Tissue regeneration during tissue expansion and choosing an expander

The current use of tissue expanders in breast reconstruction: device design, features, and technical considerations

INTRODUCTION

The use of tissue expanders (TE) in post-mastectomy breast reconstruction is a widely accepted practice, especially in patients desiring implant-based breast reconstruction. It has become the standard of care to perform a two-staged breast reconstruction using tissue expanders for the past 50 years due to its reliability, safety, cost-effectiveness, and versatility. Due to its popularity, there are numerous types and features of breast tissue expanders and various surgical approaches available for plastic surgeons.

AREAS COVERED

In this article, we will review the role of tissue expanders in breast reconstruction, the types and features of breast tissue expanders, and technical considerations.

EXPERT OPINION

The use of tissue expanders in breast reconstruction offers significant advantages of preserving the breast skin envelope and reestablishing the breast mound. With evolving approaches to breast reconstruction, tissue expander design, and application underwent several refinements and modifications. Due to these advances, studies on its long-term efficacy and safety profile typically fall behind and more studies with higher levels of evidence are needed to better evaluate the efficacy and safety profile of tissue expanders. With increased understanding, reconstructive surgeons can minimize complications and maximize reconstructive, aesthetic outcomes with high patient satisfaction.

Coexpression analysis of angiogenesis, proliferation, apoptosis, autophagy and SHH pathway genes involved in skin expansion

Skin and soft tissue expansion is a widely used technique in plastic surgery. However, the regulatory mechanisms associated with cellular processes involved in skin expansion are not well elucidated. In the present study, we aimed at exploring the transcriptome changes associated with skin expansion and profiling the difference in gene expression between the skin tissue in the top of the dilator and the skin tissue in the side of the dilator. A mouse model of skin expansion was established and RNA sequencing (RNA-Seq) was performed on samples collected at different time points. Differential expression analysis was performed using the DESeq2 package while STEM was used for time series clustering profiling. The regulatory networks were established and the functions of sets of genes were analyzed. The mRNA expression levels of candidate genes were validated by the quantitative RT-PCR. Among the skin tissue in the top of the dilator and normal samples at days 1, 3, 7, 14 and 28, 53 commonly upregulated and 7 commonly downregulated genes were identified while among the skin tissue in the side of the dilator and normal samples, 98 downregulated and 255 upregulated genes were identified. Genes differentially expressed among the skin tissue in the top of the dilator and normal samples were involved in coagulation and proliferation-associated pathways while those among the skin tissue in the side of the dilator and normal samples were involved in the inflammation, immune response, and defense response. Among the skin tissue in the top of the dilator and the skin tissue in the side of the dilator samples, 161 were constantly upregulated while 27 were constantly downregulated; these genes were enriched in the biological processes of cell adhesion and regulation of cell proliferation (n = 11). Furthermore, we identified that SHH signaling genes formed a coexpression regulatory network with cellular proliferation, apoptosis, autophagy and angiogenesis-related genes in the expanded skin. In conclusion, our findings can promote research and understanding of the mechanism of skin expansion and will find application in plastic surgery.

Air versus Saline in Initial Prepectoral Tissue Expansion: A Comparison of Complications and Perioperative Patient-Reported Outcomes

BACKGROUND

One option to optimize prepectoral tissue expander fill volume while minimizing stress on mastectomy skin flaps is to use air as an initial fill medium, with subsequent exchange to saline during postoperative expansion. The authors compared complications and early patient-reported outcomes (PROs) based on fill type in prepectoral breast reconstruction patients.

METHODS

Prepectoral breast reconstruction patients who underwent intraoperative tissue expansion with air or saline from 2018 to 2020 were reviewed to assess fill-type utilization. The primary endpoint was expander loss; secondary endpoints included seroma, hematoma, infection/cellulitis, full-thickness mastectomy skin flap necrosis requiring revision, expander exposure, and capsular contracture. PROs were assessed with the BREAST-Q Physical Well-Being of the Chest scale 2 weeks postoperatively. Propensity-matching was performed as a secondary analysis.

RESULTS

Of 560 patients (928 expanders) included in the analysis, 372 had devices initially filled with air (623 expanders), and 188 with saline (305 expanders). No differences were observed for overall rates of expander loss (4.7% versus 3.0%, P = 0.290) or overall complications (22.5% versus 17.7%, P = 0.103). No difference in BREAST-Q scores was observed ( P = 0.142). Utilization of air-filled expanders decreased substantially over the last study year. After propensity matching, no differences in loss, other complications, or PROs were observed across cohorts.

CONCLUSIONS

Tissue expanders initially filled with air seem to have no significant advantage over saline-filled expanders in maintaining mastectomy skin flap viability or PROs, including after propensity matching. These findings can help guide choice of initial tissue expander fill type.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

The Efficacy of Anterior Capsulotomy and Basal Capsulectomy Adherent to Expanded Scalp Flap During Alopecia Reconstruction in Pediatric Burned Patients

BACKGROUND

Scalp expansion is an optimal treatment for alopecia resulting from burn injuries, especially in the pediatric population through providing highly vascularized adjacent local tissues with optimal hair density, color matching, texture, and hair-bearing characteristics. The aim of this study was to evaluate the efficacy of anterior capsulotomy and basal capsulectomy adherent to expanded scalp flap during alopecia reconstruction with scalp expansion in pediatric burned patients.

METHODS

The study was conducted on 127 patients with an age range of 5 to 19 years who presented with postburn alopecia accompanied by hairline loss. The patients were divided into 2 groups: group I consisted of 58 patients who were operated on using conventional technique, and group II consisted of 69 patients who were operated using modified technique including basal capsulectomy on the skull side and anterior capsulotomy on the expanded scalp flap.

RESULTS

The Hairdex, a validated questionnaire of Hair-Specific Health-Related Quality of Life measures, showed that percentage of satisfaction concerning outcomes was 91.50%, psychological well-being was 95%, and self-confidence was 84.30% in group II, compared with 63%, 55.70%, and 66.20%, respectively, in group I. This significant values had a great positive effect on patient satisfaction, changing child's behavior and self-confidence.

CONCLUSION

Although physiological background of tissue expansion is the same, proper flap design with anterior capsulotomy on flap undersurface and basal capsulectomy on the skull side improve results of the traditional method significantly and minimize the complication rate. These surgical modifications provide maximum benefits from expanded tissue, with restoration of the hairline and a uniform hair direction.

LEVEL OF EVIDENCE

Level III, case-control study.

Clinical Application of Pre-Expanded Perforator Flaps

Background: Challenging large soft tissue defects are typically treated with microvascular free tissue transfer; however, success has been noted with pre-expanded perforator flaps. Objective: To report outcomes and complications from pre-expanded perforator flaps. Methods: A retrospective chart review of patients undergoing tissue reconstruction with pre-expanded perforator flaps between 2014 and 2020. Data collection included flap type, defect characteristics, and complications. Results: All 29 patients had successful flap reconstruction without major complication. The median area of tissue defect was 17 × 13 cm² (range 7 × 4 to 27 × 24 cm²). Mean tissue expansion period was 15.2 weeks (range 9-26 weeks). The most common flap was the pre-expanded internal mammary artery perforator flaps. Conclusion: The findings of this study suggest that combining tissue expansion with a perforator flap for large tissue reconstruction can be successful with limited complications. This technique may allow a larger pliable skin flap that deserves further investigation.

Single-Cell Transcriptomics Uncover Key Regulators of Skin Regeneration in Human Long-Term Mechanical Stretch-Mediated Expansion Therapy

Tissue expansion is a commonly performed therapy to grow extra skin invivo for reconstruction. While mechanical stretch-induced epidermal changes have been extensively studied in rodents and cell culture, little is known about the mechanobiology of the human epidermis in vivo. Here, we employed single-cell RNA sequencing to interrogate the changes in the human epidermis during long-term tissue expansion therapy in clinical settings. We also verified the main findings at the protein level by immunofluorescence analysis of independent clinical samples. Our data show that the expanding human skin epidermis maintained a cellular composition and lineage trajectory that are similar to its non-expanding neighbor, suggesting the cellular heterogeneity of long-term expanded samples differs from the early response to the expansion. Also, a decrease in proliferative cells due to the decayed regenerative competency was detected. On the other hand, profound transcriptional changes are detected for epidermal stem cells in the expanding skin versus their non-expanding peers. These include significantly enriched signatures of C-FOS, EMT, and mTOR pathways and upregulation of AREG and SERPINB2 genes. CellChat associated ligand-receptor pairs and signaling pathways were revealed. Together, our data present a single-cell atlas of human epidermal changes in long-term tissue expansion therapy, suggesting that transcriptional change in epidermal stem cells is the major mechanism underlying long-term human skin expansion therapy. We also identified novel therapeutic targets to promote human skin expansion efficiency in the future.

First Successful Separation of Craniopagus Twins in India—Plastic Surgical Considerations

Separation of total vertical craniopagus with shared venous sinuses poses multiple challenges. Provision of soft-tissue cover to the exposed brains at the time of total separation is one of them, due to the large size of the defect and paucity of local tissues. Staged separation of twins is advised with partial venous and parenchymal disconnection in the first stage and total separation in the second stage. Tissue expanders are inserted in the first stage, and second stage planned to coincide with the period of adequate expansion. In the child being reported, emergency second stage was done due to the deteriorating general condition of the children. Left with inadequate expanded skin, the critical defect in a twin was managed with bilateral trapezius myocutaneous flaps. High ionotropic support of the postoperative period resulted in superficial necrosis of the flap, which was managed by debridement, allograft application and autograft later. Both twins had well-healed wounds by 3 months.

Repair of Defects in the Scalp and Face With Expanded Superficial Temporal Artery Flaps: A Single-Center Retrospective Study

BACKGROUND AND OBJECTIVE

Defects resulted from the removal of large scars, benign tumors, severe pigmentation abnormalities, and vascular malformations, etc., in the scalp and face need to be repaired to restore the appearance. Here, the authors introduced the application of various expanded superficial temporal artery (STA) flaps in the repair of above defects.

METHODS

From Jan. 2015 to Dec. 2018, 19 patients with craniofacial secondary defects received the repair with expanded STA flaps in our clinic. The defects were resulted from the removal of scalp scar (n = 6), neurofibroma (n = 4), sebaceous nevus (n = 3), arteriovenous malformation (n = 2), facial scar (n = 2), and port-wine stain (n = 2). The expanded STA flaps included 14 cases of flaps pedicled by parietal branch of STA, 2 cases of flaps pedicled by parietal branch of STA combined with laser hair removal, 1 case of flaps pedicled by frontal branch of STA, and 2 cases of prefabricated expanded skin flap with the superficial temporal fascia in the neck.

RESULTS

The two-stage operation and water-filling expansion were accomplished in all patients. All flaps survived well, except one flap with venous congestion, which resolved after blood-letting and application of drugs promoting venous draining. In the three to six months follow-up, the flaps' color, texture, and thickness were satisfying.

CONCLUSIONS

Individual application of different types of expanded STA flaps could achieve ideal results in repairing craniofacial secondary defects.

Biomechanical Effects of Unidirectional Expansion Using Anisotropic Expanders in Horse Skin Tissue

The use of a self-inflating tissue expander is a technique to stretch cutaneous tissues for potential use in reconstructive skin surgeries. This study investigates the mechanical properties of horse skin stretched by the subcutaneous implantation of anisotropic tissue expanders at the forehead, right shoulder, and dorsomedial part of the cannon region of the right forelimb in six (n = 6) horses. After 14 days of skin expansion, expanded and normal (control) skin samples were harvested and their mechanical properties of elastic modulus (EM), maximum force (MF), maximum stress (MSs) and maximum strain (MSr) were evaluated using uniaxial tension test. The expanded skin from shoulder area has higher EM, MSs, MSr and MF than the normal skin when compared to the forehead and lower forelimb. Statistically, there was a significant (P= .02) mean difference for MSs between the expanded shoulder and lower forelimb skin, but the pairwise comparison of EM, MSr and MF showed no significant difference between the locations. The overall effect of locations on EM and MSs was statistically significant (P < .05), however, there was no overall effect of horse factor, treatment factor (normal and expanded skin) and location interaction on the EM, MSS, MF and MSr. In conclusion, the expanded skin from the frontal head and the distal limb are less elastic (stiffer) compared to that of the expanded skin of the shoulder, thus anatomical location of the skin has some degree of effect on EM and MSs.

Use of Preexpanded Forehead and Neck Skin in Case of Giant Facial Hairy Naevus: Planning and Technique

A congenital nevi is a pigmented patch which requires complete surgical excision for cosmetic reasons. Here, we report a case of a patient with facial hairy pigmented lesion, occupying the right half of her face since birth, who underwent complete surgical excision and staged reconstruction utilizing, preexpanded forehead and neck skin. We used two rectangular tissue expanders with 150 and 300 cubic cm of volumes inserted in the forehead and the neck, respectively. The length of the expanders selected were equal to 1.2 to 1.5 times the length of their respective lesions, whereas the width of the base of the expanders were approximately similar to the width of their defects. It is concluded with this case report that tissue expansion provides a good cosmetic and anatomical correction to cover large defects, with adjacent skin having similar properties.

Multifactorial analysis of the surgical outcomes of giant congenital melanocytic nevi: Single versus serial tissue expansion

BACKGROUND

Giant congenital melanocytic nevus (GCMN) is a rare disease, for which complete surgical resection is recommended. However, the size of the lesions presents problems for the management of the condition. The most popular approach is to use a tissue expander; however, single-stage expansion in reconstructive surgery for GCMN cannot always address the entire defect. Few reports have compared tissue expansion techniques. The present study compared single and serial expansion to analyze the risk factors for complications and the surgical outcomes of the two techniques.

METHODS

We retrospectively reviewed the medical charts of patients who underwent tissue expander reconstruction between March 2011 and July 2019. Serial expansion was indicated in cases of anatomically obvious defects after the first expansion, limited skin expansion with two more expander insertions, or capsular contracture after removal of the first expander.

RESULTS

Fifty-five patients (88 cases) were analyzed, of whom 31 underwent serial expansion. The number of expanders inserted was higher in the serial-expansion group (P<0.001). The back and lower extremities were the most common locations for single and serial expansion, respectively (P=0.043). Multivariate analysis showed that sex (odds ratio [OR], 0.257; P=0.015), expander size (OR, 1.016; P=0.015), and inflation volume (OR, 0.987; P=0.015) were risk factors for complications.

CONCLUSIONS

Serial expansion is a good option for GCMN management. We demonstrated that large-sized expanders and large inflation volumes can lead to complications, and therefore require risk-reducing strategies. Nonetheless, serial expansion with proper management is appropriate for certain patients and can provide aesthetically satisfactory outcomes.

Prevención de lesiones por presión: conocimientos y actitudes del personal de enfermería

OBJECTIVE

Identify, analyse and summarise the empirical evidence on nurses' knowledge and attitudes towards pressure ulcer (PU) prevention.

METHOD

A systematic literature review on articles published between 2008 y 2019 was performed following PRISMA guidelines. Databases were checked for the following terms in Spanish, English and Portuguese: attitude, knowledge, pressure ulcer, and nursing staff.

RESULTS

A total of 33 articles with a quantitative descriptive approach were included in this review. The authors found a lack of knowledge on PU prevention among nursing staff. The nurses' attitudes were considered positive. Few studies examined the correlation between knowledge, attitude and clinical practice.

CONCLUSION

There is a need for continued professional education in terms of PU prevention among nurses. Research on alternative ways to organise nursing staff's work is needed. Studying up-to-date guidelines on PU prevention on a regular basis and attending training in this subject might be beneficial to improve nurses' knowledge and attitudes towards PU prevention.

Prevención de lesiones por presión: conocimientos y actitudes del personal de enfermería

OBJECTIVE

Identify, analyse and summarise the empirical evidence on nurses' knowledge and attitudes towards pressure ulcer (PU) prevention.

METHOD

A systematic literature review on articles published between 2008 y 2019 was performed following PRISMA guidelines. Databases were checked for the following terms in Spanish, English and Portuguese: attitude, knowledge, pressure ulcer, and nursing staff.

RESULTS

A total of 33 articles with a quantitative descriptive approach were included in this review. The authors found a lack of knowledge on PU prevention among nursing staff. The nurses' attitudes were considered positive. Few studies examined the correlation between knowledge, attitude and clinical practice.

CONCLUSION

There is a need for continued professional education in terms of PU prevention among nurses. Research on alternative ways to organise nursing staff's work is needed. Studying up-to-date guidelines on PU prevention on a regular basis and attending training in this subject might be beneficial to improve nurses' knowledge and attitudes towards PU prevention.

Scarred scalp reconstruction with a rectangular expander

Scalp reconstruction is challenging because the scalp is inelastic, stiff, and has hair follicles. Tissue expansion offers aesthetically pleasing outcomes with minimal donor-site morbidity. However, in a scarred scalp, the extent of possible dissection for the expander insertion may be limited and surgeons must make use of the limited scalp tissue. We successfully reconstructed scarred scalps using rectangular expanders. This report presents two cases: a 4× 3 cm chronic defect with widespread scarring and osteomyelitis and an 11× 7.5 cm scar tissue following a skin graft. Tissue expanders were inserted in the subgaleal plane and were inflated by 195 mL and 400 mL over periods of 2 and 3 months, respectively. Subgaleal elevation of a fasciocutaneous flap was achieved with the expanded tissue. The defects were well covered, with good color, texture, and hair-bearing tissue. There were no complications involving the tissue expanders. Rectangular expanders yield more available tissue than round or crescent-shaped expanders. Moreover, since the base of the flap is well defined, the expander can be easily inserted in a limited space. Therefore, rectangular expanders are recommended for the reconstruction of scarred scalps.

Choosing the right rectangular expander and maximising the benefits from expanded tissue

OBJECTIVE

Tissue expanders are widely used in the reconstruction of tissue wounds. This study aims to demonstrate how to choose the correct size of rectangular expander in relation to wound size and the maximum advancement technique for wound coverage in order to achieve a successful outcome.

METHODS

The present study included patients who were operated on between January 2013 and January 2017. The expander height chosen was more than half the length of the wound and the expander width was chosen to be as wide as possible, based on the width of the wound. The expander was placed in a site adjacent to the wound. Maximum advancement method was used to achieve coverage of the wound.

RESULTS

A total of 19 patients were included in the study, mean age 17.5 (range: 11-25) years. Indication included burn scar (n=14) and congenital nevus (n=5). The tissue expander was inserted into the scalp in 17 patients and supraclavicular area in two patients. A successful wound repair was achieved with the planned flaps in all patients.

CONCLUSION

In expansion using rectangular expanders, the required expanded skin is gained through the height of the expanded tissue. Thus, expander size should be preoperatively planned to ensure the height of expanded tissue would be, at least, half of the wound length. Maximum benefit will be achieved from the expanded tissue through the correct placement of expanded tissue lateral flaps.

Histological changes of immediate skin expansion of the distal limb of rats

Aim:

Tissue expansion is an applicable technique to reconstruct many surgical defects. The aim of this research was to evaluate the histological changes caused by immediate skin tissue expansion in rats as an animal model.

Materials and Methods:

Immediate skin tissue expansion in 18 adult female rats was performed using three different sizes (small, medium, and big) of polymethylmethacrylate tissue expanders at the dorsal surface of the metatarsal area of the right limb. The contralateral limb was served as the control. The tissue expanders were surgically implanted and kept for 15 days.

Results:

The immediate skin expansion resulted in histological changes such as the increased thickness of the epidermal layer, the reduction of the dermal layer, an elevated number of fibroblast as well as increased vascularity. Furthermore, skin adnexal structures such as hair follicles and sebaceous glands were farther apart.

Conclusion:

The rat skin was able to rapidly adjust and compensate against a specific range of immediate mechanical expansion. The histological changes suggest that the tissues were prepared to withstand the increased external forces, in addition to create possibly additional skin in a relatively short-term period.

Reshapable hydrogel tissue expander for ridge augmentation: Results of a series of successive insertions at the same intraoral site

BACKGROUND

Oral mucosa expansion before ridge augmentation is a procedure to reduce soft tissue exposure and to improve bone graft density and volume after augmentation. This study explored a novel, shapeable hydrogel tissue expander (HTE) in intraoral sites that had undergone previous expansion and surgery.

METHODS

Nine beagle dogs had all premolar teeth extracted and adjacent alveolar bone reduced. After at least 3 months healing hydrogels were placed at 4 sites in each dog: maxilla and mandible, right and left. After 6 weeks of expansion, the hydrogels were removed and measured for volume expansion and physical condition. Punch biopsies were taken of the expanded oral mucosa. After 3 months, a second hydrogel insertion was performed at each of the same sites. After this second expansion cycle, volume and hydrogel condition were recorded. Three dogs received ultrasound imaging of the hydrogels during the second expansion. Necropsy specimens were taken of both expanded and non-expanded oral mucosa.

RESULTS

Within 2 weeks after HTE insertion in both first and second insertions, blood flow returned to the pre-insertion level. The first and second insertions resulted in linear oral mucosa gain of 8.13 mm, and 6.44 mm, respectively. First and second insertion hydrogels erupted from 4% of the first expansion sites, and 3% of the second expansion sites. There was no directional migration of the expanding hydrogel at any site. Histology found little inflammatory reaction to any hydrogel implant.

CONCLUSION

Oral mucosa can be consistently and successfully expanded before bone graft for ridge augmentation even at sites with a history of prior surgeries.

Structural and bone marrow stem cell biocompatibility studies of hydrogel synthesized via chemo-enzymatic route

Natural biopolymers have many attractive medical applications; however, complications due to fibrosis caused a reduction in diffusion and dispersal of nutrients and waste products. Consequently, severe immunocompatibility problems and poor mechanical and degradation properties in synthetic polymers ensue. Hence, the present study investigates a novel hydrogel material synthesized from caprolactone, ethylene glycol, ethylenediamine, polyethylene glycol, ammonium persulfate, and tetramethylethylenediamine via chemo-enzymatic route. Spectroscopic analyses indicated the formation of polyurea and polyhydroxyurethane as the primary building block of the hydrogel starting material. Biocompatibility studies showed positive observation in biosafety test using direct contact cytotoxicity assay in addition to active cellular growth on the hydrogel scaffold based on fluorescence observation. The synthesized hydrogel also exhibited (self)fluorescence properties under specific wavelength excitation. Hence, synthesized hydrogel could be a potential candidate for medical imaging as well as tissue engineering applications as a tissue expander, coating material, biosensor, and drug delivery system.

The effectiveness of intermittent pneumatic compression in long-term therapy of lymphedema of lower limbs

BACKGROUND

The manual lymphatic drainage in lymphedema has proved to be successful; however, this method cannot be applied to millions of patients around the world. The only solution is to offer inexpensive, easily accessible mechanical devices for pneumatic compression (IPC). These devices should be designed on parameters of edema fluid hydromechanics. Recent data point to high pressures and long time of compression.

AIM

To validate the effects of 3 years daily high pressure, long inflation time IPC therapy in terms of decrease of limb circumference/volume, tissue elasticity, histological changes, and incidental complications.

METHODS

A group of 18 patients with unilateral leg lymphedema stage II to IV was treated for a period of 3 years using an 8-chamber sleeve, sequential inflation of chambers to 100-120 mmHg for 50 sec (total 400 sec). Limb circumference and tissue tonicity were measured at monthly intervals. Correlation between decrease in calf and thigh circumference and increase in elasticity was done.

RESULTS

The treatment revealed durable permanent decrease of limb circumference and increased elasticity of tissues. The improvement was most expressed in the calf above the ankle and mid-calf. No complications as thigh ring or chronic genital edema were observed. There was no direct correlation between the decrease in limb circumference and increase in elasticity, most likely due to different mass of fibrous tissue.

CONCLUSIONS

IPC takes over the permanently missing function of the obliterated lymphatics by squeezing edema tissue fluid to the regions with normal lymphatic drainage. The limb circumference is decreased or at least does not further increase, elasticity of tissue is increased and maintained. No complications in limb tissues were observed. The long-term, high pressure IPC, long inflation timed therapy can be safely be recommended to patients with lower limb lymphedema.

The volume of fluid injected into the tissue expander and the tissue expansion

BACKGROUND

Replacement of the lost tissue is the major concerns of the plastic surgeons. Expanded area should be coherent with the surrounding tissue. Tissue expansion technique is the reforming methods the skin tissue scarcities. Several methods for tissue expansion are available; including usage of silicon balloon and injecting fluid into the tissue expander.

MATERIALS AND METHODS

In a clinical trial study, 35 patients, with burn scars, in the face, skull and neck area were studied. We provided a tissue expander device with capacities of 125, 250 and 350cc. Fluid was injected inside the device, 3 consecutive weeks with 1-week interval. After 3 months the device was set out and the tissue expansion was measured using a transparent board and the results were analyzed. Multiple regression was done by SPSS 20 to analyze the data.

RESULTS

Regression model showed Skin expansion was positively correlated with the volume of the injected fluid. For each centimeter square of skin expansion, about 6-8 ml of fluid must be injected.

CONCLUSION

Correction of skin defects resulting from burning scar is possible using tissue expanders. The tissue expansion is correlated with the amount of the injected fluid.

Optimization of the use of skin expanders

BACKGROUND

Skin expansion is a physiological process that is defined as the ability of the human skin to increase its superficial area in response to stress or to a given deformation. Skin expanders are silicon bags that are implanted underneath the skin. Because the skin presents creep or relaxation, the resulting stress decreases after a time due to the imposed deformation. Skin expansions are used to reconstruct burned areas and breasts after a mastectomy or to hide scars.

PURPOSE

The question that constantly arises during skin expansion is whether it creates a sufficient amount of skin or, in other words, whether the achieved expansion is sufficient to resurface the defect. These questions are answered with information about how much new tissue is required to achieve the reconstruction in a given context and calculating the required tissue (surface area) in relationship with the volume infiltrated.

METHOD

Surface formulas for round and rectangular, and finite elements method for crescent skin expanders are used to calculate the relation between infiltrated volume and surface area. Those results were corrected or validated by an experimental work using 3D scanners to calculate the relation between surface area and internal volumes for the three types of expanders in question.

RESULTS

The research provides information to determine the type, number, and volume of skin expanders necessary to obtain an extra amount of skin to repair a specific medical condition and to determine the amount of skin obtained even in cases when the expansion does not come to term.

SYMBOLS

fci, Correcting factor, which corrects the mathematical formulas using the experimental results, for i skin expander; i, geometry of the expander, round (c), rectangular (r), or crescent (cresc/cr); Sd , surface of the defect; Sds , surface area of the donor site; Sfi, surface area obtained using a mathematical calculation for the i skin expander; S¯fi, surface area obtained experimentally for the i skin expander; Sfi∗, corrected surface area obtained using a mathematical calculation for the i skin expander corrected by the correcting factor; S¯fi∗∗ extra flap of skin obtained by expansion for the i skin expander; Vii, internal volume infiltrated in the i skin expander; Vni, nominal internal volume of the i skin expander.