Applied Bioengineering in Tissue Reconstruction, Replacement, and Regeneration

Abstract

The use of autologous tissue in the reconstruction of tissue defects has been the gold standard. However, current standards still face many limitations and complications. Improving patient outcomes and quality of life by addressing these barriers remain imperative. This article provides historical perspective, covers the major limitations of current standards of care, and reviews recent advances and future prospects in applied bioengineering in the context of tissue reconstruction, replacement, and regeneration.

Keywords: biomaterials; donor-site morbidity; drug delivery; genetic engineering; immunobiology; reconstructive surgery; regenerative medicine; stem cells; tissue engineering; tissue replacement; wound healing.

FIG. 1.

Results of in vivo studies on engineered PEGDA expanders performed by Jamadi et al. (A) Day 0: two expanders (P6 P8) were implanted in each rat. Day 21: Both expanders generated enough swelling dilate adjacent tissue. The skin expanded in all cohorts was in good condition with viable hair growth. (B) In vivo study 4 days after subcutaneous implantation (P8). (B.I) The explanted area includes expanded skin and the developed granulation tissue that surrounded the expanders. (B.II) Granulation tissue with blood vessels magnified under loupe microscope. (B.III) The expander was explanted from the overlying expanded skin and granulation tissue and retained its original shape. (B.IV) Expanded skin (magnified under loupe microscope) demonstrated signs of mild inflammation. (C) In vivo study 21 days after subcutaneous implantation (P8). (C.I) The expanded skin and the developed fibrous capsule surrounded the expanders. (C.II) Fibrous capsule with blood vessels (magnified under loupe microscope). (C.III) The expander was explanted from the overlying expanded skin and fibrous capsule. The expander device retained its original shape. (C.IV) Skin on the site of expansion (magnified with loupe microscope) demonstrated little-to-no inflammation. (D) Representative stress–strain curves of P6 and P8 hydrogels before and after implantation (day 21), both in the expansion state (E) Mechanical and swelling properties of explanted hydrogels on PODs 4 and 21. PEGDA, poly(ethylene glycol) diacrylate; POD, postoperative day. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission from Jamadi et al. Color images are available online.

FIG. 2.

Global progress in clinical vascularized composite allotransplantation (VCA) by year of transplantation and/or publication by Edtinger et al. Figure reproduced with permission from Springer Nature, the original figure was published under the Creative Commons Attribution 4.0 International License. Individual references. Color images are available online.

FIG. 3.

Encapsulation of TAC in TGMS hydrogel and enzyme-responsive drug release by Gajanayake et al. (A) TGMS self-assembly and TAC encapsulation. (B) Transmission electron micrograph of TGMS-TAC hydrogel. (C, D) Proteolytic enzyme-responsive TAC release. Hydrogels incubated in PBS remained hydrolytically stable and did not release drug for at least 3 months. Addition of proteolytic enzymes (lipase, MMP-2, and MMP-9) induced the release of drug. *p < 0.002 and **p < 0.01, PBS versus enzyme-treated groups. (E) Schematic of LPS activation of RAW 264.7 macrophages to mimic inflammation. (F) Cell culture supernatant from activated macrophages induced drug release (gray symbols, supernatant added on days 0, 3, and 6), meanwhile supernatant from nonactivated macrophages or PBS did not (***p < 0.03). LPS, lipopolysaccharide; PBS, phosphate-buffered saline; TAC, tacrolimus; TGMS, triglycerol monostearate. Figure reproduced with permission from The American Association for the Advancement of Science. Color images are available online.

FIG. 4.

VCA survival studies and histopathological features performed by Gajanayake et al. (A, B) Brown Norway–to–Lewis orthotopic hindlimb transplantation. Control groups were left untreated (I) or were treated with TGMS as a vehicle (II). Experimental groups were treated with a single injection of 7-mg TAC subcutaneously (III) or 7-mg TGMS-TAC (IV) into the transplanted or contralateral limb (TGMS-TAC/ConLat) (V), respectively, at POD 1. Kaplan-Meier graft survival curves are shown. (C) Representative macroscopic images of hindlimb allografts. (C.i) Groups I and II showed an acute rejection with a MST of 11 days. (C.ii) Group III allografts (single injection of 7-mg TAC), rejected with a MST of 33.5 days. (C.iii) No signs of rejection were seen in the long-term survival group IV on day 100. (D, E) Representative photomicrographs of the histology (hematoxylin and eosin staining) of skin (D) and gastrocnemic muscle (E) of normal rats, no treatment, TGMS-treated, TAC only-treated, and TGMS-TAC-treated groups. Rejected grafts showed cell infiltration, edema formation, and necrosis. MST, mean survival time. Figure reproduced with permission from The American Association for the Advancement of Science. Color images are available online.

FIG. 5.

Drug delivery routes and mechanisms using MNP-based drug delivery systems created by Fisher et al. (A) MNP's can deliver therapies locally. (B) MNP's can be uptaken by cells including immune cells such as dendritic cells to act intracellularly. (C) aAPCs can modulate signals 1, 2, and 3 ultimately affecting T-cell activation. (D) MNPs can be used to induce the production of and/or recruit endogenous Tregs. MNP, microparticle/nanoparticle. Image reproduced with permission from Elsevier. Color images are available online.

FIG. 6.

Examples of nerve conduit designs for reconnection of the proximal nerve stump and the distal nerve stump by Dalamagkas et al. Figure reproduced with permission from Elsevier. Color images are available online.

FIG. 7.

Long-acting, antioxidant polymeric microparticles with on-demand release of antioxidant and anti-inflammatory drug curcumin. Studies, performed by Poole et al., showing that PPS microspheres provide sustained, on-demand, local curcumin release and reduce tissue ROS levels. (A) Curcumin-PPS microspheres release curcumin faster in the ischemic limb when compared to the nonischemic control limb. (B) ROS levels in the ischemic gastrocnemius muscle are increased at 1 day following induction of ischemic injury (ROS is 2.3-fold greater in ischemic vs. control gastrocnemius). (C) Blank PPS microspheres and curcumin-loaded PPS microspheres reduce ROS in gastrocnemius muscles extracted from ischemic limbs. Data are presented as mean ± SEM. Saline group n = 8, blank PPS group n = 11, curcumin-PPS group n = 10. *p < 0.05 is relative to saline treatment. PPS, poly(propylene sulfide); ROS, reactive oxygen species; SEM, standard error of the mean. Figure reproduced with permission from Elsevier. Color images are available online.

FIG. 8.

siRNA delivered using ROS-degradable tissue-engineered scaffolds, performed by Martin et al., promotes diabetic wound healing. Porous poly(thioketal-urethane) scaffolds implanted in diabetic wounds locally deliver siRNA that inhibits the expression of PHD2, thereby increasing vasculature, proliferating cells, and tissue development. PHD2, prolyl hydroxylase domain protein 2; siRNA, small interfering ribonucleic acid. Figure reproduced with permission from Elsevier. Color images are available online.

FIG. 9.

Schematic of ex vivo microvascular free dermal/adipose flap engineered by Zhang et al. DSAF is harvested and prepared from the donor rat and recellularized with hASCs and HUVECs in vitro. Following vascular anastomosis to the recipient site, the engineered flap construct activated an M2 macrophage-mediated constructive remodeling process in vivo. Using this strategy, DSAFs could be translated as a commercial tissue engineering product for personalized tissue repair and regeneration. DSAF, decellularized skin/adipose tissue flap; hASCs, human adipose-derived stem/stromal cells; HUVECs, human umbilical vein endothelial cells. Figure reproduced with permission from Elsevier. Color images are available online.

FIG. 10.

Surgical implantation of fabricated tissue grafts followed by flap transfer performed by Shandalov et al. (A–D) Schematic of flap fabrication. (A) Cells were seeded within biodegradable PLLA/PLGA scaffolds. (B) The fabricated tissue graft was folded around blood vessels and sutured. (C, D) Transfer of the vascularized graft into the abdominal wall defect. (E) Isolation of the femoral artery and vein. (F) The fabricated tissue graft was folded around blood vessels and sutured. (G, H) The fabricated tissue graft was then separated from the skin and the surrounding tissue using a piece of sterile latex, which was then sutured. (I) Suturing of the overlying skin. (J) Representative image of a fabricated tissue graft 1 week postimplantation. (K) Transfer of the vascularized graft into the abdominal wall defect. (L) Appearance of the flap derived from cell-embedded scaffolds 1 week after transfer. (M) Image of a piece of a cell-free scaffold applied to close the abdominal wall defect. (N) Appearance of a graft derived from a cell-free scaffold 1 week post-transfer; the graft had become necrotic. PLGA, poly(lactic acid-co-glycolic acid); PLLA, poly-l-lactic acid. Figure reproduced with permission from Proceedings of the National Academy of Sciences of the United States of America. Color images are available online.

FIG. 11.

Progress toward bioprinting composite flaps for reconstructive microsurgical implantation created by Jessop et al. Figure reproduced with permission from Elsevier. Individual references. Color images are available online.

FIG. 12.

3D vascularized tissue fabrication performed by Kolesky et al. (A) Tissue manufacturing process. (A.i) Fugitive (vascular) ink, containing pluronic and thrombin, and cell-laden inks, containing gelatin, fibrinogen, and cells, are printed within a 3D perfusion chip. (A.ii) ECM material, which contains gelatin, fibrinogen, cells, thrombin, and TG, is then cast over the printed inks. After casting, thrombin induces fibrinogen cleavage and rapid polymerization into fibrin in both the cast matrix, and through diffusion, in the printed cell ink. Similarly, TG diffuses from the molten casting matrix and slowly crosslinks the gelatin and fibrin. (A.iii) Upon cooling, the fugitive ink liquefies and is evacuated, leaving behind a pervasive vascular network, which is (A.iv) endothelialized and perfused. (B) HUVECs growing on top of the matrix in 2D, (C) hNDFs growing inside the matrix in 3D, and (D) hMSCs growing on top of the matrix in 2D. (E, F) Images of printed hMSC-laden ink prepared using gelatin (preprocessed at 95°C before ink formation) (E) as printed and (F) after 3 days in the 3D printed filament where actin (green) and nuclei (blue) are stained. (G) Gelatin preprocessing temperature affects the plateau modulus and cell viability after printing. Higher temperatures lead to lower modulus and higher hNDF viability postprinting. (H) Photographs of interpenetrated sacrificial (red) and cell inks (green) as printed on chip. (I) Top-down bright-field image of sacrificial and cell inks. (J–L) Photograph of a printed tissue construct housed within a perfusion chamber (J) and corresponding cross-sections (K, L). 2D, two dimensional; 3D, three dimensional; ECM, extracellular matrix; hNDFs, human neonatal dermal fibroblasts; TG, transglutaminase. Figure reproduced with permission from Proceedings of the National Academy of Sciences of the United States of America. Color images are available online.

FIG. 13.

Strategy for producing readily available TEVGs performed by Dahl et al. Each graft is generated in the laboratory by (A) culturing human cells on a polymer scaffold that degrades as cells produce ECM proteins to form (B) a tissue. Cellular material is then removed, leaving (C) a decellularized ECM tube (the TEVG). Cell-derived TEVGs may be implanted without ECs (D), (diameters ≥6 mm), or (E) may be seeded with ECs from the recipient for small-diameter (3–4 mm) applications. ECs, endothelial cells; TEVGs, tissue-engineered vascular grafts. Figure reproduced with permission from The American Association for the Advancement of Science. Color images are available online.

FIG. 14.

Regeneration of the transgenic epidermis in epidermolysis bullosa, performed by Hirsch et al. (a) Clinical picture of the patient showing massive epidermal loss. (b) Schematic representation of the clinical picture. The denuded skin is indicated in red; blistering areas are indicated in green; flesh-colored areas indicate currently nonblistering skin. Transgenic grafts were applied on both red and green areas. (c) Restoration of patient's entire epidermis, except for very few areas on the right thigh, buttocks, upper shoulders/neck, and left axilla (white circles, altogether ≤2% of TBSA). (d) Normal skin functionality and elasticity. (e) Absence of blister formation at sites where postgraft biopsies were taken (arrow). TBSA, total body surface area. Figure reproduced with permission from Springer Nature. Color images are available online.