Spatial sensitivity to absorption changes for various near-infrared spectroscopy methods:A compendium review

This compendium review focuses on the spatial distribution of sensitivity to localized absorption changes in optically diffuse media,particularly for measurements relevant to near-infrared spectroscopy.The three temporal domains,continuous wave,frequency domain,and time domain,each obtain different optical data types whose changes may be related to effective homogeneous changes in the absorption coefficient.Sensitivity is the relationship between a localized perturbation and the recovered effective homogeneous absorption change.Therefore,spatial sensitivity maps representing the perturbation location can be generated for the numerous optical data types in the three temporal domains.The review first presents a history of the past 30 years of work investigating this sensitivity in optically diffuse media.These works are experimental and theoretical,presenting one-,two-,and three-dimensional sensitivity maps for different Near-Infrared Spectroscopy methods,domains,and data types.Following this history,we present a compendium of sensitivity maps organized by temporal domain and then data type.This compendium provides a valuable tool to compare the spatial sensitivity of various measurement methods and parameters in one document.Methods for one to generate these maps are provided in Appendix A,including the code.This historical review and comprehensive sensitivity map compendium provides a single source researchers may use to visualize,investigate,compare,and generate sensitivity to localized absorption change maps.

DISCRIMINATION OF MENTAL WORKLOAD LEVELS IN HUMAN SUBJECTS WITH FUNCTIONAL NEAR-INFRARED SPECTROSCOPY

We have applied functional near-infrared spectroscopy(fNIRS)to the human forehead to distinguish different levels of mental workload on the basis of hemodynamic changes occurring in the prefrontal cortex.We report data on 3 subjects from a protocol involving 3 mental workload levels based on to working memory tasks.To quantify the potential of fNIRS for mental workload discrimination,we have applied a 3-nearest neighbor classification algorithm based on the amplitude of oxyhemoglobin(HbO2)and deoxyhemoglobin(HbR)concentration changes associated with the working memory tasks.We have found classification success rates in the range of 44%-72%,which are significantly higher than the corresponding chance level(for random data)of 19.1%.This work shows the potential of fNIRS for mental workload classification,especially when more parameters(rather than just the amplitude of concentration changes used here)and more sophisticated classification algorithms(rather than the simple 3-nearest neighbor algorithm used here)are considered and optimized for this application.

Recent advances in lithographic fabrication of micro-/nanostructured polydimethylsiloxanes and their soft electronic applications

The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics.Among the many classes of stretchable materials,micro-/nanostructured poly(dimethylsiloxane)(PDMS)has emerged as a vital building block based on its merits of flexibility,stretchability,simple processing,and,more importantly,high degrees of freedom of incorporation with other functional materials,including metals and semiconductors.The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays,sensors and actuators as well as in health-monitoring device platforms.Meanwhile,novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest.The aim of this review is to comprehensively summarize the progress regarding micro-/nanostructured PDMS and their promising soft electronic applications.This review is concluded with a brief outlook and further research directions.

Long-term phenotypic characterization of human bone marrow and adipose tissue derived mesenchymal stromal cells

We present methods to characterize mesenchymal stromal cells (MSC) over long time periods in vitro. The methods entail passaging cells multiple times and performing differentiation studies with the cells at each passage. Using an array of surface markers and flow cytometric quantification, the data can be correlated to traditional measures of differentiation such as PCR and staining. Using these methods to quantify the amount of differentiation, we concluded that many common MSC markers do not specifically define MSCs with true stem cell properties. Additionally, adipose-derived as opposed to bone marrow-derived MSCs show long-term CD34+ labeling. The methods described can be used to help identify stem cell markers and to characterize the state of stem cells in vitro. Compiling these data from multiple laboratories would be helpful to determine source, extraction and culture methods needed to obtain high yields of useful stem cells.

Transformational change in the field of diffuse optics:From going bananas to going nuts

The concept of region of sensitivity is central to the field of diffuse optics and is closely related to the Jacobian matrix used to solve the inverse problem in imaging.It is well known that,in diffuse reflectance,the region of sensitivity associated with a given source-detector pair is shaped as a banana,and features maximal sensitivity to the portions of the sample that are closest to the source and the detector.We have recently introduced a dual-slope(DS)method based on a special arrangement of two sources and two detectors,which results in deeper and more localized regions of sensitivity,resembling the shapes of different kinds of nuts.Here,we report the regions of sensitivity associated with a variety of source-detector arrangements for DS measurements of intensity and phase with frequency-domain spectroscopy(modulation frequency:140 MHz)in a medium with absorption and reduced scattering coefficients of 0.1 and 12 cm^(-1),respectively.The main result is that the depth of maximum sensitivity,considering only cases that use source-detector separations of 25 and 35 mm,progressively increases as we consider single-distance intensity(2.0mm),DS intensity(4.6mm),single-distance phase(7.5mm),and DS phase(10.9 mm).These results indicate the importance of DS measurements,and even more so of phase measurements,when it is desirable to selectively probe deeper portions of a sample with diffuse optics.This is certainly the case in non-invasive optical studies of brain,muscle,and breast tissue,which are located underneath the superficial tissue at variable depths.

PHASE DIFFERENCE BETWEEN LOW-FREQUENCY OSCILLATIONS OF CEREBRAL DEOXY-AND OXY-HEMOGLOBIN CONCENTRATIONS DURING A MENTAL TASK

Hemodynamic low-frequency(~0.1 Hz)spontaneous oscillations as detected in the brain by nearinfrared spectroscopy have potential applications in the study of brain activation,cerebral autoregulation,and functional connectivity.In this work,we have investigated the phase lag between oscillations of cerebral deoxy-and oxy-hemoglobin concentrations in the frequency range 0.05-0.10 Hz in a human subject during a mental workload task.We have obtained a measure of such phase lag using two different methods:(1)phase synchronization analysis as used in the theory of chaotic oscillators and(2)a novel cross-correlation phasor approach.The two methods yielded comparable initial results of a larger phase lag between low-frequency oscillations of deoxy-and oxyhemoglobin concentrations during mental workload with respect to a control,rest condition.

The meaning of “coherent” and its quantication in coherent hemodynamics spectroscopy

We have recently introduced a new technique,coherent hemodynamics spectroscopy(CHS),which aims at characterizing a specic kind of tissue hemodynamics that feature a high level of covariation with a given physiological quantity.In this study,we carry out a detailed analysis of the signicance of coherence and phase synchronization between oscillations of arterial blood pressure(ABP)and total hemoglobin concentration([Hbt]),measured with near-infrared spectroscopy(NIRS)during a typical protocol for CHS,based on a cyclic thigh cuffocclusion and release.Even though CHS is based on a linear time invariant model between ABP(input)and NIRS measurands(outputs),for practical reasons in a typical CHS protocol,we inducenite“groups”of ABP oscillations,in which each group is characterized by a different frequency.For this reason,ABP(input)and NIRS measurands(output)are not stationary processes,and we have used wavelet coherence and phase synchronization index(PSI),as a metric of coherence and phase synchronization,respectively.PSI was calculated by using both the wavelet cross spectrum and the Hilbert transform.We have also used linear coherence(which requires stationary process)for comparison with wavelet coherence.Themethod of surrogate data is used tond critical values for the signicance of covariation between ABP and[Hbt].Because we have found similar critical values for wavelet coherence and PSI by usingve of the most used methods of surrogate data,we propose to use the data-independent Gaussian random numbers(GRNs),for CHS.By using wavelet coherence and wavelet cross spectrum,and GRNs as surrogate data,we have found the same results for the signicance of coherence and phase synchronization between ABP and[Hbt]:on a total set of 20 periods of cuffoscillations,we have found 17 coherent oscillations and 17 phase synchronous oscillations.Phase synchronization assessed with Hilbert transform yielded similar results with 14 phase synchronous oscillations.Linear coherence and wavelet coherence overall yielded similar number of signicant values.We discuss possible reasons for this result.Despite the similarity of linear and wavelet coherence,we argue that wavelet coherence is preferable,especially if one wants to use baseline spontaneous oscillations,in which phase locking and coherence between signals might be only temporary.

Study of capillary transit time distribution in coherent hemodynamics spectroscopy

A recently proposed analytical hemodynamie modell[s.Fantini,Neurolmage 85,202-221(2014)]is able to predict the changes of oxy,deoxy,and total hemoglobin concentrations(model outputs)given arbitrary changes in blood flow,blood volume,and rate of oygen consumption(model inputs).One asumption of this model is that the capillary compartment is characterized by a single blood transit time.In this work,we have extended the original model by considering a distribution of capillary transit times and we have compared the outputs of both models(original and extended)for the case of sinusoidal input signals at different frequencies,which realizes the new technique of coherent hemodynamics spectroscopy(CHS).For the calculations with the original model,we have used the mean value of the distribution of capillary transit times con-sidered in the extended model.We have found that,for distributions of capillary transit times having mean values around 1 s and a standard deviation less than about 45%of the mean value,the original and extended models yield the same CHS spectra(i.e.,model outputs versus fre-quency of ocillation)within typical experimental errors.For wider capillary transit time dis-tributions,the two models yield different CHS spectra.By assuming that Poiseuille's law is valid in the capillary compartment,we have related the distribution of capillary transit times to the distributions of capillary lengths and capillary speed of blood flow to calculate the average capillary and venous saturations.We have found that,for standard deviations of the capillanry transit time distrilbution that are less than about 80%of the mean value,the average capillary saturation is always larger than the venous saturation.By contrast,the average capillary satu-ration may be less than the venous saturation for wider distributions of the capillary transit times.

Broadband diffuse optical spectroscopy of two-layered scattering media containing oxyhemoglobin,deoxyhemoglobin,water,and lipids

We investigated the relationship between chromophore concentrations in two-layered scattering media and the apparent chromophore concentrations measured with broadband optical spectroscopy in conjunction with commonly used homogeneous medium inverse models.We used diffusion theory to generate optical data from a two-layered distribution of relevant tissue absorbers,namely,oxyhemoglobin,deoxyhemoglobin,water,and lipids,with a top-layer thickness in the range 1–15 mm.The generated data consisted of broadband continuous-wave(CW)diffuse reflectance in the wavelength range 650–1024 nm,and frequency-domain(FD)diffuse reflectance at 690 and 830 nm;two source-detector distances of 25 and 35mm were used to simulate a dual-slope technique.The data were inverted using diffusion theory for a semi-infinite homogeneous medium to generate reduced scattering coeffcients at 690 and 830nm(from FD data)and effective absorption spectra in the range 650–1024nm(from CW data).The absorption spectra were then converted into effective total concentration and oxygen saturation of hemoglobin,as well as water and lipid concentrations.For absolute values,it was found that the effective hemoglobin parameters are typically representative of the bottom layer,whereas water and lipid represent some average of the respective concentrations in the two layers.For concentration changes,lipid showed a significant cross-talk with other absorber concentrations,thus indicating that lipid dynamics obtained in these conditions may not be reliable.These systematic simulations of broadband spectroscopy of two-layered media provide guidance on how to interpret effective optical properties measured with similar instrumental setups under the assumption of medium homogeneity.

NEAR-INFRARED,BROAD-BAND SPECTRAL IMAGING OF THE HUMAN BREAST FOR QUANTITATIVE OXIMETRY:APPLICATIONS TO HEALTHY AND CANCEROUS BREASTS

We have examined ten human subjects with a previously developed instrument for near-infrared diffuse spectral imaging of the female breast.The instrument is based on a tandem,planar scan of two collinear optical fibers(one for illumination and one for collection)to image a gently compressed breast in a transmission geometry.The optical data collection features a spatial sampling of 25 points/cm2 over the whole breast,and a spectral sampling of 2 points/nm in the 650-900nm wavelength range.Of the ten human subjects examined,eight are healthy subjects and two are cancer patients with unilateral invasive ductal carcinoma and ductal carcinoma in situ,respectively.For each subject,we generate second-derivative images that identify a network of highly absorbing structures in the breast that we assign to blood vessels.A previously developed paired-wavelength spectral method assigns oxygenation values to the absorbing structures displayed in the second-derivative images.The resulting oxygenation images feature average values over the whole breast that are significantly lower in cancerous breasts(69±14%,n=2)than in healthy breasts(85±7%,n=18)(p<0.01).Furthermore,in the two patients with breast cancer,the average oxygenation values in the cancerous regions are also significantly lower than in the remainder of the breast(invasive ductal carcinoma:49±11%vs 61±16%,p<0.01;ductal carcinoma in situ:58±8%vs 77±11%,p<0.001).

丝蛋白复合骨形态发生蛋白2在大鼠炎性牙髓愈合中的作用

目的：探讨将丝蛋白复合骨形态发生蛋白2（bone morphogenetic protein 2,BMP-2）作为盖髓剂,治疗由脂多糖（lipopolysaccharide,LPS）引起的大鼠炎性牙髓的效果。方法：30只雄性Wistar大鼠,随机分为5组：（1）未手术正常对照组;（2）空白对照组（无盖髓剂）;（3）氢氧化钙组;（4）静电纺丝丝蛋白组（简称丝蛋白组）;（5）静电纺丝丝蛋白复合BMP-2组（简称丝蛋白复合BMP-2组）。将第2∽5组双侧上颌第一磨牙开髓并放置LPS,不使用盖髓剂或使用相应盖髓剂,然后封闭开髓孔。所有组于术后第3、7、14天制作石蜡切片,行HE染色及CD14免疫组织化学染色,采用image-pro plus（IPP）软件测量免疫组织化学染色的光密度（D）值。结果：HE染色结果显示丝蛋白复合BMP-2组在各盖髓组中,术后7及14 d炎性细胞分级最低,其次是氢氧化钙组及丝蛋白组,空白对照组最高;修复性牙本质形成分级的高低顺序则相反。CD14免疫组织化学染色结果显示术后3及7 d,使用盖髓剂的3个组之间D值差异无统计学意义,但均显著低于空白对照组;14 d时丝蛋白复合BMP-2组D值（0.145±0.011）显著低于空白对照（0.287±0.019）、氢氧化钙（0.170±0.017）、丝蛋白（0.175±0.018）3个组（P〈0.05）。结论：丝蛋白复合BMP-2应用于炎性牙髓的盖髓,能减轻炎症,诱导修复性牙本质的形成,提高对炎性牙髓的治疗效果。

Synthetic and nature-derived lipid nanoparticles for neural regeneration

Challenges and opportunities in nerve regeneration:The central nervous system(CNS)has a limited ability to regenerate.Subsequent to spinal injury,glial scar formation,created by fibroblasts,neuroglia,monocytes,and endothelial cells,inhibits regeneration of the injured nerve.The peripheral nervous system(PNS)has a greater regeneration potential than the CNS;however,the current gold standard of treatment for a large nerve defect is still autologous nerve grafts,

COHERENT HEMODYNAMICS SPECTROSCOPY BASED ON A PACED BREATHING PARADIGM-REVISITED

A novel hemodynamic model has been recently introduced,which provides analytical relation-ships between the changes in cerebral blood volume(CBV),cerebral blood flow(CBF),andcerebral metabolic rate of oxy gen(CMRO2),and associat ed changes in the tissue concentrationsof oxy-and deoxy-hemoglobin(AO and AD)measured with near-infrared,spectroscopy(NIRS)[S.Fantini,Neuroimage 85,202-221(2014)].This novel model can be applied tomeasurements of the amplit ude and phase of induced hemodynamic oscillations as a function ofthe frequency of oscillation,realizing the novel technique of coherent hemodynamics spectroscopy(CHS)[S.Fantini,Neuroimage 85,202-221(2014);M.L.Pierro et al.,Neuroimage 85,222-233(2014)]:In a previous work,,we have demonstrated an in vivo application of CiHS on hunanSubjects during paced breat hing[M.L.Pierro et al,Neuroimage 85,222-233(2014)].In thiswork,we present a new analysis of the collected data duringpaced breat hing based on a slightlyrevised formulation of the hemodynamic model and ann efficient fitting procedure.While we haveinitially treated all 12 model parameindeependent,we have found that,in this new in-plementation of CHS,the number of independent is eight.In this article,we identifythe eight independent model parameters and,we show that our previous results are consistentwith the new formulation,once the individual parameters of the earlier analysis are combinedinto the new set of independent parameters.

The ex vivo and in vivo biological performances of graphene oxide and the impact of surfactant on graphene oxide's biocompatibility

Graphene oxide(GO)displays promising properties for biomedical applications including drug delivery and cancer therapeutics.However,GO exposure also raises safety concerns such as potential side effects on health.Here,the biological effects of GO suspended in phosphate buffered saline(PBS)with or without 1% nonionic surfactant Tween 80 were investigated.Based on the ex vivo experiments,Tween 80 significantly affected the interaction between GO and peripheral blood from mice.GO suspension in PBS tended to provoke the aggregation of diluted blood cells,which could be prevented by the addition of Tween 80.After intravenous administration,GO suspension with or without 1% Tween 80 was quickly eliminated by the mononuclear phagocyte system.Nevertheless,GO suspension without Tween 80 showed greater accumulation in lungs than that containing 1% Tween 80.In contrast,less GO was found in livers for GO suspension compared to Tween 80 assisted GO suspension.Organs including hearts,livers,lungs,spleens,kidneys,brains,and testes did not reveal histological alterations.The indexes of peripheral blood showed no change upon GO exposure.Our results together demonstrated that Tween 80 could greatly alter GO's biological performance and determine the pattern of its biodistribution in mice.

Tailoring combinatorial lipid nanoparticles for intracellular delivery of nucleic acids, proteins,and drugs

Lipid nanoparticle(LNP)-based drug delivery systems have become the most clinically advanced non-viral delivery technology.LNPs can encapsulate and deliver a wide variety of bioactive agents,including the small molecule drugs,proteins and peptides,and nucleic acids.However,as the physicochemical properties of small-and macromolecular cargos can vary drastically,every LNP carrier system needs to be carefully tailored in order to deliver the cargo molecules in a safe and efficient manner.Our group applied the combinatorial library synthesis approach and in vitro and in vivo screening strategy for the development of LNP delivery systems for drug delivery.In this Review,we highlight our recent progress in the design,synthesis,characterization,evaluation,and optimization of combinatorial LNPs with novel structures and properties for the delivery of small-and macromolecular therapeutics both in vitro and in vivo.These delivery systems have enormous potentials for cancer therapy,antimicrobial applications,gene silencing,genome editing,and more.We also discuss the key challenges to the mechanistic study and clinical translation of new LNP-enabled therapeutics.

Biocompatibility and degradation of tendon-derived scaffolds

Decellularized extracellular matrix has often been used as a biomaterial for tissue engineering applications.Its function,once implanted can be crucial to determining whether a tissue engineered construct will be successful,both in terms of how the material breaks down,and how the body reacts to the material’s presence in the first place.Collagen is one of the primary components of extracellular matrix and has been used for a number of biomedical applications.Scaffolds comprised of highly aligned collagen fibrils can be fabricated directly from decellularized tendon using a slicing,stacking,and rolling technique,to create two-and three-dimensional constructs.Here,the degradation characteristics of the material are evaluated in vitro,showing that chemical crosslinking can reduce degradation while maintaining fiber structure.In vivo,non-crosslinked and crosslinked samples are implanted,and their biological response and degradation evaluated through histological sectioning,trichrome staining,and immunohistochemical staining for macrophages.Non-crosslinked samples are rapidly degraded and lose fiber morphology while crosslinked samples retain both macroscopic structure as well as fiber orientation.The cellular response of both materials is also investigated.The in vivo response demonstrates that the decellularized tendon material is biocompatible,biodegradable and can be crosslinked to maintain surface features for extended periods of time in vivo.This study provides material characteristics for the use of decellularized tendon as biomaterial for tissue engineering.

A toolkit of thread-based microfluidics,sensors,and electronics for 3D tissue embedding for medical diagnostics

Threads,traditionally used in the apparel industry,have recently emerged as a promising material for the creation of tissue constructs and biomedical implants for organ replacement and repair.The wicking property and flexibility of threads also make them promising candidates for the creation of three-dimensional(3D)microfluidic circuits.In this paper,we report on thread-based microfluidic networks that interface intimately with biological tissues in three dimensions.We have also developed a suite of physical and chemical sensors integrated with microfluidic networks to monitor physiochemical tissue properties,all made from thread,for direct integration with tissues toward the realization of a thread-based diagnostic device(TDD)platform.The physical and chemical sensors are fabricated from nanomaterial-infused conductive threads and are connected to electronic circuitry using thread-based flexible interconnects for readout,signal conditioning,and wireless transmission.To demonstrate the suite of integrated sensors,we utilized TDD platforms to measure strain,as well as gastric and subcutaneous pH in vitro and in vivo.

Low-cost and cleanroom-free fabrication of microneedles

We present a facile,low-cost and cleanroom-free technique for the fabrication of microneedles using molds created by laser ablation.Microneedle mold with high aspect ratios is achieved on acrylic sheet by engraving a specific pattern of crossover lines(COL)using CO2 laser cutter.Ablating COL pattern on the acrylic sheet creates a sharp conical shape in the center of the design.We have shown that a variety of microneedle shapes with different heights and tip angles can be easily achieved by changing the number and the length of the COL.Polydimethylsiloxane(PDMS)microneedles were fabricated by casting the PDMS on the mold.The resulted PDMS microneedles are oxygen plasma treated and then silanized.Another PDMS layer is casted on PDMS microneedles and detached after curing.The silanization prevents those two layers of PDMS from bonding to each other and makes them easily detachable.After detachment of the PDMS mold of microneedles,the mold is used to fabricate degradable polyvinyl alcohol microneedle patch suitable for transdermal drug delivery.The release kinetics of the needles are also shown and discussed in order to prove the applicability of the needles.

High-throughput physical phenotyping of cell differentiation

In this report,we present multiparameter deformability cytometry(m-DC),in which we explore a large set of parameters describing the physical phenotypes of pluripotent cells and their derivatives.m-DC utilizes microfluidic inertial focusing and hydrodynamic stretching of single cells in conjunction with high-speed video recording to realize high-throughput characterization of over 20 different cell motion and morphology-derived parameters.Parameters extracted from videos include size,deformability,deformation kinetics,and morphology.We train support vector machines that provide evidence that these additional physical measurements improve classification of induced pluripotent stem cells,mesenchymal stem cells,neural stem cells,and their derivatives compared to size and deformability alone.In addition,we utilize visual interactive stochastic neighbor embedding to visually map the high-dimensional physical phenotypic spaces occupied by these stem cells and their progeny and the pathways traversed during differentiation.This report demonstrates the potential of m-DC for improving understanding of physical differences that arise as cells differentiate and identifying cell subpopulations in a label-free manner.Ultimately,such approaches could broaden our understanding of subtle changes in cell phenotypes and their roles in human biology.

From biomimicry to bioelectronics:Smart materials for cardiac tissue engineering

Effective strategies in cardiac tissue engineering require matrices that recapitulate the mechanical,topographic and electrical cues present in the native extracellular matrix.In this review,we discuss recent efforts in materials science and nanotechnology to achieve functional three-dimensional(3D)scaffolds that modulate and monitor cardiac tissue function.We consider key design considerations,including choice of biopolymer matrix,cell sources,and delivery methods for eventual therapies.We then discuss how solid-state nanomaterials may be integrated within these systems to provide unique electrical and nanotopographic cues that improve electromechanical synchrony.We describe how these approaches may be extended to complex,spatially heterogeneous constructs using 3D bioprinting techniques.Finally,we describe how scaffold materials may be augmented with bioelectronic components to achieve hybrid myocardium that monitors or controls electrophysiological activity.Collectively,these approaches provide a framework for achieving cardiac tissues with tunable,rationally-designed functionalities.We discuss future prospects and remaining challenges for clinical translation.