Fluid Flow

Mast cells(MCs)play an important role in the immune system.Through connective tissues,mechanical stimuli activate intracellular calcium signaling pathways,induce a variety of mediators including leukotriene C4(LTC4)release,and affect MCs’microenvironment.This paper focuses on MCs’intracellular calcium dynamics and LTC4 release responding to mechanical stimuli,explores signaling pathways in MCs and the effect of interstitial fluid flow on the transport of biological messengers and feedback in the MCs network.We use a mathematical model to show that(i)mechanical stimuli including shear stress induced by interstitial fluid flow can activate mechano-sensitive(MS)ion channels on MCs’membrane and allow Ca^(2+)entry,which increases intracellular Ca^(2+)concentration and leads to LTC4 release;(ii)LTC4 in the extracellular space(ECS)acts on surface cysteinyl leukotriene receptors(LTC4R)on adjacent cells,leading to Ca^(2+)influx through Ca^(2+)release-activated Ca^(2+)(CRAC)channels.An elevated intracellular Ca^(2+)concentration further stimulates LTC4 release and creates a positive feedback in the MCs network.The findings of this study may facilitate our understanding of the mechanotransduction process in MCs induced by mechanical stimuli,contribute to understanding of interstitial flow-related mechanobiology in MCs network,and provide a methodology for quantitatively analyzing physical treatment methods including acupuncture and massage in traditional Chinese medicine(TCM).

The Integrative Five-Fluid Circulation System in the Human Body

Water is the key medium to transport numerous constituents and to provide a platform for physiological processes to take place in the living organisms in general;it also participates actively in many of these processes. In humans, there are different vehicles to contain water and its constituents. Our objective is to find out whether there is an overall water-base circulation system in the human body by analyzing the updated findings of different research groups on the physiological functions of various seemingly isolated fluid systems. By 1963, there were five separate fluid systems discovered in mammalians: (i) The Primo Vasculature Fluid (PVF) with protein precursors and micro cells held in the Primo Vasculature System (PVS). (ii) Blood with its constituents held in the cardio vasculature. (iii) Extracranial interstitial fluid (ISF) whose vehicle had a very irregular structure—the interstitium all over the body. (iv) The cerebrospinal fluid had been considered to be within the brain ventricles and spinal canal. (v) The extra-cranial lymphatic system which drained ISF, and had been known to join the subclavian vein. Fluid (i) was first reported in 1963 and fluids (ii) to (v) have been known for many decades, but the failure to detect a lymphatic system inside the skull has also been a mystery for many decades. The intra-cranial ISF (which we name as BISF) has drawn little attention, apart from discussing the mechanism of the blood-brain-barrier. During the past decade, there has been direct evidence indicating that CSF and BISF are actually mixed. After that, the intracranial lymphatic system was discovered and confirmed in animal models only slightly over one year back, and we called such fluid as glymphatic-fluid. After reviewing the stated “classical” five fluid systems together with the new findings in Sections 2 - 7, we propose, for the first time, that the PVF, the blood, ISF, a mixture of CSF-BISF, and a mixture of glymphatic-fluid and lymph form an integrative circulation system in water base in the human and other mammalian bodies, as schematically represented in the last section. In this paper, we point out the positive correlation of chronic neuro degenerative diseases such as Alzheimer’s disease, Parkinson’s diseases and the insufficient brain wastes clearance by the glymphatic system. We also discuss the role played by the venous vessels as part of such clearance in upright posture. Moreover, simple non-invasive maneuver techniques are introduced here, as one example of enhancement of glymphatic fluid flow out of the skull to join the lymphatic system. A series of questions are raised in Section 8, the answers to which would help us to understand the transition from physio- to pathological states in the development of many diseases. Detailed analysis of this paper leads us to consider that research in understanding this integrative circulation system is only at the infancy stage, and fluid dynamics investigation seems to be the plausible modality of approach in the near future.

An analytical poroelastic model for laboratorial mechanical testing of the articular cartilage (AC)

The articular cartilage （AC） can be seen as a biphasic poroelastic material. The cartilage deformation under compression mainly leads to an interstitial fluid flow in the porous solid phase. In this paper, an analytical poroelastic model for the AC under laboratorial mechanical testing is developed. The solutions of interstitial fluid pressure and velocity are obtained. The results show the following facts. （i） Both the pressure and fluid velocity amplitudes are proportional to the strain loading amplitude. （ii） Both the amplitudes of pore fluid pressure and velocity in the AC depend more on the loading amplitude than on the frequency. Thus, in order to obtain the considerable fluid stimulus for the AC cell responses, the most effective way is to increase the loading amplitude rather than the frequency. （iii） Both the interstitiM fluid pressure and velocity are strongly affected by permeability variations. This model can be used in experimental tests of the parameters of AC or other poroelastic materials, and in research of mechanotransduction and injury mechanism involved interstitial fluid flow.