Skin Ingrowth Research Articles

Temporary Botulinum Immobilization of Residuum Muscles for Facilitation of the Initial Ingrowth of Skin to the Porous Skin and Bone Integrated Pylon in the Technology of Direct Skeletal Attachment: Large Animal Model.

Enhancing the technology of bone-anchored limb prosthetics, we present a modified porcine model for developing an infection-free integration between the skin and a percutaneous bone implant. The deeply porous Skin and Bone Integrated Pylon (SBIP) presented an infection-free skin-implant interface both after implantation into the dorsum and after implantation into the residuum after below-knee amputation. However, deep ingrowth of skin into the porous cladding of the SBIP was achieved better in the dorsal procedure, while implantation to the residuum sometimes developed a stoma, probably due to the high mobility of the skin and soft tissues in the pig’s thigh. Uncontrolled high skin mobility during the first week after implantation constituted a limitation for the porcine animal model, which we tried to address in the current study. As our previous studies showed that casting of the leg residuum did not sufficiently limit the skin’s movement around the implant, we tested a modified protocol of the implantation, which included injection of botulinum toxin into the thigh muscles. During the course of the study, we identified proper botulinum toxin componentry, dosage, and the period after injections to achieve a maximal effect of immobilization of the muscles affecting skin movements. To verify the immobilization, we used kinetic data on the asymmetry of loading during gait with the Strideway System, Tekscan, Inc., Boston, MA, USA. We found that injections in the four muscles of the distal thigh of the left hind leg with MYOBLOC® (rimabotulinumtoxinB; 5,000 units/muscle) were sufficient to provide noticeable immobilization by the fourth week after the procedure. This conclusion was made based on the analysis of the dynamics of asymmetry in vertical ground reactions on the injected (left hind) and uninvolved (right hind) legs during gait over an instrumented walkway.

Recent Progress in Animal Studies of the Skin- and Bone-integrated Pylon With Deep Porosity for Bone-Anchored Limb Prosthetics With and Without Neural Interface.

The three major unresolved problems in bone-anchored limb prosthetics are stable, infection-free integration of skin with a percutaneous bone implant, robust skeletal fixation between the implant and host bone, and a secure interface of sensory nerves and muscles with a prosthesis for the intuitive bidirectional prosthetic control. Here we review results of our completed work and report on recent progress. Eight female adult cats received skin- and bone-integrated pylon (SBIP) and eight male adult cats received SBIP-peripheral neural interface (PNI) pylon into the right distal tibia. The latter pylons provided PNI for connection between a powered sensing transtibial prosthesis and electrodes in residual soleus muscle and on residual distal tibial nerve. If signs of infection were absent 28-70 days after implantation, cats started wearing a passive prosthesis. We recorded and analyzed full-body mechanics of level and slope locomotion in five cats with passive prostheses and in one cat with a powered sensing prosthesis. We also performed histological analyses of tissue integration with the implants in nine cats. Six cats from the SBIP groups had implant for 70 days. One cat developed infection and did not receive prosthesis. Five cats had pylon for 148 to 183 days, showed substantial loading of the prosthesis during locomotion (40.4% below presurgery control), and demonstrated deep ingrowth of skin and bone tissue into SBIP (over 60%). Seven of eight cats from the SBIP-PNI group demonstrated poor pylon integration without clinical signs of infection. One cat had prosthesis for 824 days (27 months). The use of the bidirectionally controlled prosthesis by this animal during level walking demonstrated increased vertical loading to nearly normal values, although the propulsion force was significantly reduced. Cats with SBIP (n = 5) and SBIP-PNI (n = 1) pylons developed a sound interface with the residuum skin and bone and demonstrated substantial loading of prosthetic limb during locomotion. One animal with SBIP developed infection and seven cats with SBIP-PNI demonstrated poor bone integration without signs of infection. Future studies of the SBIP-PNI should focus on reliability of integration with the residuum. Ongoing study with pigs requires decreasing the extra mobility of skin and soft tissues until the skin seal is developed within the SBIP implant.

Protecting the skin-implant interface with transcutaneous silver-coated skin-and-bone-integrated pylon in pig and rabbit dorsum models.

Implant-associated soft tissue infections at the skin-implant interface represent the most frequent complications in reconstructive surgery and lead to implant failures and revisions. Titanium implants with deep porosity, called skin-and-bone-integrated-pylons (SBIP), allow for skin ingrowth in the morphologically natural direction, thus restoring a reliable dermal barrier and reducing the risk of infection. Silver coating of the SBIP implant surface using physical vapor deposition technique offers the possibility of preventing biofilm formation and exerting a direct antimicrobial effect during the wound healing phase. In vivo studies employing pig and rabbit dorsum models for assessment of skin ingrowth into the pores of the pylon demonstrated the safety of transcutaneous implantation of the SBIP system. No postoperative complications were reported at the end of the follow-up period of 6 months. Histological analysis proved skin ingrowth in the minipig model without signs of silver toxicity. Analysis of silver release (using energy dispersive X-ray spectroscopy) in the model of intramedullary-inserted silver-coated SBIP in New Zealand rabbits demonstrated trace amounts of silver after 3 months of in-bone implantation. In conclusion, selected temporary silver coating of the SBIP implant surface is powerful at preventing the periprosthetic infections without imparing skin ingrowth and can be considered for clinical application.

A New Approach to Manufacturing Biocomposite Sandwich Structures: Investigation of Preform Shell Behavior

The manufacture of natural fiber and core preforms for biocomposite sandwich structures that bound together with fungal mycelium-based polymer is investigated. The complete manufacturing process involves: (1) cutting individual textile plies; (2) impregnating multi-ply layups with natural glue conducive to mycelium growth; (3) simultaneously forming, sterilizing and setting impregnated skins; (4) filling formed skins with mycelium-laden agri-waste; (5) allowing mycelium to colonize and bind together core substrate and skins into a unitized preform; (6) high temperature drying that also inactivates fungus; and (7) infusing skins with bioresin using resin transfer molding. Aspects of steps 3–6 related to the preform shells and sandwich structure are the main focus of this paper. Three-point bending tests are performed on dry, natural glue-bonded, four-ply specimens in a full-factorial experimental design, and test results are analyzed by analysis of variance (ANOVA) to assess process parameter effects and sensitivities along with environmental condition effects. New specimens are then made using the optimized process and tested for beam bending in creep within an environmental chamber that mimics the actual mycelium growth environment for three days. Two- and six-ply specimens loaded to provide identical maximum tensile stress in flexure are tested, and useful conclusions are drawn based on all creep test results. Finally, preforms in the shape of a viable commercial product are filled with mycelium-inoculated substrate, grown and dried, and part quality is evaluated based on the amount of skin ingrowth and deviation between the measured and desired shapes.

Highly porous transcutaneous implants of varying material and pore geometry promote healing and in-growth of skin after surgical implantation into rabbits

Event Abstract Back to Event Highly porous transcutaneous implants of varying material and pore geometry promote healing and in-growth of skin after surgical implantation into rabbits Kyle J. Spivack1, Ian D. Dickey2, James A. Weber3, Alex Caddell1, Anne B. Lichtenwalner3 and David J. Neivandt1, 2 1 University of Maine, Department of Chemical and Biological Engineering, United States 2 University of Maine, Graduate School of Biomedical Sciences and Engineering, United States 3 University of Maine, School of Food and Agriculture, United States Recent developments in additive manufacturing have enabled the production of implantable metallic devices with highly mutable structures, including porous designs, and it is now possible to perform systematic studies of the efficacy of porous materials for supporting tissue in-growth. Studies of porous implants performed to date have largely focused on orthopedic applications. While a small number of studies have shown that highly porous devices, when implanted into subcutaneous tissue, facilitate fibrous tissue in-growth with significant attachment strength[1]-[7], the exact mechanism of soft tissue in-growth remains unclear. Further, no in-vivo analyses of transcutaneous porous implants, in which the implants penetrate through all dermal layers and into subcutaneous tissue, have been performed. Such studies are required in order to determine the potential for porous implants to promote wound healing in applications where contamination of the tissue-implant interface is unavoidable, such as percutaneous pin fixation of orthopedic fractures. We hypothesized that skin in-growth into a transcutaneous implant may form an effective biological seal, which would prevent bacteria from migrating into the subcutaneous and deeper tissues, causing infections. Reduction of infections could promote the development of healthy tissue in-growth in subcutaneous layers. The present pilot study was performed to determine the efficacy of additively manufactured, highly porous devices implanted in a transcutaneous fashion, and to qualitatively analyze the soft tissue in-growth capacity of such devices. A rabbit model was employed in the present study. Each of eight rabbits received four transcutaneous implants (two plastic, two titanium) for durations of one, two, three or seven weeks (two rabbits per time period). Implants harbored a rhombic dodecahedral porous network, or separately, a random highly porous foam network. Histology and histomorphometry were performed on implants from one rabbit at each post-surgical time period, including surrounding tissues, after surgical removal on the day of sacrifice. Implants were evaluated for responses consistent with inflammation and infection. The percentage of in-growth of soft tissues (granulation tissue, subcutaneous tissue and dermis) based on surface area was evaluated. Transcutaneous, porous implants comprised of either titanium or plastic promoted soft tissue in-growth as early as one week post-surgery and remained uninfected at, or deep to, the biologic interface between the dermal layer and the implant for up to seven weeks post surgery. Histological and histomorphological analyses showed that skin, subcutaneous and granular tissue grew into the porous networks of both the titanium and plastic implants. The present study demonstrated the efficacy of highly porous transcutaneous implants. Skin in-growth into porous transcutaneous implants formed an effective biological seal, preventing the establishment of infection-causing bacteria in tissues adjacent to the implants. Titanium implants with dodecahedral pore geometries performed better in several aspects than the plastic implants with dodecahedral pore geometries. Titanium implants with random highly porous foam geometry were more successful at promoting dermal tissue in-growth than titanium implants with uniform dodecahedral geometry. The authors gratefully acknowledge the University of Maine Institute for Molecular Biophysics for funding, AccelLab (Montreal, Canada) for performing histology and histomorphology analyses, Alexander French of the University of Maine Advanced Manufacturing Center for CAD design work, and GROWit, and Stryker Corporation for manufacturing the implants used in the present study.

An animal model to evaluate skin–implant–bone integration and gait with a prosthesis directly attached to the residual limb

BackgroundDespite the number of advantages of bone-anchored prostheses, their use in patients is limited due to the lack of complete skin–implant integration. The objective of the present study was to develop an animal model that would permit both detailed investigations of gait with a bone-anchored limb prosthesis and histological analysis of the skin–implant–bone interface after physiological loading of the implant during standing and walking. MethodsFull-body mechanics of walking in two cats were recorded and analyzed before and after implantation of a percutaneous porous titanium pylon into the right tibia and attachment of a prosthesis. The rehabilitation procedures included initial limb casting, progressively increasing loading on the implant, and standing and locomotor training. Detailed histological analysis of bone and skin ingrowth into implant was performed at the end of the study. FindingsThe two animals adopted the bone-anchored prosthesis for standing and locomotion, although loads on the prosthetic limb during walking decreased by 22% and 62%, respectively, 4months after implantation. The animals shifted body weight to the contralateral side and increased propulsion forces by the contralateral hindlimb. Histological analysis of the limb implants demonstrated bone and skin ingrowth. InterpretationThe developed animal model to study prosthetic gait and tissue integration with the implant demonstrated that porous titanium implants may permit bone and skin integration and prosthetic gait with a bone-anchored prosthesis. Future studies with this model will help optimize the implant and prosthesis properties.

Effects of pore size, implantation time, and nano‐surface properties on rat skin ingrowth into percutaneous porous titanium implants

The main problem of percutaneous osseointegrated implants is poor skin-implant integration, which may cause infection. This study investigated the effects of pore size (Small, 40-100 μm and Large, 100-160 μm), nanotubular surface treatment (Nano), and duration of implantation (3 and 6 weeks) on skin ingrowth into porous titanium. Each implant type was percutaneously inserted in the back of 35 rats randomly assigned to seven groups. Implant extrusion rate was measured weekly and skin ingrowth into implants was determined histologically after harvesting implants. It was found that all three types of implants demonstrated skin tissue ingrowth of over 30% (at week 3) and 50% (at weeks 4-6) of total implant porous area under the skin; longer implantation resulted in greater skin ingrowth (p < 0.05). Only one case of infection was observed (infection rate 2.9%). Small and Nano groups showed the same implant extrusion rate which was lower than the Large group rate (0.06 ± 0.01 vs. 0.16 ± 0.02 cm/week; p < 0.05). Ingrowth area was comparable in the Small, Large, and Nano implants. However, qualitatively, the Nano implants showed greatest cellular inhabitation within first 3 weeks. We concluded that percutaneous porous titanium implants allow for skin integration with the potential for a safe seal.

Mathematical modeling and mechanical and histopathological testing of porous prosthetic pylon for direct skeletal attachment.

This article presents recent results in the development of the skin and bone integrated pylon (SBIP) intended for direct skeletal attachment of limb prostheses. In our previous studies of the porous SBIP-1 and SBIP-2 prototypes, the bond site between the porous pylons and residuum bone and skin did not show the inflammation characteristically observed when solid pylons are used. At the same time, porosity diminished the strength of the pylon. To find a reasonable balance between the biological conductivity and the strength of the porous pylon, we developed a mathematical model of the composite permeable structure. A novel manufacturing process was implemented, and the new SBIP-3 prototype was tested mechanically. The minimal strength requirements established earlier for the SBIP were exceeded threefold. The first histopathological analysis of skin, bone, and the implanted SBIP-2 pylons was conducted on two rats and one cat. The histopathological analysis provided new evidence of inflammation-free, deep ingrowth of skin and bone cells throughout the SBIP structure.

Maggot therapy for wound debridement in a traumatic foot-degloving injury: a case report

A 43-year-old man was treated for a traumatic degloving injury to his foot with a transmetatarsal amputation and wound care because of the extensive soft tissue loss. After biweekly sharp debridements in the office for 4 weeks, very minimal skin ingrowth was noted. Maggot therapy was then implemented for a 48-hour treatment and a second treatment for 72 hours to help reduce excessive fibrosis and to painlessly debride the tissues to expose the granular base. Daily dressing changes for the next 6 weeks successfully allowed complete wound closure without any additional interventions. During the follow-up course, no complications were encountered and the patient has returned to ambulation with the use of a cane.

Effect of Basic Fibroblast Growth Factor on Perforated Chinchilla Tympanic Membranes

Basic fibroblast growth factor (bFGF) is a polypeptide mitogen which stimulates proliferation of epidermal and connective tissue cells. When applied to tympanic membrane perforations it has been reported to enhance healing and produce connective tissue hyperplasia. Previous work with animal models has shown that hyperplastic alterations of the tympanic membrane play an essential role in cholesteatoma development. This study was designed to further investigate the hyperplastic effects of bFGF and to determine if it might induce cholesteatoma formation during the healing process. Ten chinchillas received bilateral tympanic membrane perforations. In each animal, three doses of bFGF (400 nanograms per dose) were applied to the perforated tympanic membrane on one side; the opposite (control) ear received saline alone. The animals were terminated at either two or four weeks and studied histologically. Although the dosage and administration schedule used were consistent with previous studies utilizing other rodent species, there was little evidence that bFGF affected tympanic membrane healing in chinchillas. In both control and bFGF-treated ears, dense connective tissue occupied the lamina propria of the tympanic membrane, providing an effective barrier against ingrowth of skin toward the middle ear. No cholesteatomas developed in any animals included in the study. The results of this work indicate that the risk of cholesteatoma formation following administration of bFGF is minimal when it is applied short-term to acute perforations.

The repair of depressed tracheotomy scars.

Tracheotomy wounds, healing as they do by secondary intention, leave, at best, unsightly scars which are often complicated by large depressions due to the ingrowth of skin, which communicates directly with the mucosa of the trachea (Fig. 1). Proper repair requires that a bed be formed to fill the depression in the suprasternal notch. In 3 instances where efforts to repair such defects were unsuccessfully attempted by other means, excellent cosmetic results have been obtained by utilizing the sternal heads of the sternocleidomastoid muscles as a bed to fill the depression and cover the defect. The operation is performed under local anesthesia, with the patient breathing air and oxygen through a face mask under the head drape, or the area is prepared as for a thyroidectomy. The area of the scar is outlined with methylene blue, and any local anesthetic of

Response of the Skin to Focused Ultrasound

Skin of mice has been irradiated with focused ultrasound of one megacycle frequency. Skin in the growing phase of the hair growth cycle becomes ulcerated within two days following treatment while skin in the resting phase of the cycle is relatively unaffected. It is concluded that the response of the skin to ultrasound depends upon the physiological state of the organ at the time of irradiation. Thermal changes which occur during irradiation with ultrasound were measured in resting and growing skin, and no significant difference in absorption of acoustic energy between the systems was found. Since the capacities of the respective systems for absorbing ultrasound are equal this factor can be eliminated as a possible cause for the differential response of the skin. It is also suggested that the differential response of the skin cannot be attributed to structural differences between resting and growing follicles. When skin is irradiated with focused light which produces the same thermal change as that produced by ultrasound, skin in growth is ulcerated and skin at rest is unaffected. The heating component of ultrasound appears to be the physical factor to which the biological response can be attributed.

SUPPURATIVE OTITIS MEDIA AND ITS COMPLICATIONS

The literature on otitis media and its complications, with the omission of meningitis, is reviewed from January 1941 to July 1942. As might be expected, the paramount interest lies in chemotherapy. GENERAL CONSIDERATIONS Day 1 presents an interesting paper on cholesteatoma, in which he states that cholesteatoma resulting from ingrowth of epithelium through the drum membrane should be called pseudocholesteatoma. The lesion may be primary, arising from a defect of Shrapnell's membrane, regarding which there is a difference of opinion, or secondary (more common), from the ingrowth of skin from the external canal into the middle ear, replacing destroyed mucosa. He believes that retraction of Shrapnell's membrane is caused by a closing off of the attic from the middle ear due to the entrance of irritating fluids or foreign material into the latter. One of the causes is the prone-back position in which bottle-feeding infants are placed. Diamant 2 studied the air