Using the cavitation collapse time to indicate the extent of histotripsy-induced tissue fractionation

Histotripsy is an ultrasonic tissue ablation method based on acoustic cavitation. It has been shown that cavitation dynamics change depending on the mechanical properties of the host medium. During histotripsy treatment, the target-tissue is gradually fractionated and eventually liquefied to acellular homogenate. In this study, the change in the collapse time (t _col) of the cavitation bubble cloud over the course of histotripsy treatment is investigated as an indicator for progression of the tissue fractionation process throughout treatment. A 500 kHz histotripsy transducer is used to generate single-location lesions within tissue-mimicking agar phantoms of varying stiffness levels as well as ex vivo bovine liver samples. Cavitation collapse signals are acquired with broadband hydrophones, and cavitation is imaged optically using a high-speed camera in transparent tissue-mimicking phantoms. The high-speed-camera-acquired measurements of t _col validate the acoustic hydrophone measurements. Increases in t _col are observed both with decreasing phantom stiffness and throughout histotripsy treatment with increasing number of pulses applied. The increasing trend of t _col throughout the histotripsy treatment correlates well with the progression of lesion formation generated in tissue-mimicking phantoms (R ²  =  0.87). Finally, the increasing trend of t _col over the histotripsy treatment is validated in ex vivo bovine liver.

Magnetoelastic vibrational biomaterials for real-time monitoring and modulation of the host response

Magnetoelastic (ME) biomaterials are ferromagnetic materials that physically deform when exposed to a magnetic field. This work describes the real-time control and monitoring capabilities of ME biomaterials in wound healing. Studies were conducted to demonstrate the capacity of the materials to monitor changes in protein adsorption and matrix stiffness. In vitro experiments demonstrated that ME biomaterials can monitor cell adhesion and growth in real-time, and a long-term in vivo study demonstrated their ability to monitor the host response (wound healing) to an implant and control local cell density and collagen matrix production at the soft tissue-implant interface. This approach represents a potentially self-aware and post-deployment activated biomaterial coating as a means to monitor an implant surface and provide an adjuvant therapy for implant fibrosis.

Bioactive Magnetoelastic Materials as Coatings for Implantable Biomaterials

Enhanced fibroblast activity at the soft tissue-implant interface can dramatically decrease the stability, function, and lifespan of biomedical implants such as bone anchored prostheses. Although bone anchoring systems dramatically improve prosthetic limb mechanical stability, uncontrolled fibrosis at the soft tissue-mounting post interface is a significant problem. The aberrant cell growth leads to irregular skin folds that prevent proper sealing to the bone anchoring post and also serves as a site for opportunistic infection and failure of the prosthetic system. We are developing a bioactive vibrational coating to control fibrous tissue overgrowth. The coating is based on a magnetoelastic (ME) material that can be set to vibrate at a predetermined amplitude and frequency using a controlled magnetic field. We hypothesize that small local vibrations can be used to selectively control cell adhesion and gene expression to promote and maintain functional stability at the implant-tissue interface. For bone anchored prostheses, the ME coating would be applied around the mounting post at the soft tissue interface. The specific aims of this work were to (1) modify the coating for use in contact with a biologic environment and (2) determine if local vibrational strain can efficiently control cell attachment to the coating without significantly influencing viability. First, two common biocompatible polymers, polyurethane and chitosan, were deposited as thin films on the ME coating to allow for its use in tissue culture. An indirect cytotoxicity test was used to determine fibroblast (L929) viability in media conditioned for 24 and 48 hours with uncoated, chitosan coated, and polyurethane coated ME materials. Results demonstrated that both polymer coatings returned cell survival to levels statistically indistinguishable from controls (cells cultured on tissue cultured polystyrene, TCP) with cell viability over 96% under all coating conditions. Second, the affect of local vibrations on cell adhesion was tested in vitro. A cell viability assay (Calcein-AM) followed by fluorescent imaging was used to quantify attachment and viability of fibroblasts cultured directly on the bioactive ME material. Results clearly indicated that controlled local vibrations can induce complete cell detachment from the ME material compared with non-vibrated controls at up to 72 hours post-seeding. Further, cells detached via applied vibrations showed no significant decrease in viability compared to adherent controls. These results suggest the potential for this novel coating to effectively control fibrous tissue overgrowth using the mild application of tunable local vibrations, a significant and cost-effective approach that could improve the stability, function, and lifespan of biomedical implants and reduce the need for surgical revision.