Implantable, multifunctional, bioresorbable optics

Abstract

Advances in personalized medicine are symbiotic with the development of novel technologies for biomedical devices. We present an approach that combines enhanced imaging of malignancies, therapeutics, and feedback about therapeutics in a single implantable, biocompatible, and resorbable device. This confluence of form and function is accomplished by capitalizing on the unique properties of silk proteins as a mechanically robust, biocompatible, optically clear biomaterial matrix that can house, stabilize, and retain the function of therapeutic components. By developing a form of high-quality microstructured optical elements, improved imaging of malignancies and of treatment monitoring can be achieved. The results demonstrate a unique family of devices for in vitro and in vivo use that provide functional biomaterials with built-in optical signal and contrast enhancement, demonstrated here with simultaneous drug delivery and feedback about drug delivery with no adverse biological effects, all while slowly degrading to regenerate native tissue.

Fig. 1.

(A) Scanning electron microscope image of a silk microprism array (MPA). (B) The schematic of the experimental setup for the evaluation of the performance of a replicated MPA. Incoherent white-light illumination was provided to the silk reflector from a fixed height and a backscattering reflection probe is used to collect the response from the same height and couple it to a spectrometer. (C) The silk MPA shows significant increase in reflected signal compared with the unpatterned plain film. (D and E) Results from in vitro experiments from tissue layers characterized with the setup shown in B, where a silk MPA is placed underneath a spectrally responsive element, a layer of cellulose embedded with red pigment, to capture scattered photons in the forward direction and enhanced the backscattered signal. (D) Comparison between the signal detected from (1) the spectral element covered by one layer of fat, (2) the same covered by two fat layers, and (3) the same as in (2) but with the silk MPA under the spectral element. The reflectivity response was significantly higher when the mirror was present. The same experiment was repeated by using layers of muscle tissue. The data are presented in E that compare (1) the response due to the spectral element covered with two layers of muscle tissue with (2) the same with the reflector in place. The arrows indicate the absorption peaks of the tissue.

Fig. 2.

Phantom results for demonstrating signal and contrast enhancement with the MPAs in deep tissue. (A) The schematic of the experimental setup with a variable source–detector separation for imaging deeper layers. Illumination was provided to the phantom, with the fiber tip touching the phantom surface. The detection fiber is scanned along the phantom and the reflector is placed in a depth of 1 cm. The detection fiber was coupled to a spectrometer. (B) The MPA shows significant increase in reflected signal compared with measuring reflectance from the phantom alone. (C) This increase in signal reduces with larger source–detector distances. (D) Scanning geometry for contrast imaging. For contrast measurements, an 8 × 8-mm ND filter is additionally put on top of the reflector, mimicking a local inclusion. (E) The contrast enhancement for measuring the ND filter is increased 3.5 times at source–detector distance of 12 mm and also decreases with larger separations (F), still showing a two times increase at 20 mm.

Fig. 3.

In vivo results from the use of silk MPAs and Au-NP MPAs. (A) The MPAs for implantation were prepared with a size of ∼1 × 1 cm. (B) The s.c. implantation of a silk MPA in the dorsal region of a mouse. (C) The backscattered signal was measured in vivo and shows ∼3× enhancement due to the MPA right after implantation. (D) Au-NP–doped silk MPAs with dimensions of ∼1 × 1 cm were prepared for implantation. (E) The Au-NP–silk solution, which was used to cast MPAs, show enhanced absorption due to the Au-NP doping, as illustrated in (F). The backscattered signal of the implanted silk MPA was measured and compared with a control signal taken from an Au-NPs–doped flat (e.g., unpatterned) silk film also implanted in the mouse’s dorsal region as a control. The measurement shows signal enhancement similar to that of the undoped counterparts in C.

Fig. 4.

Multifunctional optical device. Chemotherapeutic, doxorubicin-loaded silk reflectors (DxR MPAs) are characterized in vitro under enzymatic degradation (proteinase k with a concentration of 0.1 mg/mL). (A) The drug release (Upper) and the reflectivity of the DxR MPAs (Lower) and the optical microscope image of a portion of the DxR-doped microprisms (Inset). The data are collected during the burst release (hourly up to 6 h) and during the sustained-release phase (every 6 h up to 30 h) (n = 6). (B) SEM images of DxR-MPA structures at 0, 6, and 30 h, showing a gradual breakdown of the microprisms due to the enzymatic degradation. (Scale bar, 50 μm.) (C) A comparison between DxR dissolved in ultrapure water and DxR-loaded silk MPAs (both with a concentration of 0.8 mg/mL) after storage at −20 °C and 60 °C for 3 wk. The silk DxR MPA maintains the fluorescence of the DxR after 3 wk at 60 °C in contrast to the solution. (D) The DxR MPAs were then fully degraded with 10 mg/mL proteinase k solution and were compared with the DxR solution by measuring the fluorescence intensity (excitation = 430 nm, emission = 550 nm) to determine the chemical activity of the drug. DxR fluorescence decreases when stored in solution, whereas the fluorescence of the DxR stored in MPAs does not significantly decrease with the 80 °C increase in storage temperature (two-tailed P value: P < 0.02 at −20 °C and P < 0.001 at 60 °C, Student t test).